internal/app: handle LookupGroup error

This could return errnos from the cgo calls.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/hakurei/command.go

@@ -6,11 +6,9 @@ import (
 	"io"
 	"log"
 	"os"
-	"os/signal"
 	"os/user"
 	"strconv"
 	"sync"
-	"syscall"
 	"time"
 
 	"hakurei.app/command"
@@ -20,11 +18,12 @@ import (
 	"hakurei.app/internal/app"
 	"hakurei.app/internal/app/state"
 	"hakurei.app/internal/hlog"
+	"hakurei.app/internal/sys"
 	"hakurei.app/system"
 	"hakurei.app/system/dbus"
 )
 
-func buildCommand(out io.Writer) command.Command {
+func buildCommand(ctx context.Context, out io.Writer) command.Command {
 	var (
 		flagVerbose bool
 		flagJSON    bool
@@ -44,35 +43,35 @@ func buildCommand(out io.Writer) command.Command {
 		config := tryPath(args[0])
 		config.Args = append(config.Args, args[1:]...)
 
-		runApp(config)
+		app.Main(ctx, std, config)
 		panic("unreachable")
 	})
 
 	{
 		var (
-			dbusConfigSession string
-			dbusConfigSystem  string
-			mpris             bool
-			dbusVerbose       bool
+			flagDBusConfigSession string
+			flagDBusConfigSystem  string
+			flagDBusMpris         bool
+			flagDBusVerbose       bool
 
-			fid      string
-			aid      int
-			groups   command.RepeatableFlag
-			homeDir  string
-			userName string
+			flagID       string
+			flagIdentity int
+			flagGroups   command.RepeatableFlag
+			flagHomeDir  string
+			flagUserName string
 
-			wayland, x11, dBus, pulse bool
+			flagWayland, flagX11, flagDBus, flagPulse bool
 		)
 
 		c.NewCommand("run", "Configure and start a permissive default sandbox", func(args []string) error {
 			// initialise config from flags
 			config := &hst.Config{
-				ID:   fid,
+				ID:   flagID,
 				Args: args,
 			}
 
-			if aid < 0 || aid > 9999 {
-				log.Fatalf("aid %d out of range", aid)
+			if flagIdentity < 0 || flagIdentity > 9999 {
+				log.Fatalf("identity %d out of range", flagIdentity)
 			}
 
 			// resolve home/username from os when flag is unset
@@ -80,14 +79,7 @@ func buildCommand(out io.Writer) command.Command {
 				passwd     *user.User
 				passwdOnce sync.Once
 				passwdFunc = func() {
-					var us string
-					if uid, err := std.Uid(aid); err != nil {
-						hlog.PrintBaseError(err, "cannot obtain uid from setuid wrapper:")
-						os.Exit(1)
-					} else {
-						us = strconv.Itoa(uid)
-					}
-
+					us := strconv.Itoa(sys.MustUid(std, flagIdentity))
 					if u, err := user.LookupId(us); err != nil {
 						hlog.Verbosef("cannot look up uid %s", us)
 						passwd = &user.User{
@@ -103,21 +95,21 @@ func buildCommand(out io.Writer) command.Command {
 				}
 			)
 
-			if homeDir == "os" {
+			if flagHomeDir == "os" {
 				passwdOnce.Do(passwdFunc)
-				homeDir = passwd.HomeDir
+				flagHomeDir = passwd.HomeDir
 			}
 
-			if userName == "chronos" {
+			if flagUserName == "chronos" {
 				passwdOnce.Do(passwdFunc)
-				userName = passwd.Username
+				flagUserName = passwd.Username
 			}
 
-			config.Identity = aid
-			config.Groups = groups
-			config.Username = userName
+			config.Identity = flagIdentity
+			config.Groups = flagGroups
+			config.Username = flagUserName
 
-			if a, err := container.NewAbs(homeDir); err != nil {
+			if a, err := container.NewAbs(flagHomeDir); err != nil {
 				log.Fatal(err.Error())
 				return err
 			} else {
@@ -125,105 +117,112 @@ func buildCommand(out io.Writer) command.Command {
 			}
 
 			var e system.Enablement
-			if wayland {
+			if flagWayland {
 				e |= system.EWayland
 			}
-			if x11 {
+			if flagX11 {
 				e |= system.EX11
 			}
-			if dBus {
+			if flagDBus {
 				e |= system.EDBus
 			}
-			if pulse {
+			if flagPulse {
 				e |= system.EPulse
 			}
 			config.Enablements = hst.NewEnablements(e)
 
 			// parse D-Bus config file from flags if applicable
-			if dBus {
-				if dbusConfigSession == "builtin" {
-					config.SessionBus = dbus.NewConfig(fid, true, mpris)
+			if flagDBus {
+				if flagDBusConfigSession == "builtin" {
+					config.SessionBus = dbus.NewConfig(flagID, true, flagDBusMpris)
 				} else {
-					if conf, err := dbus.NewConfigFromFile(dbusConfigSession); err != nil {
-						log.Fatalf("cannot load session bus proxy config from %q: %s", dbusConfigSession, err)
+					if conf, err := dbus.NewConfigFromFile(flagDBusConfigSession); err != nil {
+						log.Fatalf("cannot load session bus proxy config from %q: %s", flagDBusConfigSession, err)
 					} else {
 						config.SessionBus = conf
 					}
 				}
 
 				// system bus proxy is optional
-				if dbusConfigSystem != "nil" {
-					if conf, err := dbus.NewConfigFromFile(dbusConfigSystem); err != nil {
-						log.Fatalf("cannot load system bus proxy config from %q: %s", dbusConfigSystem, err)
+				if flagDBusConfigSystem != "nil" {
+					if conf, err := dbus.NewConfigFromFile(flagDBusConfigSystem); err != nil {
+						log.Fatalf("cannot load system bus proxy config from %q: %s", flagDBusConfigSystem, err)
 					} else {
 						config.SystemBus = conf
 					}
 				}
 
 				// override log from configuration
-				if dbusVerbose {
-					config.SessionBus.Log = true
-					config.SystemBus.Log = true
+				if flagDBusVerbose {
+					if config.SessionBus != nil {
+						config.SessionBus.Log = true
+					}
+					if config.SystemBus != nil {
+						config.SystemBus.Log = true
+					}
 				}
 			}
 
-			// invoke app
-			runApp(config)
+			app.Main(ctx, std, config)
 			panic("unreachable")
 		}).
-			Flag(&dbusConfigSession, "dbus-config", command.StringFlag("builtin"),
+			Flag(&flagDBusConfigSession, "dbus-config", command.StringFlag("builtin"),
 				"Path to session bus proxy config file, or \"builtin\" for defaults").
-			Flag(&dbusConfigSystem, "dbus-system", command.StringFlag("nil"),
+			Flag(&flagDBusConfigSystem, "dbus-system", command.StringFlag("nil"),
 				"Path to system bus proxy config file, or \"nil\" to disable").
-			Flag(&mpris, "mpris", command.BoolFlag(false),
+			Flag(&flagDBusMpris, "mpris", command.BoolFlag(false),
 				"Allow owning MPRIS D-Bus path, has no effect if custom config is available").
-			Flag(&dbusVerbose, "dbus-log", command.BoolFlag(false),
+			Flag(&flagDBusVerbose, "dbus-log", command.BoolFlag(false),
 				"Force buffered logging in the D-Bus proxy").
-			Flag(&fid, "id", command.StringFlag(""),
+			Flag(&flagID, "id", command.StringFlag(""),
 				"Reverse-DNS style Application identifier, leave empty to inherit instance identifier").
-			Flag(&aid, "a", command.IntFlag(0),
+			Flag(&flagIdentity, "a", command.IntFlag(0),
 				"Application identity").
-			Flag(nil, "g", &groups,
+			Flag(nil, "g", &flagGroups,
 				"Groups inherited by all container processes").
-			Flag(&homeDir, "d", command.StringFlag("os"),
+			Flag(&flagHomeDir, "d", command.StringFlag("os"),
 				"Container home directory").
-			Flag(&userName, "u", command.StringFlag("chronos"),
+			Flag(&flagUserName, "u", command.StringFlag("chronos"),
 				"Passwd user name within sandbox").
-			Flag(&wayland, "wayland", command.BoolFlag(false),
+			Flag(&flagWayland, "wayland", command.BoolFlag(false),
 				"Enable connection to Wayland via security-context-v1").
-			Flag(&x11, "X", command.BoolFlag(false),
+			Flag(&flagX11, "X", command.BoolFlag(false),
 				"Enable direct connection to X11").
-			Flag(&dBus, "dbus", command.BoolFlag(false),
+			Flag(&flagDBus, "dbus", command.BoolFlag(false),
 				"Enable proxied connection to D-Bus").
-			Flag(&pulse, "pulse", command.BoolFlag(false),
+			Flag(&flagPulse, "pulse", command.BoolFlag(false),
 				"Enable direct connection to PulseAudio")
 	}
 
-	var showFlagShort bool
-	c.NewCommand("show", "Show live or local app configuration", func(args []string) error {
-		switch len(args) {
-		case 0: // system
-			printShowSystem(os.Stdout, showFlagShort, flagJSON)
+	{
+		var flagShort bool
+		c.NewCommand("show", "Show live or local app configuration", func(args []string) error {
+			switch len(args) {
+			case 0: // system
+				printShowSystem(os.Stdout, flagShort, flagJSON)
 
-		case 1: // instance
-			name := args[0]
-			config, entry := tryShort(name)
-			if config == nil {
-				config = tryPath(name)
+			case 1: // instance
+				name := args[0]
+				config, entry := tryShort(name)
+				if config == nil {
+					config = tryPath(name)
+				}
+				printShowInstance(os.Stdout, time.Now().UTC(), entry, config, flagShort, flagJSON)
+
+			default:
+				log.Fatal("show requires 1 argument")
 			}
-			printShowInstance(os.Stdout, time.Now().UTC(), entry, config, showFlagShort, flagJSON)
+			return errSuccess
+		}).Flag(&flagShort, "short", command.BoolFlag(false), "Omit filesystem information")
+	}
 
-		default:
-			log.Fatal("show requires 1 argument")
-		}
-		return errSuccess
-	}).Flag(&showFlagShort, "short", command.BoolFlag(false), "Omit filesystem information")
-
-	var psFlagShort bool
-	c.NewCommand("ps", "List active instances", func(args []string) error {
-		printPs(os.Stdout, time.Now().UTC(), state.NewMulti(std.Paths().RunDirPath.String()), psFlagShort, flagJSON)
-		return errSuccess
-	}).Flag(&psFlagShort, "short", command.BoolFlag(false), "Print instance id")
+	{
+		var flagShort bool
+		c.NewCommand("ps", "List active instances", func(args []string) error {
+			printPs(os.Stdout, time.Now().UTC(), state.NewMulti(std.Paths().RunDirPath.String()), flagShort, flagJSON)
+			return errSuccess
+		}).Flag(&flagShort, "short", command.BoolFlag(false), "Print instance id")
+	}
 
 	c.Command("version", "Display version information", func(args []string) error {
 		fmt.Println(internal.Version())
@@ -247,20 +246,3 @@ func buildCommand(out io.Writer) command.Command {
 
 	return c
 }
-
-func runApp(config *hst.Config) {
-	ctx, stop := signal.NotifyContext(context.Background(),
-		syscall.SIGINT, syscall.SIGTERM)
-	defer stop() // unreachable
-	a := app.MustNew(ctx, std)
-
-	rs := new(app.RunState)
-	if sa, err := a.Seal(config); err != nil {
-		hlog.PrintBaseError(err, "cannot seal app:")
-		internal.Exit(1)
-	} else {
-		internal.Exit(app.PrintRunStateErr(rs, sa.Run(rs)))
-	}
-
-	*(*int)(nil) = 0 // not reached
-}

cmd/hakurei/command_test.go

@@ -68,7 +68,7 @@ Flags:
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
 			out := new(bytes.Buffer)
-			c := buildCommand(out)
+			c := buildCommand(t.Context(), out)
 			if err := c.Parse(tc.args); !errors.Is(err, command.ErrHelp) && !errors.Is(err, flag.ErrHelp) {
 				t.Errorf("Parse: error = %v; want %v",
 					err, command.ErrHelp)

cmd/hakurei/main.go

@@ -4,10 +4,13 @@ package main
 //go:generate cp ../../LICENSE .
 
 import (
+	"context"
 	_ "embed"
 	"errors"
 	"log"
 	"os"
+	"os/signal"
+	"syscall"
 
 	"hakurei.app/container"
 	"hakurei.app/internal"
@@ -44,7 +47,11 @@ func main() {
 		log.Fatal("this program must not run as root")
 	}
 
-	buildCommand(os.Stderr).MustParse(os.Args[1:], func(err error) {
+	ctx, stop := signal.NotifyContext(context.Background(),
+		syscall.SIGINT, syscall.SIGTERM)
+	defer stop() // unreachable
+
+	buildCommand(ctx, os.Stderr).MustParse(os.Args[1:], func(err error) {
 		hlog.Verbosef("command returned %v", err)
 		if errors.Is(err, errSuccess) {
 			hlog.BeforeExit()

cmd/hakurei/print.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"io"
 	"log"
-	"os"
 	"slices"
 	"strconv"
 	"strings"
@@ -14,7 +13,7 @@ import (
 
 	"hakurei.app/hst"
 	"hakurei.app/internal/app/state"
-	"hakurei.app/internal/hlog"
+	"hakurei.app/internal/sys"
 	"hakurei.app/system/dbus"
 )
 
@@ -22,14 +21,9 @@ func printShowSystem(output io.Writer, short, flagJSON bool) {
 	t := newPrinter(output)
 	defer t.MustFlush()
 
-	info := &hst.Info{Paths: std.Paths()}
-
-	// get hid by querying uid of identity 0
-	if uid, err := std.Uid(0); err != nil {
-		hlog.PrintBaseError(err, "cannot obtain uid from setuid wrapper:")
-		os.Exit(1)
-	} else {
-		info.User = (uid / 10000) - 100
+	info := &hst.Info{
+		Paths: std.Paths(),
+		User:  sys.MustGetUserID(std),
 	}
 
 	if flagJSON {

container/autoetc.go

@@ -3,7 +3,6 @@ package container
 import (
 	"encoding/gob"
 	"fmt"
-	"io/fs"
 )
 
 func init() { gob.Register(new(AutoEtcOp)) }
@@ -24,7 +23,7 @@ func (e *AutoEtcOp) Valid() bool                                { return e != ni
 func (e *AutoEtcOp) early(*setupState, syscallDispatcher) error { return nil }
 func (e *AutoEtcOp) apply(state *setupState, k syscallDispatcher) error {
 	if state.nonrepeatable&nrAutoEtc != 0 {
-		return msg.WrapErr(fs.ErrInvalid, "autoetc is not repeatable")
+		return OpRepeatError("autoetc")
 	}
 	state.nonrepeatable |= nrAutoEtc
 
@@ -32,10 +31,10 @@ func (e *AutoEtcOp) apply(state *setupState, k syscallDispatcher) error {
 	rel := e.hostRel() + "/"
 
 	if err := k.mkdirAll(target, 0755); err != nil {
-		return wrapErrSelf(err)
+		return err
 	}
 	if d, err := k.readdir(toSysroot(e.hostPath().String())); err != nil {
-		return wrapErrSelf(err)
+		return err
 	} else {
 		for _, ent := range d {
 			n := ent.Name()
@@ -44,12 +43,12 @@ func (e *AutoEtcOp) apply(state *setupState, k syscallDispatcher) error {
 
 			case "mtab":
 				if err = k.symlink(FHSProc+"mounts", target+n); err != nil {
-					return wrapErrSelf(err)
+					return err
 				}
 
 			default:
 				if err = k.symlink(rel+n, target+n); err != nil {
-					return wrapErrSelf(err)
+					return err
 				}
 			}
 		}

container/autoetc_test.go

@@ -2,14 +2,15 @@ package container
 
 import (
 	"errors"
-	"io/fs"
 	"os"
 	"testing"
+
+	"hakurei.app/container/stub"
 )
 
 func TestAutoEtcOp(t *testing.T) {
 	t.Run("nonrepeatable", func(t *testing.T) {
-		wantErr := msg.WrapErr(fs.ErrInvalid, "autoetc is not repeatable")
+		wantErr := OpRepeatError("autoetc")
 		if err := (&AutoEtcOp{Prefix: "81ceabb30d37bbdb3868004629cb84e9"}).apply(&setupState{nonrepeatable: nrAutoEtc}, nil); !errors.Is(err, wantErr) {
 			t.Errorf("apply: error = %v, want %v", err, wantErr)
 		}
@@ -18,22 +19,22 @@ func TestAutoEtcOp(t *testing.T) {
 	checkOpBehaviour(t, []opBehaviourTestCase{
 		{"mkdirAll", new(Params), &AutoEtcOp{
 			Prefix: "81ceabb30d37bbdb3868004629cb84e9",
-		}, nil, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/etc/", os.FileMode(0755)}, nil, errUnique},
-		}, wrapErrSelf(errUnique)},
+		}, nil, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/etc/", os.FileMode(0755)}, nil, stub.UniqueError(3)),
+		}, stub.UniqueError(3)},
 
 		{"readdir", new(Params), &AutoEtcOp{
 			Prefix: "81ceabb30d37bbdb3868004629cb84e9",
-		}, nil, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/etc/", os.FileMode(0755)}, nil, nil},
-			{"readdir", expectArgs{"/sysroot/etc/.host/81ceabb30d37bbdb3868004629cb84e9"}, stubDir(), errUnique},
-		}, wrapErrSelf(errUnique)},
+		}, nil, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/etc/", os.FileMode(0755)}, nil, nil),
+			call("readdir", stub.ExpectArgs{"/sysroot/etc/.host/81ceabb30d37bbdb3868004629cb84e9"}, stubDir(), stub.UniqueError(2)),
+		}, stub.UniqueError(2)},
 
 		{"symlink", new(Params), &AutoEtcOp{
 			Prefix: "81ceabb30d37bbdb3868004629cb84e9",
-		}, nil, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/etc/", os.FileMode(0755)}, nil, nil},
-			{"readdir", expectArgs{"/sysroot/etc/.host/81ceabb30d37bbdb3868004629cb84e9"}, stubDir(".host",
+		}, nil, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/etc/", os.FileMode(0755)}, nil, nil),
+			call("readdir", stub.ExpectArgs{"/sysroot/etc/.host/81ceabb30d37bbdb3868004629cb84e9"}, stubDir(".host",
 				"alsa", "bash_logout", "bashrc", "binfmt.d", "dbus-1", "default", "dhcpcd.exit-hook", "fonts",
 				"fstab", "fuse.conf", "group", "host.conf", "hostname", "hosts", "hsurc", "inputrc", "issue", "kbd",
 				"locale.conf", "login.defs", "lsb-release", "lvm", "machine-id", "man_db.conf", "mdadm.conf",
@@ -41,15 +42,15 @@ func TestAutoEtcOp(t *testing.T) {
 				"nsswitch.conf", "os-release", "pam", "pam.d", "passwd", "pipewire", "pki", "polkit-1", "profile",
 				"protocols", "resolv.conf", "resolvconf.conf", "rpc", "services", "set-environment", "shadow", "shells",
 				"ssh", "ssl", "static", "subgid", "subuid", "sudoers", "sway", "sysctl.d", "systemd", "terminfo",
-				"tmpfiles.d", "udev", "vconsole.conf", "X11", "xdg", "zoneinfo"), nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/alsa", "/sysroot/etc/alsa"}, nil, errUnique},
-		}, wrapErrSelf(errUnique)},
+				"tmpfiles.d", "udev", "vconsole.conf", "X11", "xdg", "zoneinfo"), nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/alsa", "/sysroot/etc/alsa"}, nil, stub.UniqueError(1)),
+		}, stub.UniqueError(1)},
 
 		{"symlink mtab", new(Params), &AutoEtcOp{
 			Prefix: "81ceabb30d37bbdb3868004629cb84e9",
-		}, nil, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/etc/", os.FileMode(0755)}, nil, nil},
-			{"readdir", expectArgs{"/sysroot/etc/.host/81ceabb30d37bbdb3868004629cb84e9"}, stubDir(".host",
+		}, nil, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/etc/", os.FileMode(0755)}, nil, nil),
+			call("readdir", stub.ExpectArgs{"/sysroot/etc/.host/81ceabb30d37bbdb3868004629cb84e9"}, stubDir(".host",
 				"alsa", "bash_logout", "bashrc", "binfmt.d", "dbus-1", "default", "dhcpcd.exit-hook", "fonts",
 				"fstab", "fuse.conf", "group", "host.conf", "hostname", "hosts", "hsurc", "inputrc", "issue", "kbd",
 				"locale.conf", "login.defs", "lsb-release", "lvm", "machine-id", "man_db.conf", "mdadm.conf",
@@ -57,41 +58,41 @@ func TestAutoEtcOp(t *testing.T) {
 				"nsswitch.conf", "os-release", "pam", "pam.d", "passwd", "pipewire", "pki", "polkit-1", "profile",
 				"protocols", "resolv.conf", "resolvconf.conf", "rpc", "services", "set-environment", "shadow", "shells",
 				"ssh", "ssl", "static", "subgid", "subuid", "sudoers", "sway", "sysctl.d", "systemd", "terminfo",
-				"tmpfiles.d", "udev", "vconsole.conf", "X11", "xdg", "zoneinfo"), nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/alsa", "/sysroot/etc/alsa"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/bash_logout", "/sysroot/etc/bash_logout"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/bashrc", "/sysroot/etc/bashrc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/binfmt.d", "/sysroot/etc/binfmt.d"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/dbus-1", "/sysroot/etc/dbus-1"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/default", "/sysroot/etc/default"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/dhcpcd.exit-hook", "/sysroot/etc/dhcpcd.exit-hook"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fonts", "/sysroot/etc/fonts"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fstab", "/sysroot/etc/fstab"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fuse.conf", "/sysroot/etc/fuse.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/host.conf", "/sysroot/etc/host.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hostname", "/sysroot/etc/hostname"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hosts", "/sysroot/etc/hosts"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hsurc", "/sysroot/etc/hsurc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/inputrc", "/sysroot/etc/inputrc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/issue", "/sysroot/etc/issue"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/kbd", "/sysroot/etc/kbd"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/locale.conf", "/sysroot/etc/locale.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/login.defs", "/sysroot/etc/login.defs"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/lsb-release", "/sysroot/etc/lsb-release"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/lvm", "/sysroot/etc/lvm"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/machine-id", "/sysroot/etc/machine-id"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/man_db.conf", "/sysroot/etc/man_db.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/mdadm.conf", "/sysroot/etc/mdadm.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/modprobe.d", "/sysroot/etc/modprobe.d"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/modules-load.d", "/sysroot/etc/modules-load.d"}, nil, nil},
-			{"symlink", expectArgs{"/proc/mounts", "/sysroot/etc/mtab"}, nil, errUnique},
-		}, wrapErrSelf(errUnique)},
+				"tmpfiles.d", "udev", "vconsole.conf", "X11", "xdg", "zoneinfo"), nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/alsa", "/sysroot/etc/alsa"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/bash_logout", "/sysroot/etc/bash_logout"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/bashrc", "/sysroot/etc/bashrc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/binfmt.d", "/sysroot/etc/binfmt.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/dbus-1", "/sysroot/etc/dbus-1"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/default", "/sysroot/etc/default"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/dhcpcd.exit-hook", "/sysroot/etc/dhcpcd.exit-hook"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fonts", "/sysroot/etc/fonts"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fstab", "/sysroot/etc/fstab"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fuse.conf", "/sysroot/etc/fuse.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/host.conf", "/sysroot/etc/host.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hostname", "/sysroot/etc/hostname"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hosts", "/sysroot/etc/hosts"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hsurc", "/sysroot/etc/hsurc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/inputrc", "/sysroot/etc/inputrc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/issue", "/sysroot/etc/issue"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/kbd", "/sysroot/etc/kbd"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/locale.conf", "/sysroot/etc/locale.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/login.defs", "/sysroot/etc/login.defs"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/lsb-release", "/sysroot/etc/lsb-release"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/lvm", "/sysroot/etc/lvm"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/machine-id", "/sysroot/etc/machine-id"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/man_db.conf", "/sysroot/etc/man_db.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/mdadm.conf", "/sysroot/etc/mdadm.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/modprobe.d", "/sysroot/etc/modprobe.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/modules-load.d", "/sysroot/etc/modules-load.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{"/proc/mounts", "/sysroot/etc/mtab"}, nil, stub.UniqueError(0)),
+		}, stub.UniqueError(0)},
 
 		{"success nested", new(Params), &AutoEtcOp{
 			Prefix: "81ceabb30d37bbdb3868004629cb84e9",
-		}, nil, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/etc/", os.FileMode(0755)}, nil, nil},
-			{"readdir", expectArgs{"/sysroot/etc/.host/81ceabb30d37bbdb3868004629cb84e9"}, stubDir(".host",
+		}, nil, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/etc/", os.FileMode(0755)}, nil, nil),
+			call("readdir", stub.ExpectArgs{"/sysroot/etc/.host/81ceabb30d37bbdb3868004629cb84e9"}, stubDir(".host",
 				"alsa", "bash_logout", "bashrc", "binfmt.d", "dbus-1", "default", "dhcpcd.exit-hook", "fonts",
 				"fstab", "fuse.conf", "group", "host.conf", "hostname", "hosts", "hsurc", "inputrc", "issue", "kbd",
 				"locale.conf", "login.defs", "lsb-release", "lvm", "machine-id", "man_db.conf", "mdadm.conf",
@@ -99,79 +100,79 @@ func TestAutoEtcOp(t *testing.T) {
 				"nsswitch.conf", "os-release", "pam", "pam.d", "passwd", "pipewire", "pki", "polkit-1", "profile",
 				"protocols", "resolv.conf", "resolvconf.conf", "rpc", "services", "set-environment", "shadow", "shells",
 				"ssh", "ssl", "static", "subgid", "subuid", "sudoers", "sway", "sysctl.d", "systemd", "terminfo",
-				"tmpfiles.d", "udev", "vconsole.conf", "X11", "xdg", "zoneinfo"), nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/alsa", "/sysroot/etc/alsa"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/bash_logout", "/sysroot/etc/bash_logout"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/bashrc", "/sysroot/etc/bashrc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/binfmt.d", "/sysroot/etc/binfmt.d"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/dbus-1", "/sysroot/etc/dbus-1"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/default", "/sysroot/etc/default"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/dhcpcd.exit-hook", "/sysroot/etc/dhcpcd.exit-hook"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fonts", "/sysroot/etc/fonts"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fstab", "/sysroot/etc/fstab"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fuse.conf", "/sysroot/etc/fuse.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/host.conf", "/sysroot/etc/host.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hostname", "/sysroot/etc/hostname"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hosts", "/sysroot/etc/hosts"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hsurc", "/sysroot/etc/hsurc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/inputrc", "/sysroot/etc/inputrc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/issue", "/sysroot/etc/issue"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/kbd", "/sysroot/etc/kbd"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/locale.conf", "/sysroot/etc/locale.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/login.defs", "/sysroot/etc/login.defs"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/lsb-release", "/sysroot/etc/lsb-release"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/lvm", "/sysroot/etc/lvm"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/machine-id", "/sysroot/etc/machine-id"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/man_db.conf", "/sysroot/etc/man_db.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/mdadm.conf", "/sysroot/etc/mdadm.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/modprobe.d", "/sysroot/etc/modprobe.d"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/modules-load.d", "/sysroot/etc/modules-load.d"}, nil, nil},
-			{"symlink", expectArgs{"/proc/mounts", "/sysroot/etc/mtab"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nanorc", "/sysroot/etc/nanorc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/netgroup", "/sysroot/etc/netgroup"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nix", "/sysroot/etc/nix"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nixos", "/sysroot/etc/nixos"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/NIXOS", "/sysroot/etc/NIXOS"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nscd.conf", "/sysroot/etc/nscd.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nsswitch.conf", "/sysroot/etc/nsswitch.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/os-release", "/sysroot/etc/os-release"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pam", "/sysroot/etc/pam"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pam.d", "/sysroot/etc/pam.d"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pipewire", "/sysroot/etc/pipewire"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pki", "/sysroot/etc/pki"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/polkit-1", "/sysroot/etc/polkit-1"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/profile", "/sysroot/etc/profile"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/protocols", "/sysroot/etc/protocols"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/resolv.conf", "/sysroot/etc/resolv.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/resolvconf.conf", "/sysroot/etc/resolvconf.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/rpc", "/sysroot/etc/rpc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/services", "/sysroot/etc/services"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/set-environment", "/sysroot/etc/set-environment"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/shadow", "/sysroot/etc/shadow"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/shells", "/sysroot/etc/shells"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/ssh", "/sysroot/etc/ssh"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/ssl", "/sysroot/etc/ssl"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/static", "/sysroot/etc/static"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/subgid", "/sysroot/etc/subgid"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/subuid", "/sysroot/etc/subuid"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/sudoers", "/sysroot/etc/sudoers"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/sway", "/sysroot/etc/sway"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/sysctl.d", "/sysroot/etc/sysctl.d"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/systemd", "/sysroot/etc/systemd"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/terminfo", "/sysroot/etc/terminfo"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/tmpfiles.d", "/sysroot/etc/tmpfiles.d"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/udev", "/sysroot/etc/udev"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/vconsole.conf", "/sysroot/etc/vconsole.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/X11", "/sysroot/etc/X11"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/xdg", "/sysroot/etc/xdg"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/zoneinfo", "/sysroot/etc/zoneinfo"}, nil, nil},
+				"tmpfiles.d", "udev", "vconsole.conf", "X11", "xdg", "zoneinfo"), nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/alsa", "/sysroot/etc/alsa"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/bash_logout", "/sysroot/etc/bash_logout"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/bashrc", "/sysroot/etc/bashrc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/binfmt.d", "/sysroot/etc/binfmt.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/dbus-1", "/sysroot/etc/dbus-1"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/default", "/sysroot/etc/default"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/dhcpcd.exit-hook", "/sysroot/etc/dhcpcd.exit-hook"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fonts", "/sysroot/etc/fonts"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fstab", "/sysroot/etc/fstab"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fuse.conf", "/sysroot/etc/fuse.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/host.conf", "/sysroot/etc/host.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hostname", "/sysroot/etc/hostname"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hosts", "/sysroot/etc/hosts"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hsurc", "/sysroot/etc/hsurc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/inputrc", "/sysroot/etc/inputrc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/issue", "/sysroot/etc/issue"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/kbd", "/sysroot/etc/kbd"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/locale.conf", "/sysroot/etc/locale.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/login.defs", "/sysroot/etc/login.defs"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/lsb-release", "/sysroot/etc/lsb-release"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/lvm", "/sysroot/etc/lvm"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/machine-id", "/sysroot/etc/machine-id"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/man_db.conf", "/sysroot/etc/man_db.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/mdadm.conf", "/sysroot/etc/mdadm.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/modprobe.d", "/sysroot/etc/modprobe.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/modules-load.d", "/sysroot/etc/modules-load.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{"/proc/mounts", "/sysroot/etc/mtab"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nanorc", "/sysroot/etc/nanorc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/netgroup", "/sysroot/etc/netgroup"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nix", "/sysroot/etc/nix"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nixos", "/sysroot/etc/nixos"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/NIXOS", "/sysroot/etc/NIXOS"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nscd.conf", "/sysroot/etc/nscd.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nsswitch.conf", "/sysroot/etc/nsswitch.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/os-release", "/sysroot/etc/os-release"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pam", "/sysroot/etc/pam"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pam.d", "/sysroot/etc/pam.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pipewire", "/sysroot/etc/pipewire"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pki", "/sysroot/etc/pki"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/polkit-1", "/sysroot/etc/polkit-1"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/profile", "/sysroot/etc/profile"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/protocols", "/sysroot/etc/protocols"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/resolv.conf", "/sysroot/etc/resolv.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/resolvconf.conf", "/sysroot/etc/resolvconf.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/rpc", "/sysroot/etc/rpc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/services", "/sysroot/etc/services"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/set-environment", "/sysroot/etc/set-environment"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/shadow", "/sysroot/etc/shadow"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/shells", "/sysroot/etc/shells"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/ssh", "/sysroot/etc/ssh"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/ssl", "/sysroot/etc/ssl"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/static", "/sysroot/etc/static"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/subgid", "/sysroot/etc/subgid"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/subuid", "/sysroot/etc/subuid"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/sudoers", "/sysroot/etc/sudoers"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/sway", "/sysroot/etc/sway"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/sysctl.d", "/sysroot/etc/sysctl.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/systemd", "/sysroot/etc/systemd"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/terminfo", "/sysroot/etc/terminfo"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/tmpfiles.d", "/sysroot/etc/tmpfiles.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/udev", "/sysroot/etc/udev"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/vconsole.conf", "/sysroot/etc/vconsole.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/X11", "/sysroot/etc/X11"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/xdg", "/sysroot/etc/xdg"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/zoneinfo", "/sysroot/etc/zoneinfo"}, nil, nil),
 		}, nil},
 
 		{"success", new(Params), &AutoEtcOp{
 			Prefix: "81ceabb30d37bbdb3868004629cb84e9",
-		}, nil, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/etc/", os.FileMode(0755)}, nil, nil},
-			{"readdir", expectArgs{"/sysroot/etc/.host/81ceabb30d37bbdb3868004629cb84e9"}, stubDir(
+		}, nil, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/etc/", os.FileMode(0755)}, nil, nil),
+			call("readdir", stub.ExpectArgs{"/sysroot/etc/.host/81ceabb30d37bbdb3868004629cb84e9"}, stubDir(
 				"alsa", "bash_logout", "bashrc", "binfmt.d", "dbus-1", "default", "dhcpcd.exit-hook", "fonts",
 				"fstab", "fuse.conf", "group", "host.conf", "hostname", "hosts", "hsurc", "inputrc", "issue", "kbd",
 				"locale.conf", "login.defs", "lsb-release", "lvm", "machine-id", "man_db.conf", "mdadm.conf",
@@ -179,72 +180,72 @@ func TestAutoEtcOp(t *testing.T) {
 				"nsswitch.conf", "os-release", "pam", "pam.d", "passwd", "pipewire", "pki", "polkit-1", "profile",
 				"protocols", "resolv.conf", "resolvconf.conf", "rpc", "services", "set-environment", "shadow", "shells",
 				"ssh", "ssl", "static", "subgid", "subuid", "sudoers", "sway", "sysctl.d", "systemd", "terminfo",
-				"tmpfiles.d", "udev", "vconsole.conf", "X11", "xdg", "zoneinfo"), nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/alsa", "/sysroot/etc/alsa"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/bash_logout", "/sysroot/etc/bash_logout"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/bashrc", "/sysroot/etc/bashrc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/binfmt.d", "/sysroot/etc/binfmt.d"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/dbus-1", "/sysroot/etc/dbus-1"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/default", "/sysroot/etc/default"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/dhcpcd.exit-hook", "/sysroot/etc/dhcpcd.exit-hook"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fonts", "/sysroot/etc/fonts"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fstab", "/sysroot/etc/fstab"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fuse.conf", "/sysroot/etc/fuse.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/host.conf", "/sysroot/etc/host.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hostname", "/sysroot/etc/hostname"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hosts", "/sysroot/etc/hosts"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hsurc", "/sysroot/etc/hsurc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/inputrc", "/sysroot/etc/inputrc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/issue", "/sysroot/etc/issue"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/kbd", "/sysroot/etc/kbd"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/locale.conf", "/sysroot/etc/locale.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/login.defs", "/sysroot/etc/login.defs"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/lsb-release", "/sysroot/etc/lsb-release"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/lvm", "/sysroot/etc/lvm"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/machine-id", "/sysroot/etc/machine-id"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/man_db.conf", "/sysroot/etc/man_db.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/mdadm.conf", "/sysroot/etc/mdadm.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/modprobe.d", "/sysroot/etc/modprobe.d"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/modules-load.d", "/sysroot/etc/modules-load.d"}, nil, nil},
-			{"symlink", expectArgs{"/proc/mounts", "/sysroot/etc/mtab"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nanorc", "/sysroot/etc/nanorc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/netgroup", "/sysroot/etc/netgroup"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nix", "/sysroot/etc/nix"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nixos", "/sysroot/etc/nixos"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/NIXOS", "/sysroot/etc/NIXOS"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nscd.conf", "/sysroot/etc/nscd.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nsswitch.conf", "/sysroot/etc/nsswitch.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/os-release", "/sysroot/etc/os-release"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pam", "/sysroot/etc/pam"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pam.d", "/sysroot/etc/pam.d"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pipewire", "/sysroot/etc/pipewire"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pki", "/sysroot/etc/pki"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/polkit-1", "/sysroot/etc/polkit-1"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/profile", "/sysroot/etc/profile"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/protocols", "/sysroot/etc/protocols"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/resolv.conf", "/sysroot/etc/resolv.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/resolvconf.conf", "/sysroot/etc/resolvconf.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/rpc", "/sysroot/etc/rpc"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/services", "/sysroot/etc/services"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/set-environment", "/sysroot/etc/set-environment"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/shadow", "/sysroot/etc/shadow"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/shells", "/sysroot/etc/shells"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/ssh", "/sysroot/etc/ssh"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/ssl", "/sysroot/etc/ssl"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/static", "/sysroot/etc/static"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/subgid", "/sysroot/etc/subgid"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/subuid", "/sysroot/etc/subuid"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/sudoers", "/sysroot/etc/sudoers"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/sway", "/sysroot/etc/sway"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/sysctl.d", "/sysroot/etc/sysctl.d"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/systemd", "/sysroot/etc/systemd"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/terminfo", "/sysroot/etc/terminfo"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/tmpfiles.d", "/sysroot/etc/tmpfiles.d"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/udev", "/sysroot/etc/udev"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/vconsole.conf", "/sysroot/etc/vconsole.conf"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/X11", "/sysroot/etc/X11"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/xdg", "/sysroot/etc/xdg"}, nil, nil},
-			{"symlink", expectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/zoneinfo", "/sysroot/etc/zoneinfo"}, nil, nil},
+				"tmpfiles.d", "udev", "vconsole.conf", "X11", "xdg", "zoneinfo"), nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/alsa", "/sysroot/etc/alsa"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/bash_logout", "/sysroot/etc/bash_logout"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/bashrc", "/sysroot/etc/bashrc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/binfmt.d", "/sysroot/etc/binfmt.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/dbus-1", "/sysroot/etc/dbus-1"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/default", "/sysroot/etc/default"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/dhcpcd.exit-hook", "/sysroot/etc/dhcpcd.exit-hook"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fonts", "/sysroot/etc/fonts"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fstab", "/sysroot/etc/fstab"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/fuse.conf", "/sysroot/etc/fuse.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/host.conf", "/sysroot/etc/host.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hostname", "/sysroot/etc/hostname"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hosts", "/sysroot/etc/hosts"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/hsurc", "/sysroot/etc/hsurc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/inputrc", "/sysroot/etc/inputrc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/issue", "/sysroot/etc/issue"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/kbd", "/sysroot/etc/kbd"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/locale.conf", "/sysroot/etc/locale.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/login.defs", "/sysroot/etc/login.defs"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/lsb-release", "/sysroot/etc/lsb-release"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/lvm", "/sysroot/etc/lvm"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/machine-id", "/sysroot/etc/machine-id"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/man_db.conf", "/sysroot/etc/man_db.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/mdadm.conf", "/sysroot/etc/mdadm.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/modprobe.d", "/sysroot/etc/modprobe.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/modules-load.d", "/sysroot/etc/modules-load.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{"/proc/mounts", "/sysroot/etc/mtab"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nanorc", "/sysroot/etc/nanorc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/netgroup", "/sysroot/etc/netgroup"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nix", "/sysroot/etc/nix"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nixos", "/sysroot/etc/nixos"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/NIXOS", "/sysroot/etc/NIXOS"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nscd.conf", "/sysroot/etc/nscd.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/nsswitch.conf", "/sysroot/etc/nsswitch.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/os-release", "/sysroot/etc/os-release"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pam", "/sysroot/etc/pam"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pam.d", "/sysroot/etc/pam.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pipewire", "/sysroot/etc/pipewire"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/pki", "/sysroot/etc/pki"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/polkit-1", "/sysroot/etc/polkit-1"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/profile", "/sysroot/etc/profile"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/protocols", "/sysroot/etc/protocols"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/resolv.conf", "/sysroot/etc/resolv.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/resolvconf.conf", "/sysroot/etc/resolvconf.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/rpc", "/sysroot/etc/rpc"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/services", "/sysroot/etc/services"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/set-environment", "/sysroot/etc/set-environment"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/shadow", "/sysroot/etc/shadow"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/shells", "/sysroot/etc/shells"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/ssh", "/sysroot/etc/ssh"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/ssl", "/sysroot/etc/ssl"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/static", "/sysroot/etc/static"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/subgid", "/sysroot/etc/subgid"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/subuid", "/sysroot/etc/subuid"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/sudoers", "/sysroot/etc/sudoers"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/sway", "/sysroot/etc/sway"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/sysctl.d", "/sysroot/etc/sysctl.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/systemd", "/sysroot/etc/systemd"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/terminfo", "/sysroot/etc/terminfo"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/tmpfiles.d", "/sysroot/etc/tmpfiles.d"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/udev", "/sysroot/etc/udev"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/vconsole.conf", "/sysroot/etc/vconsole.conf"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/X11", "/sysroot/etc/X11"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/xdg", "/sysroot/etc/xdg"}, nil, nil),
+			call("symlink", stub.ExpectArgs{".host/81ceabb30d37bbdb3868004629cb84e9/zoneinfo", "/sysroot/etc/zoneinfo"}, nil, nil),
 		}, nil},
 	})
 

container/autoroot.go

@@ -3,7 +3,6 @@ package container
 import (
 	"encoding/gob"
 	"fmt"
-	"io/fs"
 )
 
 func init() { gob.Register(new(AutoRootOp)) }
@@ -30,7 +29,7 @@ func (r *AutoRootOp) Valid() bool { return r != nil && r.Host != nil }
 
 func (r *AutoRootOp) early(state *setupState, k syscallDispatcher) error {
 	if d, err := k.readdir(r.Host.String()); err != nil {
-		return wrapErrSelf(err)
+		return err
 	} else {
 		r.resolved = make([]Op, 0, len(d))
 		for _, ent := range d {
@@ -53,7 +52,7 @@ func (r *AutoRootOp) early(state *setupState, k syscallDispatcher) error {
 
 func (r *AutoRootOp) apply(state *setupState, k syscallDispatcher) error {
 	if state.nonrepeatable&nrAutoRoot != 0 {
-		return msg.WrapErr(fs.ErrInvalid, "autoroot is not repeatable")
+		return OpRepeatError("autoroot")
 	}
 	state.nonrepeatable |= nrAutoRoot
 

container/autoroot_test.go

@@ -2,14 +2,15 @@ package container
 
 import (
 	"errors"
-	"io/fs"
 	"os"
 	"testing"
+
+	"hakurei.app/container/stub"
 )
 
 func TestAutoRootOp(t *testing.T) {
 	t.Run("nonrepeatable", func(t *testing.T) {
-		wantErr := msg.WrapErr(fs.ErrInvalid, "autoroot is not repeatable")
+		wantErr := OpRepeatError("autoroot")
 		if err := new(AutoRootOp).apply(&setupState{nonrepeatable: nrAutoRoot}, nil); !errors.Is(err, wantErr) {
 			t.Errorf("apply: error = %v, want %v", err, wantErr)
 		}
@@ -19,100 +20,100 @@ func TestAutoRootOp(t *testing.T) {
 		{"readdir", &Params{ParentPerm: 0750}, &AutoRootOp{
 			Host:  MustAbs("/"),
 			Flags: BindWritable,
-		}, []kexpect{
-			{"readdir", expectArgs{"/"}, stubDir(), errUnique},
-		}, wrapErrSelf(errUnique), nil, nil},
+		}, []stub.Call{
+			call("readdir", stub.ExpectArgs{"/"}, stubDir(), stub.UniqueError(2)),
+		}, stub.UniqueError(2), nil, nil},
 
 		{"early", &Params{ParentPerm: 0750}, &AutoRootOp{
 			Host:  MustAbs("/"),
 			Flags: BindWritable,
-		}, []kexpect{
-			{"readdir", expectArgs{"/"}, stubDir("bin", "dev", "etc", "home", "lib64",
-				"lost+found", "mnt", "nix", "proc", "root", "run", "srv", "sys", "tmp", "usr", "var"), nil},
-			{"evalSymlinks", expectArgs{"/bin"}, "", errUnique},
-		}, wrapErrSelf(errUnique), nil, nil},
+		}, []stub.Call{
+			call("readdir", stub.ExpectArgs{"/"}, stubDir("bin", "dev", "etc", "home", "lib64",
+				"lost+found", "mnt", "nix", "proc", "root", "run", "srv", "sys", "tmp", "usr", "var"), nil),
+			call("evalSymlinks", stub.ExpectArgs{"/bin"}, "", stub.UniqueError(1)),
+		}, stub.UniqueError(1), nil, nil},
 
 		{"apply", &Params{ParentPerm: 0750}, &AutoRootOp{
 			Host:  MustAbs("/"),
 			Flags: BindWritable,
-		}, []kexpect{
-			{"readdir", expectArgs{"/"}, stubDir("bin", "dev", "etc", "home", "lib64",
-				"lost+found", "mnt", "nix", "proc", "root", "run", "srv", "sys", "tmp", "usr", "var"), nil},
-			{"evalSymlinks", expectArgs{"/bin"}, "/usr/bin", nil},
-			{"evalSymlinks", expectArgs{"/home"}, "/home", nil},
-			{"evalSymlinks", expectArgs{"/lib64"}, "/lib64", nil},
-			{"evalSymlinks", expectArgs{"/lost+found"}, "/lost+found", nil},
-			{"evalSymlinks", expectArgs{"/nix"}, "/nix", nil},
-			{"evalSymlinks", expectArgs{"/root"}, "/root", nil},
-			{"evalSymlinks", expectArgs{"/run"}, "/run", nil},
-			{"evalSymlinks", expectArgs{"/srv"}, "/srv", nil},
-			{"evalSymlinks", expectArgs{"/sys"}, "/sys", nil},
-			{"evalSymlinks", expectArgs{"/usr"}, "/usr", nil},
-			{"evalSymlinks", expectArgs{"/var"}, "/var", nil},
-		}, nil, []kexpect{
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/usr/bin"), MustAbs("/bin"), MustAbs("/bin"), BindWritable}}}, nil, nil},
-			{"stat", expectArgs{"/host/usr/bin"}, isDirFi(false), errUnique},
-		}, wrapErrSelf(errUnique)},
+		}, []stub.Call{
+			call("readdir", stub.ExpectArgs{"/"}, stubDir("bin", "dev", "etc", "home", "lib64",
+				"lost+found", "mnt", "nix", "proc", "root", "run", "srv", "sys", "tmp", "usr", "var"), nil),
+			call("evalSymlinks", stub.ExpectArgs{"/bin"}, "/usr/bin", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/home"}, "/home", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/lib64"}, "/lib64", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/lost+found"}, "/lost+found", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/nix"}, "/nix", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/root"}, "/root", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/run"}, "/run", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/srv"}, "/srv", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/sys"}, "/sys", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/usr"}, "/usr", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var"}, "/var", nil),
+		}, nil, []stub.Call{
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/usr/bin"), MustAbs("/bin"), MustAbs("/bin"), BindWritable}}}, nil, nil),
+			call("stat", stub.ExpectArgs{"/host/usr/bin"}, isDirFi(false), stub.UniqueError(0)),
+		}, stub.UniqueError(0)},
 
 		{"success pd", &Params{ParentPerm: 0750}, &AutoRootOp{
 			Host:  MustAbs("/"),
 			Flags: BindWritable,
-		}, []kexpect{
-			{"readdir", expectArgs{"/"}, stubDir("bin", "dev", "etc", "home", "lib64",
-				"lost+found", "mnt", "nix", "proc", "root", "run", "srv", "sys", "tmp", "usr", "var"), nil},
-			{"evalSymlinks", expectArgs{"/bin"}, "/usr/bin", nil},
-			{"evalSymlinks", expectArgs{"/home"}, "/home", nil},
-			{"evalSymlinks", expectArgs{"/lib64"}, "/lib64", nil},
-			{"evalSymlinks", expectArgs{"/lost+found"}, "/lost+found", nil},
-			{"evalSymlinks", expectArgs{"/nix"}, "/nix", nil},
-			{"evalSymlinks", expectArgs{"/root"}, "/root", nil},
-			{"evalSymlinks", expectArgs{"/run"}, "/run", nil},
-			{"evalSymlinks", expectArgs{"/srv"}, "/srv", nil},
-			{"evalSymlinks", expectArgs{"/sys"}, "/sys", nil},
-			{"evalSymlinks", expectArgs{"/usr"}, "/usr", nil},
-			{"evalSymlinks", expectArgs{"/var"}, "/var", nil},
-		}, nil, []kexpect{
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/usr/bin"), MustAbs("/bin"), MustAbs("/bin"), BindWritable}}}, nil, nil}, {"stat", expectArgs{"/host/usr/bin"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/bin", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/usr/bin", "/sysroot/bin", uintptr(0x4004), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/home"), MustAbs("/home"), MustAbs("/home"), BindWritable}}}, nil, nil}, {"stat", expectArgs{"/host/home"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/home", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/home", "/sysroot/home", uintptr(0x4004), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/lib64"), MustAbs("/lib64"), MustAbs("/lib64"), BindWritable}}}, nil, nil}, {"stat", expectArgs{"/host/lib64"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/lib64", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/lib64", "/sysroot/lib64", uintptr(0x4004), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/lost+found"), MustAbs("/lost+found"), MustAbs("/lost+found"), BindWritable}}}, nil, nil}, {"stat", expectArgs{"/host/lost+found"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/lost+found", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/lost+found", "/sysroot/lost+found", uintptr(0x4004), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/nix"), MustAbs("/nix"), MustAbs("/nix"), BindWritable}}}, nil, nil}, {"stat", expectArgs{"/host/nix"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/nix", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/nix", "/sysroot/nix", uintptr(0x4004), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/root"), MustAbs("/root"), MustAbs("/root"), BindWritable}}}, nil, nil}, {"stat", expectArgs{"/host/root"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/root", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/root", "/sysroot/root", uintptr(0x4004), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/run"), MustAbs("/run"), MustAbs("/run"), BindWritable}}}, nil, nil}, {"stat", expectArgs{"/host/run"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/run", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/run", "/sysroot/run", uintptr(0x4004), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/srv"), MustAbs("/srv"), MustAbs("/srv"), BindWritable}}}, nil, nil}, {"stat", expectArgs{"/host/srv"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/srv", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/srv", "/sysroot/srv", uintptr(0x4004), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/sys"), MustAbs("/sys"), MustAbs("/sys"), BindWritable}}}, nil, nil}, {"stat", expectArgs{"/host/sys"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/sys", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/sys", "/sysroot/sys", uintptr(0x4004), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/usr"), MustAbs("/usr"), MustAbs("/usr"), BindWritable}}}, nil, nil}, {"stat", expectArgs{"/host/usr"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/usr", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/usr", "/sysroot/usr", uintptr(0x4004), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var"), MustAbs("/var"), MustAbs("/var"), BindWritable}}}, nil, nil}, {"stat", expectArgs{"/host/var"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/var", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/var", "/sysroot/var", uintptr(0x4004), false}, nil, nil},
+		}, []stub.Call{
+			call("readdir", stub.ExpectArgs{"/"}, stubDir("bin", "dev", "etc", "home", "lib64",
+				"lost+found", "mnt", "nix", "proc", "root", "run", "srv", "sys", "tmp", "usr", "var"), nil),
+			call("evalSymlinks", stub.ExpectArgs{"/bin"}, "/usr/bin", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/home"}, "/home", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/lib64"}, "/lib64", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/lost+found"}, "/lost+found", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/nix"}, "/nix", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/root"}, "/root", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/run"}, "/run", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/srv"}, "/srv", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/sys"}, "/sys", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/usr"}, "/usr", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var"}, "/var", nil),
+		}, nil, []stub.Call{
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/usr/bin"), MustAbs("/bin"), MustAbs("/bin"), BindWritable}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/usr/bin"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/bin", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/usr/bin", "/sysroot/bin", uintptr(0x4004), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/home"), MustAbs("/home"), MustAbs("/home"), BindWritable}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/home"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/home", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/home", "/sysroot/home", uintptr(0x4004), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/lib64"), MustAbs("/lib64"), MustAbs("/lib64"), BindWritable}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/lib64"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/lib64", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/lib64", "/sysroot/lib64", uintptr(0x4004), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/lost+found"), MustAbs("/lost+found"), MustAbs("/lost+found"), BindWritable}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/lost+found"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/lost+found", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/lost+found", "/sysroot/lost+found", uintptr(0x4004), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/nix"), MustAbs("/nix"), MustAbs("/nix"), BindWritable}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/nix"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/nix", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/nix", "/sysroot/nix", uintptr(0x4004), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/root"), MustAbs("/root"), MustAbs("/root"), BindWritable}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/root"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/root", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/root", "/sysroot/root", uintptr(0x4004), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/run"), MustAbs("/run"), MustAbs("/run"), BindWritable}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/run"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/run", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/run", "/sysroot/run", uintptr(0x4004), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/srv"), MustAbs("/srv"), MustAbs("/srv"), BindWritable}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/srv"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/srv", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/srv", "/sysroot/srv", uintptr(0x4004), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/sys"), MustAbs("/sys"), MustAbs("/sys"), BindWritable}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/sys"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/sys", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/sys", "/sysroot/sys", uintptr(0x4004), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/usr"), MustAbs("/usr"), MustAbs("/usr"), BindWritable}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/usr"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/usr", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/usr", "/sysroot/usr", uintptr(0x4004), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var"), MustAbs("/var"), MustAbs("/var"), BindWritable}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/var"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/var", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/var", "/sysroot/var", uintptr(0x4004), false}, nil, nil),
 		}, nil},
 
 		{"success", &Params{ParentPerm: 0750}, &AutoRootOp{
 			Host: MustAbs("/var/lib/planterette/base/debian:f92c9052"),
-		}, []kexpect{
-			{"readdir", expectArgs{"/var/lib/planterette/base/debian:f92c9052"}, stubDir("bin", "dev", "etc", "home", "lib64",
-				"lost+found", "mnt", "nix", "proc", "root", "run", "srv", "sys", "tmp", "usr", "var"), nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052/bin"}, "/var/lib/planterette/base/debian:f92c9052/usr/bin", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052/home"}, "/var/lib/planterette/base/debian:f92c9052/home", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052/lib64"}, "/var/lib/planterette/base/debian:f92c9052/lib64", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052/lost+found"}, "/var/lib/planterette/base/debian:f92c9052/lost+found", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052/nix"}, "/var/lib/planterette/base/debian:f92c9052/nix", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052/root"}, "/var/lib/planterette/base/debian:f92c9052/root", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052/run"}, "/var/lib/planterette/base/debian:f92c9052/run", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052/srv"}, "/var/lib/planterette/base/debian:f92c9052/srv", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052/sys"}, "/var/lib/planterette/base/debian:f92c9052/sys", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052/usr"}, "/var/lib/planterette/base/debian:f92c9052/usr", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052/var"}, "/var/lib/planterette/base/debian:f92c9052/var", nil},
-		}, nil, []kexpect{
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/usr/bin"), MustAbs("/var/lib/planterette/base/debian:f92c9052/bin"), MustAbs("/bin"), 0}}}, nil, nil}, {"stat", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/usr/bin"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/bin", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/usr/bin", "/sysroot/bin", uintptr(0x4005), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/home"), MustAbs("/var/lib/planterette/base/debian:f92c9052/home"), MustAbs("/home"), 0}}}, nil, nil}, {"stat", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/home"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/home", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/home", "/sysroot/home", uintptr(0x4005), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/lib64"), MustAbs("/var/lib/planterette/base/debian:f92c9052/lib64"), MustAbs("/lib64"), 0}}}, nil, nil}, {"stat", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/lib64"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/lib64", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/lib64", "/sysroot/lib64", uintptr(0x4005), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/lost+found"), MustAbs("/var/lib/planterette/base/debian:f92c9052/lost+found"), MustAbs("/lost+found"), 0}}}, nil, nil}, {"stat", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/lost+found"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/lost+found", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/lost+found", "/sysroot/lost+found", uintptr(0x4005), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/nix"), MustAbs("/var/lib/planterette/base/debian:f92c9052/nix"), MustAbs("/nix"), 0}}}, nil, nil}, {"stat", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/nix"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/nix", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/nix", "/sysroot/nix", uintptr(0x4005), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/root"), MustAbs("/var/lib/planterette/base/debian:f92c9052/root"), MustAbs("/root"), 0}}}, nil, nil}, {"stat", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/root"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/root", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/root", "/sysroot/root", uintptr(0x4005), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/run"), MustAbs("/var/lib/planterette/base/debian:f92c9052/run"), MustAbs("/run"), 0}}}, nil, nil}, {"stat", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/run"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/run", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/run", "/sysroot/run", uintptr(0x4005), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/srv"), MustAbs("/var/lib/planterette/base/debian:f92c9052/srv"), MustAbs("/srv"), 0}}}, nil, nil}, {"stat", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/srv"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/srv", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/srv", "/sysroot/srv", uintptr(0x4005), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/sys"), MustAbs("/var/lib/planterette/base/debian:f92c9052/sys"), MustAbs("/sys"), 0}}}, nil, nil}, {"stat", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/sys"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/sys", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/sys", "/sysroot/sys", uintptr(0x4005), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/usr"), MustAbs("/var/lib/planterette/base/debian:f92c9052/usr"), MustAbs("/usr"), 0}}}, nil, nil}, {"stat", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/usr"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/usr", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/usr", "/sysroot/usr", uintptr(0x4005), false}, nil, nil},
-			{"verbosef", expectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/var"), MustAbs("/var/lib/planterette/base/debian:f92c9052/var"), MustAbs("/var"), 0}}}, nil, nil}, {"stat", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/var"}, isDirFi(true), nil}, {"mkdirAll", expectArgs{"/sysroot/var", os.FileMode(0700)}, nil, nil}, {"bindMount", expectArgs{"/host/var/lib/planterette/base/debian:f92c9052/var", "/sysroot/var", uintptr(0x4005), false}, nil, nil},
+		}, []stub.Call{
+			call("readdir", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052"}, stubDir("bin", "dev", "etc", "home", "lib64",
+				"lost+found", "mnt", "nix", "proc", "root", "run", "srv", "sys", "tmp", "usr", "var"), nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052/bin"}, "/var/lib/planterette/base/debian:f92c9052/usr/bin", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052/home"}, "/var/lib/planterette/base/debian:f92c9052/home", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052/lib64"}, "/var/lib/planterette/base/debian:f92c9052/lib64", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052/lost+found"}, "/var/lib/planterette/base/debian:f92c9052/lost+found", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052/nix"}, "/var/lib/planterette/base/debian:f92c9052/nix", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052/root"}, "/var/lib/planterette/base/debian:f92c9052/root", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052/run"}, "/var/lib/planterette/base/debian:f92c9052/run", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052/srv"}, "/var/lib/planterette/base/debian:f92c9052/srv", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052/sys"}, "/var/lib/planterette/base/debian:f92c9052/sys", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052/usr"}, "/var/lib/planterette/base/debian:f92c9052/usr", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052/var"}, "/var/lib/planterette/base/debian:f92c9052/var", nil),
+		}, nil, []stub.Call{
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/usr/bin"), MustAbs("/var/lib/planterette/base/debian:f92c9052/bin"), MustAbs("/bin"), 0}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/usr/bin"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/bin", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/usr/bin", "/sysroot/bin", uintptr(0x4005), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/home"), MustAbs("/var/lib/planterette/base/debian:f92c9052/home"), MustAbs("/home"), 0}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/home"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/home", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/home", "/sysroot/home", uintptr(0x4005), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/lib64"), MustAbs("/var/lib/planterette/base/debian:f92c9052/lib64"), MustAbs("/lib64"), 0}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/lib64"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/lib64", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/lib64", "/sysroot/lib64", uintptr(0x4005), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/lost+found"), MustAbs("/var/lib/planterette/base/debian:f92c9052/lost+found"), MustAbs("/lost+found"), 0}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/lost+found"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/lost+found", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/lost+found", "/sysroot/lost+found", uintptr(0x4005), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/nix"), MustAbs("/var/lib/planterette/base/debian:f92c9052/nix"), MustAbs("/nix"), 0}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/nix"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/nix", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/nix", "/sysroot/nix", uintptr(0x4005), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/root"), MustAbs("/var/lib/planterette/base/debian:f92c9052/root"), MustAbs("/root"), 0}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/root"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/root", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/root", "/sysroot/root", uintptr(0x4005), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/run"), MustAbs("/var/lib/planterette/base/debian:f92c9052/run"), MustAbs("/run"), 0}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/run"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/run", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/run", "/sysroot/run", uintptr(0x4005), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/srv"), MustAbs("/var/lib/planterette/base/debian:f92c9052/srv"), MustAbs("/srv"), 0}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/srv"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/srv", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/srv", "/sysroot/srv", uintptr(0x4005), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/sys"), MustAbs("/var/lib/planterette/base/debian:f92c9052/sys"), MustAbs("/sys"), 0}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/sys"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/sys", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/sys", "/sysroot/sys", uintptr(0x4005), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/usr"), MustAbs("/var/lib/planterette/base/debian:f92c9052/usr"), MustAbs("/usr"), 0}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/usr"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/usr", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/usr", "/sysroot/usr", uintptr(0x4005), false}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"%s %s", []any{"mounting", &BindMountOp{MustAbs("/var/lib/planterette/base/debian:f92c9052/var"), MustAbs("/var/lib/planterette/base/debian:f92c9052/var"), MustAbs("/var"), 0}}}, nil, nil), call("stat", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/var"}, isDirFi(true), nil), call("mkdirAll", stub.ExpectArgs{"/sysroot/var", os.FileMode(0700)}, nil, nil), call("bindMount", stub.ExpectArgs{"/host/var/lib/planterette/base/debian:f92c9052/var", "/sysroot/var", uintptr(0x4005), false}, nil, nil),
 		}, nil},
 	})
 

container/container.go

@@ -64,7 +64,7 @@ type (
 		Args []string
 		// Deliver SIGINT to the initial process on context cancellation.
 		ForwardCancel bool
-		// time to wait for linger processes after death of initial process
+		// Time to wait for processes lingering after the initial process terminates.
 		AdoptWaitDelay time.Duration
 
 		// Mapped Uid in user namespace.
@@ -99,17 +99,66 @@ type (
 	}
 )
 
-// Start starts the container init. The init process blocks until Serve is called.
-func (p *Container) Start() error {
-	if p.cmd != nil {
-		return errors.New("container: already started")
+// A StartError contains additional information on a container startup failure.
+type StartError struct {
+	// Fatal suggests whether this error should be considered fatal for the entire program.
+	Fatal bool
+	// Step refers to the part of the setup this error is returned from.
+	Step string
+	// Err is the underlying error.
+	Err error
+	// Origin is whether this error originated from the [Container.Start] method.
+	Origin bool
+	// Passthrough is whether the Error method is passed through to Err.
+	Passthrough bool
+}
+
+func (e *StartError) Unwrap() error { return e.Err }
+func (e *StartError) Error() string {
+	if e.Passthrough {
+		return e.Err.Error()
 	}
-	if p.Ops == nil || len(*p.Ops) == 0 {
-		return errors.New("container: starting an empty container")
+	if e.Origin {
+		return e.Step
 	}
 
-	ctx, cancel := context.WithCancel(p.ctx)
-	p.cancel = cancel
+	{
+		var syscallError *os.SyscallError
+		if errors.As(e.Err, &syscallError) && syscallError != nil {
+			return e.Step + " " + syscallError.Error()
+		}
+	}
+
+	return e.Step + ": " + e.Err.Error()
+}
+
+// Message returns a user-facing error message.
+func (e *StartError) Message() string {
+	if e.Passthrough {
+		switch {
+		case errors.As(e.Err, new(*os.PathError)),
+			errors.As(e.Err, new(*os.SyscallError)):
+			return "cannot " + e.Err.Error()
+
+		default:
+			return e.Err.Error()
+		}
+	}
+	if e.Origin {
+		return e.Step
+	}
+	return "cannot " + e.Error()
+}
+
+// Start starts the container init. The init process blocks until Serve is called.
+func (p *Container) Start() error {
+	if p == nil || p.cmd == nil ||
+		p.Ops == nil || len(*p.Ops) == 0 {
+		return errors.New("container: starting an invalid container")
+	}
+	if p.cmd.Process != nil {
+		return errors.New("container: already started")
+	}
 
 	// map to overflow id to work around ownership checks
 	if p.Uid < 1 {
@@ -131,9 +180,17 @@ func (p *Container) Start() error {
 		p.AdoptWaitDelay = 0
 	}
 
-	p.cmd = exec.CommandContext(ctx, MustExecutable())
+	if p.cmd.Stdin == nil {
+		p.cmd.Stdin = p.Stdin
+	}
+	if p.cmd.Stdout == nil {
+		p.cmd.Stdout = p.Stdout
+	}
+	if p.cmd.Stderr == nil {
+		p.cmd.Stderr = p.Stderr
+	}
+
 	p.cmd.Args = []string{initName}
-	p.cmd.Stdin, p.cmd.Stdout, p.cmd.Stderr = p.Stdin, p.Stdout, p.Stderr
 	p.cmd.WaitDelay = p.WaitDelay
 	if p.Cancel != nil {
 		p.cmd.Cancel = func() error { return p.Cancel(p.cmd) }
@@ -167,8 +224,7 @@ func (p *Container) Start() error {
 
 	// place setup pipe before user supplied extra files, this is later restored by init
 	if fd, e, err := Setup(&p.cmd.ExtraFiles); err != nil {
-		return wrapErrSuffix(err,
-			"cannot create shim setup pipe:")
+		return &StartError{true, "set up params stream", err, false, false}
 	} else {
 		p.setup = e
 		p.cmd.Env = []string{setupEnv + "=" + strconv.Itoa(fd)}
@@ -183,8 +239,7 @@ func (p *Container) Start() error {
 		done <- func() error { // setup depending on per-thread state must happen here
 			// PR_SET_NO_NEW_PRIVS: depends on per-thread state but acts on all processes created from that thread
 			if err := SetNoNewPrivs(); err != nil {
-				return wrapErrSuffix(err,
-					"prctl(PR_SET_NO_NEW_PRIVS):")
+				return &StartError{true, "prctl(PR_SET_NO_NEW_PRIVS)", err, false, false}
 			}
 
 			// landlock: depends on per-thread state but acts on a process group
@@ -200,28 +255,24 @@ func (p *Container) Start() error {
 						// already covered by namespaces (pid)
 						goto landlockOut
 					}
-					return wrapErrSuffix(err,
-						"landlock does not appear to be enabled:")
+					return &StartError{false, "get landlock ABI", err, false, false}
 				} else if abi < 6 {
 					if p.HostAbstract {
 						// see above comment
 						goto landlockOut
 					}
-					return msg.WrapErr(ENOSYS,
-						"kernel version too old for LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET")
+					return &StartError{false, "kernel version too old for LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET", ENOSYS, true, false}
 				} else {
 					msg.Verbosef("landlock abi version %d", abi)
 				}
 
 				if rulesetFd, err := rulesetAttr.Create(0); err != nil {
-					return wrapErrSuffix(err,
-						"cannot create landlock ruleset:")
+					return &StartError{true, "create landlock ruleset", err, false, false}
 				} else {
 					msg.Verbosef("enforcing landlock ruleset %s", rulesetAttr)
 					if err = LandlockRestrictSelf(rulesetFd, 0); err != nil {
 						_ = Close(rulesetFd)
-						return wrapErrSuffix(err,
-							"cannot enforce landlock ruleset:")
+						return &StartError{true, "enforce landlock ruleset", err, false, false}
 					}
 					if err = Close(rulesetFd); err != nil {
 						msg.Verbosef("cannot close landlock ruleset: %v", err)
@@ -234,7 +285,7 @@ func (p *Container) Start() error {
 
 			msg.Verbose("starting container init")
 			if err := p.cmd.Start(); err != nil {
-				return msg.WrapErr(err, err.Error())
+				return &StartError{false, "start container init", err, false, true}
 			}
 			return nil
 		}()
@@ -257,7 +308,7 @@ func (p *Container) Serve() error {
 
 	if p.Path == nil {
 		p.cancel()
-		return msg.WrapErr(EINVAL, "invalid executable pathname")
+		return &StartError{false, "invalid executable pathname", EINVAL, true, false}
 	}
 
 	// do not transmit nil
@@ -285,7 +336,7 @@ func (p *Container) Serve() error {
 
 // Wait waits for the container init process to exit and releases any resources associated with the [Container].
 func (p *Container) Wait() error {
-	if p.cmd == nil {
+	if p.cmd == nil || p.cmd.Process == nil {
 		return EINVAL
 	}
 
@@ -297,6 +348,36 @@ func (p *Container) Wait() error {
 	return err
 }
 
+// StdinPipe calls the [exec.Cmd] method with the same name.
+func (p *Container) StdinPipe() (w io.WriteCloser, err error) {
+	if p.Stdin != nil {
+		return nil, errors.New("container: Stdin already set")
+	}
+	w, err = p.cmd.StdinPipe()
+	p.Stdin = p.cmd.Stdin
+	return
+}
+
+// StdoutPipe calls the [exec.Cmd] method with the same name.
+func (p *Container) StdoutPipe() (r io.ReadCloser, err error) {
+	if p.Stdout != nil {
+		return nil, errors.New("container: Stdout already set")
+	}
+	r, err = p.cmd.StdoutPipe()
+	p.Stdout = p.cmd.Stdout
+	return
+}
+
+// StderrPipe calls the [exec.Cmd] method with the same name.
+func (p *Container) StderrPipe() (r io.ReadCloser, err error) {
+	if p.Stderr != nil {
+		return nil, errors.New("container: Stderr already set")
+	}
+	r, err = p.cmd.StderrPipe()
+	p.Stderr = p.cmd.Stderr
+	return
+}
+
 func (p *Container) String() string {
 	return fmt.Sprintf("argv: %q, filter: %v, rules: %d, flags: %#x, presets: %#x",
 		p.Args, !p.SeccompDisable, len(p.SeccompRules), int(p.SeccompFlags), int(p.SeccompPresets))
@@ -312,7 +393,11 @@ func (p *Container) ProcessState() *os.ProcessState {
 
 // New returns the address to a new instance of [Container] that requires further initialisation before use.
 func New(ctx context.Context) *Container {
-	return &Container{ctx: ctx, Params: Params{Ops: new(Ops)}}
+	p := &Container{ctx: ctx, Params: Params{Ops: new(Ops)}}
+	c, cancel := context.WithCancel(ctx)
+	p.cancel = cancel
+	p.cmd = exec.CommandContext(c, MustExecutable())
+	return p
 }
 
 // NewCommand calls [New] and initialises the [Params.Path] and [Params.Args] fields.

container/container_test.go

@@ -7,9 +7,11 @@ import (
 	"errors"
 	"fmt"
 	"log"
+	"net"
 	"os"
 	"os/exec"
 	"os/signal"
+	"reflect"
 	"strconv"
 	"strings"
 	"syscall"
@@ -26,6 +28,143 @@ import (
 	"hakurei.app/ldd"
 )
 
+func TestStartError(t *testing.T) {
+	testCases := []struct {
+		name string
+		err  error
+		s    string
+		is   error
+		isF  error
+		msg  string
+	}{
+		{"params env", &container.StartError{
+			Fatal: true,
+			Step:  "set up params stream",
+			Err:   container.ErrReceiveEnv,
+		},
+			"set up params stream: environment variable not set",
+			container.ErrReceiveEnv, syscall.EBADF,
+			"cannot set up params stream: environment variable not set"},
+
+		{"params", &container.StartError{
+			Fatal: true,
+			Step:  "set up params stream",
+			Err:   &os.SyscallError{Syscall: "pipe2", Err: syscall.EBADF},
+		},
+			"set up params stream pipe2: bad file descriptor",
+			syscall.EBADF, os.ErrInvalid,
+			"cannot set up params stream pipe2: bad file descriptor"},
+
+		{"PR_SET_NO_NEW_PRIVS", &container.StartError{
+			Fatal: true,
+			Step:  "prctl(PR_SET_NO_NEW_PRIVS)",
+			Err:   syscall.EPERM,
+		},
+			"prctl(PR_SET_NO_NEW_PRIVS): operation not permitted",
+			syscall.EPERM, syscall.EACCES,
+			"cannot prctl(PR_SET_NO_NEW_PRIVS): operation not permitted"},
+
+		{"landlock abi", &container.StartError{
+			Step: "get landlock ABI",
+			Err:  syscall.ENOSYS,
+		},
+			"get landlock ABI: function not implemented",
+			syscall.ENOSYS, syscall.ENOEXEC,
+			"cannot get landlock ABI: function not implemented"},
+
+		{"landlock old", &container.StartError{
+			Step:   "kernel version too old for LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET",
+			Err:    syscall.ENOSYS,
+			Origin: true,
+		},
+			"kernel version too old for LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET",
+			syscall.ENOSYS, syscall.ENOSPC,
+			"kernel version too old for LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET"},
+
+		{"landlock create", &container.StartError{
+			Fatal: true,
+			Step:  "create landlock ruleset",
+			Err:   syscall.EBADFD,
+		},
+			"create landlock ruleset: file descriptor in bad state",
+			syscall.EBADFD, syscall.EBADF,
+			"cannot create landlock ruleset: file descriptor in bad state"},
+
+		{"landlock enforce", &container.StartError{
+			Fatal: true,
+			Step:  "enforce landlock ruleset",
+			Err:   syscall.ENOTRECOVERABLE,
+		},
+			"enforce landlock ruleset: state not recoverable",
+			syscall.ENOTRECOVERABLE, syscall.ETIMEDOUT,
+			"cannot enforce landlock ruleset: state not recoverable"},
+
+		{"start", &container.StartError{
+			Step: "start container init",
+			Err: &os.PathError{
+				Op:   "fork/exec",
+				Path: "/proc/nonexistent",
+				Err:  syscall.ENOENT,
+			}, Passthrough: true,
+		},
+			"fork/exec /proc/nonexistent: no such file or directory",
+			syscall.ENOENT, syscall.ENOSYS,
+			"cannot fork/exec /proc/nonexistent: no such file or directory"},
+
+		{"start syscall", &container.StartError{
+			Step: "start container init",
+			Err: &os.SyscallError{
+				Syscall: "open",
+				Err:     syscall.ENOSYS,
+			}, Passthrough: true,
+		},
+			"open: function not implemented",
+			syscall.ENOSYS, syscall.ENOENT,
+			"cannot open: function not implemented"},
+
+		{"start other", &container.StartError{
+			Step: "start container init",
+			Err: &net.OpError{
+				Op:  "dial",
+				Net: "unix",
+				Err: syscall.ECONNREFUSED,
+			}, Passthrough: true,
+		},
+			"dial unix: connection refused",
+			syscall.ECONNREFUSED, syscall.ECONNABORTED,
+			"dial unix: connection refused"},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Run("error", func(t *testing.T) {
+				if got := tc.err.Error(); got != tc.s {
+					t.Errorf("Error: %q, want %q", got, tc.s)
+				}
+			})
+
+			t.Run("is", func(t *testing.T) {
+				if !errors.Is(tc.err, tc.is) {
+					t.Error("Is: unexpected false")
+				}
+				if errors.Is(tc.err, tc.isF) {
+					t.Errorf("Is: unexpected true")
+				}
+			})
+
+			t.Run("msg", func(t *testing.T) {
+				if got, ok := container.GetErrorMessage(tc.err); !ok {
+					if tc.msg != "" {
+						t.Errorf("GetErrorMessage: err does not implement MessageError")
+					}
+					return
+				} else if got != tc.msg {
+					t.Errorf("GetErrorMessage: %q, want %q", got, tc.msg)
+				}
+			})
+		})
+	}
+}
+
 const (
 	ignore  = "\x00"
 	ignoreV = -1
@@ -75,7 +214,7 @@ var containerTestCases = []struct {
 		1000, 100, nil, 0, seccomp.PresetExt},
 	{"custom rules", true, true, true, false,
 		emptyOps, emptyMnt,
-		1, 31, []seccomp.NativeRule{{seccomp.ScmpSyscall(syscall.SYS_SETUID), seccomp.ScmpErrno(syscall.EPERM), nil}}, 0, seccomp.PresetExt},
+		1, 31, []seccomp.NativeRule{{Syscall: seccomp.ScmpSyscall(syscall.SYS_SETUID), Errno: seccomp.ScmpErrno(syscall.EPERM)}}, 0, seccomp.PresetExt},
 
 	{"tmpfs", true, false, false, true,
 		earlyOps(new(container.Ops).
@@ -217,9 +356,11 @@ func TestContainer(t *testing.T) {
 	t.Run("cancel", testContainerCancel(nil, func(t *testing.T, c *container.Container) {
 		wantErr := context.Canceled
 		wantExitCode := 0
-		if err := c.Wait(); !errors.Is(err, wantErr) {
-			container.GetOutput().PrintBaseErr(err, "wait:")
-			t.Errorf("Wait: error = %v, want %v", err, wantErr)
+		if err := c.Wait(); !reflect.DeepEqual(err, wantErr) {
+			if m, ok := container.InternalMessageFromError(err); ok {
+				t.Error(m)
+			}
+			t.Errorf("Wait: error = %#v, want %#v", err, wantErr)
 		}
 		if ps := c.ProcessState(); ps == nil {
 			t.Errorf("ProcessState unexpectedly returned nil")
@@ -233,7 +374,9 @@ func TestContainer(t *testing.T) {
 	}, func(t *testing.T, c *container.Container) {
 		var exitError *exec.ExitError
 		if err := c.Wait(); !errors.As(err, &exitError) {
-			container.GetOutput().PrintBaseErr(err, "wait:")
+			if m, ok := container.InternalMessageFromError(err); ok {
+				t.Error(m)
+			}
 			t.Errorf("Wait: error = %v", err)
 		}
 		if code := exitError.ExitCode(); code != blockExitCodeInterrupt {
@@ -313,17 +456,26 @@ func TestContainer(t *testing.T) {
 
 			if err := c.Start(); err != nil {
 				_, _ = output.WriteTo(os.Stdout)
-				container.GetOutput().PrintBaseErr(err, "start:")
-				t.Fatalf("cannot start container: %v", err)
+				if m, ok := container.InternalMessageFromError(err); ok {
+					t.Fatal(m)
+				} else {
+					t.Fatalf("cannot start container: %v", err)
+				}
 			} else if err = c.Serve(); err != nil {
 				_, _ = output.WriteTo(os.Stdout)
-				container.GetOutput().PrintBaseErr(err, "serve:")
-				t.Errorf("cannot serve setup params: %v", err)
+				if m, ok := container.InternalMessageFromError(err); ok {
+					t.Error(m)
+				} else {
+					t.Errorf("cannot serve setup params: %v", err)
+				}
 			}
 			if err := c.Wait(); err != nil {
 				_, _ = output.WriteTo(os.Stdout)
-				container.GetOutput().PrintBaseErr(err, "wait:")
-				t.Fatalf("wait: %v", err)
+				if m, ok := container.InternalMessageFromError(err); ok {
+					t.Fatal(m)
+				} else {
+					t.Fatalf("wait: %v", err)
+				}
 			}
 		})
 	}
@@ -376,11 +528,17 @@ func testContainerCancel(
 		}
 
 		if err := c.Start(); err != nil {
-			container.GetOutput().PrintBaseErr(err, "start:")
-			t.Fatalf("cannot start container: %v", err)
+			if m, ok := container.InternalMessageFromError(err); ok {
+				t.Fatal(m)
+			} else {
+				t.Fatalf("cannot start container: %v", err)
+			}
 		} else if err = c.Serve(); err != nil {
-			container.GetOutput().PrintBaseErr(err, "serve:")
-			t.Errorf("cannot serve setup params: %v", err)
+			if m, ok := container.InternalMessageFromError(err); ok {
+				t.Error(m)
+			} else {
+				t.Errorf("cannot serve setup params: %v", err)
+			}
 		}
 		<-ready
 		cancel()

container/dispatcher.go

@@ -138,8 +138,6 @@ type syscallDispatcher interface {
 	resume() bool
 	// beforeExit provides [Msg.BeforeExit].
 	beforeExit()
-	// printBaseErr provides [Msg.PrintBaseErr].
-	printBaseErr(err error, fallback string)
 }
 
 // direct implements syscallDispatcher on the current kernel.
@@ -225,7 +223,7 @@ func (direct) pivotRoot(newroot, putold string) (err error) {
 	return syscall.PivotRoot(newroot, putold)
 }
 func (direct) mount(source, target, fstype string, flags uintptr, data string) (err error) {
-	return syscall.Mount(source, target, fstype, flags, data)
+	return mount(source, target, fstype, flags, data)
 }
 func (direct) unmount(target string, flags int) (err error) {
 	return syscall.Unmount(target, flags)
@@ -234,12 +232,11 @@ func (direct) wait4(pid int, wstatus *syscall.WaitStatus, options int, rusage *s
 	return syscall.Wait4(pid, wstatus, options, rusage)
 }
 
-func (direct) printf(format string, v ...any)          { log.Printf(format, v...) }
-func (direct) fatal(v ...any)                          { log.Fatal(v...) }
-func (direct) fatalf(format string, v ...any)          { log.Fatalf(format, v...) }
-func (direct) verbose(v ...any)                        { msg.Verbose(v...) }
-func (direct) verbosef(format string, v ...any)        { msg.Verbosef(format, v...) }
-func (direct) suspend()                                { msg.Suspend() }
-func (direct) resume() bool                            { return msg.Resume() }
-func (direct) beforeExit()                             { msg.BeforeExit() }
-func (direct) printBaseErr(err error, fallback string) { msg.PrintBaseErr(err, fallback) }
+func (direct) printf(format string, v ...any)   { log.Printf(format, v...) }
+func (direct) fatal(v ...any)                   { log.Fatal(v...) }
+func (direct) fatalf(format string, v ...any)   { log.Fatalf(format, v...) }
+func (direct) verbose(v ...any)                 { msg.Verbose(v...) }
+func (direct) verbosef(format string, v ...any) { msg.Verbosef(format, v...) }
+func (direct) suspend()                         { msg.Suspend() }
+func (direct) resume() bool                     { return msg.Resume() }
+func (direct) beforeExit()                      { msg.BeforeExit() }

container/dispatcher_test.go

@@ -2,7 +2,6 @@ package container
 
 import (
 	"bytes"
-	"errors"
 	"io"
 	"io/fs"
 	"os"
@@ -11,16 +10,14 @@ import (
 	"runtime"
 	"slices"
 	"strings"
-	"sync"
 	"syscall"
 	"testing"
 	"time"
 
 	"hakurei.app/container/seccomp"
+	"hakurei.app/container/stub"
 )
 
-var errUnique = errors.New("unique error injected by the test suite")
-
 type opValidTestCase struct {
 	name string
 	op   Op
@@ -28,9 +25,15 @@ type opValidTestCase struct {
 }
 
 func checkOpsValid(t *testing.T, testCases []opValidTestCase) {
+	t.Helper()
+
 	t.Run("valid", func(t *testing.T) {
+		t.Helper()
+
 		for _, tc := range testCases {
 			t.Run(tc.name, func(t *testing.T) {
+				t.Helper()
+
 				if got := tc.op.Valid(); got != tc.want {
 					t.Errorf("Valid: %v, want %v", got, tc.want)
 				}
@@ -46,9 +49,15 @@ type opsBuilderTestCase struct {
 }
 
 func checkOpsBuilder(t *testing.T, testCases []opsBuilderTestCase) {
+	t.Helper()
+
 	t.Run("build", func(t *testing.T) {
+		t.Helper()
+
 		for _, tc := range testCases {
 			t.Run(tc.name, func(t *testing.T) {
+				t.Helper()
+
 				if !slices.EqualFunc(*tc.ops, tc.want, func(op Op, v Op) bool { return op.Is(v) }) {
 					t.Errorf("Ops: %#v, want %#v", tc.ops, tc.want)
 				}
@@ -64,9 +73,15 @@ type opIsTestCase struct {
 }
 
 func checkOpIs(t *testing.T, testCases []opIsTestCase) {
+	t.Helper()
+
 	t.Run("is", func(t *testing.T) {
+		t.Helper()
+
 		for _, tc := range testCases {
 			t.Run(tc.name, func(t *testing.T) {
+				t.Helper()
+
 				if got := tc.op.Is(tc.v); got != tc.want {
 					t.Errorf("Is: %v, want %v", got, tc.want)
 				}
@@ -84,16 +99,26 @@ type opMetaTestCase struct {
 }
 
 func checkOpMeta(t *testing.T, testCases []opMetaTestCase) {
+	t.Helper()
+
 	t.Run("meta", func(t *testing.T) {
+		t.Helper()
+
 		for _, tc := range testCases {
 			t.Run(tc.name, func(t *testing.T) {
+				t.Helper()
+
 				t.Run("prefix", func(t *testing.T) {
+					t.Helper()
+
 					if got := tc.op.prefix(); got != tc.wantPrefix {
 						t.Errorf("prefix: %q, want %q", got, tc.wantPrefix)
 					}
 				})
 
 				t.Run("string", func(t *testing.T) {
+					t.Helper()
+
 					if got := tc.op.String(); got != tc.wantString {
 						t.Errorf("String: %s, want %s", got, tc.wantString)
 					}
@@ -103,23 +128,36 @@ func checkOpMeta(t *testing.T, testCases []opMetaTestCase) {
 	})
 }
 
+// call initialises a [stub.Call].
+// This keeps composites analysis happy without making the test cases too bloated.
+func call(name string, args stub.ExpectArgs, ret any, err error) stub.Call {
+	return stub.Call{Name: name, Args: args, Ret: ret, Err: err}
+}
+
 type simpleTestCase struct {
 	name    string
 	f       func(k syscallDispatcher) error
-	want    [][]kexpect
+	want    stub.Expect
 	wantErr error
 }
 
 func checkSimple(t *testing.T, fname string, testCases []simpleTestCase) {
+	t.Helper()
+
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
-			defer handleExitStub()
-			k := &kstub{t: t, want: tc.want, wg: new(sync.WaitGroup)}
-			if err := tc.f(k); !errors.Is(err, tc.wantErr) {
+			t.Helper()
+
+			wait4signal := make(chan struct{})
+			k := &kstub{wait4signal, stub.New(t, func(s *stub.Stub[syscallDispatcher]) syscallDispatcher { return &kstub{wait4signal, s} }, tc.want)}
+			defer stub.HandleExit(t)
+			if err := tc.f(k); !reflect.DeepEqual(err, tc.wantErr) {
 				t.Errorf("%s: error = %v, want %v", fname, err, tc.wantErr)
 			}
-			k.handleIncomplete(func(k *kstub) {
-				t.Errorf("%s: %d calls, want %d (track %d)", fname, k.pos, len(k.want[k.track]), k.track)
+			k.VisitIncomplete(func(s *stub.Stub[syscallDispatcher]) {
+				t.Helper()
+
+				t.Errorf("%s: %d calls, want %d", fname, s.Pos(), s.Len())
 			})
 		})
 	}
@@ -130,36 +168,45 @@ type opBehaviourTestCase struct {
 	params *Params
 	op     Op
 
-	early        []kexpect
+	early        []stub.Call
 	wantErrEarly error
 
-	apply        []kexpect
+	apply        []stub.Call
 	wantErrApply error
 }
 
 func checkOpBehaviour(t *testing.T, testCases []opBehaviourTestCase) {
+	t.Helper()
+
 	t.Run("behaviour", func(t *testing.T) {
+		t.Helper()
+
 		for _, tc := range testCases {
 			t.Run(tc.name, func(t *testing.T) {
-				defer handleExitStub()
+				t.Helper()
+
 				state := &setupState{Params: tc.params}
-				k := &kstub{t: t, want: [][]kexpect{slices.Concat(tc.early, []kexpect{{name: "\x00"}}, tc.apply)}, wg: new(sync.WaitGroup)}
+				k := &kstub{nil, stub.New(t,
+					func(s *stub.Stub[syscallDispatcher]) syscallDispatcher { return &kstub{nil, s} },
+					stub.Expect{Calls: slices.Concat(tc.early, []stub.Call{{Name: stub.CallSeparator}}, tc.apply)},
+				)}
+				defer stub.HandleExit(t)
 				errEarly := tc.op.early(state, k)
-				k.expect("\x00")
-				if !errors.Is(errEarly, tc.wantErrEarly) {
+				k.Expects(stub.CallSeparator)
+				if !reflect.DeepEqual(errEarly, tc.wantErrEarly) {
 					t.Errorf("early: error = %v, want %v", errEarly, tc.wantErrEarly)
 				}
 				if errEarly != nil {
 					goto out
 				}
 
-				if err := tc.op.apply(state, k); !errors.Is(err, tc.wantErrApply) {
+				if err := tc.op.apply(state, k); !reflect.DeepEqual(err, tc.wantErrApply) {
 					t.Errorf("apply: error = %v, want %v", err, tc.wantErrApply)
 				}
 
 			out:
-				k.handleIncomplete(func(k *kstub) {
-					count := k.pos - 1 // separator
+				k.VisitIncomplete(func(s *stub.Stub[syscallDispatcher]) {
+					count := k.Pos() - 1 // separator
 					if count < len(tc.early) {
 						t.Errorf("early: %d calls, want %d", count, len(tc.early))
 					} else {
@@ -226,8 +273,6 @@ func (writeErrOsFile) Stat() (fs.FileInfo, error)  { panic("unreachable") }
 func (writeErrOsFile) Read([]byte) (int, error)    { panic("unreachable") }
 func (writeErrOsFile) Close() error                { panic("unreachable") }
 
-type expectArgs = [5]any
-
 type isDirFi bool
 
 func (isDirFi) Name() string       { panic("unreachable") }
@@ -252,184 +297,94 @@ func (nameDentry) IsDir() bool                { panic("unreachable") }
 func (nameDentry) Type() fs.FileMode          { panic("unreachable") }
 func (nameDentry) Info() (fs.FileInfo, error) { panic("unreachable") }
 
-type kexpect struct {
-	name string
-	args expectArgs
-	ret  any
-	err  error
-}
-
-func (k *kexpect) error(ok ...bool) error {
-	if !slices.Contains(ok, false) {
-		return k.err
-	}
-	return syscall.ENOTRECOVERABLE
-}
-
-func handleExitStub() {
-	r := recover()
-	if r == 0xdeadbeef {
-		return
-	}
-	if r != nil {
-		panic(r)
-	}
-}
+const (
+	// magicWait4Signal must be used in a single pair of signal and wait4 calls across two goroutines
+	// originating from the same toplevel kstub.
+	// To enable this behaviour this value must be the last element of the args field in the wait4 call
+	// and the ret value of the signal call.
+	magicWait4Signal = 0xdef
+)
 
 type kstub struct {
-	t *testing.T
-
-	want [][]kexpect
-	// pos is the current position in want[track].
-	pos int
-	// track is the current active want.
-	track int
-	// sub stores addresses of kstub created by new.
-	sub []*kstub
-	// wg waits for all descendants to complete.
-	wg *sync.WaitGroup
+	wait4signal chan struct{}
+	*stub.Stub[syscallDispatcher]
 }
 
-// handleIncomplete calls f on an incomplete k and all its descendants.
-func (k *kstub) handleIncomplete(f func(k *kstub)) {
-	k.wg.Wait()
+func (k *kstub) new(f func(k syscallDispatcher)) { k.Helper(); k.New(f) }
 
-	if k.want != nil && len(k.want[k.track]) != k.pos {
-		f(k)
-	}
-	for _, sk := range k.sub {
-		sk.handleIncomplete(f)
-	}
-}
-
-// expect checks name and returns the current kexpect and advances pos.
-func (k *kstub) expect(name string) (expect *kexpect) {
-	if len(k.want[k.track]) == k.pos {
-		k.t.Fatal("expect: want too short")
-	}
-	expect = &k.want[k.track][k.pos]
-	if name != expect.name {
-		if expect.name == "\x00" {
-			k.t.Fatalf("expect: func = %s, separator overrun", name)
-		}
-		if name == "\x00" {
-			k.t.Fatalf("expect: separator, want %s", expect.name)
-		}
-		k.t.Fatalf("expect: func = %s, want %s", name, expect.name)
-	}
-	k.pos++
-	return
-}
-
-// checkArg checks an argument comparable with the == operator. Avoid using this with pointers.
-func checkArg[T comparable](k *kstub, arg string, got T, n int) bool {
-	if k.pos == 0 {
-		panic("invalid call to checkArg")
-	}
-	expect := k.want[k.track][k.pos-1]
-	want, ok := expect.args[n].(T)
-	if !ok || got != want {
-		k.t.Errorf("%s: %s = %#v, want %#v (%d)", expect.name, arg, got, want, k.pos-1)
-		return false
-	}
-	return true
-}
-
-// checkArgReflect checks an argument of any type.
-func checkArgReflect(k *kstub, arg string, got any, n int) bool {
-	if k.pos == 0 {
-		panic("invalid call to checkArgReflect")
-	}
-	expect := k.want[k.track][k.pos-1]
-	want := expect.args[n]
-	if !reflect.DeepEqual(got, want) {
-		k.t.Errorf("%s: %s = %#v, want %#v (%d)", expect.name, arg, got, want, k.pos-1)
-		return false
-	}
-	return true
-}
-
-func (k *kstub) new(f func(k syscallDispatcher)) {
-	k.expect("new")
-	if len(k.want) <= k.track+1 {
-		k.t.Fatalf("new: track overrun")
-	}
-	sk := &kstub{t: k.t, want: k.want, track: len(k.sub) + 1, wg: k.wg}
-	k.sub = append(k.sub, sk)
-	k.wg.Add(1)
-	go func() {
-		defer k.wg.Done()
-		defer handleExitStub()
-		f(sk)
-	}()
-}
-
-func (k *kstub) lockOSThread() { k.expect("lockOSThread") }
+func (k *kstub) lockOSThread() { k.Helper(); k.Expects("lockOSThread") }
 
 func (k *kstub) setPtracer(pid uintptr) error {
-	return k.expect("setPtracer").error(
-		checkArg(k, "pid", pid, 0))
+	k.Helper()
+	return k.Expects("setPtracer").Error(
+		stub.CheckArg(k.Stub, "pid", pid, 0))
 }
 
 func (k *kstub) setDumpable(dumpable uintptr) error {
-	return k.expect("setDumpable").error(
-		checkArg(k, "dumpable", dumpable, 0))
+	k.Helper()
+	return k.Expects("setDumpable").Error(
+		stub.CheckArg(k.Stub, "dumpable", dumpable, 0))
 }
 
-func (k *kstub) setNoNewPrivs() error { return k.expect("setNoNewPrivs").err }
-func (k *kstub) lastcap() uintptr     { return k.expect("lastcap").ret.(uintptr) }
+func (k *kstub) setNoNewPrivs() error { k.Helper(); return k.Expects("setNoNewPrivs").Err }
+func (k *kstub) lastcap() uintptr     { k.Helper(); return k.Expects("lastcap").Ret.(uintptr) }
 
 func (k *kstub) capset(hdrp *capHeader, datap *[2]capData) error {
-	return k.expect("capset").error(
-		checkArgReflect(k, "hdrp", hdrp, 0),
-		checkArgReflect(k, "datap", datap, 1))
+	k.Helper()
+	return k.Expects("capset").Error(
+		stub.CheckArgReflect(k.Stub, "hdrp", hdrp, 0),
+		stub.CheckArgReflect(k.Stub, "datap", datap, 1))
 }
 
 func (k *kstub) capBoundingSetDrop(cap uintptr) error {
-	return k.expect("capBoundingSetDrop").error(
-		checkArg(k, "cap", cap, 0))
+	k.Helper()
+	return k.Expects("capBoundingSetDrop").Error(
+		stub.CheckArg(k.Stub, "cap", cap, 0))
 }
 
-func (k *kstub) capAmbientClearAll() error { return k.expect("capAmbientClearAll").err }
+func (k *kstub) capAmbientClearAll() error { k.Helper(); return k.Expects("capAmbientClearAll").Err }
 
 func (k *kstub) capAmbientRaise(cap uintptr) error {
-	return k.expect("capAmbientRaise").error(
-		checkArg(k, "cap", cap, 0))
+	k.Helper()
+	return k.Expects("capAmbientRaise").Error(
+		stub.CheckArg(k.Stub, "cap", cap, 0))
 }
 
 func (k *kstub) isatty(fd int) bool {
-	expect := k.expect("isatty")
-	if !checkArg(k, "fd", fd, 0) {
-		k.t.FailNow()
+	k.Helper()
+	expect := k.Expects("isatty")
+	if !stub.CheckArg(k.Stub, "fd", fd, 0) {
+		k.FailNow()
 	}
-	return expect.ret.(bool)
+	return expect.Ret.(bool)
 }
 
 func (k *kstub) receive(key string, e any, fdp *uintptr) (closeFunc func() error, err error) {
-	expect := k.expect("receive")
+	k.Helper()
+	expect := k.Expects("receive")
 
 	var closed bool
 	closeFunc = func() error {
 		if closed {
-			k.t.Error("closeFunc called more than once")
+			k.Error("closeFunc called more than once")
 			return os.ErrClosed
 		}
 		closed = true
 
-		if expect.ret != nil {
+		if expect.Ret != nil {
 			// use return stored in kexpect for closeFunc instead
-			return expect.ret.(error)
+			return expect.Ret.(error)
 		}
 		return nil
 	}
-	err = expect.error(
-		checkArg(k, "key", key, 0),
-		checkArgReflect(k, "e", e, 1),
-		checkArgReflect(k, "fdp", fdp, 2))
+	err = expect.Error(
+		stub.CheckArg(k.Stub, "key", key, 0),
+		stub.CheckArgReflect(k.Stub, "e", e, 1),
+		stub.CheckArgReflect(k.Stub, "fdp", fdp, 2))
 
 	// 3 is unused so stores params
-	if expect.args[3] != nil {
-		if v, ok := expect.args[3].(*initParams); ok && v != nil {
+	if expect.Args[3] != nil {
+		if v, ok := expect.Args[3].(*initParams); ok && v != nil {
 			if p, ok0 := e.(*initParams); ok0 && p != nil {
 				*p = *v
 			}
@@ -437,8 +392,8 @@ func (k *kstub) receive(key string, e any, fdp *uintptr) (closeFunc func() error
 	}
 
 	// 4 is unused so stores fd
-	if expect.args[4] != nil {
-		if v, ok := expect.args[4].(uintptr); ok && v >= 3 {
+	if expect.Args[4] != nil {
+		if v, ok := expect.Args[4].(uintptr); ok && v >= 3 {
 			if fdp != nil {
 				*fdp = v
 			}
@@ -449,246 +404,291 @@ func (k *kstub) receive(key string, e any, fdp *uintptr) (closeFunc func() error
 }
 
 func (k *kstub) bindMount(source, target string, flags uintptr, eq bool) error {
-	return k.expect("bindMount").error(
-		checkArg(k, "source", source, 0),
-		checkArg(k, "target", target, 1),
-		checkArg(k, "flags", flags, 2),
-		checkArg(k, "eq", eq, 3))
+	k.Helper()
+	return k.Expects("bindMount").Error(
+		stub.CheckArg(k.Stub, "source", source, 0),
+		stub.CheckArg(k.Stub, "target", target, 1),
+		stub.CheckArg(k.Stub, "flags", flags, 2),
+		stub.CheckArg(k.Stub, "eq", eq, 3))
 }
 
 func (k *kstub) remount(target string, flags uintptr) error {
-	return k.expect("remount").error(
-		checkArg(k, "target", target, 0),
-		checkArg(k, "flags", flags, 1))
+	k.Helper()
+	return k.Expects("remount").Error(
+		stub.CheckArg(k.Stub, "target", target, 0),
+		stub.CheckArg(k.Stub, "flags", flags, 1))
 }
 
 func (k *kstub) mountTmpfs(fsname, target string, flags uintptr, size int, perm os.FileMode) error {
-	return k.expect("mountTmpfs").error(
-		checkArg(k, "fsname", fsname, 0),
-		checkArg(k, "target", target, 1),
-		checkArg(k, "flags", flags, 2),
-		checkArg(k, "size", size, 3),
-		checkArg(k, "perm", perm, 4))
+	k.Helper()
+	return k.Expects("mountTmpfs").Error(
+		stub.CheckArg(k.Stub, "fsname", fsname, 0),
+		stub.CheckArg(k.Stub, "target", target, 1),
+		stub.CheckArg(k.Stub, "flags", flags, 2),
+		stub.CheckArg(k.Stub, "size", size, 3),
+		stub.CheckArg(k.Stub, "perm", perm, 4))
 }
 
 func (k *kstub) ensureFile(name string, perm, pperm os.FileMode) error {
-
-	return k.expect("ensureFile").error(
-		checkArg(k, "name", name, 0),
-		checkArg(k, "perm", perm, 1),
-		checkArg(k, "pperm", pperm, 2))
+	k.Helper()
+	return k.Expects("ensureFile").Error(
+		stub.CheckArg(k.Stub, "name", name, 0),
+		stub.CheckArg(k.Stub, "perm", perm, 1),
+		stub.CheckArg(k.Stub, "pperm", pperm, 2))
 }
 
 func (k *kstub) seccompLoad(rules []seccomp.NativeRule, flags seccomp.ExportFlag) error {
-	return k.expect("seccompLoad").error(
-		checkArgReflect(k, "rules", rules, 0),
-		checkArg(k, "flags", flags, 1))
+	k.Helper()
+	return k.Expects("seccompLoad").Error(
+		stub.CheckArgReflect(k.Stub, "rules", rules, 0),
+		stub.CheckArg(k.Stub, "flags", flags, 1))
 }
 
 func (k *kstub) notify(c chan<- os.Signal, sig ...os.Signal) {
-	expect := k.expect("notify")
-	if c == nil || expect.error(
-		checkArgReflect(k, "sig", sig, 1)) != nil {
-		k.t.FailNow()
+	k.Helper()
+	expect := k.Expects("notify")
+	if c == nil || expect.Error(
+		stub.CheckArgReflect(k.Stub, "sig", sig, 1)) != nil {
+		k.FailNow()
 	}
 
 	// export channel for external instrumentation
-	if chanf, ok := expect.args[0].(func(c chan<- os.Signal)); ok && chanf != nil {
+	if chanf, ok := expect.Args[0].(func(c chan<- os.Signal)); ok && chanf != nil {
 		chanf(c)
 	}
 }
 
 func (k *kstub) start(c *exec.Cmd) error {
-	expect := k.expect("start")
-	err := expect.error(
-		checkArg(k, "c.Path", c.Path, 0),
-		checkArgReflect(k, "c.Args", c.Args, 1),
-		checkArgReflect(k, "c.Env", c.Env, 2),
-		checkArg(k, "c.Dir", c.Dir, 3))
+	k.Helper()
+	expect := k.Expects("start")
+	err := expect.Error(
+		stub.CheckArg(k.Stub, "c.Path", c.Path, 0),
+		stub.CheckArgReflect(k.Stub, "c.Args", c.Args, 1),
+		stub.CheckArgReflect(k.Stub, "c.Env", c.Env, 2),
+		stub.CheckArg(k.Stub, "c.Dir", c.Dir, 3))
 
-	if process, ok := expect.ret.(*os.Process); ok && process != nil {
+	if process, ok := expect.Ret.(*os.Process); ok && process != nil {
 		c.Process = process
 	}
 	return err
 }
 
 func (k *kstub) signal(c *exec.Cmd, sig os.Signal) error {
-	return k.expect("signal").error(
-		checkArg(k, "c.Path", c.Path, 0),
-		checkArgReflect(k, "c.Args", c.Args, 1),
-		checkArgReflect(k, "c.Env", c.Env, 2),
-		checkArg(k, "c.Dir", c.Dir, 3),
-		checkArg(k, "sig", sig, 4))
+	k.Helper()
+	expect := k.Expects("signal")
+	if v, ok := expect.Ret.(int); ok && v == magicWait4Signal {
+		if k.wait4signal == nil {
+			panic("kstub not initialised for wait4 simulation")
+		}
+		defer func() { close(k.wait4signal) }()
+	}
+	return expect.Error(
+		stub.CheckArg(k.Stub, "c.Path", c.Path, 0),
+		stub.CheckArgReflect(k.Stub, "c.Args", c.Args, 1),
+		stub.CheckArgReflect(k.Stub, "c.Env", c.Env, 2),
+		stub.CheckArg(k.Stub, "c.Dir", c.Dir, 3),
+		stub.CheckArg(k.Stub, "sig", sig, 4))
 }
 
 func (k *kstub) evalSymlinks(path string) (string, error) {
-	expect := k.expect("evalSymlinks")
-	return expect.ret.(string), expect.error(
-		checkArg(k, "path", path, 0))
+	k.Helper()
+	expect := k.Expects("evalSymlinks")
+	return expect.Ret.(string), expect.Error(
+		stub.CheckArg(k.Stub, "path", path, 0))
 }
 
 func (k *kstub) exit(code int) {
-	k.expect("exit")
-	if !checkArg(k, "code", code, 0) {
-		k.t.FailNow()
+	k.Helper()
+	k.Expects("exit")
+	if !stub.CheckArg(k.Stub, "code", code, 0) {
+		k.FailNow()
 	}
-	panic(0xdeadbeef)
+	panic(stub.PanicExit)
 }
 
-func (k *kstub) getpid() int { return k.expect("getpid").ret.(int) }
+func (k *kstub) getpid() int { k.Helper(); return k.Expects("getpid").Ret.(int) }
 
 func (k *kstub) stat(name string) (os.FileInfo, error) {
-	expect := k.expect("stat")
-	return expect.ret.(os.FileInfo), expect.error(
-		checkArg(k, "name", name, 0))
+	k.Helper()
+	expect := k.Expects("stat")
+	return expect.Ret.(os.FileInfo), expect.Error(
+		stub.CheckArg(k.Stub, "name", name, 0))
 }
 
 func (k *kstub) mkdir(name string, perm os.FileMode) error {
-	return k.expect("mkdir").error(
-		checkArg(k, "name", name, 0),
-		checkArg(k, "perm", perm, 1))
+	k.Helper()
+	return k.Expects("mkdir").Error(
+		stub.CheckArg(k.Stub, "name", name, 0),
+		stub.CheckArg(k.Stub, "perm", perm, 1))
 }
 
 func (k *kstub) mkdirTemp(dir, pattern string) (string, error) {
-	expect := k.expect("mkdirTemp")
-	return expect.ret.(string), expect.error(
-		checkArg(k, "dir", dir, 0),
-		checkArg(k, "pattern", pattern, 1))
+	k.Helper()
+	expect := k.Expects("mkdirTemp")
+	return expect.Ret.(string), expect.Error(
+		stub.CheckArg(k.Stub, "dir", dir, 0),
+		stub.CheckArg(k.Stub, "pattern", pattern, 1))
 }
 
 func (k *kstub) mkdirAll(path string, perm os.FileMode) error {
-	return k.expect("mkdirAll").error(
-		checkArg(k, "path", path, 0),
-		checkArg(k, "perm", perm, 1))
+	k.Helper()
+	return k.Expects("mkdirAll").Error(
+		stub.CheckArg(k.Stub, "path", path, 0),
+		stub.CheckArg(k.Stub, "perm", perm, 1))
 }
 
 func (k *kstub) readdir(name string) ([]os.DirEntry, error) {
-	expect := k.expect("readdir")
-	return expect.ret.([]os.DirEntry), expect.error(
-		checkArg(k, "name", name, 0))
+	k.Helper()
+	expect := k.Expects("readdir")
+	return expect.Ret.([]os.DirEntry), expect.Error(
+		stub.CheckArg(k.Stub, "name", name, 0))
 }
 
 func (k *kstub) openNew(name string) (osFile, error) {
-	expect := k.expect("openNew")
-	return expect.ret.(osFile), expect.error(
-		checkArg(k, "name", name, 0))
+	k.Helper()
+	expect := k.Expects("openNew")
+	return expect.Ret.(osFile), expect.Error(
+		stub.CheckArg(k.Stub, "name", name, 0))
 }
 
 func (k *kstub) writeFile(name string, data []byte, perm os.FileMode) error {
-	return k.expect("writeFile").error(
-		checkArg(k, "name", name, 0),
-		checkArgReflect(k, "data", data, 1),
-		checkArg(k, "perm", perm, 2))
+	k.Helper()
+	return k.Expects("writeFile").Error(
+		stub.CheckArg(k.Stub, "name", name, 0),
+		stub.CheckArgReflect(k.Stub, "data", data, 1),
+		stub.CheckArg(k.Stub, "perm", perm, 2))
 }
 
 func (k *kstub) createTemp(dir, pattern string) (osFile, error) {
-	expect := k.expect("createTemp")
-	return expect.ret.(osFile), expect.error(
-		checkArg(k, "dir", dir, 0),
-		checkArg(k, "pattern", pattern, 1))
+	k.Helper()
+	expect := k.Expects("createTemp")
+	return expect.Ret.(osFile), expect.Error(
+		stub.CheckArg(k.Stub, "dir", dir, 0),
+		stub.CheckArg(k.Stub, "pattern", pattern, 1))
 }
 
 func (k *kstub) remove(name string) error {
-	return k.expect("remove").error(
-		checkArg(k, "name", name, 0))
+	k.Helper()
+	return k.Expects("remove").Error(
+		stub.CheckArg(k.Stub, "name", name, 0))
 }
 
 func (k *kstub) newFile(fd uintptr, name string) *os.File {
-	expect := k.expect("newFile")
-	if expect.error(
-		checkArg(k, "fd", fd, 0),
-		checkArg(k, "name", name, 1)) != nil {
-		k.t.FailNow()
+	k.Helper()
+	expect := k.Expects("newFile")
+	if expect.Error(
+		stub.CheckArg(k.Stub, "fd", fd, 0),
+		stub.CheckArg(k.Stub, "name", name, 1)) != nil {
+		k.FailNow()
 	}
-	return expect.ret.(*os.File)
+	return expect.Ret.(*os.File)
 }
 
 func (k *kstub) symlink(oldname, newname string) error {
-	return k.expect("symlink").error(
-		checkArg(k, "oldname", oldname, 0),
-		checkArg(k, "newname", newname, 1))
+	k.Helper()
+	return k.Expects("symlink").Error(
+		stub.CheckArg(k.Stub, "oldname", oldname, 0),
+		stub.CheckArg(k.Stub, "newname", newname, 1))
 }
 
 func (k *kstub) readlink(name string) (string, error) {
-	expect := k.expect("readlink")
-	return expect.ret.(string), expect.error(
-		checkArg(k, "name", name, 0))
+	k.Helper()
+	expect := k.Expects("readlink")
+	return expect.Ret.(string), expect.Error(
+		stub.CheckArg(k.Stub, "name", name, 0))
 }
 
 func (k *kstub) umask(mask int) (oldmask int) {
-	expect := k.expect("umask")
-	if !checkArg(k, "mask", mask, 0) {
-		k.t.FailNow()
+	k.Helper()
+	expect := k.Expects("umask")
+	if !stub.CheckArg(k.Stub, "mask", mask, 0) {
+		k.FailNow()
 	}
-	return expect.ret.(int)
+	return expect.Ret.(int)
 }
 
 func (k *kstub) sethostname(p []byte) (err error) {
-	return k.expect("sethostname").error(
-		checkArgReflect(k, "p", p, 0))
+	k.Helper()
+	return k.Expects("sethostname").Error(
+		stub.CheckArgReflect(k.Stub, "p", p, 0))
 }
 
 func (k *kstub) chdir(path string) (err error) {
-	return k.expect("chdir").error(
-		checkArg(k, "path", path, 0))
+	k.Helper()
+	return k.Expects("chdir").Error(
+		stub.CheckArg(k.Stub, "path", path, 0))
 }
 
 func (k *kstub) fchdir(fd int) (err error) {
-	return k.expect("fchdir").error(
-		checkArg(k, "fd", fd, 0))
+	k.Helper()
+	return k.Expects("fchdir").Error(
+		stub.CheckArg(k.Stub, "fd", fd, 0))
 }
 
 func (k *kstub) open(path string, mode int, perm uint32) (fd int, err error) {
-	expect := k.expect("open")
-	return expect.ret.(int), expect.error(
-		checkArg(k, "path", path, 0),
-		checkArg(k, "mode", mode, 1),
-		checkArg(k, "perm", perm, 2))
+	k.Helper()
+	expect := k.Expects("open")
+	return expect.Ret.(int), expect.Error(
+		stub.CheckArg(k.Stub, "path", path, 0),
+		stub.CheckArg(k.Stub, "mode", mode, 1),
+		stub.CheckArg(k.Stub, "perm", perm, 2))
 }
 
 func (k *kstub) close(fd int) (err error) {
-	return k.expect("close").error(
-		checkArg(k, "fd", fd, 0))
+	k.Helper()
+	return k.Expects("close").Error(
+		stub.CheckArg(k.Stub, "fd", fd, 0))
 }
 
 func (k *kstub) pivotRoot(newroot, putold string) (err error) {
-	return k.expect("pivotRoot").error(
-		checkArg(k, "newroot", newroot, 0),
-		checkArg(k, "putold", putold, 1))
+	k.Helper()
+	return k.Expects("pivotRoot").Error(
+		stub.CheckArg(k.Stub, "newroot", newroot, 0),
+		stub.CheckArg(k.Stub, "putold", putold, 1))
 }
 
 func (k *kstub) mount(source, target, fstype string, flags uintptr, data string) (err error) {
-	return k.expect("mount").error(
-		checkArg(k, "source", source, 0),
-		checkArg(k, "target", target, 1),
-		checkArg(k, "fstype", fstype, 2),
-		checkArg(k, "flags", flags, 3),
-		checkArg(k, "data", data, 4))
+	k.Helper()
+	return k.Expects("mount").Error(
+		stub.CheckArg(k.Stub, "source", source, 0),
+		stub.CheckArg(k.Stub, "target", target, 1),
+		stub.CheckArg(k.Stub, "fstype", fstype, 2),
+		stub.CheckArg(k.Stub, "flags", flags, 3),
+		stub.CheckArg(k.Stub, "data", data, 4))
 }
 
 func (k *kstub) unmount(target string, flags int) (err error) {
-	return k.expect("unmount").error(
-		checkArg(k, "target", target, 0),
-		checkArg(k, "flags", flags, 1))
+	k.Helper()
+	return k.Expects("unmount").Error(
+		stub.CheckArg(k.Stub, "target", target, 0),
+		stub.CheckArg(k.Stub, "flags", flags, 1))
 }
 
 func (k *kstub) wait4(pid int, wstatus *syscall.WaitStatus, options int, rusage *syscall.Rusage) (wpid int, err error) {
-	expect := k.expect("wait4")
-	// special case to prevent leaking the wait4 goroutine when testing initEntrypoint
-	if v, ok := expect.args[4].(int); ok && v == 0xdeadbeef {
-		k.t.Log("terminating current goroutine as requested by kexpect")
-		panic(0xdeadbeef)
+	k.Helper()
+	expect := k.Expects("wait4")
+	if v, ok := expect.Args[4].(int); ok {
+		switch v {
+		case stub.PanicExit: // special case to prevent leaking the wait4 goroutine while testing initEntrypoint
+			panic(stub.PanicExit)
+
+		case magicWait4Signal: // block until corresponding signal call
+			if k.wait4signal == nil {
+				panic("kstub not initialised for wait4 simulation")
+			}
+			<-k.wait4signal
+		}
 	}
 
-	wpid = expect.ret.(int)
-	err = expect.error(
-		checkArg(k, "pid", pid, 0),
-		checkArg(k, "options", options, 2))
+	wpid = expect.Ret.(int)
+	err = expect.Error(
+		stub.CheckArg(k.Stub, "pid", pid, 0),
+		stub.CheckArg(k.Stub, "options", options, 2))
 
-	if wstatusV, ok := expect.args[1].(syscall.WaitStatus); wstatus != nil && ok {
+	if wstatusV, ok := expect.Args[1].(syscall.WaitStatus); wstatus != nil && ok {
 		*wstatus = wstatusV
 	}
-	if rusageV, ok := expect.args[3].(syscall.Rusage); rusage != nil && ok {
+	if rusageV, ok := expect.Args[3].(syscall.Rusage); rusage != nil && ok {
 		*rusage = rusageV
 	}
 
@@ -696,53 +696,50 @@ func (k *kstub) wait4(pid int, wstatus *syscall.WaitStatus, options int, rusage
 }
 
 func (k *kstub) printf(format string, v ...any) {
-	if k.expect("printf").error(
-		checkArg(k, "format", format, 0),
-		checkArgReflect(k, "v", v, 1)) != nil {
-		k.t.FailNow()
+	k.Helper()
+	if k.Expects("printf").Error(
+		stub.CheckArg(k.Stub, "format", format, 0),
+		stub.CheckArgReflect(k.Stub, "v", v, 1)) != nil {
+		k.FailNow()
 	}
 }
 
 func (k *kstub) fatal(v ...any) {
-	if k.expect("fatal").error(
-		checkArgReflect(k, "v", v, 0)) != nil {
-		k.t.FailNow()
+	k.Helper()
+	if k.Expects("fatal").Error(
+		stub.CheckArgReflect(k.Stub, "v", v, 0)) != nil {
+		k.FailNow()
 	}
-	panic(0xdeadbeef)
+	panic(stub.PanicExit)
 }
 
 func (k *kstub) fatalf(format string, v ...any) {
-	if k.expect("fatalf").error(
-		checkArg(k, "format", format, 0),
-		checkArgReflect(k, "v", v, 1)) != nil {
-		k.t.FailNow()
+	k.Helper()
+	if k.Expects("fatalf").Error(
+		stub.CheckArg(k.Stub, "format", format, 0),
+		stub.CheckArgReflect(k.Stub, "v", v, 1)) != nil {
+		k.FailNow()
 	}
-	panic(0xdeadbeef)
+	panic(stub.PanicExit)
 }
 
 func (k *kstub) verbose(v ...any) {
-	if k.expect("verbose").error(
-		checkArgReflect(k, "v", v, 0)) != nil {
-		k.t.FailNow()
+	k.Helper()
+	if k.Expects("verbose").Error(
+		stub.CheckArgReflect(k.Stub, "v", v, 0)) != nil {
+		k.FailNow()
 	}
 }
 
 func (k *kstub) verbosef(format string, v ...any) {
-	if k.expect("verbosef").error(
-		checkArg(k, "format", format, 0),
-		checkArgReflect(k, "v", v, 1)) != nil {
-		k.t.FailNow()
+	k.Helper()
+	if k.Expects("verbosef").Error(
+		stub.CheckArg(k.Stub, "format", format, 0),
+		stub.CheckArgReflect(k.Stub, "v", v, 1)) != nil {
+		k.FailNow()
 	}
 }
 
-func (k *kstub) suspend()     { k.expect("suspend") }
-func (k *kstub) resume() bool { return k.expect("resume").ret.(bool) }
-func (k *kstub) beforeExit()  { k.expect("beforeExit") }
-
-func (k *kstub) printBaseErr(err error, fallback string) {
-	if k.expect("printBaseErr").error(
-		checkArgReflect(k, "err", err, 0),
-		checkArg(k, "fallback", fallback, 1)) != nil {
-		k.t.FailNow()
-	}
-}
+func (k *kstub) suspend()     { k.Helper(); k.Expects("suspend") }
+func (k *kstub) resume() bool { k.Helper(); return k.Expects("resume").Ret.(bool) }
+func (k *kstub) beforeExit()  { k.Helper(); k.Expects("beforeExit") }

container/errors.go

@@ -0,0 +1,112 @@
+package container
+
+import (
+	"errors"
+	"os"
+	"syscall"
+
+	"hakurei.app/container/vfs"
+)
+
+// messageFromError returns a printable error message for a supported concrete type.
+func messageFromError(err error) (string, bool) {
+	if m, ok := messagePrefixP[MountError]("cannot ", err); ok {
+		return m, ok
+	}
+	if m, ok := messagePrefixP[os.PathError]("cannot ", err); ok {
+		return m, ok
+	}
+	if m, ok := messagePrefixP[AbsoluteError]("", err); ok {
+		return m, ok
+	}
+	if m, ok := messagePrefix[OpRepeatError]("", err); ok {
+		return m, ok
+	}
+	if m, ok := messagePrefix[OpStateError]("", err); ok {
+		return m, ok
+	}
+
+	if m, ok := messagePrefixP[vfs.DecoderError]("cannot ", err); ok {
+		return m, ok
+	}
+	if m, ok := messagePrefix[TmpfsSizeError]("", err); ok {
+		return m, ok
+	}
+
+	return zeroString, false
+}
+
+// messagePrefix checks and prefixes the error message of a non-pointer error.
+// While this is usable for pointer errors, such use should be avoided as nil check is omitted.
+func messagePrefix[T error](prefix string, err error) (string, bool) {
+	var targetError T
+	if errors.As(err, &targetError) {
+		return prefix + targetError.Error(), true
+	}
+	return zeroString, false
+}
+
+// messagePrefixP checks and prefixes the error message of a pointer error.
+func messagePrefixP[V any, T interface {
+	*V
+	error
+}](prefix string, err error) (string, bool) {
+	var targetError T
+	if errors.As(err, &targetError) && targetError != nil {
+		return prefix + targetError.Error(), true
+	}
+	return zeroString, false
+}
+
+type MountError struct {
+	Source, Target, Fstype string
+
+	Flags uintptr
+	Data  string
+	syscall.Errno
+}
+
+func (e *MountError) Unwrap() error {
+	if e.Errno == 0 {
+		return nil
+	}
+	return e.Errno
+}
+
+func (e *MountError) Error() string {
+	if e.Flags&syscall.MS_BIND != 0 {
+		if e.Flags&syscall.MS_REMOUNT != 0 {
+			return "remount " + e.Target + ": " + e.Errno.Error()
+		}
+		return "bind " + e.Source + " on " + e.Target + ": " + e.Errno.Error()
+	}
+
+	if e.Fstype != FstypeNULL {
+		return "mount " + e.Fstype + " on " + e.Target + ": " + e.Errno.Error()
+	}
+
+	// fallback case: if this is reached, the conditions for it to occur should be handled above
+	return "mount " + e.Target + ": " + e.Errno.Error()
+}
+
+// errnoFallback returns the concrete errno from an error, or a [os.PathError] fallback.
+func errnoFallback(op, path string, err error) (syscall.Errno, *os.PathError) {
+	var errno syscall.Errno
+	if !errors.As(err, &errno) {
+		return 0, &os.PathError{Op: op, Path: path, Err: err}
+	}
+	return errno, nil
+}
+
+// mount wraps syscall.Mount for error handling.
+func mount(source, target, fstype string, flags uintptr, data string) error {
+	err := syscall.Mount(source, target, fstype, flags, data)
+	if err == nil {
+		return nil
+	}
+	if errno, pathError := errnoFallback("mount", target, err); pathError != nil {
+		return pathError
+	} else {
+		return &MountError{source, target, fstype, flags, data, errno}
+	}
+}

container/errors_test.go

@@ -0,0 +1,168 @@
+package container
+
+import (
+	"errors"
+	"os"
+	"reflect"
+	"strconv"
+	"syscall"
+	"testing"
+
+	"hakurei.app/container/stub"
+	"hakurei.app/container/vfs"
+)
+
+func TestMessageFromError(t *testing.T) {
+	testCases := []struct {
+		name   string
+		err    error
+		want   string
+		wantOk bool
+	}{
+		{"mount", &MountError{
+			Source: SourceTmpfsEphemeral,
+			Target: "/sysroot/tmp",
+			Fstype: FstypeTmpfs,
+			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
+			Data:   zeroString,
+			Errno:  syscall.EINVAL,
+		}, "cannot mount tmpfs on /sysroot/tmp: invalid argument", true},
+
+		{"path", &os.PathError{
+			Op:   "mount",
+			Path: "/sysroot",
+			Err:  stub.UniqueError(0xdeadbeef),
+		}, "cannot mount /sysroot: unique error 3735928559 injected by the test suite", true},
+
+		{"absolute", &AbsoluteError{"etc/mtab"},
+			`path "etc/mtab" is not absolute`, true},
+
+		{"repeat", OpRepeatError("autoetc"),
+			"autoetc is not repeatable", true},
+
+		{"state", OpStateError("overlay"),
+			"impossible overlay state reached", true},
+
+		{"vfs parse", &vfs.DecoderError{Op: "parse", Line: 0xdeadbeef, Err: &strconv.NumError{Func: "Atoi", Num: "meow", Err: strconv.ErrSyntax}},
+			`cannot parse mountinfo at line 3735928559: numeric field "meow" invalid syntax`, true},
+
+		{"tmpfs", TmpfsSizeError(-1),
+			"tmpfs size -1 out of bounds", true},
+
+		{"unsupported", stub.UniqueError(0xdeadbeef), zeroString, false},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			got, ok := messageFromError(tc.err)
+			if got != tc.want {
+				t.Errorf("messageFromError: %q, want %q", got, tc.want)
+			}
+			if ok != tc.wantOk {
+				t.Errorf("messageFromError: ok = %v, want %v", ok, tc.wantOk)
+			}
+		})
+	}
+}
+
+func TestMountError(t *testing.T) {
+	testCases := []struct {
+		name  string
+		err   error
+		errno syscall.Errno
+		want  string
+	}{
+		{"bind", &MountError{
+			Source: "/host/nix/store",
+			Target: "/sysroot/nix/store",
+			Fstype: FstypeNULL,
+			Flags:  syscall.MS_SILENT | syscall.MS_BIND | syscall.MS_REC,
+			Data:   zeroString,
+			Errno:  syscall.ENOSYS,
+		}, syscall.ENOSYS,
+			"bind /host/nix/store on /sysroot/nix/store: function not implemented"},
+
+		{"remount", &MountError{
+			Source: SourceNone,
+			Target: "/sysroot/nix/store",
+			Fstype: FstypeNULL,
+			Flags:  syscall.MS_SILENT | syscall.MS_BIND | syscall.MS_REMOUNT,
+			Data:   zeroString,
+			Errno:  syscall.EPERM,
+		}, syscall.EPERM,
+			"remount /sysroot/nix/store: operation not permitted"},
+
+		{"overlay", &MountError{
+			Source: SourceOverlay,
+			Target: sysrootPath,
+			Fstype: FstypeOverlay,
+			Data:   `lowerdir=/host/var/lib/planterette/base/debian\:f92c9052`,
+			Errno:  syscall.EINVAL,
+		}, syscall.EINVAL,
+			"mount overlay on /sysroot: invalid argument"},
+
+		{"fallback", &MountError{
+			Source: SourceNone,
+			Target: sysrootPath,
+			Fstype: FstypeNULL,
+			Errno:  syscall.ENOTRECOVERABLE,
+		}, syscall.ENOTRECOVERABLE,
+			"mount /sysroot: state not recoverable"},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Run("is", func(t *testing.T) {
+				if !errors.Is(tc.err, tc.errno) {
+					t.Errorf("Is: %#v is not %v", tc.err, tc.errno)
+				}
+			})
+			t.Run("error", func(t *testing.T) {
+				if got := tc.err.Error(); got != tc.want {
+					t.Errorf("Error: %q, want %q", got, tc.want)
+				}
+			})
+		})
+	}
+
+	t.Run("zero", func(t *testing.T) {
+		if errors.Is(new(MountError), syscall.Errno(0)) {
+			t.Errorf("Is: zero MountError unexpected true")
+		}
+	})
+}
+
+func TestErrnoFallback(t *testing.T) {
+	testCases := []struct {
+		name      string
+		err       error
+		wantErrno syscall.Errno
+		wantPath  *os.PathError
+	}{
+		{"mount", &MountError{
+			Errno: syscall.ENOTRECOVERABLE,
+		}, syscall.ENOTRECOVERABLE, nil},
+
+		{"path errno", &os.PathError{
+			Err: syscall.ETIMEDOUT,
+		}, syscall.ETIMEDOUT, nil},
+
+		{"fallback", stub.UniqueError(0xcafebabe), 0, &os.PathError{
+			Op:   "fallback",
+			Path: "/proc/nonexistent",
+			Err:  stub.UniqueError(0xcafebabe),
+		}},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			errno, err := errnoFallback(tc.name, Nonexistent, tc.err)
+			if errno != tc.wantErrno {
+				t.Errorf("errnoFallback: errno = %v, want %v", errno, tc.wantErrno)
+			}
+			if !reflect.DeepEqual(err, tc.wantPath) {
+				t.Errorf("errnoFallback: pathError = %#v, want %#v", err, tc.wantPath)
+			}
+		})
+	}
+}
+
+// InternalMessageFromError exports messageFromError for other tests.
+func InternalMessageFromError(err error) (string, bool) { return messageFromError(err) }

container/init.go

@@ -68,6 +68,16 @@ const (
 	nrAutoRoot
 )
 
+// OpRepeatError is returned applying a repeated nonrepeatable [Op].
+type OpRepeatError string
+
+func (e OpRepeatError) Error() string { return string(e) + " is not repeatable" }
+
+// OpStateError indicates an impossible internal state has been reached in an [Op].
+type OpStateError string
+
+func (o OpStateError) Error() string { return "impossible " + string(o) + " state reached" }
+
 // initParams are params passed from parent.
 type initParams struct {
 	Params
@@ -106,7 +116,7 @@ func initEntrypoint(k syscallDispatcher, prepareLogger func(prefix string), setV
 		if errors.Is(err, EBADF) {
 			k.fatal("invalid setup descriptor")
 		}
-		if errors.Is(err, ErrNotSet) {
+		if errors.Is(err, ErrReceiveEnv) {
 			k.fatal("HAKUREI_SETUP not set")
 		}
 
@@ -174,10 +184,11 @@ func initEntrypoint(k syscallDispatcher, prepareLogger func(prefix string), setV
 		}
 
 		if err := op.early(state, k); err != nil {
-			k.printBaseErr(err,
-				fmt.Sprintf("cannot prepare op at index %d:", i))
-			k.beforeExit()
-			k.exit(1)
+			if m, ok := messageFromError(err); ok {
+				k.fatal(m)
+			} else {
+				k.fatalf("cannot prepare op at index %d: %v", i, err)
+			}
 		}
 	}
 
@@ -214,10 +225,11 @@ func initEntrypoint(k syscallDispatcher, prepareLogger func(prefix string), setV
 		// ops already checked during early setup
 		k.verbosef("%s %s", op.prefix(), op)
 		if err := op.apply(state, k); err != nil {
-			k.printBaseErr(err,
-				fmt.Sprintf("cannot apply op at index %d:", i))
-			k.beforeExit()
-			k.exit(1)
+			if m, ok := messageFromError(err); ok {
+				k.fatal(m)
+			} else {
+				k.fatalf("cannot apply op at index %d: %v", i, err)
+			}
 		}
 	}
 

container/initbind.go

@@ -43,7 +43,7 @@ func (b *BindMountOp) Valid() bool {
 func (b *BindMountOp) early(_ *setupState, k syscallDispatcher) error {
 	if b.Flags&BindEnsure != 0 {
 		if err := k.mkdirAll(b.Source.String(), 0700); err != nil {
-			return wrapErrSelf(err)
+			return err
 		}
 	}
 
@@ -52,7 +52,7 @@ func (b *BindMountOp) early(_ *setupState, k syscallDispatcher) error {
 			// leave sourceFinal as nil
 			return nil
 		}
-		return wrapErrSelf(err)
+		return err
 	} else {
 		b.sourceFinal, err = NewAbs(pathname)
 		return err
@@ -63,7 +63,7 @@ func (b *BindMountOp) apply(_ *setupState, k syscallDispatcher) error {
 	if b.sourceFinal == nil {
 		if b.Flags&BindOptional == 0 {
 			// unreachable
-			return msg.WrapErr(os.ErrClosed, "impossible bind state reached")
+			return OpStateError("bind")
 		}
 		return nil
 	}
@@ -74,10 +74,10 @@ func (b *BindMountOp) apply(_ *setupState, k syscallDispatcher) error {
 	// this perm value emulates bwrap behaviour as it clears bits from 0755 based on
 	// op->perms which is never set for any bind setup op so always results in 0700
 	if fi, err := k.stat(source); err != nil {
-		return wrapErrSelf(err)
+		return err
 	} else if fi.IsDir() {
 		if err = k.mkdirAll(target, 0700); err != nil {
-			return wrapErrSelf(err)
+			return err
 		}
 	} else if err = k.ensureFile(target, 0444, 0700); err != nil {
 		return err

container/initbind_test.go

@@ -5,6 +5,8 @@ import (
 	"os"
 	"syscall"
 	"testing"
+
+	"hakurei.app/container/stub"
 )
 
 func TestBindMountOp(t *testing.T) {
@@ -12,138 +14,138 @@ func TestBindMountOp(t *testing.T) {
 		{"ENOENT not optional", new(Params), &BindMountOp{
 			Source: MustAbs("/bin/"),
 			Target: MustAbs("/bin/"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/bin/"}, "", syscall.ENOENT},
-		}, wrapErrSelf(syscall.ENOENT), nil, nil},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "", syscall.ENOENT),
+		}, syscall.ENOENT, nil, nil},
 
 		{"skip optional", new(Params), &BindMountOp{
 			Source: MustAbs("/bin/"),
 			Target: MustAbs("/bin/"),
 			Flags:  BindOptional,
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/bin/"}, "", syscall.ENOENT},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "", syscall.ENOENT),
 		}, nil, nil, nil},
 
 		{"success optional", new(Params), &BindMountOp{
 			Source: MustAbs("/bin/"),
 			Target: MustAbs("/bin/"),
 			Flags:  BindOptional,
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/bin/"}, "/usr/bin", nil},
-		}, nil, []kexpect{
-			{"stat", expectArgs{"/host/usr/bin"}, isDirFi(true), nil},
-			{"mkdirAll", expectArgs{"/sysroot/bin", os.FileMode(0700)}, nil, nil},
-			{"bindMount", expectArgs{"/host/usr/bin", "/sysroot/bin", uintptr(0x4005), false}, nil, nil},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", nil),
+		}, nil, []stub.Call{
+			call("stat", stub.ExpectArgs{"/host/usr/bin"}, isDirFi(true), nil),
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/bin", os.FileMode(0700)}, nil, nil),
+			call("bindMount", stub.ExpectArgs{"/host/usr/bin", "/sysroot/bin", uintptr(0x4005), false}, nil, nil),
 		}, nil},
 
 		{"ensureFile device", new(Params), &BindMountOp{
 			Source: MustAbs("/dev/null"),
 			Target: MustAbs("/dev/null"),
 			Flags:  BindWritable | BindDevice,
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/dev/null"}, "/dev/null", nil},
-		}, nil, []kexpect{
-			{"stat", expectArgs{"/host/dev/null"}, isDirFi(false), nil},
-			{"ensureFile", expectArgs{"/sysroot/dev/null", os.FileMode(0444), os.FileMode(0700)}, nil, errUnique},
-		}, errUnique},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/dev/null"}, "/dev/null", nil),
+		}, nil, []stub.Call{
+			call("stat", stub.ExpectArgs{"/host/dev/null"}, isDirFi(false), nil),
+			call("ensureFile", stub.ExpectArgs{"/sysroot/dev/null", os.FileMode(0444), os.FileMode(0700)}, nil, stub.UniqueError(5)),
+		}, stub.UniqueError(5)},
 
 		{"mkdirAll ensure", new(Params), &BindMountOp{
 			Source: MustAbs("/bin/"),
 			Target: MustAbs("/bin/"),
 			Flags:  BindEnsure,
-		}, []kexpect{
-			{"mkdirAll", expectArgs{"/bin/", os.FileMode(0700)}, nil, errUnique},
-		}, wrapErrSelf(errUnique), nil, nil},
+		}, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/bin/", os.FileMode(0700)}, nil, stub.UniqueError(4)),
+		}, stub.UniqueError(4), nil, nil},
 
 		{"success ensure", new(Params), &BindMountOp{
 			Source: MustAbs("/bin/"),
 			Target: MustAbs("/usr/bin/"),
 			Flags:  BindEnsure,
-		}, []kexpect{
-			{"mkdirAll", expectArgs{"/bin/", os.FileMode(0700)}, nil, nil},
-			{"evalSymlinks", expectArgs{"/bin/"}, "/usr/bin", nil},
-		}, nil, []kexpect{
-			{"stat", expectArgs{"/host/usr/bin"}, isDirFi(true), nil},
-			{"mkdirAll", expectArgs{"/sysroot/usr/bin", os.FileMode(0700)}, nil, nil},
-			{"bindMount", expectArgs{"/host/usr/bin", "/sysroot/usr/bin", uintptr(0x4005), false}, nil, nil},
+		}, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/bin/", os.FileMode(0700)}, nil, nil),
+			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", nil),
+		}, nil, []stub.Call{
+			call("stat", stub.ExpectArgs{"/host/usr/bin"}, isDirFi(true), nil),
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/usr/bin", os.FileMode(0700)}, nil, nil),
+			call("bindMount", stub.ExpectArgs{"/host/usr/bin", "/sysroot/usr/bin", uintptr(0x4005), false}, nil, nil),
 		}, nil},
 
 		{"success device ro", new(Params), &BindMountOp{
 			Source: MustAbs("/dev/null"),
 			Target: MustAbs("/dev/null"),
 			Flags:  BindDevice,
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/dev/null"}, "/dev/null", nil},
-		}, nil, []kexpect{
-			{"stat", expectArgs{"/host/dev/null"}, isDirFi(false), nil},
-			{"ensureFile", expectArgs{"/sysroot/dev/null", os.FileMode(0444), os.FileMode(0700)}, nil, nil},
-			{"bindMount", expectArgs{"/host/dev/null", "/sysroot/dev/null", uintptr(0x4001), false}, nil, nil},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/dev/null"}, "/dev/null", nil),
+		}, nil, []stub.Call{
+			call("stat", stub.ExpectArgs{"/host/dev/null"}, isDirFi(false), nil),
+			call("ensureFile", stub.ExpectArgs{"/sysroot/dev/null", os.FileMode(0444), os.FileMode(0700)}, nil, nil),
+			call("bindMount", stub.ExpectArgs{"/host/dev/null", "/sysroot/dev/null", uintptr(0x4001), false}, nil, nil),
 		}, nil},
 
 		{"success device", new(Params), &BindMountOp{
 			Source: MustAbs("/dev/null"),
 			Target: MustAbs("/dev/null"),
 			Flags:  BindWritable | BindDevice,
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/dev/null"}, "/dev/null", nil},
-		}, nil, []kexpect{
-			{"stat", expectArgs{"/host/dev/null"}, isDirFi(false), nil},
-			{"ensureFile", expectArgs{"/sysroot/dev/null", os.FileMode(0444), os.FileMode(0700)}, nil, nil},
-			{"bindMount", expectArgs{"/host/dev/null", "/sysroot/dev/null", uintptr(0x4000), false}, nil, nil},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/dev/null"}, "/dev/null", nil),
+		}, nil, []stub.Call{
+			call("stat", stub.ExpectArgs{"/host/dev/null"}, isDirFi(false), nil),
+			call("ensureFile", stub.ExpectArgs{"/sysroot/dev/null", os.FileMode(0444), os.FileMode(0700)}, nil, nil),
+			call("bindMount", stub.ExpectArgs{"/host/dev/null", "/sysroot/dev/null", uintptr(0x4000), false}, nil, nil),
 		}, nil},
 
 		{"evalSymlinks", new(Params), &BindMountOp{
 			Source: MustAbs("/bin/"),
 			Target: MustAbs("/bin/"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/bin/"}, "/usr/bin", errUnique},
-		}, wrapErrSelf(errUnique), nil, nil},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", stub.UniqueError(3)),
+		}, stub.UniqueError(3), nil, nil},
 
 		{"stat", new(Params), &BindMountOp{
 			Source: MustAbs("/bin/"),
 			Target: MustAbs("/bin/"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/bin/"}, "/usr/bin", nil},
-		}, nil, []kexpect{
-			{"stat", expectArgs{"/host/usr/bin"}, isDirFi(true), errUnique},
-		}, wrapErrSelf(errUnique)},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", nil),
+		}, nil, []stub.Call{
+			call("stat", stub.ExpectArgs{"/host/usr/bin"}, isDirFi(true), stub.UniqueError(2)),
+		}, stub.UniqueError(2)},
 
 		{"mkdirAll", new(Params), &BindMountOp{
 			Source: MustAbs("/bin/"),
 			Target: MustAbs("/bin/"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/bin/"}, "/usr/bin", nil},
-		}, nil, []kexpect{
-			{"stat", expectArgs{"/host/usr/bin"}, isDirFi(true), nil},
-			{"mkdirAll", expectArgs{"/sysroot/bin", os.FileMode(0700)}, nil, errUnique},
-		}, wrapErrSelf(errUnique)},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", nil),
+		}, nil, []stub.Call{
+			call("stat", stub.ExpectArgs{"/host/usr/bin"}, isDirFi(true), nil),
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/bin", os.FileMode(0700)}, nil, stub.UniqueError(1)),
+		}, stub.UniqueError(1)},
 
 		{"bindMount", new(Params), &BindMountOp{
 			Source: MustAbs("/bin/"),
 			Target: MustAbs("/bin/"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/bin/"}, "/usr/bin", nil},
-		}, nil, []kexpect{
-			{"stat", expectArgs{"/host/usr/bin"}, isDirFi(true), nil},
-			{"mkdirAll", expectArgs{"/sysroot/bin", os.FileMode(0700)}, nil, nil},
-			{"bindMount", expectArgs{"/host/usr/bin", "/sysroot/bin", uintptr(0x4005), false}, nil, errUnique},
-		}, errUnique},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", nil),
+		}, nil, []stub.Call{
+			call("stat", stub.ExpectArgs{"/host/usr/bin"}, isDirFi(true), nil),
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/bin", os.FileMode(0700)}, nil, nil),
+			call("bindMount", stub.ExpectArgs{"/host/usr/bin", "/sysroot/bin", uintptr(0x4005), false}, nil, stub.UniqueError(0)),
+		}, stub.UniqueError(0)},
 
 		{"success", new(Params), &BindMountOp{
 			Source: MustAbs("/bin/"),
 			Target: MustAbs("/bin/"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/bin/"}, "/usr/bin", nil},
-		}, nil, []kexpect{
-			{"stat", expectArgs{"/host/usr/bin"}, isDirFi(true), nil},
-			{"mkdirAll", expectArgs{"/sysroot/bin", os.FileMode(0700)}, nil, nil},
-			{"bindMount", expectArgs{"/host/usr/bin", "/sysroot/bin", uintptr(0x4005), false}, nil, nil},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", nil),
+		}, nil, []stub.Call{
+			call("stat", stub.ExpectArgs{"/host/usr/bin"}, isDirFi(true), nil),
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/bin", os.FileMode(0700)}, nil, nil),
+			call("bindMount", stub.ExpectArgs{"/host/usr/bin", "/sysroot/bin", uintptr(0x4005), false}, nil, nil),
 		}, nil},
 	})
 
 	t.Run("unreachable", func(t *testing.T) {
 		t.Run("nil sourceFinal not optional", func(t *testing.T) {
-			wantErr := msg.WrapErr(os.ErrClosed, "impossible bind state reached")
+			wantErr := OpStateError("bind")
 			if err := new(BindMountOp).apply(nil, nil); !errors.Is(err, wantErr) {
 				t.Errorf("apply: error = %v, want %v", err, wantErr)
 			}

container/initdev.go

@@ -59,7 +59,7 @@ func (d *MountDevOp) apply(state *setupState, k syscallDispatcher) error {
 			FHSProc+"self/fd/"+string(rune(i+'0')),
 			path.Join(target, name),
 		); err != nil {
-			return wrapErrSelf(err)
+			return err
 		}
 	}
 	for _, pair := range [][2]string{
@@ -68,7 +68,7 @@ func (d *MountDevOp) apply(state *setupState, k syscallDispatcher) error {
 		{"pts/ptmx", "ptmx"},
 	} {
 		if err := k.symlink(pair[0], path.Join(target, pair[1])); err != nil {
-			return wrapErrSelf(err)
+			return err
 		}
 	}
 
@@ -76,14 +76,13 @@ func (d *MountDevOp) apply(state *setupState, k syscallDispatcher) error {
 	devPtsPath := path.Join(target, "pts")
 	for _, name := range []string{devShmPath, devPtsPath} {
 		if err := k.mkdir(name, state.ParentPerm); err != nil {
-			return wrapErrSelf(err)
+			return err
 		}
 	}
 
 	if err := k.mount(SourceDevpts, devPtsPath, FstypeDevpts, MS_NOSUID|MS_NOEXEC,
 		"newinstance,ptmxmode=0666,mode=620"); err != nil {
-		return wrapErrSuffix(err,
-			fmt.Sprintf("cannot mount devpts on %q:", devPtsPath))
+		return err
 	}
 
 	if state.RetainSession {
@@ -93,7 +92,7 @@ func (d *MountDevOp) apply(state *setupState, k syscallDispatcher) error {
 				return err
 			}
 			if name, err := k.readlink(hostProc.stdout()); err != nil {
-				return wrapErrSelf(err)
+				return err
 			} else if err = k.bindMount(
 				toHost(name),
 				consolePath,
@@ -108,10 +107,10 @@ func (d *MountDevOp) apply(state *setupState, k syscallDispatcher) error {
 	if d.Mqueue {
 		mqueueTarget := path.Join(target, "mqueue")
 		if err := k.mkdir(mqueueTarget, state.ParentPerm); err != nil {
-			return wrapErrSelf(err)
+			return err
 		}
 		if err := k.mount(SourceMqueue, mqueueTarget, FstypeMqueue, MS_NOSUID|MS_NOEXEC|MS_NODEV, zeroString); err != nil {
-			return wrapErrSuffix(err, "cannot mount mqueue:")
+			return err
 		}
 	}
 
@@ -120,8 +119,7 @@ func (d *MountDevOp) apply(state *setupState, k syscallDispatcher) error {
 	}
 
 	if err := k.remount(target, MS_RDONLY); err != nil {
-		return wrapErrSuffix(k.remount(target, MS_RDONLY),
-			fmt.Sprintf("cannot remount %q:", target))
+		return err
 	}
 	return k.mountTmpfs(SourceTmpfs, devShmPath, MS_NOSUID|MS_NODEV, 0, 01777)
 }

container/initmkdir.go

@@ -23,7 +23,7 @@ type MkdirOp struct {
 func (m *MkdirOp) Valid() bool                                { return m != nil && m.Path != nil }
 func (m *MkdirOp) early(*setupState, syscallDispatcher) error { return nil }
 func (m *MkdirOp) apply(_ *setupState, k syscallDispatcher) error {
-	return wrapErrSelf(k.mkdirAll(toSysroot(m.Path.String()), m.Perm))
+	return k.mkdirAll(toSysroot(m.Path.String()), m.Perm)
 }
 
 func (m *MkdirOp) Is(op Op) bool {

container/initmkdir_test.go

@@ -3,6 +3,8 @@ package container
 import (
 	"os"
 	"testing"
+
+	"hakurei.app/container/stub"
 )
 
 func TestMkdirOp(t *testing.T) {
@@ -10,8 +12,8 @@ func TestMkdirOp(t *testing.T) {
 		{"success", new(Params), &MkdirOp{
 			Path: MustAbs("/.hakurei"),
 			Perm: 0500,
-		}, nil, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/.hakurei", os.FileMode(0500)}, nil, nil},
+		}, nil, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/.hakurei", os.FileMode(0500)}, nil, nil),
 		}, nil},
 	})
 

container/initoverlay.go

@@ -3,7 +3,6 @@ package container
 import (
 	"encoding/gob"
 	"fmt"
-	"io/fs"
 	"slices"
 	"strings"
 )
@@ -19,6 +18,39 @@ const (
 
 func init() { gob.Register(new(MountOverlayOp)) }
 
+const (
+	// OverlayEphemeralUnexpectedUpper is set when [MountOverlayOp.Work] is nil
+	// and [MountOverlayOp.Upper] holds an unexpected value.
+	OverlayEphemeralUnexpectedUpper = iota
+	// OverlayReadonlyLower is set when [MountOverlayOp.Lower] contains less than
+	// two entries when mounting readonly.
+	OverlayReadonlyLower
+	// OverlayEmptyLower is set when [MountOverlayOp.Lower] has length of zero.
+	OverlayEmptyLower
+)
+
+// OverlayArgumentError is returned for [MountOverlayOp] supplied with invalid argument.
+type OverlayArgumentError struct {
+	Type  uintptr
+	Value string
+}
+
+func (e *OverlayArgumentError) Error() string {
+	switch e.Type {
+	case OverlayEphemeralUnexpectedUpper:
+		return fmt.Sprintf("upperdir has unexpected value %q", e.Value)
+
+	case OverlayReadonlyLower:
+		return "readonly overlay requires at least two lowerdir"
+
+	case OverlayEmptyLower:
+		return "overlay requires at least one lowerdir"
+
+	default:
+		return fmt.Sprintf("invalid overlay argument error %#x", e.Type)
+	}
+}
+
 // Overlay appends an [Op] that mounts the overlay pseudo filesystem on [MountOverlayOp.Target].
 func (f *Ops) Overlay(target, state, work *Absolute, layers ...*Absolute) *Ops {
 	*f = append(*f, &MountOverlayOp{
@@ -89,7 +121,7 @@ func (o *MountOverlayOp) early(_ *setupState, k syscallDispatcher) error {
 			o.ephemeral = true // intermediate root not yet available
 
 		default:
-			return msg.WrapErr(fs.ErrInvalid, fmt.Sprintf("upperdir has unexpected value %q", o.Upper))
+			return &OverlayArgumentError{OverlayEphemeralUnexpectedUpper, o.Upper.String()}
 		}
 	}
 	// readonly handled in apply
@@ -97,12 +129,12 @@ func (o *MountOverlayOp) early(_ *setupState, k syscallDispatcher) error {
 	if !o.ephemeral {
 		if o.Upper != o.Work && (o.Upper == nil || o.Work == nil) {
 			// unreachable
-			return msg.WrapErr(fs.ErrClosed, "impossible overlay state reached")
+			return OpStateError("overlay")
 		}
 
 		if o.Upper != nil {
 			if v, err := k.evalSymlinks(o.Upper.String()); err != nil {
-				return wrapErrSelf(err)
+				return err
 			} else {
 				o.upper = EscapeOverlayDataSegment(toHost(v))
 			}
@@ -110,7 +142,7 @@ func (o *MountOverlayOp) early(_ *setupState, k syscallDispatcher) error {
 
 		if o.Work != nil {
 			if v, err := k.evalSymlinks(o.Work.String()); err != nil {
-				return wrapErrSelf(err)
+				return err
 			} else {
 				o.work = EscapeOverlayDataSegment(toHost(v))
 			}
@@ -120,7 +152,7 @@ func (o *MountOverlayOp) early(_ *setupState, k syscallDispatcher) error {
 	o.lower = make([]string, len(o.Lower))
 	for i, a := range o.Lower { // nil checked in Valid
 		if v, err := k.evalSymlinks(a.String()); err != nil {
-			return wrapErrSelf(err)
+			return err
 		} else {
 			o.lower[i] = EscapeOverlayDataSegment(toHost(v))
 		}
@@ -134,17 +166,17 @@ func (o *MountOverlayOp) apply(state *setupState, k syscallDispatcher) error {
 		target = toSysroot(target)
 	}
 	if err := k.mkdirAll(target, state.ParentPerm); err != nil {
-		return wrapErrSelf(err)
+		return err
 	}
 
 	if o.ephemeral {
 		var err error
 		// these directories are created internally, therefore early (absolute, symlink, prefix, escape) is bypassed
 		if o.upper, err = k.mkdirTemp(FHSRoot, intermediatePatternOverlayUpper); err != nil {
-			return wrapErrSelf(err)
+			return err
 		}
 		if o.work, err = k.mkdirTemp(FHSRoot, intermediatePatternOverlayWork); err != nil {
-			return wrapErrSelf(err)
+			return err
 		}
 	}
 
@@ -152,12 +184,12 @@ func (o *MountOverlayOp) apply(state *setupState, k syscallDispatcher) error {
 
 	if o.upper == zeroString && o.work == zeroString { // readonly
 		if len(o.Lower) < 2 {
-			return msg.WrapErr(fs.ErrInvalid, "readonly overlay requires at least two lowerdir")
+			return &OverlayArgumentError{OverlayReadonlyLower, zeroString}
 		}
 		// "upperdir=" and "workdir=" may be omitted. In that case the overlay will be read-only
 	} else {
 		if len(o.Lower) == 0 {
-			return msg.WrapErr(fs.ErrInvalid, "overlay requires at least one lowerdir")
+			return &OverlayArgumentError{OverlayEmptyLower, zeroString}
 		}
 		options = append(options,
 			OptionOverlayUpperdir+"="+o.upper,
@@ -167,8 +199,7 @@ func (o *MountOverlayOp) apply(state *setupState, k syscallDispatcher) error {
 		OptionOverlayLowerdir+"="+strings.Join(o.lower, SpecialOverlayPath),
 		OptionOverlayUserxattr)
 
-	return wrapErrSuffix(k.mount(SourceOverlay, target, FstypeOverlay, 0, strings.Join(options, SpecialOverlayOption)),
-		fmt.Sprintf("cannot mount overlay on %q:", o.Target))
+	return k.mount(SourceOverlay, target, FstypeOverlay, 0, strings.Join(options, SpecialOverlayOption))
 }
 
 func (o *MountOverlayOp) Is(op Op) bool {

container/initoverlay_test.go

@@ -2,12 +2,40 @@ package container
 
 import (
 	"errors"
-	"io/fs"
 	"os"
 	"testing"
+
+	"hakurei.app/container/stub"
 )
 
 func TestMountOverlayOp(t *testing.T) {
+	t.Run("argument error", func(t *testing.T) {
+		testCases := []struct {
+			name string
+			err  *OverlayArgumentError
+			want string
+		}{
+			{"unexpected upper", &OverlayArgumentError{OverlayEphemeralUnexpectedUpper, "/proc/"},
+				`upperdir has unexpected value "/proc/"`},
+
+			{"lower ro short", &OverlayArgumentError{OverlayReadonlyLower, zeroString},
+				"readonly overlay requires at least two lowerdir"},
+
+			{"lower short", &OverlayArgumentError{OverlayEmptyLower, zeroString},
+				"overlay requires at least one lowerdir"},
+
+			{"oob", &OverlayArgumentError{0xdeadbeef, zeroString},
+				"invalid overlay argument error 0xdeadbeef"},
+		}
+		for _, tc := range testCases {
+			t.Run(tc.name, func(t *testing.T) {
+				if got := tc.err.Error(); got != tc.want {
+					t.Errorf("Error: %q, want %q", got, tc.want)
+				}
+			})
+		}
+	})
+
 	checkOpBehaviour(t, []opBehaviourTestCase{
 		{"mkdirTemp invalid ephemeral", &Params{ParentPerm: 0705}, &MountOverlayOp{
 			Target: MustAbs("/"),
@@ -16,7 +44,7 @@ func TestMountOverlayOp(t *testing.T) {
 				MustAbs("/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"),
 			},
 			Upper: MustAbs("/proc/"),
-		}, nil, msg.WrapErr(fs.ErrInvalid, `upperdir has unexpected value "/proc/"`), nil, nil},
+		}, nil, &OverlayArgumentError{OverlayEphemeralUnexpectedUpper, "/proc/"}, nil, nil},
 
 		{"mkdirTemp upper ephemeral", &Params{ParentPerm: 0705}, &MountOverlayOp{
 			Target: MustAbs("/"),
@@ -25,13 +53,13 @@ func TestMountOverlayOp(t *testing.T) {
 				MustAbs("/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"),
 			},
 			Upper: MustAbs("/"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052"}, "/var/lib/planterette/base/debian:f92c9052", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"}, "/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052", nil},
-		}, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot", os.FileMode(0705)}, nil, nil},
-			{"mkdirTemp", expectArgs{"/", "overlay.upper.*"}, "overlay.upper.32768", errUnique},
-		}, wrapErrSelf(errUnique)},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052"}, "/var/lib/planterette/base/debian:f92c9052", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"}, "/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052", nil),
+		}, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot", os.FileMode(0705)}, nil, nil),
+			call("mkdirTemp", stub.ExpectArgs{"/", "overlay.upper.*"}, "overlay.upper.32768", stub.UniqueError(6)),
+		}, stub.UniqueError(6)},
 
 		{"mkdirTemp work ephemeral", &Params{ParentPerm: 0705}, &MountOverlayOp{
 			Target: MustAbs("/"),
@@ -40,14 +68,14 @@ func TestMountOverlayOp(t *testing.T) {
 				MustAbs("/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"),
 			},
 			Upper: MustAbs("/"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052"}, "/var/lib/planterette/base/debian:f92c9052", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"}, "/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052", nil},
-		}, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot", os.FileMode(0705)}, nil, nil},
-			{"mkdirTemp", expectArgs{"/", "overlay.upper.*"}, "overlay.upper.32768", nil},
-			{"mkdirTemp", expectArgs{"/", "overlay.work.*"}, "overlay.work.32768", errUnique},
-		}, wrapErrSelf(errUnique)},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052"}, "/var/lib/planterette/base/debian:f92c9052", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"}, "/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052", nil),
+		}, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot", os.FileMode(0705)}, nil, nil),
+			call("mkdirTemp", stub.ExpectArgs{"/", "overlay.upper.*"}, "overlay.upper.32768", nil),
+			call("mkdirTemp", stub.ExpectArgs{"/", "overlay.work.*"}, "overlay.work.32768", stub.UniqueError(5)),
+		}, stub.UniqueError(5)},
 
 		{"success ephemeral", &Params{ParentPerm: 0705}, &MountOverlayOp{
 			Target: MustAbs("/"),
@@ -56,20 +84,20 @@ func TestMountOverlayOp(t *testing.T) {
 				MustAbs("/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"),
 			},
 			Upper: MustAbs("/"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/base/debian:f92c9052"}, "/var/lib/planterette/base/debian:f92c9052", nil},
-			{"evalSymlinks", expectArgs{"/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"}, "/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052", nil},
-		}, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot", os.FileMode(0705)}, nil, nil},
-			{"mkdirTemp", expectArgs{"/", "overlay.upper.*"}, "overlay.upper.32768", nil},
-			{"mkdirTemp", expectArgs{"/", "overlay.work.*"}, "overlay.work.32768", nil},
-			{"mount", expectArgs{"overlay", "/sysroot", "overlay", uintptr(0), "" +
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/base/debian:f92c9052"}, "/var/lib/planterette/base/debian:f92c9052", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"}, "/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052", nil),
+		}, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot", os.FileMode(0705)}, nil, nil),
+			call("mkdirTemp", stub.ExpectArgs{"/", "overlay.upper.*"}, "overlay.upper.32768", nil),
+			call("mkdirTemp", stub.ExpectArgs{"/", "overlay.work.*"}, "overlay.work.32768", nil),
+			call("mount", stub.ExpectArgs{"overlay", "/sysroot", "overlay", uintptr(0), "" +
 				"upperdir=overlay.upper.32768," +
 				"workdir=overlay.work.32768," +
 				"lowerdir=" +
 				`/host/var/lib/planterette/base/debian\:f92c9052:` +
 				`/host/var/lib/planterette/app/org.chromium.Chromium@debian\:f92c9052,` +
-				"userxattr"}, nil, nil},
+				"userxattr"}, nil, nil),
 		}, nil},
 
 		{"short lower ro", &Params{ParentPerm: 0755}, &MountOverlayOp{
@@ -77,11 +105,11 @@ func TestMountOverlayOp(t *testing.T) {
 			Lower: []*Absolute{
 				MustAbs("/mnt-root/nix/.ro-store"),
 			},
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/.ro-store", nil},
-		}, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/nix/store", os.FileMode(0755)}, nil, nil},
-		}, msg.WrapErr(fs.ErrInvalid, "readonly overlay requires at least two lowerdir")},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/.ro-store", nil),
+		}, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/nix/store", os.FileMode(0755)}, nil, nil),
+		}, &OverlayArgumentError{OverlayReadonlyLower, zeroString}},
 
 		{"success ro noPrefix", &Params{ParentPerm: 0755}, &MountOverlayOp{
 			Target: MustAbs("/nix/store"),
@@ -90,16 +118,16 @@ func TestMountOverlayOp(t *testing.T) {
 				MustAbs("/mnt-root/nix/.ro-store0"),
 			},
 			noPrefix: true,
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/.ro-store", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store0"}, "/mnt-root/nix/.ro-store0", nil},
-		}, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/nix/store", os.FileMode(0755)}, nil, nil},
-			{"mount", expectArgs{"overlay", "/nix/store", "overlay", uintptr(0), "" +
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/.ro-store", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store0"}, "/mnt-root/nix/.ro-store0", nil),
+		}, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/nix/store", os.FileMode(0755)}, nil, nil),
+			call("mount", stub.ExpectArgs{"overlay", "/nix/store", "overlay", uintptr(0), "" +
 				"lowerdir=" +
 				"/host/mnt-root/nix/.ro-store:" +
 				"/host/mnt-root/nix/.ro-store0," +
-				"userxattr"}, nil, nil},
+				"userxattr"}, nil, nil),
 		}, nil},
 
 		{"success ro", &Params{ParentPerm: 0755}, &MountOverlayOp{
@@ -108,102 +136,102 @@ func TestMountOverlayOp(t *testing.T) {
 				MustAbs("/mnt-root/nix/.ro-store"),
 				MustAbs("/mnt-root/nix/.ro-store0"),
 			},
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/.ro-store", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store0"}, "/mnt-root/nix/.ro-store0", nil},
-		}, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/nix/store", os.FileMode(0755)}, nil, nil},
-			{"mount", expectArgs{"overlay", "/sysroot/nix/store", "overlay", uintptr(0), "" +
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/.ro-store", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store0"}, "/mnt-root/nix/.ro-store0", nil),
+		}, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/nix/store", os.FileMode(0755)}, nil, nil),
+			call("mount", stub.ExpectArgs{"overlay", "/sysroot/nix/store", "overlay", uintptr(0), "" +
 				"lowerdir=" +
 				"/host/mnt-root/nix/.ro-store:" +
 				"/host/mnt-root/nix/.ro-store0," +
-				"userxattr"}, nil, nil},
+				"userxattr"}, nil, nil),
 		}, nil},
 
 		{"nil lower", &Params{ParentPerm: 0700}, &MountOverlayOp{
 			Target: MustAbs("/nix/store"),
 			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
 			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", nil},
-		}, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/nix/store", os.FileMode(0700)}, nil, nil},
-		}, msg.WrapErr(fs.ErrInvalid, "overlay requires at least one lowerdir")},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", nil),
+		}, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/nix/store", os.FileMode(0700)}, nil, nil),
+		}, &OverlayArgumentError{OverlayEmptyLower, zeroString}},
 
 		{"evalSymlinks upper", &Params{ParentPerm: 0700}, &MountOverlayOp{
 			Target: MustAbs("/nix/store"),
 			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
 			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
 			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", errUnique},
-		}, wrapErrSelf(errUnique), nil, nil},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", stub.UniqueError(4)),
+		}, stub.UniqueError(4), nil, nil},
 
 		{"evalSymlinks work", &Params{ParentPerm: 0700}, &MountOverlayOp{
 			Target: MustAbs("/nix/store"),
 			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
 			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
 			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", errUnique},
-		}, wrapErrSelf(errUnique), nil, nil},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", stub.UniqueError(3)),
+		}, stub.UniqueError(3), nil, nil},
 
 		{"evalSymlinks lower", &Params{ParentPerm: 0700}, &MountOverlayOp{
 			Target: MustAbs("/nix/store"),
 			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
 			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
 			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/ro-store", errUnique},
-		}, wrapErrSelf(errUnique), nil, nil},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/ro-store", stub.UniqueError(2)),
+		}, stub.UniqueError(2), nil, nil},
 
 		{"mkdirAll", &Params{ParentPerm: 0700}, &MountOverlayOp{
 			Target: MustAbs("/nix/store"),
 			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
 			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
 			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/ro-store", nil},
-		}, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/nix/store", os.FileMode(0700)}, nil, errUnique},
-		}, wrapErrSelf(errUnique)},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/ro-store", nil),
+		}, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/nix/store", os.FileMode(0700)}, nil, stub.UniqueError(1)),
+		}, stub.UniqueError(1)},
 
 		{"mount", &Params{ParentPerm: 0700}, &MountOverlayOp{
 			Target: MustAbs("/nix/store"),
 			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
 			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
 			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/ro-store", nil},
-		}, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/nix/store", os.FileMode(0700)}, nil, nil},
-			{"mount", expectArgs{"overlay", "/sysroot/nix/store", "overlay", uintptr(0), "upperdir=/host/mnt-root/nix/.rw-store/.upper,workdir=/host/mnt-root/nix/.rw-store/.work,lowerdir=/host/mnt-root/nix/ro-store,userxattr"}, nil, errUnique},
-		}, wrapErrSuffix(errUnique, `cannot mount overlay on "/nix/store":`)},
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/ro-store", nil),
+		}, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/nix/store", os.FileMode(0700)}, nil, nil),
+			call("mount", stub.ExpectArgs{"overlay", "/sysroot/nix/store", "overlay", uintptr(0), "upperdir=/host/mnt-root/nix/.rw-store/.upper,workdir=/host/mnt-root/nix/.rw-store/.work,lowerdir=/host/mnt-root/nix/ro-store,userxattr"}, nil, stub.UniqueError(0)),
+		}, stub.UniqueError(0)},
 
 		{"success single layer", &Params{ParentPerm: 0700}, &MountOverlayOp{
 			Target: MustAbs("/nix/store"),
 			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
 			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
 			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/ro-store", nil},
-		}, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/nix/store", os.FileMode(0700)}, nil, nil},
-			{"mount", expectArgs{"overlay", "/sysroot/nix/store", "overlay", uintptr(0), "" +
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/ro-store", nil),
+		}, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/nix/store", os.FileMode(0700)}, nil, nil),
+			call("mount", stub.ExpectArgs{"overlay", "/sysroot/nix/store", "overlay", uintptr(0), "" +
 				"upperdir=/host/mnt-root/nix/.rw-store/.upper," +
 				"workdir=/host/mnt-root/nix/.rw-store/.work," +
 				"lowerdir=/host/mnt-root/nix/ro-store," +
-				"userxattr"}, nil, nil},
+				"userxattr"}, nil, nil),
 		}, nil},
 
 		{"success", &Params{ParentPerm: 0700}, &MountOverlayOp{
@@ -217,17 +245,17 @@ func TestMountOverlayOp(t *testing.T) {
 			},
 			Upper: MustAbs("/mnt-root/nix/.rw-store/upper"),
 			Work:  MustAbs("/mnt-root/nix/.rw-store/work"),
-		}, []kexpect{
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/ro-store", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store0"}, "/mnt-root/nix/ro-store0", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store1"}, "/mnt-root/nix/ro-store1", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store2"}, "/mnt-root/nix/ro-store2", nil},
-			{"evalSymlinks", expectArgs{"/mnt-root/nix/.ro-store3"}, "/mnt-root/nix/ro-store3", nil},
-		}, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/nix/store", os.FileMode(0700)}, nil, nil},
-			{"mount", expectArgs{"overlay", "/sysroot/nix/store", "overlay", uintptr(0), "" +
+		}, []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/upper"}, "/mnt-root/nix/.rw-store/.upper", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.rw-store/work"}, "/mnt-root/nix/.rw-store/.work", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/ro-store", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store0"}, "/mnt-root/nix/ro-store0", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store1"}, "/mnt-root/nix/ro-store1", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store2"}, "/mnt-root/nix/ro-store2", nil),
+			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store3"}, "/mnt-root/nix/ro-store3", nil),
+		}, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/nix/store", os.FileMode(0700)}, nil, nil),
+			call("mount", stub.ExpectArgs{"overlay", "/sysroot/nix/store", "overlay", uintptr(0), "" +
 				"upperdir=/host/mnt-root/nix/.rw-store/.upper," +
 				"workdir=/host/mnt-root/nix/.rw-store/.work," +
 				"lowerdir=" +
@@ -236,13 +264,13 @@ func TestMountOverlayOp(t *testing.T) {
 				"/host/mnt-root/nix/ro-store1:" +
 				"/host/mnt-root/nix/ro-store2:" +
 				"/host/mnt-root/nix/ro-store3," +
-				"userxattr"}, nil, nil},
+				"userxattr"}, nil, nil),
 		}, nil},
 	})
 
 	t.Run("unreachable", func(t *testing.T) {
 		t.Run("nil Upper non-nil Work not ephemeral", func(t *testing.T) {
-			wantErr := msg.WrapErr(fs.ErrClosed, "impossible overlay state reached")
+			wantErr := OpStateError("overlay")
 			if err := (&MountOverlayOp{
 				Work: MustAbs("/"),
 			}).early(nil, nil); !errors.Is(err, wantErr) {

container/initplace.go

@@ -39,13 +39,11 @@ func (t *TmpfileOp) early(*setupState, syscallDispatcher) error { return nil }
 func (t *TmpfileOp) apply(state *setupState, k syscallDispatcher) error {
 	var tmpPath string
 	if f, err := k.createTemp(FHSRoot, intermediatePatternTmpfile); err != nil {
-		return wrapErrSelf(err)
+		return err
 	} else if _, err = f.Write(t.Data); err != nil {
-		return wrapErrSuffix(err,
-			"cannot write to intermediate file:")
+		return err
 	} else if err = f.Close(); err != nil {
-		return wrapErrSuffix(err,
-			"cannot close intermediate file:")
+		return err
 	} else {
 		tmpPath = f.Name()
 	}
@@ -61,7 +59,7 @@ func (t *TmpfileOp) apply(state *setupState, k syscallDispatcher) error {
 	); err != nil {
 		return err
 	} else if err = k.remove(tmpPath); err != nil {
-		return wrapErrSelf(err)
+		return err
 	}
 	return nil
 }

container/initplace_test.go

@@ -3,6 +3,8 @@ package container
 import (
 	"os"
 	"testing"
+
+	"hakurei.app/container/stub"
 )
 
 func TestTmpfileOp(t *testing.T) {
@@ -16,59 +18,59 @@ func TestTmpfileOp(t *testing.T) {
 		{"createTemp", &Params{ParentPerm: 0700}, &TmpfileOp{
 			Path: samplePath,
 			Data: sampleData,
-		}, nil, nil, []kexpect{
-			{"createTemp", expectArgs{"/", "tmp.*"}, newCheckedFile(t, "tmp.32768", sampleDataString, nil), errUnique},
-		}, wrapErrSelf(errUnique)},
+		}, nil, nil, []stub.Call{
+			call("createTemp", stub.ExpectArgs{"/", "tmp.*"}, newCheckedFile(t, "tmp.32768", sampleDataString, nil), stub.UniqueError(5)),
+		}, stub.UniqueError(5)},
 
 		{"Write", &Params{ParentPerm: 0700}, &TmpfileOp{
 			Path: samplePath,
 			Data: sampleData,
-		}, nil, nil, []kexpect{
-			{"createTemp", expectArgs{"/", "tmp.*"}, writeErrOsFile{errUnique}, nil},
-		}, wrapErrSuffix(errUnique, "cannot write to intermediate file:")},
+		}, nil, nil, []stub.Call{
+			call("createTemp", stub.ExpectArgs{"/", "tmp.*"}, writeErrOsFile{stub.UniqueError(4)}, nil),
+		}, stub.UniqueError(4)},
 
 		{"Close", &Params{ParentPerm: 0700}, &TmpfileOp{
 			Path: samplePath,
 			Data: sampleData,
-		}, nil, nil, []kexpect{
-			{"createTemp", expectArgs{"/", "tmp.*"}, newCheckedFile(t, "tmp.32768", sampleDataString, errUnique), nil},
-		}, wrapErrSuffix(errUnique, "cannot close intermediate file:")},
+		}, nil, nil, []stub.Call{
+			call("createTemp", stub.ExpectArgs{"/", "tmp.*"}, newCheckedFile(t, "tmp.32768", sampleDataString, stub.UniqueError(3)), nil),
+		}, stub.UniqueError(3)},
 
 		{"ensureFile", &Params{ParentPerm: 0700}, &TmpfileOp{
 			Path: samplePath,
 			Data: sampleData,
-		}, nil, nil, []kexpect{
-			{"createTemp", expectArgs{"/", "tmp.*"}, newCheckedFile(t, "tmp.32768", sampleDataString, nil), nil},
-			{"ensureFile", expectArgs{"/sysroot/etc/passwd", os.FileMode(0444), os.FileMode(0700)}, nil, errUnique},
-		}, errUnique},
+		}, nil, nil, []stub.Call{
+			call("createTemp", stub.ExpectArgs{"/", "tmp.*"}, newCheckedFile(t, "tmp.32768", sampleDataString, nil), nil),
+			call("ensureFile", stub.ExpectArgs{"/sysroot/etc/passwd", os.FileMode(0444), os.FileMode(0700)}, nil, stub.UniqueError(2)),
+		}, stub.UniqueError(2)},
 
 		{"bindMount", &Params{ParentPerm: 0700}, &TmpfileOp{
 			Path: samplePath,
 			Data: sampleData,
-		}, nil, nil, []kexpect{
-			{"createTemp", expectArgs{"/", "tmp.*"}, newCheckedFile(t, "tmp.32768", sampleDataString, nil), nil},
-			{"ensureFile", expectArgs{"/sysroot/etc/passwd", os.FileMode(0444), os.FileMode(0700)}, nil, nil},
-			{"bindMount", expectArgs{"tmp.32768", "/sysroot/etc/passwd", uintptr(0x5), false}, nil, errUnique},
-		}, errUnique},
+		}, nil, nil, []stub.Call{
+			call("createTemp", stub.ExpectArgs{"/", "tmp.*"}, newCheckedFile(t, "tmp.32768", sampleDataString, nil), nil),
+			call("ensureFile", stub.ExpectArgs{"/sysroot/etc/passwd", os.FileMode(0444), os.FileMode(0700)}, nil, nil),
+			call("bindMount", stub.ExpectArgs{"tmp.32768", "/sysroot/etc/passwd", uintptr(0x5), false}, nil, stub.UniqueError(1)),
+		}, stub.UniqueError(1)},
 
 		{"remove", &Params{ParentPerm: 0700}, &TmpfileOp{
 			Path: samplePath,
 			Data: sampleData,
-		}, nil, nil, []kexpect{
-			{"createTemp", expectArgs{"/", "tmp.*"}, newCheckedFile(t, "tmp.32768", sampleDataString, nil), nil},
-			{"ensureFile", expectArgs{"/sysroot/etc/passwd", os.FileMode(0444), os.FileMode(0700)}, nil, nil},
-			{"bindMount", expectArgs{"tmp.32768", "/sysroot/etc/passwd", uintptr(0x5), false}, nil, nil},
-			{"remove", expectArgs{"tmp.32768"}, nil, errUnique},
-		}, wrapErrSelf(errUnique)},
+		}, nil, nil, []stub.Call{
+			call("createTemp", stub.ExpectArgs{"/", "tmp.*"}, newCheckedFile(t, "tmp.32768", sampleDataString, nil), nil),
+			call("ensureFile", stub.ExpectArgs{"/sysroot/etc/passwd", os.FileMode(0444), os.FileMode(0700)}, nil, nil),
+			call("bindMount", stub.ExpectArgs{"tmp.32768", "/sysroot/etc/passwd", uintptr(0x5), false}, nil, nil),
+			call("remove", stub.ExpectArgs{"tmp.32768"}, nil, stub.UniqueError(0)),
+		}, stub.UniqueError(0)},
 
 		{"success", &Params{ParentPerm: 0700}, &TmpfileOp{
 			Path: samplePath,
 			Data: sampleData,
-		}, nil, nil, []kexpect{
-			{"createTemp", expectArgs{"/", "tmp.*"}, newCheckedFile(t, "tmp.32768", sampleDataString, nil), nil},
-			{"ensureFile", expectArgs{"/sysroot/etc/passwd", os.FileMode(0444), os.FileMode(0700)}, nil, nil},
-			{"bindMount", expectArgs{"tmp.32768", "/sysroot/etc/passwd", uintptr(0x5), false}, nil, nil},
-			{"remove", expectArgs{"tmp.32768"}, nil, nil},
+		}, nil, nil, []stub.Call{
+			call("createTemp", stub.ExpectArgs{"/", "tmp.*"}, newCheckedFile(t, "tmp.32768", sampleDataString, nil), nil),
+			call("ensureFile", stub.ExpectArgs{"/sysroot/etc/passwd", os.FileMode(0444), os.FileMode(0700)}, nil, nil),
+			call("bindMount", stub.ExpectArgs{"tmp.32768", "/sysroot/etc/passwd", uintptr(0x5), false}, nil, nil),
+			call("remove", stub.ExpectArgs{"tmp.32768"}, nil, nil),
 		}, nil},
 	})
 

container/initproc.go

@@ -22,10 +22,9 @@ func (p *MountProcOp) early(*setupState, syscallDispatcher) error { return nil }
 func (p *MountProcOp) apply(state *setupState, k syscallDispatcher) error {
 	target := toSysroot(p.Target.String())
 	if err := k.mkdirAll(target, state.ParentPerm); err != nil {
-		return wrapErrSelf(err)
+		return err
 	}
-	return wrapErrSuffix(k.mount(SourceProc, target, FstypeProc, MS_NOSUID|MS_NOEXEC|MS_NODEV, zeroString),
-		fmt.Sprintf("cannot mount proc on %q:", p.Target.String()))
+	return k.mount(SourceProc, target, FstypeProc, MS_NOSUID|MS_NOEXEC|MS_NODEV, zeroString)
 }
 
 func (p *MountProcOp) Is(op Op) bool {

container/initproc_test.go

@@ -3,6 +3,8 @@ package container
 import (
 	"os"
 	"testing"
+
+	"hakurei.app/container/stub"
 )
 
 func TestMountProcOp(t *testing.T) {
@@ -10,16 +12,16 @@ func TestMountProcOp(t *testing.T) {
 		{"mkdir", &Params{ParentPerm: 0755},
 			&MountProcOp{
 				Target: MustAbs("/proc/"),
-			}, nil, nil, []kexpect{
-				{"mkdirAll", expectArgs{"/sysroot/proc", os.FileMode(0755)}, nil, errUnique},
-			}, wrapErrSelf(errUnique)},
+			}, nil, nil, []stub.Call{
+				call("mkdirAll", stub.ExpectArgs{"/sysroot/proc", os.FileMode(0755)}, nil, stub.UniqueError(0)),
+			}, stub.UniqueError(0)},
 
 		{"success", &Params{ParentPerm: 0700},
 			&MountProcOp{
 				Target: MustAbs("/proc/"),
-			}, nil, nil, []kexpect{
-				{"mkdirAll", expectArgs{"/sysroot/proc", os.FileMode(0700)}, nil, nil},
-				{"mount", expectArgs{"proc", "/sysroot/proc", "proc", uintptr(0xe), ""}, nil, nil},
+			}, nil, nil, []stub.Call{
+				call("mkdirAll", stub.ExpectArgs{"/sysroot/proc", os.FileMode(0700)}, nil, nil),
+				call("mount", stub.ExpectArgs{"proc", "/sysroot/proc", "proc", uintptr(0xe), ""}, nil, nil),
 			}, nil},
 	})
 

container/initremount.go

@@ -22,8 +22,7 @@ type RemountOp struct {
 func (r *RemountOp) Valid() bool                              { return r != nil && r.Target != nil }
 func (*RemountOp) early(*setupState, syscallDispatcher) error { return nil }
 func (r *RemountOp) apply(_ *setupState, k syscallDispatcher) error {
-	return wrapErrSuffix(k.remount(toSysroot(r.Target.String()), r.Flags),
-		fmt.Sprintf("cannot remount %q:", r.Target))
+	return k.remount(toSysroot(r.Target.String()), r.Flags)
 }
 
 func (r *RemountOp) Is(op Op) bool {

container/initremount_test.go

@@ -3,6 +3,8 @@ package container
 import (
 	"syscall"
 	"testing"
+
+	"hakurei.app/container/stub"
 )
 
 func TestRemountOp(t *testing.T) {
@@ -10,8 +12,8 @@ func TestRemountOp(t *testing.T) {
 		{"success", new(Params), &RemountOp{
 			Target: MustAbs("/"),
 			Flags:  syscall.MS_RDONLY,
-		}, nil, nil, []kexpect{
-			{"remount", expectArgs{"/sysroot", uintptr(1)}, nil, nil},
+		}, nil, nil, []stub.Call{
+			call("remount", stub.ExpectArgs{"/sysroot", uintptr(1)}, nil, nil),
 		}, nil},
 	})
 

container/initsymlink.go

@@ -3,7 +3,6 @@ package container
 import (
 	"encoding/gob"
 	"fmt"
-	"io/fs"
 	"path"
 )
 
@@ -30,10 +29,10 @@ func (l *SymlinkOp) Valid() bool { return l != nil && l.Target != nil && l.LinkN
 func (l *SymlinkOp) early(_ *setupState, k syscallDispatcher) error {
 	if l.Dereference {
 		if !isAbs(l.LinkName) {
-			return msg.WrapErr(fs.ErrInvalid, fmt.Sprintf("path %q is not absolute", l.LinkName))
+			return &AbsoluteError{l.LinkName}
 		}
 		if name, err := k.readlink(l.LinkName); err != nil {
-			return wrapErrSelf(err)
+			return err
 		} else {
 			l.LinkName = name
 		}
@@ -44,9 +43,9 @@ func (l *SymlinkOp) early(_ *setupState, k syscallDispatcher) error {
 func (l *SymlinkOp) apply(state *setupState, k syscallDispatcher) error {
 	target := toSysroot(l.Target.String())
 	if err := k.mkdirAll(path.Dir(target), state.ParentPerm); err != nil {
-		return wrapErrSelf(err)
+		return err
 	}
-	return wrapErrSelf(k.symlink(l.LinkName, target))
+	return k.symlink(l.LinkName, target)
 }
 
 func (l *SymlinkOp) Is(op Op) bool {

container/initsymlink_test.go

@@ -1,9 +1,10 @@
 package container
 
 import (
-	"io/fs"
 	"os"
 	"testing"
+
+	"hakurei.app/container/stub"
 )
 
 func TestSymlinkOp(t *testing.T) {
@@ -11,41 +12,41 @@ func TestSymlinkOp(t *testing.T) {
 		{"mkdir", &Params{ParentPerm: 0700}, &SymlinkOp{
 			Target:   MustAbs("/etc/nixos"),
 			LinkName: "/etc/static/nixos",
-		}, nil, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/etc", os.FileMode(0700)}, nil, errUnique},
-		}, wrapErrSelf(errUnique)},
+		}, nil, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/etc", os.FileMode(0700)}, nil, stub.UniqueError(1)),
+		}, stub.UniqueError(1)},
 
 		{"abs", &Params{ParentPerm: 0755}, &SymlinkOp{
 			Target:      MustAbs("/etc/mtab"),
 			LinkName:    "etc/mtab",
 			Dereference: true,
-		}, nil, msg.WrapErr(fs.ErrInvalid, `path "etc/mtab" is not absolute`), nil, nil},
+		}, nil, &AbsoluteError{"etc/mtab"}, nil, nil},
 
 		{"readlink", &Params{ParentPerm: 0755}, &SymlinkOp{
 			Target:      MustAbs("/etc/mtab"),
 			LinkName:    "/etc/mtab",
 			Dereference: true,
-		}, []kexpect{
-			{"readlink", expectArgs{"/etc/mtab"}, "/proc/mounts", errUnique},
-		}, wrapErrSelf(errUnique), nil, nil},
+		}, []stub.Call{
+			call("readlink", stub.ExpectArgs{"/etc/mtab"}, "/proc/mounts", stub.UniqueError(0)),
+		}, stub.UniqueError(0), nil, nil},
 
 		{"success noderef", &Params{ParentPerm: 0700}, &SymlinkOp{
 			Target:   MustAbs("/etc/nixos"),
 			LinkName: "/etc/static/nixos",
-		}, nil, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/etc", os.FileMode(0700)}, nil, nil},
-			{"symlink", expectArgs{"/etc/static/nixos", "/sysroot/etc/nixos"}, nil, nil},
+		}, nil, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/etc", os.FileMode(0700)}, nil, nil),
+			call("symlink", stub.ExpectArgs{"/etc/static/nixos", "/sysroot/etc/nixos"}, nil, nil),
 		}, nil},
 
 		{"success", &Params{ParentPerm: 0755}, &SymlinkOp{
 			Target:      MustAbs("/etc/mtab"),
 			LinkName:    "/etc/mtab",
 			Dereference: true,
-		}, []kexpect{
-			{"readlink", expectArgs{"/etc/mtab"}, "/proc/mounts", nil},
-		}, nil, []kexpect{
-			{"mkdirAll", expectArgs{"/sysroot/etc", os.FileMode(0755)}, nil, nil},
-			{"symlink", expectArgs{"/proc/mounts", "/sysroot/etc/mtab"}, nil, nil},
+		}, []stub.Call{
+			call("readlink", stub.ExpectArgs{"/etc/mtab"}, "/proc/mounts", nil),
+		}, nil, []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/etc", os.FileMode(0755)}, nil, nil),
+			call("symlink", stub.ExpectArgs{"/proc/mounts", "/sysroot/etc/mtab"}, nil, nil),
 		}, nil},
 	})
 

container/inittmpfs.go

@@ -3,14 +3,20 @@ package container
 import (
 	"encoding/gob"
 	"fmt"
-	"io/fs"
 	"math"
 	"os"
+	"strconv"
 	. "syscall"
 )
 
 func init() { gob.Register(new(MountTmpfsOp)) }
 
+type TmpfsSizeError int
+
+func (e TmpfsSizeError) Error() string {
+	return "tmpfs size " + strconv.Itoa(int(e)) + " out of bounds"
+}
+
 // Tmpfs appends an [Op] that mounts tmpfs on container path [MountTmpfsOp.Path].
 func (f *Ops) Tmpfs(target *Absolute, size int, perm os.FileMode) *Ops {
 	*f = append(*f, &MountTmpfsOp{SourceTmpfsEphemeral, target, MS_NOSUID | MS_NODEV, size, perm})
@@ -36,7 +42,7 @@ func (t *MountTmpfsOp) Valid() bool                                { return t !=
 func (t *MountTmpfsOp) early(*setupState, syscallDispatcher) error { return nil }
 func (t *MountTmpfsOp) apply(_ *setupState, k syscallDispatcher) error {
 	if t.Size < 0 || t.Size > math.MaxUint>>1 {
-		return msg.WrapErr(fs.ErrInvalid, fmt.Sprintf("size %d out of bounds", t.Size))
+		return TmpfsSizeError(t.Size)
 	}
 	return k.mountTmpfs(t.FSName, toSysroot(t.Path.String()), t.Flags, t.Size, t.Perm)
 }

container/inittmpfs_test.go

@@ -1,31 +1,40 @@
 package container
 
 import (
-	"io/fs"
 	"os"
 	"syscall"
 	"testing"
+
+	"hakurei.app/container/stub"
 )
 
 func TestMountTmpfsOp(t *testing.T) {
+	t.Run("size error", func(t *testing.T) {
+		tmpfsSizeError := TmpfsSizeError(-1)
+		want := "tmpfs size -1 out of bounds"
+		if got := tmpfsSizeError.Error(); got != want {
+			t.Errorf("Error: %q, want %q", got, want)
+		}
+	})
+
 	checkOpBehaviour(t, []opBehaviourTestCase{
 		{"size oob", new(Params), &MountTmpfsOp{
 			Size: -1,
-		}, nil, nil, nil, msg.WrapErr(fs.ErrInvalid, "size -1 out of bounds")},
+		}, nil, nil, nil, TmpfsSizeError(-1)},
 
 		{"success", new(Params), &MountTmpfsOp{
 			FSName: "ephemeral",
 			Path:   MustAbs("/run/user/1000/"),
 			Size:   1 << 10,
 			Perm:   0700,
-		}, nil, nil, []kexpect{
-			{"mountTmpfs", expectArgs{
+		}, nil, nil, []stub.Call{
+			call("mountTmpfs", stub.ExpectArgs{
 				"ephemeral",              // fsname
 				"/sysroot/run/user/1000", // target
 				uintptr(0),               // flags
 				0x400,                    // size
 				os.FileMode(0700),        // perm
-			}, nil, nil},
+			}, nil, nil),
 		}, nil},
 	})
 

container/mount.go

@@ -106,8 +106,7 @@ func (p *procPaths) bindMount(source, target string, flags uintptr, eq bool) err
 	}
 
 	if err := p.k.mount(source, target, FstypeNULL, MS_SILENT|MS_BIND|flags&MS_REC, zeroString); err != nil {
-		return wrapErrSuffix(err,
-			fmt.Sprintf("cannot mount %q on %q:", source, target))
+		return err
 	}
 
 	return p.k.remount(target, flags)
@@ -119,7 +118,7 @@ func (p *procPaths) remount(target string, flags uintptr) error {
 
 	var targetFinal string
 	if v, err := p.k.evalSymlinks(target); err != nil {
-		return wrapErrSelf(err)
+		return err
 	} else {
 		targetFinal = v
 		if targetFinal != target {
@@ -135,14 +134,12 @@ func (p *procPaths) remount(target string, flags uintptr) error {
 			destFd, err = p.k.open(targetFinal, O_PATH|O_CLOEXEC, 0)
 			return
 		}); err != nil {
-			return wrapErrSuffix(err,
-				fmt.Sprintf("cannot open %q:", targetFinal))
+			return &os.PathError{Op: "open", Path: targetFinal, Err: err}
 		}
 		if v, err := p.k.readlink(p.fd(destFd)); err != nil {
-			return wrapErrSelf(err)
+			return err
 		} else if err = p.k.close(destFd); err != nil {
-			return wrapErrSuffix(err,
-				fmt.Sprintf("cannot close %q:", targetFinal))
+			return &os.PathError{Op: "close", Path: targetFinal, Err: err}
 		} else {
 			targetKFinal = v
 		}
@@ -152,17 +149,11 @@ func (p *procPaths) remount(target string, flags uintptr) error {
 	return p.mountinfo(func(d *vfs.MountInfoDecoder) error {
 		n, err := d.Unfold(targetKFinal)
 		if err != nil {
-			if errors.Is(err, ESTALE) {
-				return msg.WrapErr(err,
-					fmt.Sprintf("mount point %q never appeared in mountinfo", targetKFinal))
-			}
-			return wrapErrSuffix(err,
-				"cannot unfold mount hierarchy:")
+			return err
 		}
 
 		if err = remountWithFlags(p.k, n, mf); err != nil {
-			return wrapErrSuffix(err,
-				fmt.Sprintf("cannot remount %q:", n.Clean))
+			return err
 		}
 		if flags&MS_REC == 0 {
 			return nil
@@ -174,11 +165,8 @@ func (p *procPaths) remount(target string, flags uintptr) error {
 				continue
 			}
 
-			err = remountWithFlags(p.k, cur, mf)
-
-			if err != nil && !errors.Is(err, EACCES) {
-				return wrapErrSuffix(err,
-					fmt.Sprintf("cannot propagate flags to %q:", cur.Clean))
+			if err = remountWithFlags(p.k, cur, mf); err != nil && !errors.Is(err, EACCES) {
+				return err
 			}
 		}
 
@@ -207,15 +195,13 @@ func mountTmpfs(k syscallDispatcher, fsname, target string, flags uintptr, size
 	// syscallDispatcher.mountTmpfs must not be called from this function
 
 	if err := k.mkdirAll(target, parentPerm(perm)); err != nil {
-		return wrapErrSelf(err)
+		return err
 	}
 	opt := fmt.Sprintf("mode=%#o", perm)
 	if size > 0 {
 		opt += fmt.Sprintf(",size=%d", size)
 	}
-	return wrapErrSuffix(
-		k.mount(fsname, target, FstypeTmpfs, flags, opt),
-		fmt.Sprintf("cannot mount tmpfs on %q:", target))
+	return k.mount(fsname, target, FstypeTmpfs, flags, opt)
 }
 
 func parentPerm(perm os.FileMode) os.FileMode {

container/mount_test.go

@@ -5,6 +5,7 @@ import (
 	"syscall"
 	"testing"
 
+	"hakurei.app/container/stub"
 	"hakurei.app/container/vfs"
 )
 
@@ -12,25 +13,25 @@ func TestBindMount(t *testing.T) {
 	checkSimple(t, "bindMount", []simpleTestCase{
 		{"mount", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).bindMount("/host/nix", "/sysroot/nix", syscall.MS_RDONLY, true)
-		}, [][]kexpect{{
-			{"verbosef", expectArgs{"resolved %q flags %#x", []any{"/sysroot/nix", uintptr(1)}}, nil, nil},
-			{"mount", expectArgs{"/host/nix", "/sysroot/nix", "", uintptr(0x9000), ""}, nil, errUnique},
-		}}, wrapErrSuffix(errUnique, `cannot mount "/host/nix" on "/sysroot/nix":`)},
+		}, stub.Expect{Calls: []stub.Call{
+			call("verbosef", stub.ExpectArgs{"resolved %q flags %#x", []any{"/sysroot/nix", uintptr(1)}}, nil, nil),
+			call("mount", stub.ExpectArgs{"/host/nix", "/sysroot/nix", "", uintptr(0x9000), ""}, nil, stub.UniqueError(0xbad)),
+		}}, stub.UniqueError(0xbad)},
 
 		{"success ne", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).bindMount("/host/nix", "/sysroot/.host-nix", syscall.MS_RDONLY, false)
-		}, [][]kexpect{{
-			{"verbosef", expectArgs{"resolved %q on %q flags %#x", []any{"/host/nix", "/sysroot/.host-nix", uintptr(1)}}, nil, nil},
-			{"mount", expectArgs{"/host/nix", "/sysroot/.host-nix", "", uintptr(0x9000), ""}, nil, nil},
-			{"remount", expectArgs{"/sysroot/.host-nix", uintptr(1)}, nil, nil},
+		}, stub.Expect{Calls: []stub.Call{
+			call("verbosef", stub.ExpectArgs{"resolved %q on %q flags %#x", []any{"/host/nix", "/sysroot/.host-nix", uintptr(1)}}, nil, nil),
+			call("mount", stub.ExpectArgs{"/host/nix", "/sysroot/.host-nix", "", uintptr(0x9000), ""}, nil, nil),
+			call("remount", stub.ExpectArgs{"/sysroot/.host-nix", uintptr(1)}, nil, nil),
 		}}, nil},
 
 		{"success", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).bindMount("/host/nix", "/sysroot/nix", syscall.MS_RDONLY, true)
-		}, [][]kexpect{{
-			{"verbosef", expectArgs{"resolved %q flags %#x", []any{"/sysroot/nix", uintptr(1)}}, nil, nil},
-			{"mount", expectArgs{"/host/nix", "/sysroot/nix", "", uintptr(0x9000), ""}, nil, nil},
-			{"remount", expectArgs{"/sysroot/nix", uintptr(1)}, nil, nil},
+		}, stub.Expect{Calls: []stub.Call{
+			call("verbosef", stub.ExpectArgs{"resolved %q flags %#x", []any{"/sysroot/nix", uintptr(1)}}, nil, nil),
+			call("mount", stub.ExpectArgs{"/host/nix", "/sysroot/nix", "", uintptr(0x9000), ""}, nil, nil),
+			call("remount", stub.ExpectArgs{"/sysroot/nix", uintptr(1)}, nil, nil),
 		}}, nil},
 	})
 }
@@ -81,138 +82,138 @@ func TestRemount(t *testing.T) {
 	checkSimple(t, "remount", []simpleTestCase{
 		{"evalSymlinks", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/nix"}, "/sysroot/nix", errUnique},
-		}}, wrapErrSelf(errUnique)},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/nix"}, "/sysroot/nix", stub.UniqueError(6)),
+		}}, stub.UniqueError(6)},
 
 		{"open", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/nix"}, "/sysroot/nix", nil},
-			{"open", expectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, errUnique},
-		}}, wrapErrSuffix(errUnique, `cannot open "/sysroot/nix":`)},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/nix"}, "/sysroot/nix", nil),
+			call("open", stub.ExpectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, stub.UniqueError(5)),
+		}}, &os.PathError{Op: "open", Path: "/sysroot/nix", Err: stub.UniqueError(5)}},
 
 		{"readlink", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/nix"}, "/sysroot/nix", nil},
-			{"open", expectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil},
-			{"readlink", expectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", errUnique},
-		}}, wrapErrSelf(errUnique)},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/nix"}, "/sysroot/nix", nil),
+			call("open", stub.ExpectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil),
+			call("readlink", stub.ExpectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", stub.UniqueError(4)),
+		}}, stub.UniqueError(4)},
 
 		{"close", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/nix"}, "/sysroot/nix", nil},
-			{"open", expectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil},
-			{"readlink", expectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil},
-			{"close", expectArgs{0xdeadbeef}, nil, errUnique},
-		}}, wrapErrSuffix(errUnique, `cannot close "/sysroot/nix":`)},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/nix"}, "/sysroot/nix", nil),
+			call("open", stub.ExpectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil),
+			call("readlink", stub.ExpectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil),
+			call("close", stub.ExpectArgs{0xdeadbeef}, nil, stub.UniqueError(3)),
+		}}, &os.PathError{Op: "close", Path: "/sysroot/nix", Err: stub.UniqueError(3)}},
 
-		{"mountinfo stale", func(k syscallDispatcher) error {
+		{"mountinfo no match", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/nix"}, "/sysroot/.hakurei", nil},
-			{"verbosef", expectArgs{"target resolves to %q", []any{"/sysroot/.hakurei"}}, nil, nil},
-			{"open", expectArgs{"/sysroot/.hakurei", 0x280000, uint32(0)}, 0xdeadbeef, nil},
-			{"readlink", expectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/.hakurei", nil},
-			{"close", expectArgs{0xdeadbeef}, nil, nil},
-			{"openNew", expectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil},
-		}}, msg.WrapErr(syscall.ESTALE, `mount point "/sysroot/.hakurei" never appeared in mountinfo`)},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/nix"}, "/sysroot/.hakurei", nil),
+			call("verbosef", stub.ExpectArgs{"target resolves to %q", []any{"/sysroot/.hakurei"}}, nil, nil),
+			call("open", stub.ExpectArgs{"/sysroot/.hakurei", 0x280000, uint32(0)}, 0xdeadbeef, nil),
+			call("readlink", stub.ExpectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/.hakurei", nil),
+			call("close", stub.ExpectArgs{0xdeadbeef}, nil, nil),
+			call("openNew", stub.ExpectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil),
+		}}, &vfs.DecoderError{Op: "unfold", Line: -1, Err: vfs.UnfoldTargetError("/sysroot/.hakurei")}},
 
 		{"mountinfo", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/nix"}, "/sysroot/nix", nil},
-			{"open", expectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil},
-			{"readlink", expectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil},
-			{"close", expectArgs{0xdeadbeef}, nil, nil},
-			{"openNew", expectArgs{"/host/proc/self/mountinfo"}, newConstFile("\x00"), nil},
-		}}, wrapErrSuffix(vfs.ErrMountInfoFields, `cannot parse mountinfo:`)},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/nix"}, "/sysroot/nix", nil),
+			call("open", stub.ExpectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil),
+			call("readlink", stub.ExpectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil),
+			call("close", stub.ExpectArgs{0xdeadbeef}, nil, nil),
+			call("openNew", stub.ExpectArgs{"/host/proc/self/mountinfo"}, newConstFile("\x00"), nil),
+		}}, &vfs.DecoderError{Op: "parse", Line: 0, Err: vfs.ErrMountInfoFields}},
 
 		{"mount", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/nix"}, "/sysroot/nix", nil},
-			{"open", expectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil},
-			{"readlink", expectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil},
-			{"close", expectArgs{0xdeadbeef}, nil, nil},
-			{"openNew", expectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil},
-			{"mount", expectArgs{"none", "/sysroot/nix", "", uintptr(0x209027), ""}, nil, errUnique},
-		}}, wrapErrSuffix(errUnique, `cannot remount "/sysroot/nix":`)},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/nix"}, "/sysroot/nix", nil),
+			call("open", stub.ExpectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil),
+			call("readlink", stub.ExpectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil),
+			call("close", stub.ExpectArgs{0xdeadbeef}, nil, nil),
+			call("openNew", stub.ExpectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix", "", uintptr(0x209027), ""}, nil, stub.UniqueError(2)),
+		}}, stub.UniqueError(2)},
 
 		{"mount propagate", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/nix"}, "/sysroot/nix", nil},
-			{"open", expectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil},
-			{"readlink", expectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil},
-			{"close", expectArgs{0xdeadbeef}, nil, nil},
-			{"openNew", expectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil},
-			{"mount", expectArgs{"none", "/sysroot/nix", "", uintptr(0x209027), ""}, nil, nil},
-			{"mount", expectArgs{"none", "/sysroot/nix/.ro-store", "", uintptr(0x209027), ""}, nil, errUnique},
-		}}, wrapErrSuffix(errUnique, `cannot propagate flags to "/sysroot/nix/.ro-store":`)},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/nix"}, "/sysroot/nix", nil),
+			call("open", stub.ExpectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil),
+			call("readlink", stub.ExpectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil),
+			call("close", stub.ExpectArgs{0xdeadbeef}, nil, nil),
+			call("openNew", stub.ExpectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix", "", uintptr(0x209027), ""}, nil, nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix/.ro-store", "", uintptr(0x209027), ""}, nil, stub.UniqueError(1)),
+		}}, stub.UniqueError(1)},
 
 		{"success toplevel", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/bin", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/bin"}, "/sysroot/bin", nil},
-			{"open", expectArgs{"/sysroot/bin", 0x280000, uint32(0)}, 0xbabe, nil},
-			{"readlink", expectArgs{"/host/proc/self/fd/47806"}, "/sysroot/bin", nil},
-			{"close", expectArgs{0xbabe}, nil, nil},
-			{"openNew", expectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil},
-			{"mount", expectArgs{"none", "/sysroot/bin", "", uintptr(0x209027), ""}, nil, nil},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/bin"}, "/sysroot/bin", nil),
+			call("open", stub.ExpectArgs{"/sysroot/bin", 0x280000, uint32(0)}, 0xbabe, nil),
+			call("readlink", stub.ExpectArgs{"/host/proc/self/fd/47806"}, "/sysroot/bin", nil),
+			call("close", stub.ExpectArgs{0xbabe}, nil, nil),
+			call("openNew", stub.ExpectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/bin", "", uintptr(0x209027), ""}, nil, nil),
 		}}, nil},
 
 		{"success EACCES", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/nix"}, "/sysroot/nix", nil},
-			{"open", expectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil},
-			{"readlink", expectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil},
-			{"close", expectArgs{0xdeadbeef}, nil, nil},
-			{"openNew", expectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil},
-			{"mount", expectArgs{"none", "/sysroot/nix", "", uintptr(0x209027), ""}, nil, nil},
-			{"mount", expectArgs{"none", "/sysroot/nix/.ro-store", "", uintptr(0x209027), ""}, nil, syscall.EACCES},
-			{"mount", expectArgs{"none", "/sysroot/nix/store", "", uintptr(0x209027), ""}, nil, nil},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/nix"}, "/sysroot/nix", nil),
+			call("open", stub.ExpectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil),
+			call("readlink", stub.ExpectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil),
+			call("close", stub.ExpectArgs{0xdeadbeef}, nil, nil),
+			call("openNew", stub.ExpectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix", "", uintptr(0x209027), ""}, nil, nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix/.ro-store", "", uintptr(0x209027), ""}, nil, syscall.EACCES),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix/store", "", uintptr(0x209027), ""}, nil, nil),
 		}}, nil},
 
 		{"success no propagate", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/nix", syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/nix"}, "/sysroot/nix", nil},
-			{"open", expectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil},
-			{"readlink", expectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil},
-			{"close", expectArgs{0xdeadbeef}, nil, nil},
-			{"openNew", expectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil},
-			{"mount", expectArgs{"none", "/sysroot/nix", "", uintptr(0x209027), ""}, nil, nil},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/nix"}, "/sysroot/nix", nil),
+			call("open", stub.ExpectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil),
+			call("readlink", stub.ExpectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil),
+			call("close", stub.ExpectArgs{0xdeadbeef}, nil, nil),
+			call("openNew", stub.ExpectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix", "", uintptr(0x209027), ""}, nil, nil),
 		}}, nil},
 
 		{"success case sensitive", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/nix"}, "/sysroot/nix", nil},
-			{"open", expectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil},
-			{"readlink", expectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil},
-			{"close", expectArgs{0xdeadbeef}, nil, nil},
-			{"openNew", expectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil},
-			{"mount", expectArgs{"none", "/sysroot/nix", "", uintptr(0x209027), ""}, nil, nil},
-			{"mount", expectArgs{"none", "/sysroot/nix/.ro-store", "", uintptr(0x209027), ""}, nil, nil},
-			{"mount", expectArgs{"none", "/sysroot/nix/store", "", uintptr(0x209027), ""}, nil, nil},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/nix"}, "/sysroot/nix", nil),
+			call("open", stub.ExpectArgs{"/sysroot/nix", 0x280000, uint32(0)}, 0xdeadbeef, nil),
+			call("readlink", stub.ExpectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil),
+			call("close", stub.ExpectArgs{0xdeadbeef}, nil, nil),
+			call("openNew", stub.ExpectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix", "", uintptr(0x209027), ""}, nil, nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix/.ro-store", "", uintptr(0x209027), ""}, nil, nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix/store", "", uintptr(0x209027), ""}, nil, nil),
 		}}, nil},
 
 		{"success", func(k syscallDispatcher) error {
 			return newProcPaths(k, hostPath).remount("/sysroot/.nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
-		}, [][]kexpect{{
-			{"evalSymlinks", expectArgs{"/sysroot/.nix"}, "/sysroot/NIX", nil},
-			{"verbosef", expectArgs{"target resolves to %q", []any{"/sysroot/NIX"}}, nil, nil},
-			{"open", expectArgs{"/sysroot/NIX", 0x280000, uint32(0)}, 0xdeadbeef, nil},
-			{"readlink", expectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil},
-			{"close", expectArgs{0xdeadbeef}, nil, nil},
-			{"openNew", expectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil},
-			{"mount", expectArgs{"none", "/sysroot/nix", "", uintptr(0x209027), ""}, nil, nil},
-			{"mount", expectArgs{"none", "/sysroot/nix/.ro-store", "", uintptr(0x209027), ""}, nil, nil},
-			{"mount", expectArgs{"none", "/sysroot/nix/store", "", uintptr(0x209027), ""}, nil, nil},
+		}, stub.Expect{Calls: []stub.Call{
+			call("evalSymlinks", stub.ExpectArgs{"/sysroot/.nix"}, "/sysroot/NIX", nil),
+			call("verbosef", stub.ExpectArgs{"target resolves to %q", []any{"/sysroot/NIX"}}, nil, nil),
+			call("open", stub.ExpectArgs{"/sysroot/NIX", 0x280000, uint32(0)}, 0xdeadbeef, nil),
+			call("readlink", stub.ExpectArgs{"/host/proc/self/fd/3735928559"}, "/sysroot/nix", nil),
+			call("close", stub.ExpectArgs{0xdeadbeef}, nil, nil),
+			call("openNew", stub.ExpectArgs{"/host/proc/self/mountinfo"}, newConstFile(sampleMountinfoNix), nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix", "", uintptr(0x209027), ""}, nil, nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix/.ro-store", "", uintptr(0x209027), ""}, nil, nil),
+			call("mount", stub.ExpectArgs{"none", "/sysroot/nix/store", "", uintptr(0x209027), ""}, nil, nil),
 		}}, nil},
 	})
 }
@@ -221,18 +222,18 @@ func TestRemountWithFlags(t *testing.T) {
 	checkSimple(t, "remountWithFlags", []simpleTestCase{
 		{"noop unmatched", func(k syscallDispatcher) error {
 			return remountWithFlags(k, &vfs.MountInfoNode{MountInfoEntry: &vfs.MountInfoEntry{VfsOptstr: "rw,relatime,cat"}}, 0)
-		}, [][]kexpect{{
-			{"verbosef", expectArgs{"unmatched vfs options: %q", []any{[]string{"cat"}}}, nil, nil},
+		}, stub.Expect{Calls: []stub.Call{
+			call("verbosef", stub.ExpectArgs{"unmatched vfs options: %q", []any{[]string{"cat"}}}, nil, nil),
 		}}, nil},
 
 		{"noop", func(k syscallDispatcher) error {
 			return remountWithFlags(k, &vfs.MountInfoNode{MountInfoEntry: &vfs.MountInfoEntry{VfsOptstr: "rw,relatime"}}, 0)
-		}, nil, nil},
+		}, stub.Expect{}, nil},
 
 		{"success", func(k syscallDispatcher) error {
 			return remountWithFlags(k, &vfs.MountInfoNode{MountInfoEntry: &vfs.MountInfoEntry{VfsOptstr: "rw,relatime"}}, syscall.MS_RDONLY)
-		}, [][]kexpect{{
-			{"mount", expectArgs{"none", "", "", uintptr(0x209021), ""}, nil, nil},
+		}, stub.Expect{Calls: []stub.Call{
+			call("mount", stub.ExpectArgs{"none", "", "", uintptr(0x209021), ""}, nil, nil),
 		}}, nil},
 	})
 }
@@ -241,22 +242,22 @@ func TestMountTmpfs(t *testing.T) {
 	checkSimple(t, "mountTmpfs", []simpleTestCase{
 		{"mkdirAll", func(k syscallDispatcher) error {
 			return mountTmpfs(k, "ephemeral", "/sysroot/run/user/1000", 0, 1<<10, 0700)
-		}, [][]kexpect{{
-			{"mkdirAll", expectArgs{"/sysroot/run/user/1000", os.FileMode(0700)}, nil, errUnique},
-		}}, wrapErrSelf(errUnique)},
+		}, stub.Expect{Calls: []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/run/user/1000", os.FileMode(0700)}, nil, stub.UniqueError(0)),
+		}}, stub.UniqueError(0)},
 
 		{"success no size", func(k syscallDispatcher) error {
 			return mountTmpfs(k, "ephemeral", "/sysroot/run/user/1000", 0, 0, 0710)
-		}, [][]kexpect{{
-			{"mkdirAll", expectArgs{"/sysroot/run/user/1000", os.FileMode(0750)}, nil, nil},
-			{"mount", expectArgs{"ephemeral", "/sysroot/run/user/1000", "tmpfs", uintptr(0), "mode=0710"}, nil, nil},
+		}, stub.Expect{Calls: []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/run/user/1000", os.FileMode(0750)}, nil, nil),
+			call("mount", stub.ExpectArgs{"ephemeral", "/sysroot/run/user/1000", "tmpfs", uintptr(0), "mode=0710"}, nil, nil),
 		}}, nil},
 
 		{"success", func(k syscallDispatcher) error {
 			return mountTmpfs(k, "ephemeral", "/sysroot/run/user/1000", 0, 1<<10, 0700)
-		}, [][]kexpect{{
-			{"mkdirAll", expectArgs{"/sysroot/run/user/1000", os.FileMode(0700)}, nil, nil},
-			{"mount", expectArgs{"ephemeral", "/sysroot/run/user/1000", "tmpfs", uintptr(0), "mode=0700,size=1024"}, nil, nil},
+		}, stub.Expect{Calls: []stub.Call{
+			call("mkdirAll", stub.ExpectArgs{"/sysroot/run/user/1000", os.FileMode(0700)}, nil, nil),
+			call("mount", stub.ExpectArgs{"ephemeral", "/sysroot/run/user/1000", "tmpfs", uintptr(0), "mode=0700,size=1024"}, nil, nil),
 		}}, nil},
 	})
 }

container/msg.go

@@ -2,24 +2,34 @@ package container
 
 import (
 	"errors"
-	"fmt"
 	"log"
-	"os"
-	"reflect"
 	"sync/atomic"
-	"testing"
 )
 
+// MessageError is an error with a user-facing message.
+type MessageError interface {
+	// Message returns a user-facing error message.
+	Message() string
+
+	error
+}
+
+// GetErrorMessage returns whether an error implements [MessageError], and the message if it does.
+func GetErrorMessage(err error) (string, bool) {
+	var e MessageError
+	if !errors.As(err, &e) || e == nil {
+		return zeroString, false
+	}
+	return e.Message(), true
+}
+
 type Msg interface {
 	IsVerbose() bool
 	Verbose(v ...any)
 	Verbosef(format string, v ...any)
-	WrapErr(err error, a ...any) error
-	PrintBaseErr(err error, fallback string)
 
 	Suspend()
 	Resume() bool
-
 	BeforeExit()
 }
 
@@ -37,32 +47,6 @@ func (msg *DefaultMsg) Verbosef(format string, v ...any) {
 	}
 }
 
-// checkedWrappedErr implements error with strict checks for wrapped values.
-type checkedWrappedErr struct {
-	err error
-	a   []any
-}
-
-func (c *checkedWrappedErr) Error() string { return fmt.Sprintf("%v, a = %s", c.err, c.a) }
-func (c *checkedWrappedErr) Is(err error) bool {
-	var concreteErr *checkedWrappedErr
-	if !errors.As(err, &concreteErr) {
-		return false
-	}
-	return reflect.DeepEqual(c, concreteErr)
-}
-
-func (msg *DefaultMsg) WrapErr(err error, a ...any) error {
-	// provide a mostly bulletproof path to bypass this behaviour in tests
-	if testing.Testing() && os.Getenv("GOPATH") != Nonexistent {
-		return &checkedWrappedErr{err, a}
-	}
-
-	log.Println(a...)
-	return err
-}
-func (msg *DefaultMsg) PrintBaseErr(err error, fallback string) { log.Println(fallback, err) }
-
 func (msg *DefaultMsg) Suspend()     { msg.inactive.Store(true) }
 func (msg *DefaultMsg) Resume() bool { return msg.inactive.CompareAndSwap(true, false) }
 func (msg *DefaultMsg) BeforeExit()  {}

container/msg_test.go

@@ -9,13 +9,36 @@ import (
 	"testing"
 
 	"hakurei.app/container"
-	"hakurei.app/internal/hlog"
 )
 
-func TestDefaultMsg(t *testing.T) {
-	// bypass WrapErr testing behaviour
-	t.Setenv("GOPATH", container.Nonexistent)
+func TestMessageError(t *testing.T) {
+	testCases := []struct {
+		name   string
+		err    error
+		want   string
+		wantOk bool
+	}{
+		{"nil", nil, "", false},
+		{"new", errors.New(":3"), "", false},
+		{"start", &container.StartError{
+			Step: "meow",
+			Err:  syscall.ENOTRECOVERABLE,
+		}, "cannot meow: state not recoverable", true},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			got, ok := container.GetErrorMessage(tc.err)
+			if got != tc.want {
+				t.Errorf("GetErrorMessage: %q, want %q", got, tc.want)
+			}
+			if ok != tc.wantOk {
+				t.Errorf("GetErrorMessage: ok = %v, want %v", ok, tc.wantOk)
+			}
+		})
+	}
+}
 
+func TestDefaultMsg(t *testing.T) {
 	{
 		w := log.Writer()
 		f := log.Flags()
@@ -48,21 +71,6 @@ func TestDefaultMsg(t *testing.T) {
 		}
 	})
 
-	t.Run("wrapErr", func(t *testing.T) {
-		buf := new(strings.Builder)
-		log.SetOutput(buf)
-		log.SetFlags(0)
-		if err := msg.WrapErr(syscall.EBADE, "\x00", "\x00"); err != syscall.EBADE {
-			t.Errorf("WrapErr: %v", err)
-		}
-		msg.PrintBaseErr(syscall.ENOTRECOVERABLE, "cannot cuddle cat:")
-
-		want := "\x00 \x00\ncannot cuddle cat: state not recoverable\n"
-		if buf.String() != want {
-			t.Errorf("WrapErr: %q, want %q", buf.String(), want)
-		}
-	})
-
 	t.Run("inactive", func(t *testing.T) {
 		{
 			inactive := msg.Resume()
@@ -83,25 +91,6 @@ func TestDefaultMsg(t *testing.T) {
 
 	// the function is a noop
 	t.Run("beforeExit", func(t *testing.T) { msg.BeforeExit() })
-
-	t.Run("checkedWrappedErr", func(t *testing.T) {
-		// temporarily re-enable testing behaviour
-		t.Setenv("GOPATH", "")
-		wrappedErr := msg.WrapErr(syscall.ENOTRECOVERABLE, "cannot cuddle cat:", syscall.ENOTRECOVERABLE)
-
-		t.Run("string", func(t *testing.T) {
-			want := "state not recoverable, a = [cannot cuddle cat: state not recoverable]"
-			if got := wrappedErr.Error(); got != want {
-				t.Errorf("Error: %q, want %q", got, want)
-			}
-		})
-
-		t.Run("bad concrete type", func(t *testing.T) {
-			if errors.Is(wrappedErr, syscall.ENOTRECOVERABLE) {
-				t.Error("incorrect type assertion")
-			}
-		})
-	})
 }
 
 type panicWriter struct{}
@@ -139,9 +128,6 @@ func (out *testOutput) Verbosef(format string, v ...any) {
 	out.t.Logf(format, v...)
 }
 
-func (out *testOutput) WrapErr(err error, a ...any) error       { return hlog.WrapErr(err, a...) }
-func (out *testOutput) PrintBaseErr(err error, fallback string) { hlog.PrintBaseError(err, fallback) }
-
 func (out *testOutput) Suspend() {
 	if out.suspended.CompareAndSwap(false, true) {
 		out.Verbose("suspend called")

container/output.go

@@ -10,17 +10,3 @@ func SetOutput(v Msg) {
 		msg = v
 	}
 }
-
-func wrapErrSuffix(err error, a ...any) error {
-	if err == nil {
-		return nil
-	}
-	return msg.WrapErr(err, append(a, err)...)
-}
-
-func wrapErrSelf(err error) error {
-	if err == nil {
-		return nil
-	}
-	return msg.WrapErr(err, err.Error())
-}

container/output_test.go

@@ -1,8 +1,6 @@
 package container
 
 import (
-	"reflect"
-	"syscall"
 	"testing"
 )
 
@@ -31,80 +29,13 @@ func TestGetSetOutput(t *testing.T) {
 	})
 }
 
-func TestWrapErr(t *testing.T) {
-	{
-		out := GetOutput()
-		t.Cleanup(func() { SetOutput(out) })
-	}
-
-	var wrapFp *func(error, ...any) error
-	s := new(stubOutput)
-	SetOutput(s)
-	wrapFp = &s.wrapF
-
-	testCases := []struct {
-		name    string
-		f       func(t *testing.T)
-		wantErr error
-		wantA   []any
-	}{
-		{"suffix nil", func(t *testing.T) {
-			if err := wrapErrSuffix(nil, "\x00"); err != nil {
-				t.Errorf("wrapErrSuffix: %v", err)
-			}
-		}, nil, nil},
-		{"suffix val", func(t *testing.T) {
-			if err := wrapErrSuffix(syscall.ENOTRECOVERABLE, "\x00\x00"); err != syscall.ENOTRECOVERABLE {
-				t.Errorf("wrapErrSuffix: %v", err)
-			}
-		}, syscall.ENOTRECOVERABLE, []any{"\x00\x00", syscall.ENOTRECOVERABLE}},
-		{"self nil", func(t *testing.T) {
-			if err := wrapErrSelf(nil); err != nil {
-				t.Errorf("wrapErrSelf: %v", err)
-			}
-		}, nil, nil},
-		{"self val", func(t *testing.T) {
-			if err := wrapErrSelf(syscall.ENOTRECOVERABLE); err != syscall.ENOTRECOVERABLE {
-				t.Errorf("wrapErrSelf: %v", err)
-			}
-		}, syscall.ENOTRECOVERABLE, []any{"state not recoverable"}},
-	}
-
-	for _, tc := range testCases {
-		t.Run(tc.name, func(t *testing.T) {
-			var (
-				gotErr error
-				gotA   []any
-			)
-			*wrapFp = func(err error, a ...any) error { gotErr = err; gotA = a; return err }
-
-			tc.f(t)
-			if gotErr != tc.wantErr {
-				t.Errorf("WrapErr: err = %v, want %v", gotErr, tc.wantErr)
-			}
-
-			if !reflect.DeepEqual(gotA, tc.wantA) {
-				t.Errorf("WrapErr: a = %v, want %v", gotA, tc.wantA)
-			}
-		})
-	}
-}
-
 type stubOutput struct {
 	wrapF func(error, ...any) error
 }
 
-func (*stubOutput) IsVerbose() bool            { panic("unreachable") }
-func (*stubOutput) Verbose(...any)             { panic("unreachable") }
-func (*stubOutput) Verbosef(string, ...any)    { panic("unreachable") }
-func (*stubOutput) PrintBaseErr(error, string) { panic("unreachable") }
-func (*stubOutput) Suspend()                   { panic("unreachable") }
-func (*stubOutput) Resume() bool               { panic("unreachable") }
-func (*stubOutput) BeforeExit()                { panic("unreachable") }
-
-func (s *stubOutput) WrapErr(err error, v ...any) error {
-	if s.wrapF == nil {
-		panic("unreachable")
-	}
-	return s.wrapF(err, v...)
-}
+func (*stubOutput) IsVerbose() bool         { panic("unreachable") }
+func (*stubOutput) Verbose(...any)          { panic("unreachable") }
+func (*stubOutput) Verbosef(string, ...any) { panic("unreachable") }
+func (*stubOutput) Suspend()                { panic("unreachable") }
+func (*stubOutput) Resume() bool            { panic("unreachable") }
+func (*stubOutput) BeforeExit()             { panic("unreachable") }

container/params.go

@@ -8,11 +8,6 @@ import (
 	"syscall"
 )
 
-var (
-	ErrNotSet   = errors.New("environment variable not set")
-	ErrFdFormat = errors.New("bad file descriptor representation")
-)
-
 // Setup appends the read end of a pipe for setup params transmission and returns its fd.
 func Setup(extraFiles *[]*os.File) (int, *gob.Encoder, error) {
 	if r, w, err := os.Pipe(); err != nil {
@@ -24,19 +19,23 @@ func Setup(extraFiles *[]*os.File) (int, *gob.Encoder, error) {
 	}
 }
 
+var (
+	ErrReceiveEnv = errors.New("environment variable not set")
+)
+
 // Receive retrieves setup fd from the environment and receives params.
 func Receive(key string, e any, fdp *uintptr) (func() error, error) {
 	var setup *os.File
 
 	if s, ok := os.LookupEnv(key); !ok {
-		return nil, ErrNotSet
+		return nil, ErrReceiveEnv
 	} else {
 		if fd, err := strconv.Atoi(s); err != nil {
-			return nil, ErrFdFormat
+			return nil, errors.Unwrap(err)
 		} else {
 			setup = os.NewFile(uintptr(fd), "setup")
 			if setup == nil {
-				return nil, syscall.EBADF
+				return nil, syscall.EDOM
 			}
 			if fdp != nil {
 				*fdp = setup.Fd()

container/params_test.go

@@ -29,8 +29,8 @@ func TestSetupReceive(t *testing.T) {
 			})
 		}
 
-		if _, err := container.Receive(key, nil, nil); !errors.Is(err, container.ErrNotSet) {
-			t.Errorf("Receive: error = %v, want %v", err, container.ErrNotSet)
+		if _, err := container.Receive(key, nil, nil); !errors.Is(err, container.ErrReceiveEnv) {
+			t.Errorf("Receive: error = %v, want %v", err, container.ErrReceiveEnv)
 		}
 	})
 
@@ -38,8 +38,8 @@ func TestSetupReceive(t *testing.T) {
 		const key = "TEST_ENV_FORMAT"
 		t.Setenv(key, "")
 
-		if _, err := container.Receive(key, nil, nil); !errors.Is(err, container.ErrFdFormat) {
-			t.Errorf("Receive: error = %v, want %v", err, container.ErrFdFormat)
+		if _, err := container.Receive(key, nil, nil); !errors.Is(err, strconv.ErrSyntax) {
+			t.Errorf("Receive: error = %v, want %v", err, strconv.ErrSyntax)
 		}
 	})
 
@@ -47,8 +47,8 @@ func TestSetupReceive(t *testing.T) {
 		const key = "TEST_ENV_RANGE"
 		t.Setenv(key, "-1")
 
-		if _, err := container.Receive(key, nil, nil); !errors.Is(err, syscall.EBADF) {
-			t.Errorf("Receive: error = %v, want %v", err, syscall.EBADF)
+		if _, err := container.Receive(key, nil, nil); !errors.Is(err, syscall.EDOM) {
+			t.Errorf("Receive: error = %v, want %v", err, syscall.EDOM)
 		}
 	})
 

container/path.go

@@ -2,7 +2,6 @@ package container
 
 import (
 	"errors"
-	"fmt"
 	"io/fs"
 	"os"
 	"path"
@@ -103,30 +102,29 @@ func toHost(name string) string {
 
 func createFile(name string, perm, pperm os.FileMode, content []byte) error {
 	if err := os.MkdirAll(path.Dir(name), pperm); err != nil {
-		return wrapErrSelf(err)
+		return err
 	}
 	f, err := os.OpenFile(name, syscall.O_CREAT|syscall.O_EXCL|syscall.O_WRONLY, perm)
 	if err != nil {
-		return wrapErrSelf(err)
+		return err
 	}
 	if content != nil {
 		_, err = f.Write(content)
 	}
-	return errors.Join(f.Close(), wrapErrSelf(err))
+	return errors.Join(f.Close(), err)
 }
 
 func ensureFile(name string, perm, pperm os.FileMode) error {
 	fi, err := os.Stat(name)
 	if err != nil {
 		if !os.IsNotExist(err) {
-			return wrapErrSelf(err)
+			return err
 		}
 		return createFile(name, perm, pperm, nil)
 	}
 
 	if mode := fi.Mode(); mode&fs.ModeDir != 0 || mode&fs.ModeSymlink != 0 {
-		err = msg.WrapErr(syscall.EISDIR,
-			fmt.Sprintf("path %q is a directory", name))
+		err = &os.PathError{Op: "ensure", Path: name, Err: syscall.EISDIR}
 	}
 	return err
 }
@@ -147,15 +145,14 @@ func (p *procPaths) stdout() string   { return p.self + "/fd/1" }
 func (p *procPaths) fd(fd int) string { return p.self + "/fd/" + strconv.Itoa(fd) }
 func (p *procPaths) mountinfo(f func(d *vfs.MountInfoDecoder) error) error {
 	if r, err := p.k.openNew(p.self + "/mountinfo"); err != nil {
-		return wrapErrSelf(err)
+		return err
 	} else {
 		d := vfs.NewMountInfoDecoder(r)
 		err0 := f(d)
 		if err = r.Close(); err != nil {
-			return wrapErrSelf(err)
+			return err
 		} else if err = d.Err(); err != nil {
-			return wrapErrSuffix(err,
-				"cannot parse mountinfo:")
+			return err
 		}
 		return err0
 	}

container/path_test.go

@@ -1,8 +1,6 @@
 package container
 
 import (
-	"errors"
-	"fmt"
 	"io"
 	"math"
 	"os"
@@ -56,20 +54,27 @@ func InternalToHostOvlEscape(s string) string { return EscapeOverlayDataSegment(
 
 func TestCreateFile(t *testing.T) {
 	t.Run("nonexistent", func(t *testing.T) {
-		if err := createFile(path.Join(Nonexistent, ":3"), 0644, 0755, nil); !errors.Is(err, wrapErrSelf(&os.PathError{
-			Op:   "mkdir",
-			Path: "/proc/nonexistent",
-			Err:  syscall.ENOENT,
-		})) {
-			t.Errorf("createFile: error = %v", err)
-		}
-		if err := createFile(path.Join(Nonexistent), 0644, 0755, nil); !errors.Is(err, wrapErrSelf(&os.PathError{
-			Op:   "open",
-			Path: "/proc/nonexistent",
-			Err:  syscall.ENOENT,
-		})) {
-			t.Errorf("createFile: error = %v", err)
-		}
+		t.Run("mkdir", func(t *testing.T) {
+			wantErr := &os.PathError{
+				Op:   "mkdir",
+				Path: "/proc/nonexistent",
+				Err:  syscall.ENOENT,
+			}
+			if err := createFile(path.Join(Nonexistent, ":3"), 0644, 0755, nil); !reflect.DeepEqual(err, wantErr) {
+				t.Errorf("createFile: error = %#v, want %#v", err, wantErr)
+			}
+		})
+
+		t.Run("open", func(t *testing.T) {
+			wantErr := &os.PathError{
+				Op:   "open",
+				Path: "/proc/nonexistent",
+				Err:  syscall.ENOENT,
+			}
+			if err := createFile(path.Join(Nonexistent), 0644, 0755, nil); !reflect.DeepEqual(err, wantErr) {
+				t.Errorf("createFile: error = %#v, want %#v", err, wantErr)
+			}
+		})
 	})
 
 	t.Run("touch", func(t *testing.T) {
@@ -120,13 +125,13 @@ func TestEnsureFile(t *testing.T) {
 				t.Fatalf("Chmod: error = %v", err)
 			}
 
-			wantErr := wrapErrSelf(&os.PathError{
+			wantErr := &os.PathError{
 				Op:   "stat",
 				Path: pathname,
 				Err:  syscall.EACCES,
-			})
-			if err := ensureFile(pathname, 0644, 0755); !errors.Is(err, wantErr) {
-				t.Errorf("ensureFile: error = %v, want %v", err, wantErr)
+			}
+			if err := ensureFile(pathname, 0644, 0755); !reflect.DeepEqual(err, wantErr) {
+				t.Errorf("ensureFile: error = %#v, want %#v", err, wantErr)
 			}
 
 			if err := os.Chmod(tempDir, 0755); err != nil {
@@ -136,9 +141,9 @@ func TestEnsureFile(t *testing.T) {
 
 		t.Run("directory", func(t *testing.T) {
 			pathname := t.TempDir()
-			wantErr := msg.WrapErr(syscall.EISDIR, fmt.Sprintf("path %q is a directory", pathname))
-			if err := ensureFile(pathname, 0644, 0755); !errors.Is(err, wantErr) {
-				t.Errorf("ensureFile: error = %v, want %v", err, wantErr)
+			wantErr := &os.PathError{Op: "ensure", Path: pathname, Err: syscall.EISDIR}
+			if err := ensureFile(pathname, 0644, 0755); !reflect.DeepEqual(err, wantErr) {
+				t.Errorf("ensureFile: error = %#v, want %#v", err, wantErr)
 			}
 		})
 
@@ -177,12 +182,12 @@ func TestProcPaths(t *testing.T) {
 	t.Run("mountinfo", func(t *testing.T) {
 		t.Run("nonexistent", func(t *testing.T) {
 			nonexistentProc := newProcPaths(direct{}, t.TempDir())
-			wantErr := wrapErrSelf(&os.PathError{
+			wantErr := &os.PathError{
 				Op:   "open",
 				Path: nonexistentProc.self + "/mountinfo",
 				Err:  syscall.ENOENT,
-			})
-			if err := nonexistentProc.mountinfo(func(*vfs.MountInfoDecoder) error { return syscall.EINVAL }); !errors.Is(err, wantErr) {
+			}
+			if err := nonexistentProc.mountinfo(func(*vfs.MountInfoDecoder) error { return syscall.EINVAL }); !reflect.DeepEqual(err, wantErr) {
 				t.Errorf("mountinfo: error = %v, want %v", err, wantErr)
 			}
 		})
@@ -217,11 +222,11 @@ func TestProcPaths(t *testing.T) {
 
 			t.Run("closed", func(t *testing.T) {
 				p := newProcPaths(direct{}, tempDir)
-				wantErr := wrapErrSelf(&os.PathError{
+				wantErr := &os.PathError{
 					Op:   "close",
 					Path: p.self + "/mountinfo",
 					Err:  os.ErrClosed,
-				})
+				}
 				if err := p.mountinfo(func(d *vfs.MountInfoDecoder) error {
 					v := reflect.ValueOf(d).Elem().FieldByName("s").Elem().FieldByName("r")
 					v = reflect.NewAt(v.Type(), unsafe.Pointer(v.UnsafeAddr()))
@@ -231,8 +236,8 @@ func TestProcPaths(t *testing.T) {
 					} else {
 						return f.Close()
 					}
-				}); !errors.Is(err, wantErr) {
-					t.Errorf("mountinfo: error = %v, want %v", err, wantErr)
+				}); !reflect.DeepEqual(err, wantErr) {
+					t.Errorf("mountinfo: error = %#v, want %#v", err, wantErr)
 				}
 			})
 
@@ -242,8 +247,8 @@ func TestProcPaths(t *testing.T) {
 					t.Fatalf("WriteFile: error = %v", err)
 				}
 
-				wantErr := wrapErrSuffix(vfs.ErrMountInfoFields, "cannot parse mountinfo:")
-				if err := newProcPaths(direct{}, tempDir).mountinfo(func(d *vfs.MountInfoDecoder) error { return d.Decode(new(*vfs.MountInfo)) }); !errors.Is(err, wantErr) {
+				wantErr := &vfs.DecoderError{Op: "parse", Line: 0, Err: vfs.ErrMountInfoFields}
+				if err := newProcPaths(direct{}, tempDir).mountinfo(func(d *vfs.MountInfoDecoder) error { return d.Decode(new(*vfs.MountInfo)) }); !reflect.DeepEqual(err, wantErr) {
 					t.Fatalf("mountinfo: error = %v, want %v", err, wantErr)
 				}
 			})

container/stub/call.go

@@ -0,0 +1,37 @@
+package stub
+
+import (
+	"slices"
+)
+
+// ExpectArgs is an array primarily for storing expected function arguments.
+// Its actual use is defined by the implementation.
+type ExpectArgs = [5]any
+
+// An Expect stores expected calls of a goroutine.
+type Expect struct {
+	Calls []Call
+
+	// Tracks are handed out to descendant goroutines in order.
+	Tracks []Expect
+}
+
+// A Call holds expected arguments of a function call and its outcome.
+type Call struct {
+	// Name is the function Name of this call. Must be unique.
+	Name string
+	// Args are the expected arguments of this Call.
+	Args ExpectArgs
+	// Ret is the return value of this Call.
+	Ret any
+	// Err is the returned error of this Call.
+	Err error
+}
+
+// Error returns [Call.Err] if all arguments are true, or [ErrCheck] otherwise.
+func (k *Call) Error(ok ...bool) error {
+	if !slices.Contains(ok, false) {
+		return k.Err
+	}
+	return ErrCheck
+}

container/stub/call_test.go

@@ -0,0 +1,23 @@
+package stub_test
+
+import (
+	"reflect"
+	"testing"
+
+	"hakurei.app/container/stub"
+)
+
+func TestCallError(t *testing.T) {
+	t.Run("contains false", func(t *testing.T) {
+		if err := new(stub.Call).Error(true, false, true); !reflect.DeepEqual(err, stub.ErrCheck) {
+			t.Errorf("Error: %#v, want %#v", err, stub.ErrCheck)
+		}
+	})
+
+	t.Run("passthrough", func(t *testing.T) {
+		wantErr := stub.UniqueError(0xbabe)
+		if err := (&stub.Call{Err: wantErr}).Error(true); !reflect.DeepEqual(err, wantErr) {
+			t.Errorf("Error: %#v, want %#v", err, wantErr)
+		}
+	})
+}

container/stub/errors.go

@@ -0,0 +1,25 @@
+package stub
+
+import (
+	"errors"
+	"strconv"
+)
+
+var (
+	ErrCheck = errors.New("one or more arguments did not match")
+)
+
+// UniqueError is an error that only equivalates to other [UniqueError] with the same magic value.
+type UniqueError uintptr
+
+func (e UniqueError) Error() string {
+	return "unique error " + strconv.Itoa(int(e)) + " injected by the test suite"
+}
+
+func (e UniqueError) Is(target error) bool {
+	var u UniqueError
+	if !errors.As(target, &u) {
+		return false
+	}
+	return e == u
+}

container/stub/errors_test.go

@@ -0,0 +1,35 @@
+package stub_test
+
+import (
+	"errors"
+	"syscall"
+	"testing"
+
+	"hakurei.app/container/stub"
+)
+
+func TestUniqueError(t *testing.T) {
+	t.Run("format", func(t *testing.T) {
+		want := "unique error 2989 injected by the test suite"
+		if got := stub.UniqueError(0xbad).Error(); got != want {
+			t.Errorf("Error: %q, want %q", got, want)
+		}
+	})
+
+	t.Run("is", func(t *testing.T) {
+		t.Run("type", func(t *testing.T) {
+			if errors.Is(stub.UniqueError(0), syscall.ENOTRECOVERABLE) {
+				t.Error("Is: unexpected true")
+			}
+		})
+
+		t.Run("val", func(t *testing.T) {
+			if errors.Is(stub.UniqueError(0), stub.UniqueError(1)) {
+				t.Error("Is: unexpected true")
+			}
+			if !errors.Is(stub.UniqueError(0xbad), stub.UniqueError(0xbad)) {
+				t.Error("Is: unexpected false")
+			}
+		})
+	})
+}

container/stub/exit.go

@@ -0,0 +1,44 @@
+package stub
+
+import "testing"
+
+// PanicExit is a magic panic value treated as a simulated exit.
+const PanicExit = 0xdeadbeef
+
+const (
+	panicFailNow = 0xcafe0000 + iota
+	panicFatal
+	panicFatalf
+)
+
+// HandleExit must be deferred before calling with the stub.
+func HandleExit(t testing.TB) {
+	switch r := recover(); r {
+	case PanicExit:
+		break
+
+	case panicFailNow:
+		t.FailNow()
+
+	case panicFatal, panicFatalf, nil:
+		break
+
+	default:
+		panic(r)
+	}
+}
+
+// handleExitNew handles exits from goroutines created by [Stub.New].
+func handleExitNew(t testing.TB) {
+	switch r := recover(); r {
+	case PanicExit, panicFatal, panicFatalf, nil:
+		break
+
+	case panicFailNow:
+		t.Fail()
+		break
+
+	default:
+		panic(r)
+	}
+}

container/stub/exit_test.go

@@ -0,0 +1,93 @@
+package stub_test
+
+import (
+	"testing"
+	_ "unsafe"
+
+	"hakurei.app/container/stub"
+)
+
+//go:linkname handleExitNew hakurei.app/container/stub.handleExitNew
+func handleExitNew(_ testing.TB)
+
+// overrideTFailNow overrides the Fail and FailNow method.
+type overrideTFailNow struct {
+	*testing.T
+	failNow bool
+	fail    bool
+}
+
+func (o *overrideTFailNow) FailNow() {
+	if o.failNow {
+		o.Errorf("attempted to FailNow twice")
+	}
+	o.failNow = true
+}
+
+func (o *overrideTFailNow) Fail() {
+	if o.fail {
+		o.Errorf("attempted to Fail twice")
+	}
+	o.fail = true
+}
+
+func TestHandleExit(t *testing.T) {
+	t.Run("exit", func(t *testing.T) {
+		defer stub.HandleExit(t)
+		panic(stub.PanicExit)
+	})
+
+	t.Run("goexit", func(t *testing.T) {
+		t.Run("FailNow", func(t *testing.T) {
+			ot := &overrideTFailNow{T: t}
+			defer func() {
+				if !ot.failNow {
+					t.Errorf("FailNow was never called")
+				}
+			}()
+			defer stub.HandleExit(ot)
+			panic(0xcafe0000)
+		})
+
+		t.Run("Fail", func(t *testing.T) {
+			ot := &overrideTFailNow{T: t}
+			defer func() {
+				if !ot.fail {
+					t.Errorf("Fail was never called")
+				}
+			}()
+			defer handleExitNew(ot)
+			panic(0xcafe0000)
+		})
+	})
+
+	t.Run("nil", func(t *testing.T) {
+		defer stub.HandleExit(t)
+	})
+
+	t.Run("passthrough", func(t *testing.T) {
+		t.Run("toplevel", func(t *testing.T) {
+			defer func() {
+				want := 0xcafebabe
+				if r := recover(); r != want {
+					t.Errorf("recover: %v, want %v", r, want)
+				}
+
+			}()
+			defer stub.HandleExit(t)
+			panic(0xcafebabe)
+		})
+
+		t.Run("new", func(t *testing.T) {
+			defer func() {
+				want := 0xcafe
+				if r := recover(); r != want {
+					t.Errorf("recover: %v, want %v", r, want)
+				}
+
+			}()
+			defer handleExitNew(t)
+			panic(0xcafe)
+		})
+	})
+}

container/stub/stub.go

@@ -0,0 +1,148 @@
+// Package stub provides function call level stubbing and validation
+// for library functions that are impossible to check otherwise.
+package stub
+
+import (
+	"reflect"
+	"sync"
+	"testing"
+)
+
+// this should prevent stub from being inadvertently imported outside tests
+var _ = func() {
+	if !testing.Testing() {
+		panic("stub imported while not in a test")
+	}
+}
+
+const (
+	// A CallSeparator denotes an injected separation between two groups of calls.
+	CallSeparator = "\x00"
+)
+
+// A Stub is a collection of tracks of expected calls.
+type Stub[K any] struct {
+	testing.TB
+
+	// makeK creates a new K for a descendant [Stub].
+	// This function may be called concurrently.
+	makeK func(s *Stub[K]) K
+
+	// want is a hierarchy of expected calls.
+	want Expect
+	// pos is the current position in [Expect.Calls].
+	pos int
+	// goroutine counts the number of goroutines created by this [Stub].
+	goroutine int
+	// sub stores the addresses of descendant [Stub] created by New.
+	sub []*Stub[K]
+	// wg waits for all descendants to complete.
+	wg *sync.WaitGroup
+}
+
+// New creates a root [Stub].
+func New[K any](tb testing.TB, makeK func(s *Stub[K]) K, want Expect) *Stub[K] {
+	return &Stub[K]{TB: tb, makeK: makeK, want: want, wg: new(sync.WaitGroup)}
+}
+
+func (s *Stub[K]) FailNow()                          { panic(panicFailNow) }
+func (s *Stub[K]) Fatal(args ...any)                 { s.Error(args...); panic(panicFatal) }
+func (s *Stub[K]) Fatalf(format string, args ...any) { s.Errorf(format, args...); panic(panicFatalf) }
+func (s *Stub[K]) SkipNow()                          { panic("invalid call to SkipNow") }
+func (s *Stub[K]) Skip(...any)                       { panic("invalid call to Skip") }
+func (s *Stub[K]) Skipf(string, ...any)              { panic("invalid call to Skipf") }
+
+// New calls f in a new goroutine
+func (s *Stub[K]) New(f func(k K)) {
+	s.Helper()
+
+	s.Expects("New")
+	if len(s.want.Tracks) <= s.goroutine {
+		s.Fatal("New: track overrun")
+	}
+	ds := &Stub[K]{TB: s.TB, makeK: s.makeK, want: s.want.Tracks[s.goroutine], wg: s.wg}
+	s.goroutine++
+	s.sub = append(s.sub, ds)
+	s.wg.Add(1)
+	go func() {
+		s.Helper()
+
+		defer s.wg.Done()
+		defer handleExitNew(s.TB)
+		f(s.makeK(ds))
+	}()
+}
+
+// Pos returns the current position of [Stub] in its [Expect.Calls]
+func (s *Stub[K]) Pos() int { return s.pos }
+
+// Len returns the length of [Expect.Calls].
+func (s *Stub[K]) Len() int { return len(s.want.Calls) }
+
+// VisitIncomplete calls f on an incomplete s and all its descendants.
+func (s *Stub[K]) VisitIncomplete(f func(s *Stub[K])) {
+	s.Helper()
+	s.wg.Wait()
+
+	if s.want.Calls != nil && len(s.want.Calls) != s.pos {
+		f(s)
+	}
+	for _, ds := range s.sub {
+		ds.VisitIncomplete(f)
+	}
+}
+
+// Expects checks the name of and returns the current [Call] and advances pos.
+func (s *Stub[K]) Expects(name string) (expect *Call) {
+	s.Helper()
+
+	if len(s.want.Calls) == s.pos {
+		s.Fatal("Expects: advancing beyond expected calls")
+	}
+	expect = &s.want.Calls[s.pos]
+	if name != expect.Name {
+		if expect.Name == CallSeparator {
+			s.Fatalf("Expects: func = %s, separator overrun", name)
+		}
+		if name == CallSeparator {
+			s.Fatalf("Expects: separator, want %s", expect.Name)
+		}
+		s.Fatalf("Expects: func = %s, want %s", name, expect.Name)
+	}
+	s.pos++
+	return
+}
+
+// CheckArg checks an argument comparable with the == operator. Avoid using this with pointers.
+func CheckArg[T comparable, K any](s *Stub[K], arg string, got T, n int) bool {
+	s.Helper()
+
+	pos := s.pos - 1
+	if pos < 0 || pos >= len(s.want.Calls) {
+		panic("invalid call to CheckArg")
+	}
+	expect := s.want.Calls[pos]
+	want, ok := expect.Args[n].(T)
+	if !ok || got != want {
+		s.Errorf("%s: %s = %#v, want %#v (%d)", expect.Name, arg, got, want, pos)
+		return false
+	}
+	return true
+}
+
+// CheckArgReflect checks an argument of any type.
+func CheckArgReflect[K any](s *Stub[K], arg string, got any, n int) bool {
+	s.Helper()
+
+	pos := s.pos - 1
+	if pos < 0 || pos >= len(s.want.Calls) {
+		panic("invalid call to CheckArgReflect")
+	}
+	expect := s.want.Calls[pos]
+	want := expect.Args[n]
+	if !reflect.DeepEqual(got, want) {
+		s.Errorf("%s: %s = %#v, want %#v (%d)", expect.Name, arg, got, want, pos)
+		return false
+	}
+	return true
+}

container/stub/stub_test.go

@@ -0,0 +1,296 @@
+package stub
+
+import (
+	"reflect"
+	"sync/atomic"
+	"testing"
+)
+
+// stubHolder embeds [Stub].
+type stubHolder struct{ *Stub[stubHolder] }
+
+// overrideT allows some methods of [testing.T] to be overridden.
+type overrideT struct {
+	*testing.T
+
+	error  atomic.Pointer[func(args ...any)]
+	errorf atomic.Pointer[func(format string, args ...any)]
+}
+
+func (t *overrideT) Error(args ...any) {
+	fp := t.error.Load()
+	if fp == nil || *fp == nil {
+		t.T.Error(args...)
+		return
+	}
+	(*fp)(args...)
+}
+
+func (t *overrideT) Errorf(format string, args ...any) {
+	fp := t.errorf.Load()
+	if fp == nil || *fp == nil {
+		t.T.Errorf(format, args...)
+		return
+	}
+	(*fp)(format, args...)
+}
+
+func TestStub(t *testing.T) {
+	t.Run("goexit", func(t *testing.T) {
+		t.Run("FailNow", func(t *testing.T) {
+			defer func() {
+				if r := recover(); r != panicFailNow {
+					t.Errorf("recover: %v", r)
+				}
+			}()
+			new(stubHolder).FailNow()
+		})
+
+		t.Run("SkipNow", func(t *testing.T) {
+			defer func() {
+				want := "invalid call to SkipNow"
+				if r := recover(); r != want {
+					t.Errorf("recover: %v, want %v", r, want)
+				}
+			}()
+			new(stubHolder).SkipNow()
+		})
+
+		t.Run("Skip", func(t *testing.T) {
+			defer func() {
+				want := "invalid call to Skip"
+				if r := recover(); r != want {
+					t.Errorf("recover: %v, want %v", r, want)
+				}
+			}()
+			new(stubHolder).Skip()
+		})
+
+		t.Run("Skipf", func(t *testing.T) {
+			defer func() {
+				want := "invalid call to Skipf"
+				if r := recover(); r != want {
+					t.Errorf("recover: %v, want %v", r, want)
+				}
+			}()
+			new(stubHolder).Skipf("")
+		})
+	})
+
+	t.Run("new", func(t *testing.T) {
+		t.Run("success", func(t *testing.T) {
+			s := New(t, func(s *Stub[stubHolder]) stubHolder { return stubHolder{s} }, Expect{Calls: []Call{
+				{"New", ExpectArgs{}, nil, nil},
+			}, Tracks: []Expect{{Calls: []Call{
+				{"done", ExpectArgs{0xbabe}, nil, nil},
+			}}}})
+
+			s.New(func(k stubHolder) {
+				expect := k.Expects("done")
+				if expect.Name != "done" {
+					t.Errorf("New: Name = %s, want done", expect.Name)
+				}
+				if expect.Args != (ExpectArgs{0xbabe}) {
+					t.Errorf("New: Args = %#v", expect.Args)
+				}
+				if expect.Ret != nil {
+					t.Errorf("New: Ret = %#v", expect.Ret)
+				}
+				if expect.Err != nil {
+					t.Errorf("New: Err = %#v", expect.Err)
+				}
+			})
+
+			if pos := s.Pos(); pos != 1 {
+				t.Errorf("Pos: %d, want 1", pos)
+			}
+			if l := s.Len(); l != 1 {
+				t.Errorf("Len: %d, want 1", l)
+			}
+
+			s.VisitIncomplete(func(s *Stub[stubHolder]) { panic("unreachable") })
+		})
+
+		t.Run("overrun", func(t *testing.T) {
+			ot := &overrideT{T: t}
+			ot.error.Store(checkError(t, "New: track overrun"))
+			s := New(ot, func(s *Stub[stubHolder]) stubHolder { return stubHolder{s} }, Expect{Calls: []Call{
+				{"New", ExpectArgs{}, nil, nil},
+				{"panic", ExpectArgs{"unreachable"}, nil, nil},
+			}})
+			func() { defer HandleExit(t); s.New(func(k stubHolder) { panic("unreachable") }) }()
+
+			var visit int
+			s.VisitIncomplete(func(s *Stub[stubHolder]) {
+				visit++
+				if visit > 1 {
+					panic("unexpected visit count")
+				}
+
+				want := Call{"panic", ExpectArgs{"unreachable"}, nil, nil}
+				if got := s.want.Calls[s.pos]; !reflect.DeepEqual(got, want) {
+					t.Errorf("VisitIncomplete: %#v, want %#v", got, want)
+				}
+			})
+		})
+
+		t.Run("expects", func(t *testing.T) {
+			t.Run("overrun", func(t *testing.T) {
+				ot := &overrideT{T: t}
+				ot.error.Store(checkError(t, "Expects: advancing beyond expected calls"))
+				s := New(ot, func(s *Stub[stubHolder]) stubHolder { return stubHolder{s} }, Expect{})
+				func() { defer HandleExit(t); s.Expects("unreachable") }()
+			})
+
+			t.Run("separator", func(t *testing.T) {
+				t.Run("overrun", func(t *testing.T) {
+					ot := &overrideT{T: t}
+					ot.errorf.Store(checkErrorf(t, "Expects: func = %s, separator overrun", "meow"))
+					s := New(ot, func(s *Stub[stubHolder]) stubHolder { return stubHolder{s} }, Expect{Calls: []Call{
+						{CallSeparator, ExpectArgs{}, nil, nil},
+					}})
+					func() { defer HandleExit(t); s.Expects("meow") }()
+				})
+
+				t.Run("mismatch", func(t *testing.T) {
+					ot := &overrideT{T: t}
+					ot.errorf.Store(checkErrorf(t, "Expects: separator, want %s", "panic"))
+					s := New(ot, func(s *Stub[stubHolder]) stubHolder { return stubHolder{s} }, Expect{Calls: []Call{
+						{"panic", ExpectArgs{}, nil, nil},
+					}})
+					func() { defer HandleExit(t); s.Expects(CallSeparator) }()
+				})
+			})
+
+			t.Run("mismatch", func(t *testing.T) {
+				ot := &overrideT{T: t}
+				ot.errorf.Store(checkErrorf(t, "Expects: func = %s, want %s", "meow", "nya"))
+				s := New(ot, func(s *Stub[stubHolder]) stubHolder { return stubHolder{s} }, Expect{Calls: []Call{
+					{"nya", ExpectArgs{}, nil, nil},
+				}})
+				func() { defer HandleExit(t); s.Expects("meow") }()
+			})
+		})
+	})
+}
+
+func TestCheckArg(t *testing.T) {
+	t.Run("oob negative", func(t *testing.T) {
+		defer func() {
+			want := "invalid call to CheckArg"
+			if r := recover(); r != want {
+				t.Errorf("recover: %v, want %v", r, want)
+			}
+		}()
+		s := New(t, func(s *Stub[stubHolder]) stubHolder { return stubHolder{s} }, Expect{})
+		CheckArg(s, "unreachable", struct{}{}, 0)
+	})
+
+	ot := &overrideT{T: t}
+	s := New(ot, func(s *Stub[stubHolder]) stubHolder { return stubHolder{s} }, Expect{Calls: []Call{
+		{"panic", ExpectArgs{PanicExit}, nil, nil},
+		{"meow", ExpectArgs{-1}, nil, nil},
+	}})
+	t.Run("match", func(t *testing.T) {
+		s.Expects("panic")
+		if !CheckArg(s, "v", PanicExit, 0) {
+			t.Errorf("CheckArg: unexpected false")
+		}
+	})
+	t.Run("mismatch", func(t *testing.T) {
+		defer HandleExit(t)
+		s.Expects("meow")
+		ot.errorf.Store(checkErrorf(t, "%s: %s = %#v, want %#v (%d)", "meow", "time", 0, -1, 1))
+		if CheckArg(s, "time", 0, 0) {
+			t.Errorf("CheckArg: unexpected true")
+		}
+	})
+	t.Run("oob", func(t *testing.T) {
+		s.pos++
+		defer func() {
+			want := "invalid call to CheckArg"
+			if r := recover(); r != want {
+				t.Errorf("recover: %v, want %v", r, want)
+			}
+		}()
+		CheckArg(s, "unreachable", struct{}{}, 0)
+	})
+}
+
+func TestCheckArgReflect(t *testing.T) {
+	t.Run("oob lower", func(t *testing.T) {
+		defer func() {
+			want := "invalid call to CheckArgReflect"
+			if r := recover(); r != want {
+				t.Errorf("recover: %v, want %v", r, want)
+			}
+		}()
+		s := New(t, func(s *Stub[stubHolder]) stubHolder { return stubHolder{s} }, Expect{})
+		CheckArgReflect(s, "unreachable", struct{}{}, 0)
+	})
+
+	ot := &overrideT{T: t}
+	s := New(ot, func(s *Stub[stubHolder]) stubHolder { return stubHolder{s} }, Expect{Calls: []Call{
+		{"panic", ExpectArgs{PanicExit}, nil, nil},
+		{"meow", ExpectArgs{-1}, nil, nil},
+	}})
+	t.Run("match", func(t *testing.T) {
+		s.Expects("panic")
+		if !CheckArgReflect(s, "v", PanicExit, 0) {
+			t.Errorf("CheckArgReflect: unexpected false")
+		}
+	})
+	t.Run("mismatch", func(t *testing.T) {
+		defer HandleExit(t)
+		s.Expects("meow")
+		ot.errorf.Store(checkErrorf(t, "%s: %s = %#v, want %#v (%d)", "meow", "time", 0, -1, 1))
+		if CheckArgReflect(s, "time", 0, 0) {
+			t.Errorf("CheckArgReflect: unexpected true")
+		}
+	})
+	t.Run("oob", func(t *testing.T) {
+		s.pos++
+		defer func() {
+			want := "invalid call to CheckArgReflect"
+			if r := recover(); r != want {
+				t.Errorf("recover: %v, want %v", r, want)
+			}
+		}()
+		CheckArgReflect(s, "unreachable", struct{}{}, 0)
+	})
+}
+
+func checkError(t *testing.T, wantArgs ...any) *func(args ...any) {
+	var called bool
+	f := func(args ...any) {
+		if called {
+			panic("invalid call to error")
+		}
+		called = true
+
+		if !reflect.DeepEqual(args, wantArgs) {
+			t.Errorf("Error: %#v, want %#v", args, wantArgs)
+		}
+		panic(PanicExit)
+	}
+	return &f
+}
+
+func checkErrorf(t *testing.T, wantFormat string, wantArgs ...any) *func(format string, args ...any) {
+	var called bool
+	f := func(format string, args ...any) {
+		if called {
+			panic("invalid call to errorf")
+		}
+		called = true
+
+		if format != wantFormat {
+			t.Errorf("Errorf: format = %q, want %q", format, wantFormat)
+		}
+		if !reflect.DeepEqual(args, wantArgs) {
+			t.Errorf("Errorf: args = %#v, want %#v", args, wantArgs)
+		}
+		panic(PanicExit)
+	}
+	return &f
+}

container/vfs/mountinfo.go

@@ -24,6 +24,32 @@ var (
 	ErrMountInfoSep    = errors.New("bad optional fields separator")
 )
 
+type DecoderError struct {
+	Op   string
+	Line int
+	Err  error
+}
+
+func (e *DecoderError) Unwrap() error { return e.Err }
+func (e *DecoderError) Error() string {
+	var s string
+
+	var numError *strconv.NumError
+	switch {
+	case errors.As(e.Err, &numError) && numError != nil:
+		s = "numeric field " + strconv.Quote(numError.Num) + " " + numError.Err.Error()
+
+	default:
+		s = e.Err.Error()
+	}
+
+	var atLine string
+	if e.Line >= 0 {
+		atLine = " at line " + strconv.Itoa(e.Line)
+	}
+	return e.Op + " mountinfo" + atLine + ": " + s
+}
+
 type (
 	// A MountInfoDecoder reads and decodes proc_pid_mountinfo(5) entries from an input stream.
 	MountInfoDecoder struct {
@@ -32,6 +58,7 @@ type (
 
 		current  *MountInfo
 		parseErr error
+		curLine  int
 		complete bool
 	}
 
@@ -132,9 +159,12 @@ func (d *MountInfoDecoder) Entries() iter.Seq[*MountInfoEntry] {
 
 func (d *MountInfoDecoder) Err() error {
 	if err := d.s.Err(); err != nil {
-		return err
+		return &DecoderError{"scan", d.curLine, err}
 	}
-	return d.parseErr
+	if d.parseErr != nil {
+		return &DecoderError{"parse", d.curLine, d.parseErr}
+	}
+	return nil
 }
 
 func (d *MountInfoDecoder) scan() bool {
@@ -160,6 +190,7 @@ func (d *MountInfoDecoder) scan() bool {
 		d.current.Next = m
 		d.current = d.current.Next
 	}
+	d.curLine++
 	return true
 }
 

container/vfs/mountinfo_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"errors"
 	"iter"
+	"os"
 	"path"
 	"reflect"
 	"slices"
@@ -15,62 +16,102 @@ import (
 	"hakurei.app/container/vfs"
 )
 
+func TestDecoderError(t *testing.T) {
+	testCases := []struct {
+		name    string
+		err     *vfs.DecoderError
+		want    string
+		target  error
+		targetF error
+	}{
+		{"errno", &vfs.DecoderError{Op: "parse", Line: 0xdeadbeef, Err: syscall.ENOTRECOVERABLE},
+			"parse mountinfo at line 3735928559: state not recoverable", syscall.ENOTRECOVERABLE, syscall.EROFS},
+
+		{"strconv", &vfs.DecoderError{Op: "parse", Line: 0xdeadbeef, Err: &strconv.NumError{Func: "Atoi", Num: "meow", Err: strconv.ErrSyntax}},
+			`parse mountinfo at line 3735928559: numeric field "meow" invalid syntax`, strconv.ErrSyntax, os.ErrInvalid},
+
+		{"unfold", &vfs.DecoderError{Op: "unfold", Line: -1, Err: vfs.UnfoldTargetError("/proc/nonexistent")},
+			"unfold mountinfo: mount point /proc/nonexistent never appeared in mountinfo", vfs.UnfoldTargetError("/proc/nonexistent"), os.ErrNotExist},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Run("error", func(t *testing.T) {
+				if got := tc.err.Error(); got != tc.want {
+					t.Errorf("Error: %s, want %s", got, tc.want)
+				}
+			})
+
+			t.Run("is", func(t *testing.T) {
+				if !errors.Is(tc.err, tc.target) {
+					t.Errorf("Is: unexpected false")
+				}
+				if errors.Is(tc.err, tc.targetF) {
+					t.Errorf("Is: unexpected true")
+				}
+			})
+		})
+	}
+}
+
 func TestMountInfo(t *testing.T) {
 	testCases := []mountInfoTest{
 		{"count", sampleMountinfoBase + `
 21 20 0:53/ /mnt/test rw,relatime - tmpfs  rw
 21 16 0:17 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,mode=755`,
-			vfs.ErrMountInfoFields, "", nil, nil, nil},
+			&vfs.DecoderError{Op: "parse", Line: 6, Err: vfs.ErrMountInfoFields},
+			"", nil, nil, nil},
 
 		{"sep", sampleMountinfoBase + `
 21 20 0:53 / /mnt/test rw,relatime shared:212 _ tmpfs  rw
 21 16 0:17 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,mode=755`,
-			vfs.ErrMountInfoSep, "", nil, nil, nil},
+			&vfs.DecoderError{Op: "parse", Line: 6, Err: vfs.ErrMountInfoSep},
+			"", nil, nil, nil},
 
 		{"id", sampleMountinfoBase + `
 id 20 0:53 / /mnt/test rw,relatime shared:212 - tmpfs  rw
 21 16 0:17 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,mode=755`,
-			strconv.ErrSyntax, "", nil, nil, nil},
+			&vfs.DecoderError{Op: "parse", Line: 6, Err: &strconv.NumError{Func: "Atoi", Num: "id", Err: strconv.ErrSyntax}},
+			"", nil, nil, nil},
 
 		{"parent", sampleMountinfoBase + `
 21 parent 0:53 / /mnt/test rw,relatime shared:212 - tmpfs  rw
 21 16 0:17 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,mode=755`,
-			strconv.ErrSyntax, "", nil, nil, nil},
+			&vfs.DecoderError{Op: "parse", Line: 6, Err: &strconv.NumError{Func: "Atoi", Num: "parent", Err: strconv.ErrSyntax}}, "", nil, nil, nil},
 
 		{"devno", sampleMountinfoBase + `
 21 20 053 / /mnt/test rw,relatime shared:212 - tmpfs  rw
 21 16 0:17 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,mode=755`,
-			nil, "unexpected EOF", nil, nil, nil},
+			nil, "parse mountinfo at line 6: unexpected EOF", nil, nil, nil},
 
 		{"maj", sampleMountinfoBase + `
 21 20 maj:53 / /mnt/test rw,relatime shared:212 - tmpfs  rw
 21 16 0:17 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,mode=755`,
-			nil, "expected integer", nil, nil, nil},
+			nil, "parse mountinfo at line 6: expected integer", nil, nil, nil},
 
 		{"min", sampleMountinfoBase + `
 21 20 0:min / /mnt/test rw,relatime shared:212 - tmpfs  rw
 21 16 0:17 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,mode=755`,
-			nil, "expected integer", nil, nil, nil},
+			nil, "parse mountinfo at line 6: expected integer", nil, nil, nil},
 
 		{"mountroot", sampleMountinfoBase + `
 21 20 0:53  /mnt/test rw,relatime - tmpfs  rw
 21 16 0:17 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,mode=755`,
-			vfs.ErrMountInfoEmpty, "", nil, nil, nil},
+			&vfs.DecoderError{Op: "parse", Line: 6, Err: vfs.ErrMountInfoEmpty}, "", nil, nil, nil},
 
 		{"target", sampleMountinfoBase + `
 21 20 0:53 /  rw,relatime - tmpfs  rw
 21 16 0:17 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,mode=755`,
-			vfs.ErrMountInfoEmpty, "", nil, nil, nil},
+			&vfs.DecoderError{Op: "parse", Line: 6, Err: vfs.ErrMountInfoEmpty}, "", nil, nil, nil},
 
 		{"vfs options", sampleMountinfoBase + `
 21 20 0:53 / /mnt/test  - tmpfs  rw
 21 16 0:17 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,mode=755`,
-			vfs.ErrMountInfoEmpty, "", nil, nil, nil},
+			&vfs.DecoderError{Op: "parse", Line: 6, Err: vfs.ErrMountInfoEmpty}, "", nil, nil, nil},
 
 		{"FS type", sampleMountinfoBase + `
-21 20 0:53 / /mnt/test rw,relatime -   rw
-21 16 0:17 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,mode=755`,
-			vfs.ErrMountInfoEmpty, "", nil, nil, nil},
+21 16 0:17 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,mode=755
+21 20 0:53 / /mnt/test rw,relatime -   rw`,
+			&vfs.DecoderError{Op: "parse", Line: 7, Err: vfs.ErrMountInfoEmpty}, "", nil, nil, nil},
 
 		{"base", sampleMountinfoBase, nil, "", []*wantMountInfo{
 			m(15, 20, 0, 3, "/", "/proc", "rw,relatime", o(), "proc", "/proc", "rw", syscall.MS_RELATIME, nil),
@@ -266,9 +307,9 @@ func (tc *mountInfoTest) check(t *testing.T, d *vfs.MountInfoDecoder, funcName s
 		})
 	} else if tc.wantNode != nil || tc.wantCollectF != nil {
 		panic("invalid test case")
-	} else if _, err := d.Unfold("/"); !errors.Is(err, tc.wantErr) {
+	} else if _, err := d.Unfold("/"); !reflect.DeepEqual(err, tc.wantErr) {
 		if tc.wantError == "" {
-			t.Errorf("Unfold: error = %v, wantErr %v",
+			t.Errorf("Unfold: error = %#v, wantErr %#v",
 				err, tc.wantErr)
 		} else if err != nil && err.Error() != tc.wantError {
 			t.Errorf("Unfold: error = %q, wantError %q",
@@ -276,9 +317,9 @@ func (tc *mountInfoTest) check(t *testing.T, d *vfs.MountInfoDecoder, funcName s
 		}
 	}
 
-	if err := gotErr(); !errors.Is(err, tc.wantErr) {
+	if err := gotErr(); !reflect.DeepEqual(err, tc.wantErr) {
 		if tc.wantError == "" {
-			t.Errorf("%s: error = %v, wantErr %v",
+			t.Errorf("%s: error = %#v, wantErr %#v",
 				funcName, err, tc.wantErr)
 		} else if err != nil && err.Error() != tc.wantError {
 			t.Errorf("%s: error = %q, wantError %q",

container/vfs/unfold.go

@@ -4,9 +4,14 @@ import (
 	"iter"
 	"path"
 	"strings"
-	"syscall"
 )
 
+type UnfoldTargetError string
+
+func (e UnfoldTargetError) Error() string {
+	return "mount point " + string(e) + " never appeared in mountinfo"
+}
+
 // MountInfoNode positions a [MountInfoEntry] in its mount hierarchy.
 type MountInfoNode struct {
 	*MountInfoEntry
@@ -65,7 +70,8 @@ func (d *MountInfoDecoder) Unfold(target string) (*MountInfoNode, error) {
 	}
 
 	if targetIndex == -1 {
-		return nil, syscall.ESTALE
+		// target does not exist in parsed mountinfo
+		return nil, &DecoderError{Op: "unfold", Line: -1, Err: UnfoldTargetError(targetClean)}
 	}
 
 	for _, cur := range mountinfo {

container/vfs/unfold_test.go

@@ -1,11 +1,9 @@
 package vfs_test
 
 import (
-	"errors"
 	"reflect"
 	"slices"
 	"strings"
-	"syscall"
 	"testing"
 
 	"hakurei.app/container/vfs"
@@ -26,7 +24,7 @@ func TestUnfold(t *testing.T) {
 			"no match",
 			sampleMountinfoBase,
 			"/mnt",
-			syscall.ESTALE, nil, nil, nil,
+			&vfs.DecoderError{Op: "unfold", Line: -1, Err: vfs.UnfoldTargetError("/mnt")}, nil, nil, nil,
 		},
 		{
 			"cover",
@@ -55,7 +53,7 @@ func TestUnfold(t *testing.T) {
 			d := vfs.NewMountInfoDecoder(strings.NewReader(tc.sample))
 			got, err := d.Unfold(tc.target)
 
-			if !errors.Is(err, tc.wantErr) {
+			if !reflect.DeepEqual(err, tc.wantErr) {
 				t.Errorf("Unfold: error = %v, wantErr %v",
 					err, tc.wantErr)
 			}

flake.lock

@@ -7,11 +7,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1753479839,
-        "narHash": "sha256-E/rPVh7vyPMJUFl2NAew+zibNGfVbANr8BP8nLRbLkQ=",
+        "lastModified": 1756679287,
+        "narHash": "sha256-Xd1vOeY9ccDf5VtVK12yM0FS6qqvfUop8UQlxEB+gTQ=",
         "owner": "nix-community",
         "repo": "home-manager",
-        "rev": "0b9bf983db4d064764084cd6748efb1ab8297d1e",
+        "rev": "07fc025fe10487dd80f2ec694f1cd790e752d0e8",
         "type": "github"
       },
       "original": {
@@ -23,11 +23,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1753345091,
-        "narHash": "sha256-CdX2Rtvp5I8HGu9swBmYuq+ILwRxpXdJwlpg8jvN4tU=",
+        "lastModified": 1757020766,
+        "narHash": "sha256-PLoSjHRa2bUbi1x9HoXgTx2AiuzNXs54c8omhadyvp0=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "3ff0e34b1383648053bba8ed03f201d3466f90c9",
+        "rev": "fe83bbdde2ccdc2cb9573aa846abe8363f79a97a",
         "type": "github"
       },
       "original": {

helper/container_test.go

@@ -11,10 +11,10 @@ import (
 )
 
 func TestContainer(t *testing.T) {
-	t.Run("start empty container", func(t *testing.T) {
+	t.Run("start invalid container", func(t *testing.T) {
 		h := helper.New(t.Context(), container.MustAbs(container.Nonexistent), "hakurei", argsWt, false, argF, nil, nil)
 
-		wantErr := "container: starting an empty container"
+		wantErr := "container: starting an invalid container"
 		if err := h.Start(); err == nil || err.Error() != wantErr {
 			t.Errorf("Start: error = %v, wantErr %q",
 				err, wantErr)

helper/helper_test.go

@@ -6,8 +6,10 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"reflect"
 	"strconv"
 	"strings"
+	"syscall"
 	"testing"
 	"time"
 
@@ -47,6 +49,10 @@ func argFChecked(argsFd, statFd int) (args []string) {
 	return
 }
 
+const (
+	containerTimeout = 30 * time.Second
+)
+
 // this function tests an implementation of the helper.Helper interface
 func testHelper(t *testing.T, createHelper func(ctx context.Context, setOutput func(stdoutP, stderrP *io.Writer), stat bool) helper.Helper) {
 	oldWaitDelay := helper.WaitDelay
@@ -54,18 +60,15 @@ func testHelper(t *testing.T, createHelper func(ctx context.Context, setOutput f
 	t.Cleanup(func() { helper.WaitDelay = oldWaitDelay })
 
 	t.Run("start helper with status channel and wait", func(t *testing.T) {
-		ctx, cancel := context.WithTimeout(t.Context(), 5*time.Second)
+		ctx, cancel := context.WithTimeout(t.Context(), containerTimeout)
 		stdout := new(strings.Builder)
 		h := createHelper(ctx, func(stdoutP, stderrP *io.Writer) { *stdoutP, *stderrP = stdout, os.Stderr }, true)
 
 		t.Run("wait not yet started helper", func(t *testing.T) {
-			defer func() {
-				r := recover()
-				if r == nil {
-					t.Fatalf("Wait did not panic")
-				}
-			}()
-			panic(fmt.Sprintf("unreachable: %v", h.Wait()))
+			if err := h.Wait(); !reflect.DeepEqual(err, syscall.EINVAL) &&
+				!reflect.DeepEqual(err, errors.New("exec: not started")) {
+				t.Errorf("Wait: error = %v", err)
+			}
 		})
 
 		t.Log("starting helper stub")
@@ -108,7 +111,7 @@ func testHelper(t *testing.T, createHelper func(ctx context.Context, setOutput f
 	})
 
 	t.Run("start helper and wait", func(t *testing.T) {
-		ctx, cancel := context.WithTimeout(t.Context(), 5*time.Second)
+		ctx, cancel := context.WithTimeout(t.Context(), containerTimeout)
 		defer cancel()
 		stdout := new(strings.Builder)
 		h := createHelper(ctx, func(stdoutP, stderrP *io.Writer) { *stdoutP, *stderrP = stdout, os.Stderr }, false)

hst/config.go

@@ -87,7 +87,9 @@ type (
 
 		// initial process environment variables
 		Env map[string]string `json:"env"`
-		// map target user uid to privileged user uid in the user namespace
+		// map target user uid to privileged user uid in the user namespace;
+		// some programs fail to connect to dbus session running as a different uid,
+		// this option works around it by mapping priv-side caller uid in container
 		MapRealUID bool `json:"map_real_uid"`
 
 		// pass through all devices

hst/hst.go

@@ -2,12 +2,42 @@
 package hst
 
 import (
+	"errors"
+	"net"
+	"os"
+
 	"hakurei.app/container"
 	"hakurei.app/container/seccomp"
 	"hakurei.app/system"
 	"hakurei.app/system/dbus"
 )
 
+// An AppError is returned while starting an app according to [hst.Config].
+type AppError struct {
+	Step string
+	Err  error
+	Msg  string
+}
+
+func (e *AppError) Error() string { return e.Err.Error() }
+func (e *AppError) Unwrap() error { return e.Err }
+func (e *AppError) Message() string {
+	if e.Msg != "" {
+		return e.Msg
+	}
+
+	switch {
+	case errors.As(e.Err, new(*os.PathError)),
+		errors.As(e.Err, new(*os.LinkError)),
+		errors.As(e.Err, new(*os.SyscallError)),
+		errors.As(e.Err, new(*net.OpError)):
+		return "cannot " + e.Error()
+
+	default:
+		return "cannot " + e.Step + ": " + e.Error()
+	}
+}
+
 // Paths contains environment-dependent paths used by hakurei.
 type Paths struct {
 	// temporary directory returned by [os.TempDir] (usually `/tmp`)

hst/hst_test.go

@@ -2,11 +2,93 @@ package hst_test
 
 import (
 	"encoding/json"
+	"errors"
+	"net"
+	"os"
+	"syscall"
 	"testing"
 
+	"hakurei.app/container"
+	"hakurei.app/container/stub"
 	"hakurei.app/hst"
 )
 
+func TestAppError(t *testing.T) {
+	testCases := []struct {
+		name    string
+		err     error
+		s       string
+		message string
+		is, isF error
+	}{
+		{"message", &hst.AppError{Step: "obtain uid from hsu", Err: stub.UniqueError(0),
+			Msg: "the setuid helper is missing: /run/wrappers/bin/hsu"},
+			"unique error 0 injected by the test suite",
+			"the setuid helper is missing: /run/wrappers/bin/hsu",
+			stub.UniqueError(0), os.ErrNotExist},
+
+		{"os.PathError", &hst.AppError{Step: "passthrough os.PathError",
+			Err: &os.PathError{Op: "stat", Path: "/proc/nonexistent", Err: os.ErrNotExist}},
+			"stat /proc/nonexistent: file does not exist",
+			"cannot stat /proc/nonexistent: file does not exist",
+			os.ErrNotExist, stub.UniqueError(0xdeadbeef)},
+
+		{"os.LinkError", &hst.AppError{Step: "passthrough os.LinkError",
+			Err: &os.LinkError{Op: "link", Old: "/proc/self", New: "/proc/nonexistent", Err: os.ErrNotExist}},
+			"link /proc/self /proc/nonexistent: file does not exist",
+			"cannot link /proc/self /proc/nonexistent: file does not exist",
+			os.ErrNotExist, stub.UniqueError(0xdeadbeef)},
+
+		{"os.SyscallError", &hst.AppError{Step: "passthrough os.SyscallError",
+			Err: &os.SyscallError{Syscall: "meow", Err: syscall.ENOSYS}},
+			"meow: function not implemented",
+			"cannot meow: function not implemented",
+			syscall.ENOSYS, syscall.ENOTRECOVERABLE},
+
+		{"net.OpError", &hst.AppError{Step: "passthrough net.OpError",
+			Err: &net.OpError{Op: "dial", Net: "cat", Err: net.UnknownNetworkError("cat")}},
+			"dial cat: unknown network cat",
+			"cannot dial cat: unknown network cat",
+			net.UnknownNetworkError("cat"), syscall.ENOTRECOVERABLE},
+
+		{"default", &hst.AppError{Step: "initialise container configuration", Err: stub.UniqueError(1)},
+			"unique error 1 injected by the test suite",
+			"cannot initialise container configuration: unique error 1 injected by the test suite",
+			stub.UniqueError(1), os.ErrInvalid},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Run("error", func(t *testing.T) {
+				if got := tc.err.Error(); got != tc.s {
+					t.Errorf("Error: %s, want %s", got, tc.s)
+				}
+			})
+
+			t.Run("message", func(t *testing.T) {
+				gotMessage, gotMessageOk := container.GetErrorMessage(tc.err)
+				if want := tc.message != "\x00"; gotMessageOk != want {
+					t.Errorf("GetErrorMessage: ok = %v, want %v", gotMessage, want)
+				}
+
+				if gotMessageOk {
+					if gotMessage != tc.message {
+						t.Errorf("GetErrorMessage: %s, want %s", gotMessage, tc.message)
+					}
+				}
+			})
+
+			t.Run("is", func(t *testing.T) {
+				if !errors.Is(tc.err, tc.is) {
+					t.Errorf("Is: unexpected false for %v", tc.is)
+				}
+				if errors.Is(tc.err, tc.isF) {
+					t.Errorf("Is: unexpected true for %v", tc.isF)
+				}
+			})
+		})
+	}
+}
+
 func TestTemplate(t *testing.T) {
 	const want = `{
 	"id": "org.chromium.Chromium",

internal/app/app.go

@@ -1,61 +1,30 @@
-// Package app defines the generic [App] interface.
+// Package app implements high-level hakurei container behaviour.
 package app
 
 import (
 	"context"
 	"log"
-	"syscall"
-	"time"
+	"os"
 
 	"hakurei.app/hst"
 	"hakurei.app/internal/app/state"
 	"hakurei.app/internal/sys"
 )
 
-type App interface {
-	// ID returns a copy of [ID] held by App.
-	ID() state.ID
-
-	// Seal determines the outcome of config as a [SealedApp].
-	// The value of config might be overwritten and must not be used again.
-	Seal(config *hst.Config) (SealedApp, error)
-
-	String() string
-}
-
-type SealedApp interface {
-	// Run commits sealed system setup and starts the app process.
-	Run(rs *RunState) error
-}
-
-// RunState stores the outcome of a call to [SealedApp.Run].
-type RunState struct {
-	// Time is the exact point in time where the process was created.
-	// Location must be set to UTC.
-	//
-	// Time is nil if no process was ever created.
-	Time *time.Time
-	// RevertErr is stored by the deferred revert call.
-	RevertErr error
-	// WaitErr is the generic error value created by the standard library.
-	WaitErr error
-
-	syscall.WaitStatus
-}
-
-// SetStart stores the current time in [RunState] once.
-func (rs *RunState) SetStart() {
-	if rs.Time != nil {
-		panic("attempted to store time twice")
+// Main runs an app according to [hst.Config] and terminates. Main does not return.
+func Main(ctx context.Context, k sys.State, config *hst.Config) {
+	var id state.ID
+	if err := state.NewAppID(&id); err != nil {
+		log.Fatal(err)
 	}
-	now := time.Now().UTC()
-	rs.Time = &now
-}
 
-func MustNew(ctx context.Context, os sys.State) App {
-	a, err := New(ctx, os)
-	if err != nil {
-		log.Fatalf("cannot create app: %v", err)
+	var seal outcome
+	seal.id = &stringPair[state.ID]{id, id.String()}
+	if err := seal.finalise(ctx, k, config); err != nil {
+		printMessageError("cannot seal app:", err)
+		os.Exit(1)
 	}
-	return a
+
+	seal.main()
+	panic("unreachable")
 }

internal/app/app_linux.go

@@ -1,69 +0,0 @@
-package app
-
-import (
-	"context"
-	"fmt"
-	"sync"
-
-	"hakurei.app/hst"
-	"hakurei.app/internal/app/state"
-	"hakurei.app/internal/sys"
-)
-
-func New(ctx context.Context, os sys.State) (App, error) {
-	a := new(app)
-	a.sys = os
-	a.ctx = ctx
-
-	id := new(state.ID)
-	err := state.NewAppID(id)
-	a.id = newID(id)
-
-	return a, err
-}
-
-type app struct {
-	id  *stringPair[state.ID]
-	sys sys.State
-	ctx context.Context
-
-	*outcome
-	mu sync.RWMutex
-}
-
-func (a *app) ID() state.ID { a.mu.RLock(); defer a.mu.RUnlock(); return a.id.unwrap() }
-
-func (a *app) String() string {
-	if a == nil {
-		return "(invalid app)"
-	}
-
-	a.mu.RLock()
-	defer a.mu.RUnlock()
-
-	if a.outcome != nil {
-		if a.outcome.user.uid == nil {
-			return fmt.Sprintf("(sealed app %s with invalid uid)", a.id)
-		}
-		return fmt.Sprintf("(sealed app %s as uid %s)", a.id, a.outcome.user.uid)
-	}
-
-	return fmt.Sprintf("(unsealed app %s)", a.id)
-}
-
-func (a *app) Seal(config *hst.Config) (SealedApp, error) {
-	a.mu.Lock()
-	defer a.mu.Unlock()
-
-	if a.outcome != nil {
-		panic("app sealed twice")
-	}
-
-	seal := new(outcome)
-	seal.id = a.id
-	err := seal.finalise(a.ctx, a.sys, config)
-	if err == nil {
-		a.outcome = seal
-	}
-	return seal, err
-}

internal/app/app_nixos_linux_test.go

@@ -1,6 +1,7 @@
 package app_test
 
 import (
+	"context"
 	"syscall"
 
 	"hakurei.app/container"
@@ -74,7 +75,7 @@ var testCasesNixos = []sealTestCase{
 			0x4c, 0xf0, 0x73, 0xbd,
 			0xb4, 0x6e, 0xb5, 0xc1,
 		},
-		system.New(1000001).
+		system.New(context.TODO(), 1000001).
 			Ensure("/tmp/hakurei.1971", 0711).
 			Ensure("/tmp/hakurei.1971/runtime", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/runtime", acl.Execute).
 			Ensure("/tmp/hakurei.1971/runtime/1", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/runtime/1", acl.Read, acl.Write, acl.Execute).
@@ -134,6 +135,7 @@ var testCasesNixos = []sealTestCase{
 				Proc(m("/proc/")).
 				Tmpfs(hst.AbsTmp, 4096, 0755).
 				DevWritable(m("/dev/"), true).
+				Tmpfs(m("/dev/shm"), 0, 01777).
 				Bind(m("/bin"), m("/bin"), 0).
 				Bind(m("/usr/bin/"), m("/usr/bin/"), 0).
 				Bind(m("/nix/store"), m("/nix/store"), 0).
@@ -148,7 +150,6 @@ var testCasesNixos = []sealTestCase{
 				Etc(m("/etc/"), "8e2c76b066dabe574cf073bdb46eb5c1").
 				Bind(m("/var/lib/persist/module/hakurei/0/1"), m("/var/lib/persist/module/hakurei/0/1"), container.BindWritable|container.BindEnsure).
 				Remount(m("/dev/"), syscall.MS_RDONLY).
-				Tmpfs(m("/dev/shm"), 0, 01777).
 				Tmpfs(m("/run/user/"), 4096, 0755).
 				Bind(m("/tmp/hakurei.1971/runtime/1"), m("/run/user/1971"), container.BindWritable).
 				Bind(m("/tmp/hakurei.1971/tmpdir/1"), m("/tmp/"), container.BindWritable).

internal/app/app_pd_linux_test.go

@@ -1,6 +1,7 @@
 package app_test
 
 import (
+	"context"
 	"os"
 	"syscall"
 
@@ -23,7 +24,7 @@ var testCasesPd = []sealTestCase{
 			0xbd, 0x01, 0x78, 0x0e,
 			0xb9, 0xa6, 0x07, 0xac,
 		},
-		system.New(1000000).
+		system.New(context.TODO(), 1000000).
 			Ensure("/tmp/hakurei.1971", 0711).
 			Ensure("/tmp/hakurei.1971/runtime", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/runtime", acl.Execute).
 			Ensure("/tmp/hakurei.1971/runtime/0", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/runtime/0", acl.Read, acl.Write, acl.Execute).
@@ -47,13 +48,13 @@ var testCasesPd = []sealTestCase{
 				Proc(m("/proc/")).
 				Tmpfs(hst.AbsTmp, 4096, 0755).
 				DevWritable(m("/dev/"), true).
+				Tmpfs(m("/dev/shm"), 0, 01777).
 				Bind(m("/dev/kvm"), m("/dev/kvm"), container.BindWritable|container.BindDevice|container.BindOptional).
 				Readonly(m("/var/run/nscd"), 0755).
 				Etc(m("/etc/"), "4a450b6596d7bc15bd01780eb9a607ac").
 				Tmpfs(m("/run/user/1971"), 8192, 0755).
 				Tmpfs(m("/run/dbus"), 8192, 0755).
 				Remount(m("/dev/"), syscall.MS_RDONLY).
-				Tmpfs(m("/dev/shm"), 0, 01777).
 				Tmpfs(m("/run/user/"), 4096, 0755).
 				Bind(m("/tmp/hakurei.1971/runtime/0"), m("/run/user/65534"), container.BindWritable).
 				Bind(m("/tmp/hakurei.1971/tmpdir/0"), m("/tmp/"), container.BindWritable).
@@ -115,7 +116,7 @@ var testCasesPd = []sealTestCase{
 			0x82, 0xd4, 0x13, 0x36,
 			0x9b, 0x64, 0xce, 0x7c,
 		},
-		system.New(1000009).
+		system.New(context.TODO(), 1000009).
 			Ensure("/tmp/hakurei.1971", 0711).
 			Ensure("/tmp/hakurei.1971/runtime", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/runtime", acl.Execute).
 			Ensure("/tmp/hakurei.1971/runtime/9", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/runtime/9", acl.Read, acl.Write, acl.Execute).
@@ -183,6 +184,7 @@ var testCasesPd = []sealTestCase{
 				Proc(m("/proc/")).
 				Tmpfs(hst.AbsTmp, 4096, 0755).
 				DevWritable(m("/dev/"), true).
+				Tmpfs(m("/dev/shm"), 0, 01777).
 				Bind(m("/dev/dri"), m("/dev/dri"), container.BindWritable|container.BindDevice|container.BindOptional).
 				Bind(m("/dev/kvm"), m("/dev/kvm"), container.BindWritable|container.BindDevice|container.BindOptional).
 				Readonly(m("/var/run/nscd"), 0755).
@@ -190,7 +192,6 @@ var testCasesPd = []sealTestCase{
 				Tmpfs(m("/run/user/1971"), 8192, 0755).
 				Tmpfs(m("/run/dbus"), 8192, 0755).
 				Remount(m("/dev/"), syscall.MS_RDONLY).
-				Tmpfs(m("/dev/shm"), 0, 01777).
 				Tmpfs(m("/run/user/"), 4096, 0755).
 				Bind(m("/tmp/hakurei.1971/runtime/9"), m("/run/user/65534"), container.BindWritable).
 				Bind(m("/tmp/hakurei.1971/tmpdir/9"), m("/tmp/"), container.BindWritable).

internal/app/app_test.go

@@ -11,18 +11,17 @@ import (
 	"hakurei.app/hst"
 	"hakurei.app/internal/app"
 	"hakurei.app/internal/app/state"
-	"hakurei.app/internal/hlog"
 	"hakurei.app/internal/sys"
 	"hakurei.app/system"
 )
 
 type sealTestCase struct {
-	name          string
-	os            sys.State
-	config        *hst.Config
-	id            state.ID
-	wantSys       *system.I
-	wantContainer *container.Params
+	name       string
+	os         sys.State
+	config     *hst.Config
+	id         state.ID
+	wantSys    *system.I
+	wantParams *container.Params
 }
 
 func TestApp(t *testing.T) {
@@ -30,35 +29,27 @@ func TestApp(t *testing.T) {
 
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
-			a := app.NewWithID(tc.id, tc.os)
-			var (
-				gotSys       *system.I
-				gotContainer *container.Params
-			)
-			if !t.Run("seal", func(t *testing.T) {
-				if sa, err := a.Seal(tc.config); err != nil {
-					hlog.PrintBaseError(err, "got generic error:")
-					t.Errorf("Seal: error = %v", err)
-					return
-				} else {
-					gotSys, gotContainer = app.AppIParams(a, sa)
+			t.Run("finalise", func(t *testing.T) {
+				sys, params, err := app.FinaliseIParams(t.Context(), tc.os, tc.config, &tc.id)
+				if err != nil {
+					if s, ok := container.GetErrorMessage(err); !ok {
+						t.Fatalf("Seal: error = %v", err)
+					} else {
+						t.Fatalf("Seal: %s", s)
+					}
 				}
-			}) {
-				return
-			}
 
-			t.Run("compare sys", func(t *testing.T) {
-				if !gotSys.Equal(tc.wantSys) {
-					t.Errorf("Seal: sys = %#v, want %#v",
-						gotSys, tc.wantSys)
-				}
-			})
+				t.Run("sys", func(t *testing.T) {
+					if !sys.Equal(tc.wantSys) {
+						t.Errorf("Seal: sys = %#v, want %#v", sys, tc.wantSys)
+					}
+				})
 
-			t.Run("compare params", func(t *testing.T) {
-				if !reflect.DeepEqual(gotContainer, tc.wantContainer) {
-					t.Errorf("seal: params =\n%s\n, want\n%s",
-						mustMarshal(gotContainer), mustMarshal(tc.wantContainer))
-				}
+				t.Run("params", func(t *testing.T) {
+					if !reflect.DeepEqual(params, tc.wantParams) {
+						t.Errorf("seal: params =\n%s\n, want\n%s", mustMarshal(params), mustMarshal(tc.wantParams))
+					}
+				})
 			})
 		})
 	}

internal/app/container.go

@@ -11,20 +11,18 @@ import (
 	"hakurei.app/container"
 	"hakurei.app/container/seccomp"
 	"hakurei.app/hst"
-	"hakurei.app/internal/hlog"
 	"hakurei.app/internal/sys"
 	"hakurei.app/system/dbus"
 )
 
-// in practice there should be less than 30 entries added by the runtime;
-// allocating slightly more as a margin for future expansion
+// in practice there should be less than 30 system mount points
 const preallocateOpsCount = 1 << 5
 
 // newContainer initialises [container.Params] via [hst.ContainerConfig].
 // Note that remaining container setup must be queued by the caller.
 func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid *int) (*container.Params, map[string]string, error) {
 	if s == nil {
-		return nil, nil, hlog.WrapErr(syscall.EBADE, "invalid container configuration")
+		return nil, nil, newWithMessage("invalid container configuration")
 	}
 
 	params := &container.Params{
@@ -67,8 +65,6 @@ func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid
 	}
 
 	if s.MapRealUID {
-		/* some programs fail to connect to dbus session running as a different uid
-		so this workaround is introduced to map priv-side caller uid in container */
 		params.Uid = os.Getuid()
 		*uid = params.Uid
 		params.Gid = os.Getgid()
@@ -102,8 +98,11 @@ func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid
 	} else {
 		params.Bind(container.AbsFHSDev, container.AbsFHSDev, container.BindWritable|container.BindDevice)
 	}
+	// /dev is mounted readonly later on, this prevents /dev/shm from going readonly with it
+	params.Tmpfs(container.AbsFHSDev.Append("shm"), 0, 01777)
 
 	/* retrieve paths and hide them if they're made available in the sandbox;
+
 	this feature tries to improve user experience of permissive defaults, and
 	to warn about issues in custom configuration; it is NOT a security feature
 	and should not be treated as such, ALWAYS be careful with what you bind */
@@ -233,9 +232,7 @@ func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid
 
 	// no more ContainerConfig paths beyond this point
 	if !s.Device {
-		params.
-			Remount(container.AbsFHSDev, syscall.MS_RDONLY).
-			Tmpfs(container.AbsFHSDev.Append("shm"), 0, 01777)
+		params.Remount(container.AbsFHSDev, syscall.MS_RDONLY)
 	}
 
 	return params, maps.Clone(s.Env), nil

internal/app/errors.go

@@ -1,181 +0,0 @@
-package app
-
-import (
-	"errors"
-	"log"
-
-	"hakurei.app/internal/hlog"
-)
-
-func PrintRunStateErr(rs *RunState, runErr error) (code int) {
-	code = rs.ExitStatus()
-
-	if runErr != nil {
-		if rs.Time == nil {
-			hlog.PrintBaseError(runErr, "cannot start app:")
-		} else {
-			var e *hlog.BaseError
-			if !hlog.AsBaseError(runErr, &e) {
-				log.Println("wait failed:", runErr)
-			} else {
-				// Wait only returns either *app.ProcessError or *app.StateStoreError wrapped in a *app.BaseError
-				var se *StateStoreError
-				if !errors.As(runErr, &se) {
-					// does not need special handling
-					log.Print(e.Message())
-				} else {
-					// inner error are either unwrapped store errors
-					// or joined errors returned by *appSealTx revert
-					// wrapped in *app.BaseError
-					var ej RevertCompoundError
-					if !errors.As(se.InnerErr, &ej) {
-						// does not require special handling
-						log.Print(e.Message())
-					} else {
-						errs := ej.Unwrap()
-
-						// every error here is wrapped in *app.BaseError
-						for _, ei := range errs {
-							var eb *hlog.BaseError
-							if !errors.As(ei, &eb) {
-								// unreachable
-								log.Println("invalid error type returned by revert:", ei)
-							} else {
-								// print inner *app.BaseError message
-								log.Print(eb.Message())
-							}
-						}
-					}
-				}
-			}
-		}
-
-		if code == 0 {
-			code = 126
-		}
-	}
-
-	if rs.RevertErr != nil {
-		var stateStoreError *StateStoreError
-		if !errors.As(rs.RevertErr, &stateStoreError) || stateStoreError == nil {
-			hlog.PrintBaseError(rs.RevertErr, "generic fault during cleanup:")
-			goto out
-		}
-
-		if stateStoreError.Err != nil {
-			if len(stateStoreError.Err) == 2 {
-				if stateStoreError.Err[0] != nil {
-					if joinedErrs, ok := stateStoreError.Err[0].(interface{ Unwrap() []error }); !ok {
-						hlog.PrintBaseError(stateStoreError.Err[0], "generic fault during revert:")
-					} else {
-						for _, err := range joinedErrs.Unwrap() {
-							if err != nil {
-								hlog.PrintBaseError(err, "fault during revert:")
-							}
-						}
-					}
-				}
-				if stateStoreError.Err[1] != nil {
-					log.Printf("cannot close store: %v", stateStoreError.Err[1])
-				}
-			} else {
-				log.Printf("fault during cleanup: %v",
-					errors.Join(stateStoreError.Err...))
-			}
-		}
-
-		if stateStoreError.OpErr != nil {
-			log.Printf("blind revert due to store fault: %v",
-				stateStoreError.OpErr)
-		}
-
-		if stateStoreError.DoErr != nil {
-			hlog.PrintBaseError(stateStoreError.DoErr, "state store operation unsuccessful:")
-		}
-
-		if stateStoreError.Inner && stateStoreError.InnerErr != nil {
-			hlog.PrintBaseError(stateStoreError.InnerErr, "cannot destroy state entry:")
-		}
-
-	out:
-		if code == 0 {
-			code = 128
-		}
-	}
-	if rs.WaitErr != nil {
-		hlog.Verbosef("wait: %v", rs.WaitErr)
-	}
-	return
-}
-
-// StateStoreError is returned for a failed state save
-type StateStoreError struct {
-	// whether inner function was called
-	Inner bool
-	// returned by the Save/Destroy method of [state.Cursor]
-	InnerErr error
-	// returned by the Do method of [state.Store]
-	DoErr error
-	// stores an arbitrary store operation error
-	OpErr error
-	// stores arbitrary errors
-	Err []error
-}
-
-// save saves arbitrary errors in [StateStoreError] once.
-func (e *StateStoreError) save(errs ...error) {
-	if len(errs) == 0 || e.Err != nil {
-		panic("invalid call to save")
-	}
-	e.Err = errs
-}
-
-func (e *StateStoreError) equiv(a ...any) error {
-	if e.Inner && e.InnerErr == nil && e.DoErr == nil && e.OpErr == nil && errors.Join(e.Err...) == nil {
-		return nil
-	} else {
-		return hlog.WrapErrSuffix(e, a...)
-	}
-}
-
-func (e *StateStoreError) Error() string {
-	if e.Inner && e.InnerErr != nil {
-		return e.InnerErr.Error()
-	}
-	if e.DoErr != nil {
-		return e.DoErr.Error()
-	}
-	if e.OpErr != nil {
-		return e.OpErr.Error()
-	}
-	if err := errors.Join(e.Err...); err != nil {
-		return err.Error()
-	}
-
-	// equiv nullifies e for values where this is reached
-	panic("unreachable")
-}
-
-func (e *StateStoreError) Unwrap() (errs []error) {
-	errs = make([]error, 0, 3)
-	if e.InnerErr != nil {
-		errs = append(errs, e.InnerErr)
-	}
-	if e.DoErr != nil {
-		errs = append(errs, e.DoErr)
-	}
-	if e.OpErr != nil {
-		errs = append(errs, e.OpErr)
-	}
-	if err := errors.Join(e.Err...); err != nil {
-		errs = append(errs, err)
-	}
-	return
-}
-
-// A RevertCompoundError encapsulates errors returned by
-// the Revert method of [system.I].
-type RevertCompoundError interface {
-	Error() string
-	Unwrap() []error
-}

internal/app/export_linux_test.go

@@ -1,24 +0,0 @@
-package app
-
-import (
-	"hakurei.app/container"
-	"hakurei.app/internal/app/state"
-	"hakurei.app/internal/sys"
-	"hakurei.app/system"
-)
-
-func NewWithID(id state.ID, os sys.State) App {
-	a := new(app)
-	a.id = newID(&id)
-	a.sys = os
-	return a
-}
-
-func AppIParams(a App, sa SealedApp) (*system.I, *container.Params) {
-	v := a.(*app)
-	seal := sa.(*outcome)
-	if v.outcome != seal || v.id != seal.id {
-		panic("broken app/outcome link")
-	}
-	return seal.sys, seal.container
-}

internal/app/export_test.go

@@ -0,0 +1,16 @@
+package app
+
+import (
+	"context"
+
+	"hakurei.app/container"
+	"hakurei.app/hst"
+	"hakurei.app/internal/app/state"
+	"hakurei.app/internal/sys"
+	"hakurei.app/system"
+)
+
+func FinaliseIParams(ctx context.Context, k sys.State, config *hst.Config, id *state.ID) (*system.I, *container.Params, error) {
+	seal := outcome{id: &stringPair[state.ID]{*id, id.String()}}
+	return seal.sys, seal.container, seal.finalise(ctx, k, config)
+}

internal/app/process.go

@@ -0,0 +1,339 @@
+package app
+
+import (
+	"context"
+	"encoding/gob"
+	"errors"
+	"log"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+	"syscall"
+	"time"
+
+	"hakurei.app/container"
+	"hakurei.app/internal"
+	"hakurei.app/internal/app/state"
+	"hakurei.app/internal/hlog"
+	"hakurei.app/system"
+)
+
+// duration to wait for shim to exit, after container WaitDelay has elapsed.
+const shimWaitTimeout = 5 * time.Second
+
+// mainState holds persistent state bound to outcome.main.
+type mainState struct {
+	// done is whether beforeExit has been called already.
+	done bool
+
+	// Time is the exact point in time where the process was created.
+	// Location must be set to UTC.
+	//
+	// Time is nil if no process was ever created.
+	Time *time.Time
+
+	seal    *outcome
+	store   state.Store
+	cancel  context.CancelFunc
+	cmd     *exec.Cmd
+	cmdWait chan error
+
+	uintptr
+}
+
+const (
+	// mainNeedsRevert indicates the call to Commit has succeeded.
+	mainNeedsRevert uintptr = 1 << iota
+	// mainNeedsDestroy indicates the instance state entry is present in the store.
+	mainNeedsDestroy
+)
+
+// beforeExit must be called immediately before a call to [os.Exit].
+func (ms mainState) beforeExit(isFault bool) {
+	if ms.done {
+		panic("attempting to call beforeExit twice")
+	}
+	ms.done = true
+	defer hlog.BeforeExit()
+
+	if isFault && ms.cancel != nil {
+		ms.cancel()
+	}
+
+	var hasErr bool
+	// updates hasErr but does not terminate
+	perror := func(err error, message string) {
+		hasErr = true
+		printMessageError("cannot "+message+":", err)
+	}
+	exitCode := 1
+	defer func() {
+		if hasErr {
+			os.Exit(exitCode)
+		}
+	}()
+
+	// this also handles wait for a non-fault termination
+	if ms.cmd != nil && ms.cmdWait != nil {
+		waitDone := make(chan struct{})
+		// TODO(ophestra): enforce this limit early so it does not have to be done twice
+		shimTimeoutCompensated := shimWaitTimeout
+		if ms.seal.waitDelay > MaxShimWaitDelay {
+			shimTimeoutCompensated += MaxShimWaitDelay
+		} else {
+			shimTimeoutCompensated += ms.seal.waitDelay
+		}
+		// this ties waitDone to ctx with the additional compensated timeout duration
+		go func() { <-ms.seal.ctx.Done(); time.Sleep(shimTimeoutCompensated); close(waitDone) }()
+
+		select {
+		case err := <-ms.cmdWait:
+			wstatus, ok := ms.cmd.ProcessState.Sys().(syscall.WaitStatus)
+			if ok {
+				if v := wstatus.ExitStatus(); v != 0 {
+					hasErr = true
+					exitCode = v
+				}
+			}
+
+			if hlog.Load() {
+				if !ok {
+					if err != nil {
+						hlog.Verbosef("wait: %v", err)
+					}
+				} else {
+					switch {
+					case wstatus.Exited():
+						hlog.Verbosef("process %d exited with code %d", ms.cmd.Process.Pid, wstatus.ExitStatus())
+
+					case wstatus.CoreDump():
+						hlog.Verbosef("process %d dumped core", ms.cmd.Process.Pid)
+
+					case wstatus.Signaled():
+						hlog.Verbosef("process %d got %s", ms.cmd.Process.Pid, wstatus.Signal())
+
+					default:
+						hlog.Verbosef("process %d exited with status %#x", ms.cmd.Process.Pid, wstatus)
+					}
+				}
+			}
+
+		case <-waitDone:
+			hlog.Resume()
+			// this is only reachable when shim did not exit within shimWaitTimeout, after its WaitDelay has elapsed.
+			// This is different from the container failing to terminate within its timeout period, as that is enforced
+			// by the shim. This path is instead reached when there is a lockup in shim preventing it from completing.
+			log.Printf("process %d did not terminate", ms.cmd.Process.Pid)
+		}
+
+		hlog.Resume()
+		if ms.seal.sync != nil {
+			if err := ms.seal.sync.Close(); err != nil {
+				perror(err, "close wayland security context")
+			}
+		}
+		if ms.seal.dbusMsg != nil {
+			ms.seal.dbusMsg()
+		}
+	}
+
+	if ms.uintptr&mainNeedsRevert != 0 {
+		if ok, err := ms.store.Do(ms.seal.user.identity.unwrap(), func(c state.Cursor) {
+			if ms.uintptr&mainNeedsDestroy != 0 {
+				if err := c.Destroy(ms.seal.id.unwrap()); err != nil {
+					perror(err, "destroy state entry")
+				}
+			}
+
+			var rt system.Enablement
+			if states, err := c.Load(); err != nil {
+				// it is impossible to continue from this point;
+				// revert per-process state here to limit damage
+				ec := system.Process
+				if revertErr := ms.seal.sys.Revert((*system.Criteria)(&ec)); revertErr != nil {
+					var joinError interface {
+						Unwrap() []error
+						error
+					}
+					if !errors.As(revertErr, &joinError) || joinError == nil {
+						perror(revertErr, "revert system setup")
+					} else {
+						for _, v := range joinError.Unwrap() {
+							perror(v, "revert system setup step")
+						}
+					}
+				}
+				perror(err, "load instance states")
+			} else {
+				ec := system.Process
+				if l := len(states); l == 0 {
+					ec |= system.User
+				} else {
+					hlog.Verbosef("found %d instances, cleaning up without user-scoped operations", l)
+				}
+
+				// accumulate enablements of remaining launchers
+				for i, s := range states {
+					if s.Config != nil {
+						rt |= s.Config.Enablements.Unwrap()
+					} else {
+						log.Printf("state entry %d does not contain config", i)
+					}
+				}
+
+				ec |= rt ^ (system.EWayland | system.EX11 | system.EDBus | system.EPulse)
+				if hlog.Load() {
+					if ec > 0 {
+						hlog.Verbose("reverting operations scope", system.TypeString(ec))
+					}
+				}
+
+				if err = ms.seal.sys.Revert((*system.Criteria)(&ec)); err != nil {
+					perror(err, "revert system setup")
+				}
+			}
+		}); err != nil {
+			if ok {
+				perror(err, "unlock state store")
+			} else {
+				perror(err, "open state store")
+			}
+		}
+	} else if ms.uintptr&mainNeedsDestroy != 0 {
+		panic("unreachable")
+	}
+
+	if ms.store != nil {
+		if err := ms.store.Close(); err != nil {
+			perror(err, "close state store")
+		}
+	}
+}
+
+// fatal calls printMessageError, performs necessary cleanup, followed by a call to [os.Exit](1).
+func (ms mainState) fatal(fallback string, ferr error) {
+	printMessageError(fallback, ferr)
+	ms.beforeExit(true)
+	os.Exit(1)
+}
+
+// main carries out outcome and terminates. main does not return.
+func (seal *outcome) main() {
+	if !seal.f.CompareAndSwap(false, true) {
+		panic("outcome: attempted to run twice")
+	}
+
+	// read comp value early for early failure
+	hsuPath := internal.MustHsuPath()
+
+	// ms.beforeExit required beyond this point
+	ms := &mainState{seal: seal}
+
+	if err := seal.sys.Commit(); err != nil {
+		ms.fatal("cannot commit system setup:", err)
+	}
+	ms.uintptr |= mainNeedsRevert
+	ms.store = state.NewMulti(seal.runDirPath.String())
+
+	ctx, cancel := context.WithCancel(seal.ctx)
+	defer cancel()
+	ms.cancel = cancel
+
+	ms.cmd = exec.CommandContext(ctx, hsuPath)
+	ms.cmd.Stdin, ms.cmd.Stdout, ms.cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
+	ms.cmd.Dir = container.FHSRoot // container init enters final working directory
+	// shim runs in the same session as monitor; see shim.go for behaviour
+	ms.cmd.Cancel = func() error { return ms.cmd.Process.Signal(syscall.SIGCONT) }
+
+	var e *gob.Encoder
+	if fd, encoder, err := container.Setup(&ms.cmd.ExtraFiles); err != nil {
+		ms.fatal("cannot create shim setup pipe:", err)
+	} else {
+		e = encoder
+		ms.cmd.Env = []string{
+			// passed through to shim by hsu
+			shimEnv + "=" + strconv.Itoa(fd),
+			// interpreted by hsu
+			"HAKUREI_APP_ID=" + seal.user.identity.String(),
+		}
+	}
+
+	if len(seal.user.supp) > 0 {
+		hlog.Verbosef("attaching supplementary group ids %s", seal.user.supp)
+		// interpreted by hsu
+		ms.cmd.Env = append(ms.cmd.Env, "HAKUREI_GROUPS="+strings.Join(seal.user.supp, " "))
+	}
+
+	hlog.Verbosef("setuid helper at %s", hsuPath)
+	hlog.Suspend()
+	if err := ms.cmd.Start(); err != nil {
+		ms.fatal("cannot start setuid wrapper:", err)
+	}
+	startTime := time.Now().UTC()
+	ms.cmdWait = make(chan error, 1)
+	// this ties context back to the life of the process
+	go func() { ms.cmdWait <- ms.cmd.Wait(); cancel() }()
+	ms.Time = &startTime
+
+	// unfortunately the I/O here cannot be directly canceled;
+	// the cancellation path leads to fatal in this case so that is fine
+	select {
+	case err := <-func() (setupErr chan error) {
+		setupErr = make(chan error, 1)
+		go func() {
+			setupErr <- e.Encode(&shimParams{
+				os.Getpid(),
+				seal.waitDelay,
+				seal.container,
+				hlog.Load(),
+			})
+		}()
+		return
+	}():
+		if err != nil {
+			hlog.Resume()
+			ms.fatal("cannot transmit shim config:", err)
+		}
+
+	case <-ctx.Done():
+		hlog.Resume()
+		ms.fatal("shim context canceled:", newWithMessageError("shim setup canceled", ctx.Err()))
+	}
+
+	// shim accepted setup payload, create process state
+	if ok, err := ms.store.Do(seal.user.identity.unwrap(), func(c state.Cursor) {
+		if err := c.Save(&state.State{
+			ID:   seal.id.unwrap(),
+			PID:  ms.cmd.Process.Pid,
+			Time: *ms.Time,
+		}, seal.ct); err != nil {
+			ms.fatal("cannot save state entry:", err)
+		}
+	}); err != nil {
+		if ok {
+			ms.uintptr |= mainNeedsDestroy
+			ms.fatal("cannot unlock state store:", err)
+		} else {
+			ms.fatal("cannot open state store:", err)
+		}
+	}
+	// state in store at this point, destroy defunct state entry on termination
+	ms.uintptr |= mainNeedsDestroy
+
+	// beforeExit ties shim process to context
+	ms.beforeExit(false)
+	os.Exit(0)
+}
+
+// printMessageError prints the error message according to [container.GetErrorMessage],
+// or fallback prepended to err if an error message is not available.
+func printMessageError(fallback string, err error) {
+	m, ok := container.GetErrorMessage(err)
+	if !ok {
+		log.Println(fallback, err)
+		return
+	}
+
+	log.Print(m)
+}

internal/app/process_linux.go

@@ -1,201 +0,0 @@
-package app
-
-import (
-	"context"
-	"encoding/gob"
-	"errors"
-	"log"
-	"os"
-	"os/exec"
-	"strconv"
-	"strings"
-	"syscall"
-	"time"
-
-	"hakurei.app/container"
-	"hakurei.app/internal"
-	"hakurei.app/internal/app/state"
-	"hakurei.app/internal/hlog"
-	"hakurei.app/system"
-)
-
-const shimWaitTimeout = 5 * time.Second
-
-func (seal *outcome) Run(rs *RunState) error {
-	if !seal.f.CompareAndSwap(false, true) {
-		// run does much more than just starting a process; calling it twice, even if the first call fails, will result
-		// in inconsistent state that is impossible to clean up; return here to limit damage and hopefully give the
-		// other Run a chance to return
-		return errors.New("outcome: attempted to run twice")
-	}
-
-	if rs == nil {
-		panic("invalid state")
-	}
-
-	// read comp value early to allow for early failure
-	hsuPath := internal.MustHsuPath()
-
-	if err := seal.sys.Commit(seal.ctx); err != nil {
-		return err
-	}
-	store := state.NewMulti(seal.runDirPath.String())
-	deferredStoreFunc := func(c state.Cursor) error { return nil } // noop until state in store
-	defer func() {
-		var revertErr error
-		storeErr := new(StateStoreError)
-		storeErr.Inner, storeErr.DoErr = store.Do(seal.user.aid.unwrap(), func(c state.Cursor) {
-			revertErr = func() error {
-				storeErr.InnerErr = deferredStoreFunc(c)
-
-				var rt system.Enablement
-				ec := system.Process
-				if states, err := c.Load(); err != nil {
-					// revert per-process state here to limit damage
-					storeErr.OpErr = err
-					return seal.sys.Revert((*system.Criteria)(&ec))
-				} else {
-					if l := len(states); l == 0 {
-						ec |= system.User
-					} else {
-						hlog.Verbosef("found %d instances, cleaning up without user-scoped operations", l)
-					}
-
-					// accumulate enablements of remaining launchers
-					for i, s := range states {
-						if s.Config != nil {
-							rt |= s.Config.Enablements.Unwrap()
-						} else {
-							log.Printf("state entry %d does not contain config", i)
-						}
-					}
-				}
-				ec |= rt ^ (system.EWayland | system.EX11 | system.EDBus | system.EPulse)
-				if hlog.Load() {
-					if ec > 0 {
-						hlog.Verbose("reverting operations scope", system.TypeString(ec))
-					}
-				}
-
-				return seal.sys.Revert((*system.Criteria)(&ec))
-			}()
-		})
-		storeErr.save(revertErr, store.Close())
-		rs.RevertErr = storeErr.equiv("error during cleanup:")
-	}()
-
-	ctx, cancel := context.WithCancel(seal.ctx)
-	defer cancel()
-	cmd := exec.CommandContext(ctx, hsuPath)
-	cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
-	cmd.Dir = container.FHSRoot // container init enters final working directory
-	// shim runs in the same session as monitor; see shim.go for behaviour
-	cmd.Cancel = func() error { return cmd.Process.Signal(syscall.SIGCONT) }
-
-	var e *gob.Encoder
-	if fd, encoder, err := container.Setup(&cmd.ExtraFiles); err != nil {
-		return hlog.WrapErrSuffix(err,
-			"cannot create shim setup pipe:")
-	} else {
-		e = encoder
-		cmd.Env = []string{
-			// passed through to shim by hsu
-			shimEnv + "=" + strconv.Itoa(fd),
-			// interpreted by hsu
-			"HAKUREI_APP_ID=" + seal.user.aid.String(),
-		}
-	}
-
-	if len(seal.user.supp) > 0 {
-		hlog.Verbosef("attaching supplementary group ids %s", seal.user.supp)
-		// interpreted by hsu
-		cmd.Env = append(cmd.Env, "HAKUREI_GROUPS="+strings.Join(seal.user.supp, " "))
-	}
-
-	hlog.Verbosef("setuid helper at %s", hsuPath)
-	hlog.Suspend()
-	if err := cmd.Start(); err != nil {
-		return hlog.WrapErrSuffix(err,
-			"cannot start setuid wrapper:")
-	}
-	rs.SetStart()
-
-	// this prevents blocking forever on an early failure
-	waitErr, setupErr := make(chan error, 1), make(chan error, 1)
-	go func() { waitErr <- cmd.Wait(); cancel() }()
-	go func() {
-		setupErr <- e.Encode(&shimParams{
-			os.Getpid(),
-			seal.waitDelay,
-			seal.container,
-			hlog.Load(),
-		})
-	}()
-
-	select {
-	case err := <-setupErr:
-		if err != nil {
-			hlog.Resume()
-			return hlog.WrapErrSuffix(err,
-				"cannot transmit shim config:")
-		}
-
-	case <-ctx.Done():
-		hlog.Resume()
-		return hlog.WrapErr(syscall.ECANCELED,
-			"shim setup canceled")
-	}
-
-	// returned after blocking on waitErr
-	var earlyStoreErr = new(StateStoreError)
-	{
-		// shim accepted setup payload, create process state
-		sd := state.State{
-			ID:   seal.id.unwrap(),
-			PID:  cmd.Process.Pid,
-			Time: *rs.Time,
-		}
-		earlyStoreErr.Inner, earlyStoreErr.DoErr = store.Do(seal.user.aid.unwrap(), func(c state.Cursor) {
-			earlyStoreErr.InnerErr = c.Save(&sd, seal.ct)
-		})
-	}
-
-	// state in store at this point, destroy defunct state entry on return
-	deferredStoreFunc = func(c state.Cursor) error { return c.Destroy(seal.id.unwrap()) }
-
-	waitTimeout := make(chan struct{})
-	go func() { <-seal.ctx.Done(); time.Sleep(shimWaitTimeout); close(waitTimeout) }()
-
-	select {
-	case rs.WaitErr = <-waitErr:
-		rs.WaitStatus = cmd.ProcessState.Sys().(syscall.WaitStatus)
-		if hlog.Load() {
-			switch {
-			case rs.Exited():
-				hlog.Verbosef("process %d exited with code %d", cmd.Process.Pid, rs.ExitStatus())
-			case rs.CoreDump():
-				hlog.Verbosef("process %d dumped core", cmd.Process.Pid)
-			case rs.Signaled():
-				hlog.Verbosef("process %d got %s", cmd.Process.Pid, rs.Signal())
-			default:
-				hlog.Verbosef("process %d exited with status %#x", cmd.Process.Pid, rs.WaitStatus)
-			}
-		}
-	case <-waitTimeout:
-		rs.WaitErr = syscall.ETIMEDOUT
-		hlog.Resume()
-		log.Printf("process %d did not terminate", cmd.Process.Pid)
-	}
-
-	hlog.Resume()
-	if seal.sync != nil {
-		if err := seal.sync.Close(); err != nil {
-			log.Printf("cannot close wayland security context: %v", err)
-		}
-	}
-	if seal.dbusMsg != nil {
-		seal.dbusMsg()
-	}
-
-	return earlyStoreErr.equiv("cannot save process state:")
-}

internal/app/seal.go

@@ -9,8 +9,7 @@ import (
 	"io"
 	"io/fs"
 	"os"
-	"path"
-	"regexp"
+	"os/user"
 	"slices"
 	"strconv"
 	"strings"
@@ -20,7 +19,6 @@ import (
 
 	"hakurei.app/container"
 	"hakurei.app/hst"
-	"hakurei.app/internal"
 	"hakurei.app/internal/app/state"
 	"hakurei.app/internal/hlog"
 	"hakurei.app/internal/sys"
@@ -30,39 +28,12 @@ import (
 	"hakurei.app/system/wayland"
 )
 
-const (
-	home  = "HOME"
-	shell = "SHELL"
+func newWithMessage(msg string) error { return newWithMessageError(msg, os.ErrInvalid) }
+func newWithMessageError(msg string, err error) error {
+	return &hst.AppError{Step: "finalise", Err: err, Msg: msg}
+}
 
-	xdgConfigHome   = "XDG_CONFIG_HOME"
-	xdgRuntimeDir   = "XDG_RUNTIME_DIR"
-	xdgSessionClass = "XDG_SESSION_CLASS"
-	xdgSessionType  = "XDG_SESSION_TYPE"
-
-	term    = "TERM"
-	display = "DISPLAY"
-
-	pulseServer = "PULSE_SERVER"
-	pulseCookie = "PULSE_COOKIE"
-
-	dbusSessionBusAddress = "DBUS_SESSION_BUS_ADDRESS"
-	dbusSystemBusAddress  = "DBUS_SYSTEM_BUS_ADDRESS"
-)
-
-var (
-	ErrIdent = errors.New("invalid identity")
-	ErrName  = errors.New("invalid username")
-
-	ErrXDisplay = errors.New(display + " unset")
-
-	ErrPulseCookie = errors.New("pulse cookie not present")
-	ErrPulseSocket = errors.New("pulse socket not present")
-	ErrPulseMode   = errors.New("unexpected pulse socket mode")
-)
-
-var posixUsername = regexp.MustCompilePOSIX("^[a-z_]([A-Za-z0-9_-]{0,31}|[A-Za-z0-9_-]{0,30}\\$)$")
-
-// outcome stores copies of various parts of [hst.Config]
+// An outcome is the runnable state of a hakurei container via [hst.Config].
 type outcome struct {
 	// copied from initialising [app]
 	id *stringPair[state.ID]
@@ -136,8 +107,7 @@ func (share *shareHost) runtime() *container.Absolute {
 
 // hsuUser stores post-hsu credentials and metadata
 type hsuUser struct {
-	// identity
-	aid *stringPair[int]
+	identity *stringPair[int]
 	// target uid resolved by hid:aid
 	uid *stringPair[int]
 
@@ -150,57 +120,80 @@ type hsuUser struct {
 	username string
 }
 
-func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Config) error {
+func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Config) error {
+	const (
+		home  = "HOME"
+		shell = "SHELL"
+
+		xdgConfigHome   = "XDG_CONFIG_HOME"
+		xdgRuntimeDir   = "XDG_RUNTIME_DIR"
+		xdgSessionClass = "XDG_SESSION_CLASS"
+		xdgSessionType  = "XDG_SESSION_TYPE"
+
+		term    = "TERM"
+		display = "DISPLAY"
+
+		pulseServer = "PULSE_SERVER"
+		pulseCookie = "PULSE_COOKIE"
+
+		dbusSessionBusAddress = "DBUS_SESSION_BUS_ADDRESS"
+		dbusSystemBusAddress  = "DBUS_SYSTEM_BUS_ADDRESS"
+	)
+
+	if ctx == nil {
+		// unreachable
+		panic("invalid call to finalise")
+	}
 	if seal.ctx != nil {
-		panic("finalise called twice")
+		// unreachable
+		panic("attempting to finalise twice")
 	}
 	seal.ctx = ctx
 
 	if config == nil {
-		return hlog.WrapErr(syscall.EINVAL, syscall.EINVAL.Error())
+		// unreachable
+		return newWithMessage("invalid configuration")
 	}
 	if config.Home == nil {
-		return hlog.WrapErr(os.ErrInvalid, "invalid path to home directory")
+		return newWithMessage("invalid path to home directory")
 	}
 
 	{
 		// encode initial configuration for state tracking
 		ct := new(bytes.Buffer)
 		if err := gob.NewEncoder(ct).Encode(config); err != nil {
-			return hlog.WrapErrSuffix(err,
-				"cannot encode initial config:")
+			return &hst.AppError{Step: "encode initial config", Err: err}
 		}
 		seal.ct = ct
 	}
 
-	// allowed aid range 0 to 9999, this is checked again in hsu
+	// allowed identity range 0 to 9999, this is checked again in hsu
 	if config.Identity < 0 || config.Identity > 9999 {
-		return hlog.WrapErr(ErrIdent,
-			fmt.Sprintf("identity %d out of range", config.Identity))
+		return newWithMessage(fmt.Sprintf("identity %d out of range", config.Identity))
 	}
 
 	seal.user = hsuUser{
-		aid:      newInt(config.Identity),
+		identity: newInt(config.Identity),
 		home:     config.Home,
 		username: config.Username,
 	}
+
 	if seal.user.username == "" {
 		seal.user.username = "chronos"
-	} else if !posixUsername.MatchString(seal.user.username) ||
-		len(seal.user.username) >= internal.Sysconf(internal.SC_LOGIN_NAME_MAX) {
-		return hlog.WrapErr(ErrName,
-			fmt.Sprintf("invalid user name %q", seal.user.username))
-	}
-	if u, err := sys.Uid(seal.user.aid.unwrap()); err != nil {
-		return err
-	} else {
-		seal.user.uid = newInt(u)
+	} else if !isValidUsername(seal.user.username) {
+		return newWithMessage(fmt.Sprintf("invalid user name %q", seal.user.username))
 	}
+	seal.user.uid = newInt(sys.MustUid(k, seal.user.identity.unwrap()))
+
 	seal.user.supp = make([]string, len(config.Groups))
 	for i, name := range config.Groups {
-		if g, err := sys.LookupGroup(name); err != nil {
-			return hlog.WrapErr(err,
-				fmt.Sprintf("unknown group %q", name))
+		if g, err := k.LookupGroup(name); err != nil {
+			var unknownGroupError user.UnknownGroupError
+			if errors.As(err, &unknownGroupError) {
+				return newWithMessageError(fmt.Sprintf("unknown group %q", name), unknownGroupError)
+			} else {
+				return &hst.AppError{Step: "look up group by name", Err: err}
+			}
 		} else {
 			seal.user.supp[i] = g.Gid
 		}
@@ -212,7 +205,7 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 
 		if config.Shell == nil {
 			config.Shell = container.AbsFHSRoot.Append("bin", "sh")
-			s, _ := sys.LookupEnv(shell)
+			s, _ := k.LookupEnv(shell)
 			if a, err := container.NewAbs(s); err == nil {
 				config.Shell = a
 			}
@@ -221,10 +214,10 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 		// hsu clears the environment so resolve paths early
 		if config.Path == nil {
 			if len(config.Args) > 0 {
-				if p, err := sys.LookPath(config.Args[0]); err != nil {
-					return hlog.WrapErr(err, err.Error())
+				if p, err := k.LookPath(config.Args[0]); err != nil {
+					return &hst.AppError{Step: "look up executable file", Err: err}
 				} else if config.Path, err = container.NewAbs(p); err != nil {
-					return hlog.WrapErr(err, err.Error())
+					return newWithMessageError(err.Error(), err)
 				}
 			} else {
 				config.Path = config.Shell
@@ -239,7 +232,7 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 
 			Filesystem: []hst.FilesystemConfigJSON{
 				// autoroot, includes the home directory
-				{&hst.FSBind{
+				{FilesystemConfig: &hst.FSBind{
 					Target:  container.AbsFHSRoot,
 					Source:  container.AbsFHSRoot,
 					Write:   true,
@@ -257,7 +250,7 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 
 		// hide nscd from container if present
 		nscd := container.AbsFHSVar.Append("run/nscd")
-		if _, err := sys.Stat(nscd.String()); !errors.Is(err, fs.ErrNotExist) {
+		if _, err := k.Stat(nscd.String()); !errors.Is(err, fs.ErrNotExist) {
 			conf.Filesystem = append(conf.Filesystem, hst.FilesystemConfigJSON{FilesystemConfig: &hst.FSEphemeral{Target: nscd}})
 		}
 
@@ -275,21 +268,20 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 
 	// late nil checks for pd behaviour
 	if config.Shell == nil {
-		return hlog.WrapErr(syscall.EINVAL, "invalid shell path")
+		return newWithMessage("invalid shell path")
 	}
 	if config.Path == nil {
-		return hlog.WrapErr(syscall.EINVAL, "invalid program path")
+		return newWithMessage("invalid program path")
 	}
 
 	var mapuid, mapgid *stringPair[int]
 	{
 		var uid, gid int
 		var err error
-		seal.container, seal.env, err = newContainer(config.Container, sys, seal.id.String(), &uid, &gid)
+		seal.container, seal.env, err = newContainer(config.Container, k, seal.id.String(), &uid, &gid)
 		seal.waitDelay = config.Container.WaitDelay
 		if err != nil {
-			return hlog.WrapErrSuffix(err,
-				"cannot initialise container configuration:")
+			return &hst.AppError{Step: "initialise container configuration", Err: err}
 		}
 		if len(config.Args) == 0 {
 			config.Args = []string{config.Path.String()}
@@ -310,16 +302,16 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 	seal.env[xdgSessionClass] = "user"
 	seal.env[xdgSessionType] = "tty"
 
-	share := &shareHost{seal: seal, sc: sys.Paths()}
+	share := &shareHost{seal: seal, sc: k.Paths()}
 	seal.runDirPath = share.sc.RunDirPath
-	seal.sys = system.New(seal.user.uid.unwrap())
+	seal.sys = system.New(seal.ctx, seal.user.uid.unwrap())
 	seal.sys.Ensure(share.sc.SharePath.String(), 0711)
 
 	{
 		runtimeDir := share.sc.SharePath.Append("runtime")
 		seal.sys.Ensure(runtimeDir.String(), 0700)
 		seal.sys.UpdatePermType(system.User, runtimeDir.String(), acl.Execute)
-		runtimeDirInst := runtimeDir.Append(seal.user.aid.String())
+		runtimeDirInst := runtimeDir.Append(seal.user.identity.String())
 		seal.sys.Ensure(runtimeDirInst.String(), 0700)
 		seal.sys.UpdatePermType(system.User, runtimeDirInst.String(), acl.Read, acl.Write, acl.Execute)
 		seal.container.Tmpfs(container.AbsFHSRunUser, 1<<12, 0755)
@@ -330,7 +322,7 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 		tmpdir := share.sc.SharePath.Append("tmpdir")
 		seal.sys.Ensure(tmpdir.String(), 0700)
 		seal.sys.UpdatePermType(system.User, tmpdir.String(), acl.Execute)
-		tmpdirInst := tmpdir.Append(seal.user.aid.String())
+		tmpdirInst := tmpdir.Append(seal.user.identity.String())
 		seal.sys.Ensure(tmpdirInst.String(), 01700)
 		seal.sys.UpdatePermType(system.User, tmpdirInst.String(), acl.Read, acl.Write, acl.Execute)
 		// mount inner /tmp from share so it shares persistence and storage behaviour of host /tmp
@@ -354,14 +346,14 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 	}
 
 	// pass TERM for proper terminal I/O in initial process
-	if t, ok := sys.LookupEnv(term); ok {
+	if t, ok := k.LookupEnv(term); ok {
 		seal.env[term] = t
 	}
 
 	if config.Enablements.Unwrap()&system.EWayland != 0 {
 		// outer wayland socket (usually `/run/user/%d/wayland-%d`)
 		var socketPath *container.Absolute
-		if name, ok := sys.LookupEnv(wayland.WaylandDisplay); !ok {
+		if name, ok := k.LookupEnv(wayland.WaylandDisplay); !ok {
 			hlog.Verbose(wayland.WaylandDisplay + " is not set, assuming " + wayland.FallbackName)
 			socketPath = share.sc.RuntimePath.Append(wayland.FallbackName)
 		} else if a, err := container.NewAbs(name); err != nil {
@@ -392,9 +384,8 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 	}
 
 	if config.Enablements.Unwrap()&system.EX11 != 0 {
-		if d, ok := sys.LookupEnv(display); !ok {
-			return hlog.WrapErr(ErrXDisplay,
-				"DISPLAY is not set")
+		if d, ok := k.LookupEnv(display); !ok {
+			return newWithMessage("DISPLAY is not set")
 		} else {
 			socketDir := container.AbsFHSTmp.Append(".X11-unix")
 
@@ -411,14 +402,15 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 				}
 			}
 			if socketPath != nil {
-				if _, err := sys.Stat(socketPath.String()); err != nil {
+				if _, err := k.Stat(socketPath.String()); err != nil {
 					if !errors.Is(err, fs.ErrNotExist) {
-						return hlog.WrapErrSuffix(err,
-							fmt.Sprintf("cannot access X11 socket %q:", socketPath))
+						return &hst.AppError{Step: fmt.Sprintf("access X11 socket %q", socketPath), Err: err}
 					}
 				} else {
 					seal.sys.UpdatePermType(system.EX11, socketPath.String(), acl.Read, acl.Write, acl.Execute)
-					d = "unix:" + socketPath.String()
+					if !config.Container.HostAbstract {
+						d = "unix:" + socketPath.String()
+					}
 				}
 			}
 
@@ -434,26 +426,21 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 		// PulseAudio socket (usually `/run/user/%d/pulse/native`)
 		pulseSocket := pulseRuntimeDir.Append("native")
 
-		if _, err := sys.Stat(pulseRuntimeDir.String()); err != nil {
+		if _, err := k.Stat(pulseRuntimeDir.String()); err != nil {
 			if !errors.Is(err, fs.ErrNotExist) {
-				return hlog.WrapErrSuffix(err,
-					fmt.Sprintf("cannot access PulseAudio directory %q:", pulseRuntimeDir))
+				return &hst.AppError{Step: fmt.Sprintf("access PulseAudio directory %q", pulseRuntimeDir), Err: err}
 			}
-			return hlog.WrapErr(ErrPulseSocket,
-				fmt.Sprintf("PulseAudio directory %q not found", pulseRuntimeDir))
+			return newWithMessage(fmt.Sprintf("PulseAudio directory %q not found", pulseRuntimeDir))
 		}
 
-		if s, err := sys.Stat(pulseSocket.String()); err != nil {
+		if s, err := k.Stat(pulseSocket.String()); err != nil {
 			if !errors.Is(err, fs.ErrNotExist) {
-				return hlog.WrapErrSuffix(err,
-					fmt.Sprintf("cannot access PulseAudio socket %q:", pulseSocket))
+				return &hst.AppError{Step: fmt.Sprintf("access PulseAudio socket %q", pulseSocket), Err: err}
 			}
-			return hlog.WrapErr(ErrPulseSocket,
-				fmt.Sprintf("PulseAudio directory %q found but socket does not exist", pulseRuntimeDir))
+			return newWithMessage(fmt.Sprintf("PulseAudio directory %q found but socket does not exist", pulseRuntimeDir))
 		} else {
 			if m := s.Mode(); m&0o006 != 0o006 {
-				return hlog.WrapErr(ErrPulseMode,
-					fmt.Sprintf("unexpected permissions on %q:", pulseSocket), m)
+				return newWithMessage(fmt.Sprintf("unexpected permissions on %q: %s", pulseSocket, m))
 			}
 		}
 
@@ -465,15 +452,75 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 		seal.env[pulseServer] = "unix:" + innerPulseSocket.String()
 
 		// publish current user's pulse cookie for target user
-		if src, err := discoverPulseCookie(sys); err != nil {
-			// not fatal
-			hlog.Verbose(strings.TrimSpace(err.(*hlog.BaseError).Message()))
-		} else {
+		var paCookiePath *container.Absolute
+		{
+			const paLocateStep = "locate PulseAudio cookie"
+
+			// from environment
+			if p, ok := k.LookupEnv(pulseCookie); ok {
+				if a, err := container.NewAbs(p); err != nil {
+					return &hst.AppError{Step: paLocateStep, Err: err}
+				} else {
+					// this takes precedence, do not verify whether the file is accessible
+					paCookiePath = a
+					goto out
+				}
+			}
+
+			// $HOME/.pulse-cookie
+			if p, ok := k.LookupEnv(home); ok {
+				if a, err := container.NewAbs(p); err != nil {
+					return &hst.AppError{Step: paLocateStep, Err: err}
+				} else {
+					paCookiePath = a.Append(".pulse-cookie")
+				}
+
+				if s, err := k.Stat(paCookiePath.String()); err != nil {
+					paCookiePath = nil
+					if !errors.Is(err, fs.ErrNotExist) {
+						return &hst.AppError{Step: "access PulseAudio cookie", Err: err}
+					}
+					// fallthrough
+				} else if s.IsDir() {
+					paCookiePath = nil
+				} else {
+					goto out
+				}
+			}
+
+			// $XDG_CONFIG_HOME/pulse/cookie
+			if p, ok := k.LookupEnv(xdgConfigHome); ok {
+				if a, err := container.NewAbs(p); err != nil {
+					return &hst.AppError{Step: paLocateStep, Err: err}
+				} else {
+					paCookiePath = a.Append("pulse", "cookie")
+				}
+				if s, err := k.Stat(paCookiePath.String()); err != nil {
+					paCookiePath = nil
+					if !errors.Is(err, fs.ErrNotExist) {
+						return &hst.AppError{Step: "access PulseAudio cookie", Err: err}
+					}
+					// fallthrough
+				} else if s.IsDir() {
+					paCookiePath = nil
+				} else {
+					goto out
+				}
+			}
+		out:
+		}
+
+		if paCookiePath != nil {
 			innerDst := hst.AbsTmp.Append("/pulse-cookie")
 			seal.env[pulseCookie] = innerDst.String()
 			var payload *[]byte
 			seal.container.PlaceP(innerDst, &payload)
-			seal.sys.CopyFile(payload, src, 256, 256)
+			seal.sys.CopyFile(payload, paCookiePath.String(), 256, 256)
+		} else {
+			hlog.Verbose("cannot locate PulseAudio cookie (tried " +
+				"$PULSE_COOKIE, " +
+				"$XDG_CONFIG_HOME/pulse/cookie, " +
+				"$HOME/.pulse-cookie)")
 		}
 	}
 
@@ -539,8 +586,8 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 	seal.container.Env = make([]string, 0, len(seal.env))
 	for k, v := range seal.env {
 		if strings.IndexByte(k, '=') != -1 {
-			return hlog.WrapErr(syscall.EINVAL,
-				fmt.Sprintf("invalid environment variable %s", k))
+			return &hst.AppError{Step: "flatten environment", Err: syscall.EINVAL,
+				Msg: fmt.Sprintf("invalid environment variable %s", k)}
 		}
 		seal.container.Env = append(seal.container.Env, k+"="+v)
 	}
@@ -553,42 +600,3 @@ func (seal *outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 
 	return nil
 }
-
-// discoverPulseCookie attempts various standard methods to discover the current user's PulseAudio authentication cookie
-func discoverPulseCookie(sys sys.State) (string, error) {
-	if p, ok := sys.LookupEnv(pulseCookie); ok {
-		return p, nil
-	}
-
-	// dotfile $HOME/.pulse-cookie
-	if p, ok := sys.LookupEnv(home); ok {
-		p = path.Join(p, ".pulse-cookie")
-		if s, err := sys.Stat(p); err != nil {
-			if !errors.Is(err, fs.ErrNotExist) {
-				return p, hlog.WrapErrSuffix(err,
-					fmt.Sprintf("cannot access PulseAudio cookie %q:", p))
-			}
-			// not found, try next method
-		} else if !s.IsDir() {
-			return p, nil
-		}
-	}
-
-	// $XDG_CONFIG_HOME/pulse/cookie
-	if p, ok := sys.LookupEnv(xdgConfigHome); ok {
-		p = path.Join(p, "pulse", "cookie")
-		if s, err := sys.Stat(p); err != nil {
-			if !errors.Is(err, fs.ErrNotExist) {
-				return p, hlog.WrapErrSuffix(err,
-					fmt.Sprintf("cannot access PulseAudio cookie %q:", p))
-			}
-			// not found, try next method
-		} else if !s.IsDir() {
-			return p, nil
-		}
-	}
-
-	return "", hlog.WrapErr(ErrPulseCookie,
-		fmt.Sprintf("cannot locate PulseAudio cookie (tried $%s, $%s/pulse/cookie, $%s/.pulse-cookie)",
-			pulseCookie, xdgConfigHome, home))
-}

internal/app/shim.go

@@ -45,8 +45,10 @@ const (
 	// ShimExitOrphan is returned when the shim is orphaned before monitor delivers a signal.
 	ShimExitOrphan = 3
 
+	// DefaultShimWaitDelay is used when WaitDelay has its zero value.
 	DefaultShimWaitDelay = 5 * time.Second
-	MaxShimWaitDelay     = 30 * time.Second
+	// MaxShimWaitDelay is used instead if WaitDelay exceeds its value.
+	MaxShimWaitDelay = 30 * time.Second
 )
 
 // ShimMain is the main function of the shim process and runs as the unconstrained target user.
@@ -65,7 +67,7 @@ func ShimMain() {
 		if errors.Is(err, syscall.EBADF) {
 			log.Fatal("invalid config descriptor")
 		}
-		if errors.Is(err, container.ErrNotSet) {
+		if errors.Is(err, container.ErrReceiveEnv) {
 			log.Fatal("HAKUREI_SHIM not set")
 		}
 
@@ -155,11 +157,11 @@ func ShimMain() {
 	}
 
 	if err := z.Start(); err != nil {
-		hlog.PrintBaseError(err, "cannot start container:")
+		printMessageError("cannot start container:", err)
 		os.Exit(1)
 	}
 	if err := z.Serve(); err != nil {
-		hlog.PrintBaseError(err, "cannot configure container:")
+		printMessageError("cannot configure container:", err)
 	}
 
 	if err := seccomp.Load(

internal/app/state/multi.go

@@ -27,27 +27,27 @@ type multiStore struct {
 	lock sync.RWMutex
 }
 
-func (s *multiStore) Do(aid int, f func(c Cursor)) (bool, error) {
+func (s *multiStore) Do(identity int, f func(c Cursor)) (bool, error) {
 	s.lock.RLock()
 	defer s.lock.RUnlock()
 
 	// load or initialise new backend
 	b := new(multiBackend)
 	b.lock.Lock()
-	if v, ok := s.backends.LoadOrStore(aid, b); ok {
+	if v, ok := s.backends.LoadOrStore(identity, b); ok {
 		b = v.(*multiBackend)
 	} else {
-		b.path = path.Join(s.base, strconv.Itoa(aid))
+		b.path = path.Join(s.base, strconv.Itoa(identity))
 
 		// ensure directory
 		if err := os.MkdirAll(b.path, 0700); err != nil && !errors.Is(err, fs.ErrExist) {
-			s.backends.CompareAndDelete(aid, b)
+			s.backends.CompareAndDelete(identity, b)
 			return false, err
 		}
 
 		// open locker file
 		if l, err := os.OpenFile(b.path+".lock", os.O_RDWR|os.O_CREATE, 0600); err != nil {
-			s.backends.CompareAndDelete(aid, b)
+			s.backends.CompareAndDelete(identity, b)
 			return false, err
 		} else {
 			b.lockfile = l

internal/app/state/state.go

@@ -17,7 +17,7 @@ type Store interface {
 	// Do calls f exactly once and ensures store exclusivity until f returns.
 	// Returns whether f is called and any errors during the locking process.
 	// Cursor provided to f becomes invalid as soon as f returns.
-	Do(aid int, f func(c Cursor)) (ok bool, err error)
+	Do(identity int, f func(c Cursor)) (ok bool, err error)
 
 	// List queries the store and returns a list of aids known to the store.
 	// Note that some or all returned aids might not have any active apps.

internal/app/strings.go

@@ -2,12 +2,9 @@ package app
 
 import (
 	"strconv"
-
-	"hakurei.app/internal/app/state"
 )
 
-func newInt(v int) *stringPair[int]            { return &stringPair[int]{v, strconv.Itoa(v)} }
-func newID(id *state.ID) *stringPair[state.ID] { return &stringPair[state.ID]{*id, id.String()} }
+func newInt(v int) *stringPair[int] { return &stringPair[int]{v, strconv.Itoa(v)} }
 
 // stringPair stores a value and its string representation.
 type stringPair[T comparable] struct {

internal/app/sysconf.go

@@ -0,0 +1,8 @@
+package app
+
+//#include <unistd.h>
+import "C"
+
+const _SC_LOGIN_NAME_MAX = C._SC_LOGIN_NAME_MAX
+
+func sysconf(name C.int) int { return int(C.sysconf(name)) }

internal/app/username.go

@@ -0,0 +1,12 @@
+package app
+
+import "regexp"
+
+// nameRegex is the default NAME_REGEX value from adduser.
+var nameRegex = regexp.MustCompilePOSIX(`^[a-zA-Z][a-zA-Z0-9_-]*\$?$`)
+
+// isValidUsername returns whether the argument is a valid username
+func isValidUsername(username string) bool {
+	return len(username) < sysconf(_SC_LOGIN_NAME_MAX) &&
+		nameRegex.MatchString(username)
+}

internal/hlog/errors.go

@@ -1,81 +0,0 @@
-package hlog
-
-import (
-	"fmt"
-	"log"
-	"reflect"
-	"strings"
-)
-
-// baseError implements a basic error container
-type baseError struct {
-	Err error
-}
-
-func (e *baseError) Error() string { return e.Err.Error() }
-func (e *baseError) Unwrap() error { return e.Err }
-
-// BaseError implements an error container with a user-facing message
-type BaseError struct {
-	message string
-	baseError
-}
-
-// Message returns a user-facing error message
-func (e *BaseError) Message() string { return e.message }
-
-// WrapErr wraps an error with a corresponding message.
-func WrapErr(err error, a ...any) error {
-	if err == nil {
-		return nil
-	}
-	return wrapErr(err, fmt.Sprintln(a...))
-}
-
-// WrapErrSuffix wraps an error with a corresponding message with err at the end of the message.
-func WrapErrSuffix(err error, a ...any) error {
-	if err == nil {
-		return nil
-	}
-	return wrapErr(err, fmt.Sprintln(append(a, err)...))
-}
-
-// WrapErrFunc wraps an error with a corresponding message returned by f.
-func WrapErrFunc(err error, f func(err error) string) error {
-	if err == nil {
-		return nil
-	}
-	return wrapErr(err, f(err))
-}
-
-func wrapErr(err error, message string) *BaseError {
-	return &BaseError{message, baseError{err}}
-}
-
-var (
-	baseErrorType = reflect.TypeFor[*BaseError]()
-)
-
-func AsBaseError(err error, target **BaseError) bool {
-	v := reflect.ValueOf(err)
-	if !v.CanConvert(baseErrorType) {
-		return false
-	}
-
-	*target = v.Convert(baseErrorType).Interface().(*BaseError)
-	return true
-}
-
-func PrintBaseError(err error, fallback string) {
-	var e *BaseError
-
-	if AsBaseError(err, &e) {
-		if msg := e.Message(); strings.TrimSpace(msg) != "" {
-			log.Print(msg)
-			return
-		}
-		Verbose("*"+fallback, err)
-		return
-	}
-	log.Println(fallback, err)
-}

internal/hlog/msg.go

@@ -2,11 +2,9 @@ package hlog
 
 type Output struct{}
 
-func (Output) IsVerbose() bool                         { return Load() }
-func (Output) Verbose(v ...any)                        { Verbose(v...) }
-func (Output) Verbosef(format string, v ...any)        { Verbosef(format, v...) }
-func (Output) WrapErr(err error, a ...any) error       { return WrapErr(err, a...) }
-func (Output) PrintBaseErr(err error, fallback string) { PrintBaseError(err, fallback) }
-func (Output) Suspend()                                { Suspend() }
-func (Output) Resume() bool                            { return Resume() }
-func (Output) BeforeExit()                             { BeforeExit() }
+func (Output) IsVerbose() bool                  { return Load() }
+func (Output) Verbose(v ...any)                 { Verbose(v...) }
+func (Output) Verbosef(format string, v ...any) { Verbosef(format, v...) }
+func (Output) Suspend()                         { Suspend() }
+func (Output) Resume() bool                     { return Resume() }
+func (Output) BeforeExit()                      { BeforeExit() }

internal/sys/hsu.go

@@ -0,0 +1,104 @@
+package sys
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"strconv"
+	"sync"
+
+	"hakurei.app/container"
+	"hakurei.app/hst"
+	"hakurei.app/internal"
+	"hakurei.app/internal/hlog"
+)
+
+// Hsu caches responses from cmd/hsu.
+type Hsu struct {
+	uidOnce sync.Once
+	uidCopy map[int]struct {
+		uid int
+		err error
+	}
+	uidMu sync.RWMutex
+}
+
+var ErrHsuAccess = errors.New("current user is not in the hsurc file")
+
+func (h *Hsu) Uid(identity int) (int, error) {
+	h.uidOnce.Do(func() {
+		h.uidCopy = make(map[int]struct {
+			uid int
+			err error
+		})
+	})
+
+	{
+		h.uidMu.RLock()
+		u, ok := h.uidCopy[identity]
+		h.uidMu.RUnlock()
+		if ok {
+			return u.uid, u.err
+		}
+	}
+
+	h.uidMu.Lock()
+	defer h.uidMu.Unlock()
+
+	u := struct {
+		uid int
+		err error
+	}{}
+	defer func() { h.uidCopy[identity] = u }()
+
+	u.uid = -1
+	hsuPath := internal.MustHsuPath()
+
+	cmd := exec.Command(hsuPath)
+	cmd.Path = hsuPath
+	cmd.Stderr = os.Stderr // pass through fatal messages
+	cmd.Env = []string{"HAKUREI_APP_ID=" + strconv.Itoa(identity)}
+	cmd.Dir = container.FHSRoot
+	var (
+		p         []byte
+		exitError *exec.ExitError
+	)
+
+	const step = "obtain uid from hsu"
+	if p, u.err = cmd.Output(); u.err == nil {
+		u.uid, u.err = strconv.Atoi(string(p))
+		if u.err != nil {
+			u.err = &hst.AppError{Step: step, Err: u.err, Msg: "invalid uid string from hsu"}
+		}
+	} else if errors.As(u.err, &exitError) && exitError != nil && exitError.ExitCode() == 1 {
+		// hsu prints an error message in this case
+		u.err = &hst.AppError{Step: step, Err: ErrHsuAccess}
+	} else if os.IsNotExist(u.err) {
+		u.err = &hst.AppError{Step: step, Err: os.ErrNotExist,
+			Msg: fmt.Sprintf("the setuid helper is missing: %s", hsuPath)}
+	}
+	return u.uid, u.err
+}
+
+// MustUid calls [State.Uid] and terminates on error.
+func MustUid(s State, identity int) int {
+	uid, err := s.Uid(identity)
+	if err == nil {
+		return uid
+	}
+
+	const fallback = "cannot obtain uid from setuid wrapper:"
+	if errors.Is(err, ErrHsuAccess) {
+		hlog.Verbose("*"+fallback, err)
+		os.Exit(1)
+		return -0xdeadbeef
+	} else if m, ok := container.GetErrorMessage(err); ok {
+		log.Fatal(m)
+		return -0xdeadbeef
+	} else {
+		log.Fatalln(fallback, err)
+		return -0xdeadbeef
+	}
+}

internal/sys/interface.go

@@ -49,14 +49,8 @@ type State interface {
 	Uid(identity int) (int, error)
 }
 
-// GetUserID obtains user id from hsu by querying uid of identity 0.
-func GetUserID(os State) (int, error) {
-	if uid, err := os.Uid(0); err != nil {
-		return -1, err
-	} else {
-		return (uid / 10000) - 100, nil
-	}
-}
+// MustGetUserID obtains user id from hsu by querying uid of identity 0.
+func MustGetUserID(os State) int { return (MustUid(os, 0) / 10000) - 100 }
 
 // CopyPaths is a generic implementation of [hst.Paths].
 func CopyPaths(os State, v *hst.Paths, userid int) {

internal/sys/std.go

@@ -1,16 +1,12 @@
 package sys
 
 import (
-	"errors"
-	"fmt"
 	"io/fs"
 	"os"
 	"os/exec"
 	"os/user"
 	"path/filepath"
-	"strconv"
 	"sync"
-	"syscall"
 
 	"hakurei.app/container"
 	"hakurei.app/hst"
@@ -22,13 +18,7 @@ import (
 type Std struct {
 	paths     hst.Paths
 	pathsOnce sync.Once
-
-	uidOnce sync.Once
-	uidCopy map[int]struct {
-		uid int
-		err error
-	}
-	uidMu sync.RWMutex
+	Hsu
 }
 
 func (s *Std) Getuid() int                                  { return os.Getuid() }
@@ -49,66 +39,6 @@ func (s *Std) Printf(format string, v ...any)               { hlog.Verbosef(form
 const xdgRuntimeDir = "XDG_RUNTIME_DIR"
 
 func (s *Std) Paths() hst.Paths {
-	s.pathsOnce.Do(func() {
-		if userid, err := GetUserID(s); err != nil {
-			hlog.PrintBaseError(err, "cannot obtain user id from hsu:")
-			hlog.BeforeExit()
-			s.Exit(1)
-		} else {
-			CopyPaths(s, &s.paths, userid)
-		}
-	})
+	s.pathsOnce.Do(func() { CopyPaths(s, &s.paths, MustGetUserID(s)) })
 	return s.paths
 }
-
-func (s *Std) Uid(identity int) (int, error) {
-	s.uidOnce.Do(func() {
-		s.uidCopy = make(map[int]struct {
-			uid int
-			err error
-		})
-	})
-
-	{
-		s.uidMu.RLock()
-		u, ok := s.uidCopy[identity]
-		s.uidMu.RUnlock()
-		if ok {
-			return u.uid, u.err
-		}
-	}
-
-	s.uidMu.Lock()
-	defer s.uidMu.Unlock()
-
-	u := struct {
-		uid int
-		err error
-	}{}
-	defer func() { s.uidCopy[identity] = u }()
-
-	u.uid = -1
-	hsuPath := internal.MustHsuPath()
-
-	cmd := exec.Command(hsuPath)
-	cmd.Path = hsuPath
-	cmd.Stderr = os.Stderr // pass through fatal messages
-	cmd.Env = []string{"HAKUREI_APP_ID=" + strconv.Itoa(identity)}
-	cmd.Dir = container.FHSRoot
-	var (
-		p         []byte
-		exitError *exec.ExitError
-	)
-
-	if p, u.err = cmd.Output(); u.err == nil {
-		u.uid, u.err = strconv.Atoi(string(p))
-		if u.err != nil {
-			u.err = hlog.WrapErr(u.err, "invalid uid string from hsu")
-		}
-	} else if errors.As(u.err, &exitError) && exitError != nil && exitError.ExitCode() == 1 {
-		u.err = hlog.WrapErr(syscall.EACCES, "") // hsu prints to stderr in this case
-	} else if os.IsNotExist(u.err) {
-		u.err = hlog.WrapErr(os.ErrNotExist, fmt.Sprintf("the setuid helper is missing: %s", hsuPath))
-	}
-	return u.uid, u.err
-}

internal/sysconf.go

@@ -1,8 +0,0 @@
-package internal
-
-//#include <unistd.h>
-import "C"
-
-const SC_LOGIN_NAME_MAX = C._SC_LOGIN_NAME_MAX
-
-func Sysconf(name C.int) int { return int(C.sysconf(name)) }

options.nix

@@ -203,7 +203,7 @@ in
               };
 
               extraPaths = mkOption {
-                type = anything;
+                type = listOf (attrsOf anything);
                 default = [ ];
                 description = ''
                   Extra paths to make available to the container.
@@ -261,7 +261,7 @@ in
       };
 
       commonPaths = mkOption {
-        type = types.anything;
+        type = types.listOf (types.attrsOf types.anything);
         default = [ ];
         description = ''
           Common extra paths to make available to the container.

system/acl.go

@@ -9,65 +9,59 @@ import (
 	"hakurei.app/system/acl"
 )
 
-// UpdatePerm appends an ephemeral acl update Op.
+// UpdatePerm calls UpdatePermType with the [Process] criteria.
 func (sys *I) UpdatePerm(path string, perms ...acl.Perm) *I {
 	sys.UpdatePermType(Process, path, perms...)
-
 	return sys
 }
 
-// UpdatePermType appends an acl update Op.
+// UpdatePermType maintains [acl.Perms] on a file until its [Enablement] is no longer satisfied.
 func (sys *I) UpdatePermType(et Enablement, path string, perms ...acl.Perm) *I {
-	sys.lock.Lock()
-	defer sys.lock.Unlock()
-
-	sys.ops = append(sys.ops, &ACL{et, path, perms})
-
+	sys.ops = append(sys.ops, &aclUpdateOp{et, path, perms})
 	return sys
 }
 
-type ACL struct {
+// aclUpdateOp implements [I.UpdatePermType].
+type aclUpdateOp struct {
 	et    Enablement
 	path  string
 	perms acl.Perms
 }
 
-func (a *ACL) Type() Enablement { return a.et }
+func (a *aclUpdateOp) Type() Enablement { return a.et }
 
-func (a *ACL) apply(sys *I) error {
-	msg.Verbose("applying ACL", a)
-	return wrapErrSuffix(acl.Update(a.path, sys.uid, a.perms...),
-		fmt.Sprintf("cannot apply ACL entry to %q:", a.path))
+func (a *aclUpdateOp) apply(sys *I) error {
+	sys.verbose("applying ACL", a)
+	return newOpError("acl", sys.aclUpdate(a.path, sys.uid, a.perms...), false)
 }
 
-func (a *ACL) revert(sys *I, ec *Criteria) error {
-	if ec.hasType(a) {
-		msg.Verbose("stripping ACL", a)
-		err := acl.Update(a.path, sys.uid)
+func (a *aclUpdateOp) revert(sys *I, ec *Criteria) error {
+	if ec.hasType(a.Type()) {
+		sys.verbose("stripping ACL", a)
+		err := sys.aclUpdate(a.path, sys.uid)
 		if errors.Is(err, os.ErrNotExist) {
 			// the ACL is effectively stripped if the file no longer exists
-			msg.Verbosef("target of ACL %s no longer exists", a)
+			sys.verbosef("target of ACL %s no longer exists", a)
 			err = nil
 		}
-		return wrapErrSuffix(err,
-			fmt.Sprintf("cannot strip ACL entry from %q:", a.path))
+		return newOpError("acl", err, true)
 	} else {
-		msg.Verbose("skipping ACL", a)
+		sys.verbose("skipping ACL", a)
 		return nil
 	}
 }
 
-func (a *ACL) Is(o Op) bool {
-	a0, ok := o.(*ACL)
-	return ok && a0 != nil &&
-		a.et == a0.et &&
-		a.path == a0.path &&
-		slices.Equal(a.perms, a0.perms)
+func (a *aclUpdateOp) Is(o Op) bool {
+	target, ok := o.(*aclUpdateOp)
+	return ok && a != nil && target != nil &&
+		a.et == target.et &&
+		a.path == target.path &&
+		slices.Equal(a.perms, target.perms)
 }
 
-func (a *ACL) Path() string { return a.path }
+func (a *aclUpdateOp) Path() string { return a.path }
 
-func (a *ACL) String() string {
+func (a *aclUpdateOp) String() string {
 	return fmt.Sprintf("%s type: %s path: %q",
 		a.perms, TypeString(a.et), a.path)
 }

system/acl/acl.go

@@ -29,8 +29,5 @@ func Update(name string, uid int, perms ...Perm) error {
 		(*C.acl_perm_t)(p),
 		C.size_t(len(perms)),
 	)
-	if r == 0 {
-		return nil
-	}
-	return err
+	return newAclPathError(name, int(r), err)
 }

system/acl/acl_getfacl_test.go

@@ -1,156 +0,0 @@
-package acl_test
-
-import (
-	"bufio"
-	"bytes"
-	"errors"
-	"fmt"
-	"io"
-	"os/exec"
-	"strconv"
-)
-
-type (
-	getFAclInvocation struct {
-		cmd *exec.Cmd
-		val []*getFAclResp
-		pe  []error
-	}
-
-	getFAclResp struct {
-		typ  fAclType
-		cred int32
-		val  fAclPerm
-
-		raw []byte
-	}
-
-	fAclPerm uintptr
-	fAclType uint8
-)
-
-const fAclBufSize = 16
-
-const (
-	fAclPermRead fAclPerm = 1 << iota
-	fAclPermWrite
-	fAclPermExecute
-)
-
-const (
-	fAclTypeUser fAclType = iota
-	fAclTypeGroup
-	fAclTypeMask
-	fAclTypeOther
-)
-
-func (c *getFAclInvocation) run(name string) error {
-	if c.cmd != nil {
-		panic("attempted to run twice")
-	}
-
-	c.cmd = exec.Command("getfacl", "--omit-header", "--absolute-names", "--numeric", name)
-
-	scanErr := make(chan error, 1)
-	if p, err := c.cmd.StdoutPipe(); err != nil {
-		return err
-	} else {
-		go c.parse(p, scanErr)
-	}
-
-	if err := c.cmd.Start(); err != nil {
-		return err
-	}
-
-	return errors.Join(<-scanErr, c.cmd.Wait())
-}
-
-func (c *getFAclInvocation) parse(pipe io.Reader, scanErr chan error) {
-	c.val = make([]*getFAclResp, 0, 4+fAclBufSize)
-
-	s := bufio.NewScanner(pipe)
-	for s.Scan() {
-		fields := bytes.SplitN(s.Bytes(), []byte{':'}, 3)
-		if len(fields) != 3 {
-			continue
-		}
-
-		resp := getFAclResp{}
-
-		switch string(fields[0]) {
-		case "user":
-			resp.typ = fAclTypeUser
-		case "group":
-			resp.typ = fAclTypeGroup
-		case "mask":
-			resp.typ = fAclTypeMask
-		case "other":
-			resp.typ = fAclTypeOther
-		default:
-			c.pe = append(c.pe, fmt.Errorf("unknown type %s", string(fields[0])))
-			continue
-		}
-
-		if len(fields[1]) == 0 {
-			resp.cred = -1
-		} else {
-			if cred, err := strconv.Atoi(string(fields[1])); err != nil {
-				c.pe = append(c.pe, err)
-				continue
-			} else {
-				resp.cred = int32(cred)
-				if resp.cred < 0 {
-					c.pe = append(c.pe, fmt.Errorf("credential %d out of range", resp.cred))
-					continue
-				}
-			}
-		}
-
-		if len(fields[2]) != 3 {
-			c.pe = append(c.pe, fmt.Errorf("invalid perm length %d", len(fields[2])))
-			continue
-		} else {
-			switch fields[2][0] {
-			case 'r':
-				resp.val |= fAclPermRead
-			case '-':
-			default:
-				c.pe = append(c.pe, fmt.Errorf("invalid perm %v", fields[2][0]))
-				continue
-			}
-			switch fields[2][1] {
-			case 'w':
-				resp.val |= fAclPermWrite
-			case '-':
-			default:
-				c.pe = append(c.pe, fmt.Errorf("invalid perm %v", fields[2][1]))
-				continue
-			}
-			switch fields[2][2] {
-			case 'x':
-				resp.val |= fAclPermExecute
-			case '-':
-			default:
-				c.pe = append(c.pe, fmt.Errorf("invalid perm %v", fields[2][2]))
-				continue
-			}
-		}
-
-		resp.raw = make([]byte, len(s.Bytes()))
-		copy(resp.raw, s.Bytes())
-		c.val = append(c.val, &resp)
-	}
-	scanErr <- s.Err()
-}
-
-func (r *getFAclResp) String() string {
-	if r.raw != nil && len(r.raw) > 0 {
-		return string(r.raw)
-	}
-
-	return "(user-initialised resp value)"
-}
-
-func (r *getFAclResp) equals(typ fAclType, cred int32, val fAclPerm) bool {
-	return r.typ == typ && r.cred == cred && r.val == val
-}

system/acl/acl_test.go

@@ -1,10 +1,16 @@
 package acl_test
 
 import (
+	"bufio"
+	"bytes"
 	"errors"
+	"fmt"
+	"io"
 	"os"
+	"os/exec"
 	"path"
 	"reflect"
+	"strconv"
 	"testing"
 
 	"hakurei.app/system/acl"
@@ -17,7 +23,7 @@ var (
 	cred = int32(os.Geteuid())
 )
 
-func TestUpdatePerm(t *testing.T) {
+func TestUpdate(t *testing.T) {
 	if os.Getenv("GO_TEST_SKIP_ACL") == "1" {
 		t.Log("acl test skipped")
 		t.SkipNow()
@@ -48,19 +54,19 @@ func TestUpdatePerm(t *testing.T) {
 
 	t.Run("default clear mask", func(t *testing.T) {
 		if err := acl.Update(testFilePath, uid); err != nil {
-			t.Fatalf("UpdatePerm: error = %v", err)
+			t.Fatalf("Update: error = %v", err)
 		}
 		if cur = getfacl(t, testFilePath); len(cur) != 4 {
-			t.Fatalf("UpdatePerm: %v", cur)
+			t.Fatalf("Update: %v", cur)
 		}
 	})
 
 	t.Run("default clear consistency", func(t *testing.T) {
 		if err := acl.Update(testFilePath, uid); err != nil {
-			t.Fatalf("UpdatePerm: error = %v", err)
+			t.Fatalf("Update: error = %v", err)
 		}
 		if val := getfacl(t, testFilePath); !reflect.DeepEqual(val, cur) {
-			t.Fatalf("UpdatePerm: %v, want %v", val, cur)
+			t.Fatalf("Update: %v, want %v", val, cur)
 		}
 	})
 
@@ -77,26 +83,171 @@ func testUpdate(t *testing.T, testFilePath, name string, cur []*getFAclResp, val
 	t.Run(name, func(t *testing.T) {
 		t.Cleanup(func() {
 			if err := acl.Update(testFilePath, uid); err != nil {
-				t.Fatalf("UpdatePerm: error = %v", err)
+				t.Fatalf("Update: error = %v", err)
 			}
 			if v := getfacl(t, testFilePath); !reflect.DeepEqual(v, cur) {
-				t.Fatalf("UpdatePerm: %v, want %v", v, cur)
+				t.Fatalf("Update: %v, want %v", v, cur)
 			}
 		})
 
 		if err := acl.Update(testFilePath, uid, perms...); err != nil {
-			t.Fatalf("UpdatePerm: error = %v", err)
+			t.Fatalf("Update: error = %v", err)
 		}
 		r := respByCred(getfacl(t, testFilePath), fAclTypeUser, cred)
 		if r == nil {
-			t.Fatalf("UpdatePerm did not add an ACL entry")
+			t.Fatalf("Update did not add an ACL entry")
 		}
 		if !r.equals(fAclTypeUser, cred, val) {
-			t.Fatalf("UpdatePerm(%s) = %s", name, r)
+			t.Fatalf("Update(%s) = %s", name, r)
 		}
 	})
 }
 
+type (
+	getFAclInvocation struct {
+		cmd *exec.Cmd
+		val []*getFAclResp
+		pe  []error
+	}
+
+	getFAclResp struct {
+		typ  fAclType
+		cred int32
+		val  fAclPerm
+
+		raw []byte
+	}
+
+	fAclPerm uintptr
+	fAclType uint8
+)
+
+const fAclBufSize = 16
+
+const (
+	fAclPermRead fAclPerm = 1 << iota
+	fAclPermWrite
+	fAclPermExecute
+)
+
+const (
+	fAclTypeUser fAclType = iota
+	fAclTypeGroup
+	fAclTypeMask
+	fAclTypeOther
+)
+
+func (c *getFAclInvocation) run(name string) error {
+	if c.cmd != nil {
+		panic("attempted to run twice")
+	}
+
+	c.cmd = exec.Command("getfacl", "--omit-header", "--absolute-names", "--numeric", name)
+
+	scanErr := make(chan error, 1)
+	if p, err := c.cmd.StdoutPipe(); err != nil {
+		return err
+	} else {
+		go c.parse(p, scanErr)
+	}
+
+	if err := c.cmd.Start(); err != nil {
+		return err
+	}
+
+	return errors.Join(<-scanErr, c.cmd.Wait())
+}
+
+func (c *getFAclInvocation) parse(pipe io.Reader, scanErr chan error) {
+	c.val = make([]*getFAclResp, 0, 4+fAclBufSize)
+
+	s := bufio.NewScanner(pipe)
+	for s.Scan() {
+		fields := bytes.SplitN(s.Bytes(), []byte{':'}, 3)
+		if len(fields) != 3 {
+			continue
+		}
+
+		resp := getFAclResp{}
+
+		switch string(fields[0]) {
+		case "user":
+			resp.typ = fAclTypeUser
+		case "group":
+			resp.typ = fAclTypeGroup
+		case "mask":
+			resp.typ = fAclTypeMask
+		case "other":
+			resp.typ = fAclTypeOther
+		default:
+			c.pe = append(c.pe, fmt.Errorf("unknown type %s", string(fields[0])))
+			continue
+		}
+
+		if len(fields[1]) == 0 {
+			resp.cred = -1
+		} else {
+			if cred, err := strconv.Atoi(string(fields[1])); err != nil {
+				c.pe = append(c.pe, err)
+				continue
+			} else {
+				resp.cred = int32(cred)
+				if resp.cred < 0 {
+					c.pe = append(c.pe, fmt.Errorf("credential %d out of range", resp.cred))
+					continue
+				}
+			}
+		}
+
+		if len(fields[2]) != 3 {
+			c.pe = append(c.pe, fmt.Errorf("invalid perm length %d", len(fields[2])))
+			continue
+		} else {
+			switch fields[2][0] {
+			case 'r':
+				resp.val |= fAclPermRead
+			case '-':
+			default:
+				c.pe = append(c.pe, fmt.Errorf("invalid perm %v", fields[2][0]))
+				continue
+			}
+			switch fields[2][1] {
+			case 'w':
+				resp.val |= fAclPermWrite
+			case '-':
+			default:
+				c.pe = append(c.pe, fmt.Errorf("invalid perm %v", fields[2][1]))
+				continue
+			}
+			switch fields[2][2] {
+			case 'x':
+				resp.val |= fAclPermExecute
+			case '-':
+			default:
+				c.pe = append(c.pe, fmt.Errorf("invalid perm %v", fields[2][2]))
+				continue
+			}
+		}
+
+		resp.raw = make([]byte, len(s.Bytes()))
+		copy(resp.raw, s.Bytes())
+		c.val = append(c.val, &resp)
+	}
+	scanErr <- s.Err()
+}
+
+func (r *getFAclResp) String() string {
+	if r.raw != nil && len(r.raw) > 0 {
+		return string(r.raw)
+	}
+
+	return "(user-initialised resp value)"
+}
+
+func (r *getFAclResp) equals(typ fAclType, cred int32, val fAclPerm) bool {
+	return r.typ == typ && r.cred == cred && r.val == val
+}
+
 func getfacl(t *testing.T, name string) []*getFAclResp {
 	c := new(getFAclInvocation)
 	if err := c.run(name); err != nil {

system/acl/libacl-helper.c

@@ -6,7 +6,7 @@
 
 int hakurei_acl_update_file_by_uid(const char *path_p, uid_t uid,
                                    acl_perm_t *perms, size_t plen) {
-  int ret = -1;
+  int ret;
   bool v;
   int i;
   acl_t acl;
@@ -15,51 +15,70 @@ int hakurei_acl_update_file_by_uid(const char *path_p, uid_t uid,
   void *qualifier_p;
   acl_permset_t permset;
 
+  ret = -1; /* acl_get_file */
   acl = acl_get_file(path_p, ACL_TYPE_ACCESS);
   if (acl == NULL)
     goto out;
 
-  // prune entries by uid
+  /* prune entries by uid */
   for (i = acl_get_entry(acl, ACL_FIRST_ENTRY, &entry); i == 1;
        i = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry)) {
+    ret = -2; /* acl_get_tag_type */
     if (acl_get_tag_type(entry, &tag_type) != 0)
-      return -1;
+      goto out;
     if (tag_type != ACL_USER)
       continue;
 
+    ret = -3; /* acl_get_qualifier */
     qualifier_p = acl_get_qualifier(entry);
     if (qualifier_p == NULL)
-      return -1;
+      goto out;
     v = *(uid_t *)qualifier_p == uid;
     acl_free(qualifier_p);
 
     if (!v)
       continue;
 
-    acl_delete_entry(acl, entry);
+    ret = -4; /* acl_delete_entry */
+    if (acl_delete_entry(acl, entry) != 0)
+      goto out;
   }
 
   if (plen == 0)
     goto set;
 
+  ret = -5; /* acl_create_entry */
   if (acl_create_entry(&acl, &entry) != 0)
     goto out;
+
+  ret = -6; /* acl_get_permset */
   if (acl_get_permset(entry, &permset) != 0)
     goto out;
+
+  ret = -7; /* acl_add_perm */
   for (i = 0; i < plen; i++) {
     if (acl_add_perm(permset, perms[i]) != 0)
       goto out;
   }
+
+  ret = -8; /* acl_set_tag_type */
   if (acl_set_tag_type(entry, ACL_USER) != 0)
     goto out;
+
+  ret = -9; /* acl_set_qualifier */
   if (acl_set_qualifier(entry, (void *)&uid) != 0)
     goto out;
 
 set:
+  ret = -10; /* acl_calc_mask */
   if (acl_calc_mask(&acl) != 0)
     goto out;
+
+  ret = -11; /* acl_valid */
   if (acl_valid(acl) != 0)
     goto out;
+
+  ret = -12; /* acl_set_file */
   if (acl_set_file(path_p, ACL_TYPE_ACCESS, acl) == 0)
     ret = 0;
 

system/acl/libacl-helper.go

@@ -0,0 +1,40 @@
+package acl
+
+import "os"
+
+func newAclPathError(name string, r int, err error) error {
+	pathError := &os.PathError{Path: name, Err: err}
+	switch r {
+	case 0:
+		return nil
+
+	case -1:
+		pathError.Op = "acl_get_file"
+	case -2:
+		pathError.Op = "acl_get_tag_type"
+	case -3:
+		pathError.Op = "acl_get_qualifier"
+	case -4:
+		pathError.Op = "acl_delete_entry"
+	case -5:
+		pathError.Op = "acl_create_entry"
+	case -6:
+		pathError.Op = "acl_get_permset"
+	case -7:
+		pathError.Op = "acl_add_perm"
+	case -8:
+		pathError.Op = "acl_set_tag_type"
+	case -9:
+		pathError.Op = "acl_set_qualifier"
+	case -10:
+		pathError.Op = "acl_calc_mask"
+	case -11:
+		pathError.Op = "acl_valid"
+	case -12:
+		pathError.Op = "acl_set_file"
+
+	default: // unreachable
+		pathError.Op = "setfacl"
+	}
+	return pathError
+}

system/acl/libacl-helper_test.go

@@ -0,0 +1,60 @@
+package acl
+
+import (
+	"os"
+	"reflect"
+	"syscall"
+	"testing"
+
+	"hakurei.app/container"
+)
+
+func TestNewAclPathError(t *testing.T) {
+	testCases := []struct {
+		name string
+		path string
+		r    int
+		err  error
+		want error
+	}{
+		{"nil", container.Nonexistent, 0, syscall.ENOTRECOVERABLE, nil},
+
+		{"acl_get_file", container.Nonexistent, -1, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "acl_get_file", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+		{"acl_get_tag_type", container.Nonexistent, -2, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "acl_get_tag_type", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+		{"acl_get_qualifier", container.Nonexistent, -3, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "acl_get_qualifier", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+		{"acl_delete_entry", container.Nonexistent, -4, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "acl_delete_entry", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+		{"acl_create_entry", container.Nonexistent, -5, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "acl_create_entry", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+		{"acl_get_permset", container.Nonexistent, -6, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "acl_get_permset", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+		{"acl_add_perm", container.Nonexistent, -7, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "acl_add_perm", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+		{"acl_set_tag_type", container.Nonexistent, -8, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "acl_set_tag_type", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+		{"acl_set_qualifier", container.Nonexistent, -9, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "acl_set_qualifier", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+		{"acl_calc_mask", container.Nonexistent, -10, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "acl_calc_mask", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+		{"acl_valid", container.Nonexistent, -11, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "acl_valid", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+		{"acl_set_file", container.Nonexistent, -12, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "acl_set_file", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+
+		{"acl", container.Nonexistent, -13, syscall.ENOTRECOVERABLE,
+			&os.PathError{Op: "setfacl", Path: container.Nonexistent, Err: syscall.ENOTRECOVERABLE}},
+		{"invalid", container.Nonexistent, -0xdeadbeef, nil,
+			&os.PathError{Op: "setfacl", Path: container.Nonexistent}},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := newAclPathError(tc.path, tc.r, tc.err)
+			if !reflect.DeepEqual(err, tc.want) {
+				t.Errorf("newAclPathError: %v, want %v", err, tc.want)
+			}
+		})
+	}
+}

system/acl/perms_test.go

@@ -0,0 +1,30 @@
+package acl_test
+
+import (
+	"testing"
+
+	"hakurei.app/system/acl"
+)
+
+func TestPerms(t *testing.T) {
+	testCases := []struct {
+		name  string
+		perms acl.Perms
+	}{
+		{"---", acl.Perms{}},
+		{"r--", acl.Perms{acl.Read}},
+		{"-w-", acl.Perms{acl.Write}},
+		{"--x", acl.Perms{acl.Execute}},
+		{"rw-", acl.Perms{acl.Read, acl.Read, acl.Write}},
+		{"r-x", acl.Perms{acl.Read, acl.Execute, acl.Execute}},
+		{"-wx", acl.Perms{acl.Write, acl.Write, acl.Execute, acl.Execute}},
+		{"rwx", acl.Perms{acl.Read, acl.Write, acl.Execute}},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := tc.perms.String(); got != tc.name {
+				t.Errorf("String: %q, want %q", got, tc.name)
+			}
+		})
+	}
+}

system/acl_test.go

@@ -1,91 +1,182 @@
 package system
 
 import (
+	"os"
+	"syscall"
 	"testing"
 
-	"hakurei.app/container"
+	"hakurei.app/container/stub"
 	"hakurei.app/system/acl"
 )
 
-func TestUpdatePerm(t *testing.T) {
-	testCases := []struct {
-		path  string
-		perms []acl.Perm
-	}{
-		{"/run/user/1971/hakurei", []acl.Perm{acl.Execute}},
-		{"/tmp/hakurei.1971/tmpdir/150", []acl.Perm{acl.Read, acl.Write, acl.Execute}},
-	}
+func TestACLUpdateOp(t *testing.T) {
+	checkOpBehaviour(t, []opBehaviourTestCase{
+		{"apply aclUpdate", 0xdeadbeef, 0xff,
+			&aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}, []stub.Call{
+				call("verbose", stub.ExpectArgs{[]any{"applying ACL", &aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}}}, nil, nil),
+				call("aclUpdate", stub.ExpectArgs{"/proc/nonexistent", 0xdeadbeef, []acl.Perm{acl.Read, acl.Write, acl.Execute}}, nil, stub.UniqueError(1)),
+			}, &OpError{Op: "acl", Err: stub.UniqueError(1)}, nil, nil},
 
-	for _, tc := range testCases {
-		t.Run(tc.path+permSubTestSuffix(tc.perms), func(t *testing.T) {
-			sys := New(150)
-			sys.UpdatePerm(tc.path, tc.perms...)
-			(&tcOp{Process, tc.path}).test(t, sys.ops, []Op{&ACL{Process, tc.path, tc.perms}}, "UpdatePerm")
-		})
-	}
-}
-
-func TestUpdatePermType(t *testing.T) {
-	testCases := []struct {
-		perms []acl.Perm
-		tcOp
-	}{
-		{[]acl.Perm{acl.Execute}, tcOp{User, "/tmp/hakurei.1971/tmpdir"}},
-		{[]acl.Perm{acl.Read, acl.Write, acl.Execute}, tcOp{User, "/tmp/hakurei.1971/tmpdir/150"}},
-		{[]acl.Perm{acl.Execute}, tcOp{Process, "/run/user/1971/hakurei/fcb8a12f7c482d183ade8288c3de78b5"}},
-		{[]acl.Perm{acl.Read}, tcOp{Process, "/tmp/hakurei.1971/fcb8a12f7c482d183ade8288c3de78b5/passwd"}},
-		{[]acl.Perm{acl.Read}, tcOp{Process, "/tmp/hakurei.1971/fcb8a12f7c482d183ade8288c3de78b5/group"}},
-		{[]acl.Perm{acl.Read, acl.Write, acl.Execute}, tcOp{EWayland, "/run/user/1971/wayland-0"}},
-	}
-
-	for _, tc := range testCases {
-		t.Run(tc.path+"_"+TypeString(tc.et)+permSubTestSuffix(tc.perms), func(t *testing.T) {
-			sys := New(150)
-			sys.UpdatePermType(tc.et, tc.path, tc.perms...)
-			tc.test(t, sys.ops, []Op{&ACL{tc.et, tc.path, tc.perms}}, "UpdatePermType")
-		})
-	}
-}
-
-func TestACLString(t *testing.T) {
-	testCases := []struct {
-		want  string
-		et    Enablement
-		perms []acl.Perm
-	}{
-		{`--- type: process path: "/proc/nonexistent"`, Process, []acl.Perm{}},
-		{`r-- type: user path: "/proc/nonexistent"`, User, []acl.Perm{acl.Read}},
-		{`-w- type: wayland path: "/proc/nonexistent"`, EWayland, []acl.Perm{acl.Write}},
-		{`--x type: x11 path: "/proc/nonexistent"`, EX11, []acl.Perm{acl.Execute}},
-		{`rw- type: dbus path: "/proc/nonexistent"`, EDBus, []acl.Perm{acl.Read, acl.Write}},
-		{`r-x type: pulseaudio path: "/proc/nonexistent"`, EPulse, []acl.Perm{acl.Read, acl.Execute}},
-		{`rwx type: user path: "/proc/nonexistent"`, User, []acl.Perm{acl.Read, acl.Write, acl.Execute}},
-		{`rwx type: process path: "/proc/nonexistent"`, Process, []acl.Perm{acl.Read, acl.Write, acl.Write, acl.Execute}},
-	}
-
-	for _, tc := range testCases {
-		t.Run(tc.want, func(t *testing.T) {
-			a := &ACL{et: tc.et, perms: tc.perms, path: container.Nonexistent}
-			if got := a.String(); got != tc.want {
-				t.Errorf("String() = %v, want %v",
-					got, tc.want)
-			}
-		})
-	}
-}
-
-func permSubTestSuffix(perms []acl.Perm) (suffix string) {
-	for _, perm := range perms {
-		switch perm {
-		case acl.Read:
-			suffix += "_read"
-		case acl.Write:
-			suffix += "_write"
-		case acl.Execute:
-			suffix += "_execute"
-		default:
-			panic("unreachable")
-		}
-	}
-	return
+		{"revert aclUpdate", 0xdeadbeef, 0xff,
+			&aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}, []stub.Call{
+				call("verbose", stub.ExpectArgs{[]any{"applying ACL", &aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}}}, nil, nil),
+				call("aclUpdate", stub.ExpectArgs{"/proc/nonexistent", 0xdeadbeef, []acl.Perm{acl.Read, acl.Write, acl.Execute}}, nil, nil),
+			}, nil, []stub.Call{
+				call("verbose", stub.ExpectArgs{[]any{"stripping ACL", &aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}}}, nil, nil),
+				call("aclUpdate", stub.ExpectArgs{"/proc/nonexistent", 0xdeadbeef, ([]acl.Perm)(nil)}, nil, stub.UniqueError(0)),
+			}, &OpError{Op: "acl", Err: stub.UniqueError(0), Revert: true}},
+
+		{"success revert skip", 0xdeadbeef, Process,
+			&aclUpdateOp{User, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}, []stub.Call{
+				call("verbose", stub.ExpectArgs{[]any{"applying ACL", &aclUpdateOp{User, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}}}, nil, nil),
+				call("aclUpdate", stub.ExpectArgs{"/proc/nonexistent", 0xdeadbeef, []acl.Perm{acl.Read, acl.Write, acl.Execute}}, nil, nil),
+			}, nil, []stub.Call{
+				call("verbose", stub.ExpectArgs{[]any{"skipping ACL", &aclUpdateOp{User, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}}}, nil, nil),
+			}, nil},
+
+		{"success revert aclUpdate ENOENT", 0xdeadbeef, 0xff,
+			&aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}, []stub.Call{
+				call("verbose", stub.ExpectArgs{[]any{"applying ACL", &aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}}}, nil, nil),
+				call("aclUpdate", stub.ExpectArgs{"/proc/nonexistent", 0xdeadbeef, []acl.Perm{acl.Read, acl.Write, acl.Execute}}, nil, nil),
+			}, nil, []stub.Call{
+				call("verbose", stub.ExpectArgs{[]any{"stripping ACL", &aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}}}, nil, nil),
+				call("aclUpdate", stub.ExpectArgs{"/proc/nonexistent", 0xdeadbeef, ([]acl.Perm)(nil)}, nil, &os.PathError{Op: "acl_get_file", Path: "/proc/nonexistent", Err: syscall.ENOENT}),
+				call("verbosef", stub.ExpectArgs{"target of ACL %s no longer exists", []any{&aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}}}, nil, nil),
+			}, nil},
+
+		{"success", 0xdeadbeef, 0xff,
+			&aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}, []stub.Call{
+				call("verbose", stub.ExpectArgs{[]any{"applying ACL", &aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}}}, nil, nil),
+				call("aclUpdate", stub.ExpectArgs{"/proc/nonexistent", 0xdeadbeef, []acl.Perm{acl.Read, acl.Write, acl.Execute}}, nil, nil),
+			}, nil, []stub.Call{
+				call("verbose", stub.ExpectArgs{[]any{"stripping ACL", &aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{acl.Read, acl.Write, acl.Execute}}}}, nil, nil),
+				call("aclUpdate", stub.ExpectArgs{"/proc/nonexistent", 0xdeadbeef, ([]acl.Perm)(nil)}, nil, nil),
+			}, nil},
+	})
+
+	checkOpsBuilder(t, "UpdatePermType", []opsBuilderTestCase{
+		{"simple",
+			0xdeadbeef,
+			func(_ *testing.T, sys *I) {
+				sys.
+					UpdatePerm("/run/user/1971/hakurei", acl.Execute).
+					UpdatePerm("/tmp/hakurei.0/tmpdir/150", acl.Read, acl.Write, acl.Execute)
+			}, []Op{
+				&aclUpdateOp{Process, "/run/user/1971/hakurei", []acl.Perm{acl.Execute}},
+				&aclUpdateOp{Process, "/tmp/hakurei.0/tmpdir/150", []acl.Perm{acl.Read, acl.Write, acl.Execute}},
+			}, stub.Expect{}},
+
+		{"tmpdirp", 0xdeadbeef, func(_ *testing.T, sys *I) {
+			sys.UpdatePermType(User, "/tmp/hakurei.0/tmpdir", acl.Execute)
+		}, []Op{
+			&aclUpdateOp{User, "/tmp/hakurei.0/tmpdir", []acl.Perm{acl.Execute}},
+		}, stub.Expect{}},
+
+		{"tmpdir", 0xdeadbeef, func(_ *testing.T, sys *I) {
+			sys.UpdatePermType(User, "/tmp/hakurei.0/tmpdir/150", acl.Read, acl.Write, acl.Execute)
+		}, []Op{
+			&aclUpdateOp{User, "/tmp/hakurei.0/tmpdir/150", []acl.Perm{acl.Read, acl.Write, acl.Execute}},
+		}, stub.Expect{}},
+
+		{"share", 0xdeadbeef, func(_ *testing.T, sys *I) {
+			sys.UpdatePermType(Process, "/run/user/1971/hakurei/fcb8a12f7c482d183ade8288c3de78b5", acl.Execute)
+		}, []Op{
+			&aclUpdateOp{Process, "/run/user/1971/hakurei/fcb8a12f7c482d183ade8288c3de78b5", []acl.Perm{acl.Execute}},
+		}, stub.Expect{}},
+
+		{"passwd", 0xdeadbeef, func(_ *testing.T, sys *I) {
+			sys.
+				UpdatePermType(Process, "/tmp/hakurei.0/fcb8a12f7c482d183ade8288c3de78b5/passwd", acl.Read).
+				UpdatePermType(Process, "/tmp/hakurei.0/fcb8a12f7c482d183ade8288c3de78b5/group", acl.Read)
+		}, []Op{
+			&aclUpdateOp{Process, "/tmp/hakurei.0/fcb8a12f7c482d183ade8288c3de78b5/passwd", []acl.Perm{acl.Read}},
+			&aclUpdateOp{Process, "/tmp/hakurei.0/fcb8a12f7c482d183ade8288c3de78b5/group", []acl.Perm{acl.Read}},
+		}, stub.Expect{}},
+
+		{"wayland", 0xdeadbeef, func(_ *testing.T, sys *I) {
+			sys.UpdatePermType(EWayland, "/run/user/1971/wayland-0", acl.Read, acl.Write, acl.Execute)
+		}, []Op{
+			&aclUpdateOp{EWayland, "/run/user/1971/wayland-0", []acl.Perm{acl.Read, acl.Write, acl.Execute}},
+		}, stub.Expect{}},
+	})
+
+	checkOpIs(t, []opIsTestCase{
+		{"nil", (*aclUpdateOp)(nil), (*aclUpdateOp)(nil), false},
+		{"zero", new(aclUpdateOp), new(aclUpdateOp), true},
+
+		{"et differs",
+			&aclUpdateOp{
+				EWayland, "/run/user/1971/wayland-0",
+				[]acl.Perm{acl.Read, acl.Write, acl.Execute},
+			}, &aclUpdateOp{
+				EX11, "/run/user/1971/wayland-0",
+				[]acl.Perm{acl.Read, acl.Write, acl.Execute},
+			}, false},
+
+		{"path differs", &aclUpdateOp{
+			EWayland, "/run/user/1971/wayland-0",
+			[]acl.Perm{acl.Read, acl.Write, acl.Execute},
+		}, &aclUpdateOp{
+			EWayland, "/run/user/1971/wayland-1",
+			[]acl.Perm{acl.Read, acl.Write, acl.Execute},
+		}, false},
+
+		{"perms differs", &aclUpdateOp{
+			EWayland, "/run/user/1971/wayland-0",
+			[]acl.Perm{acl.Read, acl.Write, acl.Execute},
+		}, &aclUpdateOp{
+			EWayland, "/run/user/1971/wayland-0",
+			[]acl.Perm{acl.Read, acl.Write},
+		}, false},
+
+		{"equals", &aclUpdateOp{
+			EWayland, "/run/user/1971/wayland-0",
+			[]acl.Perm{acl.Read, acl.Write, acl.Execute},
+		}, &aclUpdateOp{
+			EWayland, "/run/user/1971/wayland-0",
+			[]acl.Perm{acl.Read, acl.Write, acl.Execute},
+		}, true},
+	})
+
+	checkOpMeta(t, []opMetaTestCase{
+		{"clear",
+			&aclUpdateOp{Process, "/proc/nonexistent", []acl.Perm{}},
+			Process, "/proc/nonexistent",
+			`--- type: process path: "/proc/nonexistent"`},
+
+		{"read",
+			&aclUpdateOp{User, "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/0", []acl.Perm{acl.Read}},
+			User, "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/0",
+			`r-- type: user path: "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/0"`},
+
+		{"write",
+			&aclUpdateOp{User, "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/1", []acl.Perm{acl.Write}},
+			User, "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/1",
+			`-w- type: user path: "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/1"`},
+
+		{"execute",
+			&aclUpdateOp{User, "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/2", []acl.Perm{acl.Execute}},
+			User, "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/2",
+			`--x type: user path: "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/2"`},
+
+		{"wayland",
+			&aclUpdateOp{EWayland, "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/wayland", []acl.Perm{acl.Read, acl.Write}},
+			EWayland, "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/wayland",
+			`rw- type: wayland path: "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/wayland"`},
+
+		{"x11",
+			&aclUpdateOp{EX11, "/tmp/.X11-unix/X0", []acl.Perm{acl.Read, acl.Execute}},
+			EX11, "/tmp/.X11-unix/X0",
+			`r-x type: x11 path: "/tmp/.X11-unix/X0"`},
+
+		{"dbus",
+			&aclUpdateOp{EDBus, "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/bus", []acl.Perm{acl.Write, acl.Execute}},
+			EDBus, "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/bus",
+			`-wx type: dbus path: "/tmp/hakurei.0/27d81d567f8fae7f33278eec45da9446/bus"`},
+
+		{"pulseaudio",
+			&aclUpdateOp{EPulse, "/run/user/1971/hakurei/27d81d567f8fae7f33278eec45da9446/pulse", []acl.Perm{acl.Read, acl.Write, acl.Execute}},
+			EPulse, "/run/user/1971/hakurei/27d81d567f8fae7f33278eec45da9446/pulse",
+			`rwx type: pulseaudio path: "/run/user/1971/hakurei/27d81d567f8fae7f33278eec45da9446/pulse"`},
+	})
 }

system/dbus.go

@@ -4,11 +4,14 @@ import (
 	"bytes"
 	"context"
 	"errors"
+	"fmt"
 	"log"
+	"reflect"
 	"strings"
 	"sync"
 	"syscall"
 
+	"hakurei.app/container"
 	"hakurei.app/system/dbus"
 )
 
@@ -16,6 +19,7 @@ var (
 	ErrDBusConfig = errors.New("dbus config not supplied")
 )
 
+// MustProxyDBus calls ProxyDBus and panics if an error is returned.
 func (sys *I) MustProxyDBus(sessionPath string, session *dbus.Config, systemPath string, system *dbus.Config) *I {
 	if _, err := sys.ProxyDBus(session, system, sessionPath, systemPath); err != nil {
 		panic(err.Error())
@@ -24,35 +28,40 @@ func (sys *I) MustProxyDBus(sessionPath string, session *dbus.Config, systemPath
 	}
 }
 
+// ProxyDBus finalises configuration ahead of time and starts xdg-dbus-proxy via [dbus] and terminates it on revert.
+// This [Op] is always [Process] scoped.
 func (sys *I) ProxyDBus(session, system *dbus.Config, sessionPath, systemPath string) (func(), error) {
-	d := new(DBus)
+	d := new(dbusProxyOp)
 
 	// session bus is required as otherwise this is effectively a very expensive noop
 	if session == nil {
-		return nil, msg.WrapErr(ErrDBusConfig,
-			"attempted to create message bus proxy args without session bus config")
+		return nil, newOpErrorMessage("dbus", ErrDBusConfig,
+			"attempted to create message bus proxy args without session bus config", false)
 	}
 
 	// system bus is optional
 	d.system = system != nil
 
-	d.sessionBus[0], d.systemBus[0] = dbus.Address()
-	d.sessionBus[1], d.systemBus[1] = sessionPath, systemPath
-	d.out = &scanToFmsg{msg: new(strings.Builder)}
-	if final, err := dbus.Finalise(d.sessionBus, d.systemBus, session, system); err != nil {
+	var sessionBus, systemBus dbus.ProxyPair
+	sessionBus[0], systemBus[0] = sys.dbusAddress()
+	sessionBus[1], systemBus[1] = sessionPath, systemPath
+	d.out = &linePrefixWriter{println: log.Println, prefix: "(dbus) ", buf: new(strings.Builder)}
+	if final, err := sys.dbusFinalise(sessionBus, systemBus, session, system); err != nil {
 		if errors.Is(err, syscall.EINVAL) {
-			return nil, msg.WrapErr(err, "message bus proxy configuration contains NUL byte")
+			return nil, newOpErrorMessage("dbus", err,
+				"message bus proxy configuration contains NUL byte", false)
 		}
-		return nil, wrapErrSuffix(err, "cannot finalise message bus proxy:")
+		return nil, newOpErrorMessage("dbus", err,
+			fmt.Sprintf("cannot finalise message bus proxy: %v", err), false)
 	} else {
-		if msg.IsVerbose() {
-			msg.Verbose("session bus proxy:", session.Args(d.sessionBus))
+		if sys.isVerbose() {
+			sys.verbose("session bus proxy:", session.Args(sessionBus))
 			if system != nil {
-				msg.Verbose("system bus proxy:", system.Args(d.systemBus))
+				sys.verbose("system bus proxy:", system.Args(systemBus))
 			}
 
 			// this calls the argsWt String method
-			msg.Verbose("message bus proxy final args:", final.WriterTo)
+			sys.verbose("message bus proxy final args:", final.WriterTo)
 		}
 
 		d.final = final
@@ -62,100 +71,130 @@ func (sys *I) ProxyDBus(session, system *dbus.Config, sessionPath, systemPath st
 	return d.out.Dump, nil
 }
 
-type DBus struct {
+// dbusProxyOp implements [I.ProxyDBus].
+type dbusProxyOp struct {
 	proxy *dbus.Proxy // populated during apply
 
 	final *dbus.Final
-	out   *scanToFmsg
+	out   *linePrefixWriter
 	// whether system bus proxy is enabled
 	system bool
-
-	sessionBus, systemBus dbus.ProxyPair
 }
 
-func (d *DBus) Type() Enablement { return Process }
+func (d *dbusProxyOp) Type() Enablement { return Process }
 
-func (d *DBus) apply(sys *I) error {
-	msg.Verbosef("session bus proxy on %q for upstream %q", d.sessionBus[1], d.sessionBus[0])
+func (d *dbusProxyOp) apply(sys *I) error {
+	sys.verbosef("session bus proxy on %q for upstream %q", d.final.Session[1], d.final.Session[0])
 	if d.system {
-		msg.Verbosef("system bus proxy on %q for upstream %q", d.systemBus[1], d.systemBus[0])
+		sys.verbosef("system bus proxy on %q for upstream %q", d.final.System[1], d.final.System[0])
 	}
 
 	d.proxy = dbus.New(sys.ctx, d.final, d.out)
-	if err := d.proxy.Start(); err != nil {
+	if err := sys.dbusProxyStart(d.proxy); err != nil {
 		d.out.Dump()
-		return wrapErrSuffix(err,
-			"cannot start message bus proxy:")
+		return newOpErrorMessage("dbus", err,
+			fmt.Sprintf("cannot start message bus proxy: %v", err), false)
 	}
-	msg.Verbose("starting message bus proxy", d.proxy)
+	sys.verbose("starting message bus proxy", d.proxy)
 	return nil
 }
 
-func (d *DBus) revert(*I, *Criteria) error {
+func (d *dbusProxyOp) revert(sys *I, _ *Criteria) error {
 	// criteria ignored here since dbus is always process-scoped
-	msg.Verbose("terminating message bus proxy")
-	d.proxy.Close()
-	defer msg.Verbose("message bus proxy exit")
-	err := d.proxy.Wait()
+	sys.verbose("terminating message bus proxy")
+	sys.dbusProxyClose(d.proxy)
+
+	exitMessage := "message bus proxy exit"
+	defer func() { sys.verbose(exitMessage) }()
+
+	err := sys.dbusProxyWait(d.proxy)
 	if errors.Is(err, context.Canceled) {
-		msg.Verbose("message bus proxy canceled upstream")
+		exitMessage = "message bus proxy canceled upstream"
 		err = nil
 	}
-	return wrapErrSuffix(err, "message bus proxy error:")
+	return newOpErrorMessage("dbus", err,
+		fmt.Sprintf("message bus proxy error: %v", err), true)
 }
 
-func (d *DBus) Is(o Op) bool {
-	d0, ok := o.(*DBus)
-	return ok && d0 != nil &&
-		((d.proxy == nil && d0.proxy == nil) ||
-			(d.proxy != nil && d0.proxy != nil && d.proxy.String() == d0.proxy.String()))
+func (d *dbusProxyOp) Is(o Op) bool {
+	target, ok := o.(*dbusProxyOp)
+	return ok && d != nil && target != nil &&
+		d.system == target.system &&
+		d.final != nil && target.final != nil &&
+		d.final.Session == target.final.Session &&
+		d.final.System == target.final.System &&
+		dbus.EqualAddrEntries(d.final.SessionUpstream, target.final.SessionUpstream) &&
+		dbus.EqualAddrEntries(d.final.SystemUpstream, target.final.SystemUpstream) &&
+		reflect.DeepEqual(d.final.WriterTo, target.final.WriterTo)
 }
 
-func (d *DBus) Path() string {
-	return "(dbus proxy)"
-}
+func (d *dbusProxyOp) Path() string   { return container.Nonexistent }
+func (d *dbusProxyOp) String() string { return d.proxy.String() }
 
-func (d *DBus) String() string {
-	return d.proxy.String()
-}
+const (
+	// lpwSizeThreshold is the threshold of bytes written to linePrefixWriter which,
+	// if reached or exceeded, causes linePrefixWriter to drop all future writes.
+	lpwSizeThreshold = 1 << 24
+)
 
-type scanToFmsg struct {
-	msg    *strings.Builder
-	msgbuf []string
+// linePrefixWriter calls println with a prefix for every line written.
+type linePrefixWriter struct {
+	prefix  string
+	println func(v ...any)
+
+	n   int
+	msg []string
+	buf *strings.Builder
 
 	mu sync.RWMutex
 }
 
-func (s *scanToFmsg) Write(p []byte) (n int, err error) {
+func (s *linePrefixWriter) Write(p []byte) (n int, err error) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	return s.write(p, 0)
 }
 
-func (s *scanToFmsg) write(p []byte, a int) (int, error) {
+func (s *linePrefixWriter) write(p []byte, a int) (int, error) {
+	if s.n >= lpwSizeThreshold {
+		if len(p) == 0 {
+			return a, nil
+		}
+		return a, syscall.ENOMEM
+	}
+
 	if i := bytes.IndexByte(p, '\n'); i == -1 {
-		n, _ := s.msg.Write(p)
+		n, _ := s.buf.Write(p)
+		s.n += n
 		return a + n, nil
 	} else {
-		n, _ := s.msg.Write(p[:i])
+		n, _ := s.buf.Write(p[:i])
+		s.n += n + 1
 
-		// allow container init messages through
-		v := s.msg.String()
+		v := s.buf.String()
 		if strings.HasPrefix(v, "init: ") {
-			log.Println("(dbus) " + v)
+			s.n -= len(v) + 1
+			// pass through container init messages
+			s.println(s.prefix + v)
 		} else {
-			s.msgbuf = append(s.msgbuf, v)
+			s.msg = append(s.msg, v)
 		}
 
-		s.msg.Reset()
+		s.buf.Reset()
 		return s.write(p[i+1:], a+n+1)
 	}
 }
 
-func (s *scanToFmsg) Dump() {
+func (s *linePrefixWriter) Dump() {
 	s.mu.RLock()
-	for _, msg := range s.msgbuf {
-		log.Println("(dbus) " + msg)
+	for _, m := range s.msg {
+		s.println(s.prefix + m)
+	}
+	if s.buf != nil && s.buf.Len() != 0 {
+		s.println("*" + s.prefix + s.buf.String())
+	}
+	if s.n >= lpwSizeThreshold {
+		s.println("+" + s.prefix + "write threshold reached, output may be incomplete")
 	}
 	s.mu.RUnlock()
 }

system/dbus/address.go

@@ -13,6 +13,13 @@ type AddrEntry struct {
 	Values [][2]string `json:"values"`
 }
 
+// EqualAddrEntries returns whether two slices of [AddrEntry] are equal.
+func EqualAddrEntries(entries, target []AddrEntry) bool {
+	return slices.EqualFunc(entries, target, func(a AddrEntry, b AddrEntry) bool {
+		return a.Method == b.Method && slices.Equal(a.Values, b.Values)
+	})
+}
+
 // Parse parses D-Bus address according to
 // https://dbus.freedesktop.org/doc/dbus-specification.html#addresses
 func Parse(addr []byte) ([]AddrEntry, error) {

system/dbus/dbus_test.go

@@ -63,6 +63,10 @@ func TestProxyStartWaitCloseString(t *testing.T) {
 	t.Run("direct", func(t *testing.T) { testProxyFinaliseStartWaitCloseString(t, false) })
 }
 
+const (
+	stubProxyTimeout = 30 * time.Second
+)
+
 func testProxyFinaliseStartWaitCloseString(t *testing.T, useSandbox bool) {
 	{
 		oldWaitDelay := helper.WaitDelay
@@ -118,33 +122,33 @@ func testProxyFinaliseStartWaitCloseString(t *testing.T, useSandbox bool) {
 				}
 			})
 
-			ctx, cancel := context.WithTimeout(t.Context(), 5*time.Second)
-			defer cancel()
-			output := new(strings.Builder)
-			if !useSandbox {
-				p = dbus.NewDirect(ctx, final, output)
-			} else {
-				p = dbus.New(ctx, final, output)
-			}
-
-			t.Run("invalid wait", func(t *testing.T) {
-				wantErr := "dbus: not started"
-				if err := p.Wait(); err == nil || err.Error() != wantErr {
-					t.Errorf("Wait: error = %v, wantErr %v",
-						err, wantErr)
+			t.Run("run", func(t *testing.T) {
+				ctx, cancel := context.WithTimeout(t.Context(), stubProxyTimeout)
+				defer cancel()
+				output := new(strings.Builder)
+				if !useSandbox {
+					p = dbus.NewDirect(ctx, final, output)
+				} else {
+					p = dbus.New(ctx, final, output)
 				}
-			})
 
-			t.Run("string", func(t *testing.T) {
-				want := "(unused dbus proxy)"
-				if got := p.String(); got != want {
-					t.Errorf("String: %q, want %q",
-						got, want)
-					return
-				}
-			})
+				t.Run("invalid wait", func(t *testing.T) {
+					wantErr := "dbus: not started"
+					if err := p.Wait(); err == nil || err.Error() != wantErr {
+						t.Errorf("Wait: error = %v, wantErr %v",
+							err, wantErr)
+					}
+				})
+
+				t.Run("string", func(t *testing.T) {
+					want := "(unused dbus proxy)"
+					if got := p.String(); got != want {
+						t.Errorf("String: %q, want %q",
+							got, want)
+						return
+					}
+				})
 
-			t.Run("start", func(t *testing.T) {
 				if err := p.Start(); err != nil {
 					t.Fatalf("Start: error = %v",
 						err)

system/dbus_test.go

@@ -0,0 +1,659 @@
+package system
+
+import (
+	"context"
+	"reflect"
+	"slices"
+	"strconv"
+	"strings"
+	"syscall"
+	"testing"
+
+	"hakurei.app/container/stub"
+	"hakurei.app/helper"
+	"hakurei.app/system/dbus"
+)
+
+func TestDBusProxyOp(t *testing.T) {
+	checkOpBehaviour(t, []opBehaviourTestCase{
+		{"dbusProxyStart", 0xdeadbeef, 0xff, &dbusProxyOp{
+			final:  dbusNewFinalSample(4),
+			out:    new(linePrefixWriter), // panics on write
+			system: true,
+		}, []stub.Call{
+			call("verbosef", stub.ExpectArgs{"session bus proxy on %q for upstream %q", []any{"/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/bus", "unix:path=/run/user/1000/bus"}}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"system bus proxy on %q for upstream %q", []any{"/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/system_bus_socket", "unix:path=/run/dbus/system_bus_socket"}}, nil, nil),
+			call("dbusProxyStart", stub.ExpectArgs{dbusNewFinalSample(4)}, nil, stub.UniqueError(2)),
+		}, &OpError{
+			Op: "dbus", Err: stub.UniqueError(2),
+			Msg: "cannot start message bus proxy: unique error 2 injected by the test suite",
+		}, nil, nil},
+
+		{"dbusProxyWait", 0xdeadbeef, 0xff, &dbusProxyOp{
+			final: dbusNewFinalSample(3),
+		}, []stub.Call{
+			call("verbosef", stub.ExpectArgs{"session bus proxy on %q for upstream %q", []any{"/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/bus", "unix:path=/run/user/1000/bus"}}, nil, nil),
+			call("dbusProxyStart", stub.ExpectArgs{dbusNewFinalSample(3)}, nil, nil),
+			call("verbose", stub.ExpectArgs{[]any{"starting message bus proxy", ignoreValue{}}}, nil, nil),
+		}, nil, []stub.Call{
+			call("verbose", stub.ExpectArgs{[]any{"terminating message bus proxy"}}, nil, nil),
+			call("dbusProxyClose", stub.ExpectArgs{dbusNewFinalSample(3)}, nil, nil),
+			call("dbusProxyWait", stub.ExpectArgs{dbusNewFinalSample(3)}, nil, stub.UniqueError(1)),
+			call("verbose", stub.ExpectArgs{[]any{"message bus proxy exit"}}, nil, nil),
+		}, &OpError{
+			Op: "dbus", Err: stub.UniqueError(1), Revert: true,
+			Msg: "message bus proxy error: unique error 1 injected by the test suite",
+		}},
+
+		{"success dbusProxyWait cancel", 0xdeadbeef, 0xff, &dbusProxyOp{
+			final:  dbusNewFinalSample(2),
+			system: true,
+		}, []stub.Call{
+			call("verbosef", stub.ExpectArgs{"session bus proxy on %q for upstream %q", []any{"/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/bus", "unix:path=/run/user/1000/bus"}}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"system bus proxy on %q for upstream %q", []any{"/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/system_bus_socket", "unix:path=/run/dbus/system_bus_socket"}}, nil, nil),
+			call("dbusProxyStart", stub.ExpectArgs{dbusNewFinalSample(2)}, nil, nil),
+			call("verbose", stub.ExpectArgs{[]any{"starting message bus proxy", ignoreValue{}}}, nil, nil),
+		}, nil, []stub.Call{
+			call("verbose", stub.ExpectArgs{[]any{"terminating message bus proxy"}}, nil, nil),
+			call("dbusProxyClose", stub.ExpectArgs{dbusNewFinalSample(2)}, nil, nil),
+			call("dbusProxyWait", stub.ExpectArgs{dbusNewFinalSample(2)}, nil, context.Canceled),
+			call("verbose", stub.ExpectArgs{[]any{"message bus proxy canceled upstream"}}, nil, nil),
+		}, nil},
+
+		{"success", 0xdeadbeef, 0xff, &dbusProxyOp{
+			final:  dbusNewFinalSample(1),
+			system: true,
+		}, []stub.Call{
+			call("verbosef", stub.ExpectArgs{"session bus proxy on %q for upstream %q", []any{"/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/bus", "unix:path=/run/user/1000/bus"}}, nil, nil),
+			call("verbosef", stub.ExpectArgs{"system bus proxy on %q for upstream %q", []any{"/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/system_bus_socket", "unix:path=/run/dbus/system_bus_socket"}}, nil, nil),
+			call("dbusProxyStart", stub.ExpectArgs{dbusNewFinalSample(1)}, nil, nil),
+			call("verbose", stub.ExpectArgs{[]any{"starting message bus proxy", ignoreValue{}}}, nil, nil),
+		}, nil, []stub.Call{
+			call("verbose", stub.ExpectArgs{[]any{"terminating message bus proxy"}}, nil, nil),
+			call("dbusProxyClose", stub.ExpectArgs{dbusNewFinalSample(1)}, nil, nil),
+			call("dbusProxyWait", stub.ExpectArgs{dbusNewFinalSample(1)}, nil, nil),
+			call("verbose", stub.ExpectArgs{[]any{"message bus proxy exit"}}, nil, nil),
+		}, nil},
+	})
+
+	checkOpsBuilder(t, "ProxyDBus", []opsBuilderTestCase{
+		{"nil session", 0xcafebabe, func(t *testing.T, sys *I) {
+			wantErr := &OpError{
+				Op: "dbus", Err: ErrDBusConfig,
+				Msg: "attempted to create message bus proxy args without session bus config",
+			}
+			if f, err := sys.ProxyDBus(nil, new(dbus.Config), "", ""); !reflect.DeepEqual(err, wantErr) {
+				t.Errorf("ProxyDBus: error = %v, want %v", err, wantErr)
+			} else if f != nil {
+				t.Errorf("ProxyDBus: f = %p", f)
+			}
+		}, nil, stub.Expect{}},
+
+		{"dbusFinalise NUL", 0xcafebabe, func(_ *testing.T, sys *I) {
+			defer func() {
+				want := "message bus proxy configuration contains NUL byte"
+				if r := recover(); r != want {
+					t.Errorf("MustProxyDBus: panic = %v, want %v", r, want)
+				}
+			}()
+
+			sys.MustProxyDBus(
+				"/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/bus", &dbus.Config{
+					// use impossible value here as an implicit assert that it goes through the stub
+					Talk: []string{"session\x00"}, Filter: true,
+				}, "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/system_bus_socket", &dbus.Config{
+					// use impossible value here as an implicit assert that it goes through the stub
+					Talk: []string{"system\x00"}, Filter: true,
+				})
+		}, nil, stub.Expect{Calls: []stub.Call{
+			call("dbusAddress", stub.ExpectArgs{}, [2]string{"unix:path=/run/user/1000/bus", "unix:path=/run/dbus/system_bus_socket"}, nil),
+			call("dbusFinalise", stub.ExpectArgs{
+				dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/bus"},
+				dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/system_bus_socket"},
+				&dbus.Config{Talk: []string{"session\x00"}, Filter: true},
+				&dbus.Config{Talk: []string{"system\x00"}, Filter: true},
+			}, (*dbus.Final)(nil), syscall.EINVAL),
+		}}},
+
+		{"dbusFinalise", 0xcafebabe, func(_ *testing.T, sys *I) {
+			wantErr := &OpError{
+				Op: "dbus", Err: stub.UniqueError(0),
+				Msg: "cannot finalise message bus proxy: unique error 0 injected by the test suite",
+			}
+			if f, err := sys.ProxyDBus(
+				&dbus.Config{
+					// use impossible value here as an implicit assert that it goes through the stub
+					Talk: []string{"session\x00"}, Filter: true,
+				}, &dbus.Config{
+					// use impossible value here as an implicit assert that it goes through the stub
+					Talk: []string{"system\x00"}, Filter: true,
+				},
+				"/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/bus",
+				"/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/system_bus_socket"); !reflect.DeepEqual(err, wantErr) {
+				t.Errorf("ProxyDBus: error = %v", err)
+			} else if f != nil {
+				t.Errorf("ProxyDBus: f = %p", f)
+			}
+		}, nil, stub.Expect{Calls: []stub.Call{
+			call("dbusAddress", stub.ExpectArgs{}, [2]string{"unix:path=/run/user/1000/bus", "unix:path=/run/dbus/system_bus_socket"}, nil),
+			call("dbusFinalise", stub.ExpectArgs{
+				dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/bus"},
+				dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/system_bus_socket"},
+				&dbus.Config{Talk: []string{"session\x00"}, Filter: true},
+				&dbus.Config{Talk: []string{"system\x00"}, Filter: true},
+			}, (*dbus.Final)(nil), stub.UniqueError(0)),
+		}}},
+
+		{"full", 0xcafebabe, func(_ *testing.T, sys *I) {
+			sys.MustProxyDBus(
+				"/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/bus", &dbus.Config{
+					// use impossible value here as an implicit assert that it goes through the stub
+					Talk: []string{"session\x00"}, Filter: true,
+				}, "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/system_bus_socket", &dbus.Config{
+					// use impossible value here as an implicit assert that it goes through the stub
+					Talk: []string{"system\x00"}, Filter: true,
+				})
+		}, []Op{
+			&dbusProxyOp{
+				final:  dbusNewFinalSample(0),
+				system: true,
+			},
+		}, stub.Expect{Calls: []stub.Call{
+			call("dbusAddress", stub.ExpectArgs{}, [2]string{"unix:path=/run/user/1000/bus", "unix:path=/run/dbus/system_bus_socket"}, nil),
+			call("dbusFinalise", stub.ExpectArgs{
+				dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/bus"},
+				dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/system_bus_socket"},
+				&dbus.Config{Talk: []string{"session\x00"}, Filter: true},
+				&dbus.Config{Talk: []string{"system\x00"}, Filter: true},
+			}, dbusNewFinalSample(0), nil),
+			call("isVerbose", stub.ExpectArgs{}, true, nil),
+			call("verbose", stub.ExpectArgs{[]any{"session bus proxy:", []string{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/bus", "--filter", "--talk=session\x00"}}}, nil, nil),
+			call("verbose", stub.ExpectArgs{[]any{"system bus proxy:", []string{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/system_bus_socket", "--filter", "--talk=system\x00"}}}, nil, nil),
+			call("verbose", stub.ExpectArgs{[]any{"message bus proxy final args:", helper.MustNewCheckedArgs([]string{"unique", "value", "0", "injected", "by", "the", "test", "suite"})}}, nil, nil),
+		}}},
+	})
+
+	checkOpIs(t, []opIsTestCase{
+		{"nil", (*dbusProxyOp)(nil), (*dbusProxyOp)(nil), false},
+		{"zero", new(dbusProxyOp), new(dbusProxyOp), false},
+
+		{"system differs", &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: false,
+		}, &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, false},
+
+		{"wt differs", &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1001/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, false},
+
+		{"final system upstream differs", &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket\x00"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, false},
+
+		{"final session upstream differs", &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1001/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, false},
+
+		{"final system differs", &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.1/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, false},
+
+		{"final session differs", &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1001/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, false},
+
+		{"equals", &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, &dbusProxyOp{final: &dbus.Final{
+			Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus"},
+			System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket"},
+
+			SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+			SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"unix", "/run/dbus/system_bus_socket"}}}},
+
+			WriterTo: helper.MustNewCheckedArgs([]string{
+				"--filter", "unix:path=/run/user/1000/bus", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/bus",
+				"--filter", "unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/b186c281d9e83a39afdc66d964ef99c6/system_bus_socket",
+			}),
+		}, system: true,
+		}, true},
+	})
+
+	checkOpMeta(t, []opMetaTestCase{
+		{"dbus", new(dbusProxyOp),
+			Process, "/proc/nonexistent",
+			"(invalid dbus proxy)"},
+	})
+}
+
+func dbusNewFinalSample(v int) *dbus.Final {
+	return &dbus.Final{
+		Session: dbus.ProxyPair{"unix:path=/run/user/1000/bus", "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/bus"},
+		System:  dbus.ProxyPair{"unix:path=/run/dbus/system_bus_socket", "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f/system_bus_socket"},
+
+		SessionUpstream: []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/user/1000/bus"}}}},
+		SystemUpstream:  []dbus.AddrEntry{{Method: "unix", Values: [][2]string{{"path", "/run/dbus/system_bus_socket"}}}},
+
+		WriterTo: helper.MustNewCheckedArgs([]string{"unique", "value", strconv.Itoa(v), "injected", "by", "the", "test", "suite"}),
+	}
+}
+
+func TestLinePrefixWriter(t *testing.T) {
+	testCases := []struct {
+		name    string
+		prefix  string
+		f       func(w func(s string))
+		wantErr []error
+		wantPt  []string
+		want    []string
+		wantExt []string
+		wantBuf string
+	}{
+		{"nop", "(nop) ", func(func(string)) {}, nil, nil, nil, nil, ""},
+
+		{"partial", "(partial) ", func(w func(string)) {
+			w("C-65533: -> ")
+		}, nil, nil, nil, []string{
+			"*(partial) C-65533: -> ",
+		}, "C-65533: -> "},
+
+		{"break", "(break) ", func(w func(string)) {
+			w("C-65533: -> ")
+			w("org.freedesktop.DBus fake ListNames\n")
+		}, nil, nil, []string{
+			"C-65533: -> org.freedesktop.DBus fake ListNames",
+		}, nil, ""},
+
+		{"break pt", "(break pt) ", func(w func(string)) {
+			w("init: ")
+			w("received setup parameters\n")
+		}, nil, []string{
+			"init: received setup parameters",
+		}, nil, nil, ""},
+
+		{"threshold", "(threshold) ", func(w func(s string)) {
+			w(string(make([]byte, lpwSizeThreshold)))
+			w("\n")
+		}, []error{nil, syscall.ENOMEM}, nil, nil, []string{
+			"*(threshold) " + string(make([]byte, lpwSizeThreshold)),
+			"+(threshold) write threshold reached, output may be incomplete",
+		}, string(make([]byte, lpwSizeThreshold))},
+
+		{"threshold multi", "(threshold multi) ", func(w func(s string)) {
+			w(":3\n")
+			w(string(make([]byte, lpwSizeThreshold-3)))
+			w("\n")
+		}, []error{nil, nil, syscall.ENOMEM}, nil, []string{
+			":3",
+		}, []string{
+			"*(threshold multi) " + string(make([]byte, lpwSizeThreshold-3)),
+			"+(threshold multi) write threshold reached, output may be incomplete",
+		}, string(make([]byte, lpwSizeThreshold-3))},
+
+		{"threshold multi partial", "(threshold multi partial) ", func(w func(s string)) {
+			w(":3\n")
+			w(string(make([]byte, lpwSizeThreshold-2)))
+			w("dropped\n")
+		}, []error{nil, nil, syscall.ENOMEM}, nil, []string{
+			":3",
+		}, []string{
+			"*(threshold multi partial) " + string(make([]byte, lpwSizeThreshold-2)),
+			"+(threshold multi partial) write threshold reached, output may be incomplete",
+		}, string(make([]byte, lpwSizeThreshold-2))},
+
+		{"threshold exact", "(threshold exact) ", func(w func(s string)) {
+			w(string(make([]byte, lpwSizeThreshold-1)))
+			w("\n")
+		}, nil, nil, []string{
+			string(make([]byte, lpwSizeThreshold-1)),
+		}, []string{
+			"+(threshold exact) write threshold reached, output may be incomplete",
+		}, ""},
+
+		{"sample", "(dbus) ", func(w func(s string)) {
+			w("init: received setup parameters\n")
+			w(`init: mounting "/nix/store/5gml2l2cj28yvyfyzblzjy1laqpxmyzd-libselinux-3.8.1/lib" flags 0x0` + "\n")
+			w(`init: resolved "/host/nix/store/5gml2l2cj28yvyfyzblzjy1laqpxmyzd-libselinux-3.8.1/lib" on "/sysroot/nix/store/5gml2l2cj28yvyfyzblzjy1laqpxmyzd-libselinux-3.8.1/lib" flags 0x4005` + "\n")
+			w(`init: mounting "/nix/store/bcs094l67dlbqf7idxxbljp293zms9mh-util-linux-minimal-2.41-lib/lib" flags 0x0` + "\n")
+			w(`init: resolved "/host/nix/store/bcs094l67dlbqf7idxxbljp293zms9mh-util-linux-minimal-2.41-lib/lib" on "/sysroot/nix/store/bcs094l67dlbqf7idxxbljp293zms9mh-util-linux-minimal-2.41-lib/lib" flags 0x4005` + "\n")
+			w(`init: mounting "/nix/store/jl19fdc7gdxqz9a1s368r9d15vpirnqy-zlib-1.3.1/lib" flags 0x0` + "\n")
+			w(`init: resolved "/host/nix/store/jl19fdc7gdxqz9a1s368r9d15vpirnqy-zlib-1.3.1/lib" on "/sysroot/nix/store/jl19fdc7gdxqz9a1s368r9d15vpirnqy-zlib-1.3.1/lib" flags 0x4005` + "\n")
+			w(`init: mounting "/nix/store/rnn29mhynsa4ncmk0fkcrdr29n0j20l4-libffi-3.4.8/lib" flags 0x0` + "\n")
+			w(`init: resolved "/host/nix/store/rnn29mhynsa4ncmk0fkcrdr29n0j20l4-libffi-3.4.8/lib" on "/sysroot/nix/store/rnn29mhynsa4ncmk0fkcrdr29n0j20l4-libffi-3.4.8/lib" flags 0x4005` + "\n")
+			w(`init: mounting "/nix/store/vvp8hlss3d5q6hn0cifq04jrpnp6bini-pcre2-10.44/lib" flags 0x0` + "\n")
+			w(`init: resolved "/host/nix/store/vvp8hlss3d5q6hn0cifq04jrpnp6bini-pcre2-10.44/lib" on "/sysroot/nix/store/vvp8hlss3d5q6hn0cifq04jrpnp6bini-pcre2-10.44/lib" flags 0x4005` + "\n")
+			w(`init: mounting "/nix/store/y3nxdc2x8hwivppzgx5hkrhacsh87l21-glib-2.84.3/lib" flags 0x0` + "\n")
+			w(`init: resolved "/host/nix/store/y3nxdc2x8hwivppzgx5hkrhacsh87l21-glib-2.84.3/lib" on "/sysroot/nix/store/y3nxdc2x8hwivppzgx5hkrhacsh87l21-glib-2.84.3/lib" flags 0x4005` + "\n")
+			w(`init: mounting "/nix/store/zdpby3l6azi78sl83cpad2qjpfj25aqx-glibc-2.40-66/lib" flags 0x0` + "\n")
+			w(`init: resolved "/host/nix/store/zdpby3l6azi78sl83cpad2qjpfj25aqx-glibc-2.40-66/lib" on "/sysroot/nix/store/zdpby3l6azi78sl83cpad2qjpfj25aqx-glibc-2.40-66/lib" flags 0x4005` + "\n")
+			w(`init: mounting "/nix/store/zdpby3l6azi78sl83cpad2qjpfj25aqx-glibc-2.40-66/lib64" flags 0x0` + "\n")
+			w(`init: resolved "/host/nix/store/zdpby3l6azi78sl83cpad2qjpfj25aqx-glibc-2.40-66/lib" on "/sysroot/nix/store/zdpby3l6azi78sl83cpad2qjpfj25aqx-glibc-2.40-66/lib64" flags 0x4005` + "\n")
+			w(`init: mounting "/run/user/1000" flags 0x0` + "\n")
+			w(`init: resolved "/host/run/user/1000" on "/sysroot/run/user/1000" flags 0x4005` + "\n")
+			w(`init: mounting "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f" flags 0x2` + "\n")
+			w(`init: resolved "/host/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f" on "/sysroot/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f" flags 0x4004` + "\n")
+			w(`init: mounting "/nix/store/d2divmq2d897amikcwpdx7zrbpddxxcl-xdg-dbus-proxy-0.1.6/bin" flags 0x0` + "\n")
+			w(`init: resolved "/host/nix/store/d2divmq2d897amikcwpdx7zrbpddxxcl-xdg-dbus-proxy-0.1.6/bin" on "/sysroot/nix/store/d2divmq2d897amikcwpdx7zrbpddxxcl-xdg-dbus-proxy-0.1.6/bin" flags 0x4005` + "\n")
+			w("init: resolving presets 0xf\n")
+			w("init: 68 filter rules loaded\n")
+			w("init: starting initial program /nix/store/d2divmq2d897amikcwpdx7zrbpddxxcl-xdg-dbus-proxy-0.1.6/bin/xdg-dbus-proxy\n")
+			w("C1: -> org.freedesktop.DBus call org.freedesktop.DBus.Hello at /org/freedesktop/DBus\n")
+			w("C-65536: -> org.freedesktop.DBus fake wildcarded AddMatch for org.freedesktop.portal\n")
+			w("C-65535: -> org.freedesktop.DBus fake AddMatch for org.freedesktop.Notifications\n")
+			w("C-65534: -> org.freedesktop.DBus fake GetNameOwner for org.freedesktop.Notifications\n")
+			w("C-65533: -> org.freedesktop.DBus fake ListNames\n")
+			w("B1: <- org.freedesktop.DBus return from C1\n")
+			w("B2: <- org.freedesktop.DBus signal org.freedesktop.DBus.NameAcquired at /org/freedesktop/DBus\n")
+			w("B3: <- org.freedesktop.DBus return from C-65536\n")
+			w("*SKIPPED*\n")
+			w("B4: <- org.freedesktop.DBus return from C-65535\n")
+			w("*SKIPPED*\n")
+			w("B5: <- org.freedesktop.DBus return error org.freedesktop.DBus.Error.NameHasNoOwner from C-65534\n")
+			w("*SKIPPED*\n")
+			w("B6: <- org.freedesktop.DBus return from C-65533\n")
+			w("C-65532: -> org.freedesktop.DBus fake GetNameOwner for org.freedesktop.DBus\n")
+			w("*SKIPPED*\n")
+			w("B7: <- org.freedesktop.DBus return from C-65532\n")
+			w("*SKIPPED*\n")
+			w("C2: -> org.freedesktop.DBus call org.freedesktop.DBus.AddMatch at /org/freedesktop/DBus\n")
+			w("C3: -> org.freedesktop.DBus call org.freedesktop.DBus.GetNameOwner at /org/freedesktop/DBus\n")
+			w("C4: -> org.freedesktop.DBus call org.freedesktop.DBus.AddMatch at /org/freedesktop/DBus\n")
+			w("C5: -> org.freedesktop.DBus call org.freedesktop.DBus.StartServiceByName at /org/freedesktop/DBus\n")
+			w("B8: <- org.freedesktop.DBus return from C2\n")
+			w("B9: <- org.freedesktop.DBus return error org.freedesktop.DBus.Error.NameHasNoOwner from C3\n")
+			w("B10: <- org.freedesktop.DBus return from C4\n")
+			w("B12: <- org.freedesktop.DBus signal org.freedesktop.DBus.NameOwnerChanged at /org/freedesktop/DBus\n")
+			w("B11: <- org.freedesktop.DBus return from C5\n")
+			w("C6: -> org.freedesktop.DBus call org.freedesktop.DBus.GetNameOwner at /org/freedesktop/DBus\n")
+			w("B13: <- org.freedesktop.DBus return from C6\n")
+			w("C7: -> :1.4 call org.freedesktop.Notifications.GetServerInformation at /org/freedesktop/Notifications\n")
+			w("B4: <- :1.4 return from C7\n")
+			w("C8: -> :1.4 call org.freedesktop.Notifications.GetServerInformation at /org/freedesktop/Notifications\n")
+			w("B5: <- :1.4 return from C8\n")
+			w("C9: -> :1.4 call org.freedesktop.Notifications.Notify at /org/freedesktop/Notifications\n")
+			w("B6: <- :1.4 return from C9\n")
+			w("C10: -> org.freedesktop.DBus call org.freedesktop.DBus.RemoveMatch at /org/freedesktop/DBus\n")
+			w("C11: -> org.freedesktop.DBus call org.freedesktop.DBus.RemoveMatch at /org/freedesktop/DBus\n")
+			w("B14: <- org.freedesktop.DBus return from C10\n")
+			w("B15: <- org.freedesktop.DBus return from C11\n")
+			w("init: initial process exited with code 0\n")
+		}, nil, []string{
+			"init: received setup parameters",
+			`init: mounting "/nix/store/5gml2l2cj28yvyfyzblzjy1laqpxmyzd-libselinux-3.8.1/lib" flags 0x0`,
+			`init: resolved "/host/nix/store/5gml2l2cj28yvyfyzblzjy1laqpxmyzd-libselinux-3.8.1/lib" on "/sysroot/nix/store/5gml2l2cj28yvyfyzblzjy1laqpxmyzd-libselinux-3.8.1/lib" flags 0x4005`,
+			`init: mounting "/nix/store/bcs094l67dlbqf7idxxbljp293zms9mh-util-linux-minimal-2.41-lib/lib" flags 0x0`,
+			`init: resolved "/host/nix/store/bcs094l67dlbqf7idxxbljp293zms9mh-util-linux-minimal-2.41-lib/lib" on "/sysroot/nix/store/bcs094l67dlbqf7idxxbljp293zms9mh-util-linux-minimal-2.41-lib/lib" flags 0x4005`,
+			`init: mounting "/nix/store/jl19fdc7gdxqz9a1s368r9d15vpirnqy-zlib-1.3.1/lib" flags 0x0`,
+			`init: resolved "/host/nix/store/jl19fdc7gdxqz9a1s368r9d15vpirnqy-zlib-1.3.1/lib" on "/sysroot/nix/store/jl19fdc7gdxqz9a1s368r9d15vpirnqy-zlib-1.3.1/lib" flags 0x4005`,
+			`init: mounting "/nix/store/rnn29mhynsa4ncmk0fkcrdr29n0j20l4-libffi-3.4.8/lib" flags 0x0`,
+			`init: resolved "/host/nix/store/rnn29mhynsa4ncmk0fkcrdr29n0j20l4-libffi-3.4.8/lib" on "/sysroot/nix/store/rnn29mhynsa4ncmk0fkcrdr29n0j20l4-libffi-3.4.8/lib" flags 0x4005`,
+			`init: mounting "/nix/store/vvp8hlss3d5q6hn0cifq04jrpnp6bini-pcre2-10.44/lib" flags 0x0`,
+			`init: resolved "/host/nix/store/vvp8hlss3d5q6hn0cifq04jrpnp6bini-pcre2-10.44/lib" on "/sysroot/nix/store/vvp8hlss3d5q6hn0cifq04jrpnp6bini-pcre2-10.44/lib" flags 0x4005`,
+			`init: mounting "/nix/store/y3nxdc2x8hwivppzgx5hkrhacsh87l21-glib-2.84.3/lib" flags 0x0`,
+			`init: resolved "/host/nix/store/y3nxdc2x8hwivppzgx5hkrhacsh87l21-glib-2.84.3/lib" on "/sysroot/nix/store/y3nxdc2x8hwivppzgx5hkrhacsh87l21-glib-2.84.3/lib" flags 0x4005`,
+			`init: mounting "/nix/store/zdpby3l6azi78sl83cpad2qjpfj25aqx-glibc-2.40-66/lib" flags 0x0`,
+			`init: resolved "/host/nix/store/zdpby3l6azi78sl83cpad2qjpfj25aqx-glibc-2.40-66/lib" on "/sysroot/nix/store/zdpby3l6azi78sl83cpad2qjpfj25aqx-glibc-2.40-66/lib" flags 0x4005`,
+			`init: mounting "/nix/store/zdpby3l6azi78sl83cpad2qjpfj25aqx-glibc-2.40-66/lib64" flags 0x0`,
+			`init: resolved "/host/nix/store/zdpby3l6azi78sl83cpad2qjpfj25aqx-glibc-2.40-66/lib" on "/sysroot/nix/store/zdpby3l6azi78sl83cpad2qjpfj25aqx-glibc-2.40-66/lib64" flags 0x4005`,
+			`init: mounting "/run/user/1000" flags 0x0`,
+			`init: resolved "/host/run/user/1000" on "/sysroot/run/user/1000" flags 0x4005`,
+			`init: mounting "/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f" flags 0x2`,
+			`init: resolved "/host/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f" on "/sysroot/tmp/hakurei.0/99dd71ee2146369514e0d10783368f8f" flags 0x4004`,
+			`init: mounting "/nix/store/d2divmq2d897amikcwpdx7zrbpddxxcl-xdg-dbus-proxy-0.1.6/bin" flags 0x0`,
+			`init: resolved "/host/nix/store/d2divmq2d897amikcwpdx7zrbpddxxcl-xdg-dbus-proxy-0.1.6/bin" on "/sysroot/nix/store/d2divmq2d897amikcwpdx7zrbpddxxcl-xdg-dbus-proxy-0.1.6/bin" flags 0x4005`,
+			"init: resolving presets 0xf",
+			"init: 68 filter rules loaded",
+			"init: starting initial program /nix/store/d2divmq2d897amikcwpdx7zrbpddxxcl-xdg-dbus-proxy-0.1.6/bin/xdg-dbus-proxy",
+
+			"init: initial process exited with code 0",
+		}, []string{
+			"C1: -> org.freedesktop.DBus call org.freedesktop.DBus.Hello at /org/freedesktop/DBus",
+			"C-65536: -> org.freedesktop.DBus fake wildcarded AddMatch for org.freedesktop.portal",
+			"C-65535: -> org.freedesktop.DBus fake AddMatch for org.freedesktop.Notifications",
+			"C-65534: -> org.freedesktop.DBus fake GetNameOwner for org.freedesktop.Notifications",
+			"C-65533: -> org.freedesktop.DBus fake ListNames",
+			"B1: <- org.freedesktop.DBus return from C1",
+			"B2: <- org.freedesktop.DBus signal org.freedesktop.DBus.NameAcquired at /org/freedesktop/DBus",
+			"B3: <- org.freedesktop.DBus return from C-65536",
+			"*SKIPPED*",
+			"B4: <- org.freedesktop.DBus return from C-65535",
+			"*SKIPPED*",
+			"B5: <- org.freedesktop.DBus return error org.freedesktop.DBus.Error.NameHasNoOwner from C-65534",
+			"*SKIPPED*",
+			"B6: <- org.freedesktop.DBus return from C-65533",
+			"C-65532: -> org.freedesktop.DBus fake GetNameOwner for org.freedesktop.DBus",
+			"*SKIPPED*",
+			"B7: <- org.freedesktop.DBus return from C-65532",
+			"*SKIPPED*",
+			"C2: -> org.freedesktop.DBus call org.freedesktop.DBus.AddMatch at /org/freedesktop/DBus",
+			"C3: -> org.freedesktop.DBus call org.freedesktop.DBus.GetNameOwner at /org/freedesktop/DBus",
+			"C4: -> org.freedesktop.DBus call org.freedesktop.DBus.AddMatch at /org/freedesktop/DBus",
+			"C5: -> org.freedesktop.DBus call org.freedesktop.DBus.StartServiceByName at /org/freedesktop/DBus",
+			"B8: <- org.freedesktop.DBus return from C2",
+			"B9: <- org.freedesktop.DBus return error org.freedesktop.DBus.Error.NameHasNoOwner from C3",
+			"B10: <- org.freedesktop.DBus return from C4",
+			"B12: <- org.freedesktop.DBus signal org.freedesktop.DBus.NameOwnerChanged at /org/freedesktop/DBus",
+			"B11: <- org.freedesktop.DBus return from C5",
+			"C6: -> org.freedesktop.DBus call org.freedesktop.DBus.GetNameOwner at /org/freedesktop/DBus",
+			"B13: <- org.freedesktop.DBus return from C6",
+			"C7: -> :1.4 call org.freedesktop.Notifications.GetServerInformation at /org/freedesktop/Notifications",
+			"B4: <- :1.4 return from C7",
+			"C8: -> :1.4 call org.freedesktop.Notifications.GetServerInformation at /org/freedesktop/Notifications",
+			"B5: <- :1.4 return from C8",
+			"C9: -> :1.4 call org.freedesktop.Notifications.Notify at /org/freedesktop/Notifications",
+			"B6: <- :1.4 return from C9",
+			"C10: -> org.freedesktop.DBus call org.freedesktop.DBus.RemoveMatch at /org/freedesktop/DBus",
+			"C11: -> org.freedesktop.DBus call org.freedesktop.DBus.RemoveMatch at /org/freedesktop/DBus",
+			"B14: <- org.freedesktop.DBus return from C10",
+			"B15: <- org.freedesktop.DBus return from C11",
+		}, nil, ""},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			gotPt := make([]string, 0, len(tc.wantPt))
+			out := &linePrefixWriter{
+				prefix: tc.prefix,
+				println: func(v ...any) {
+					if len(v) != 1 {
+						t.Fatalf("invalid call to println: %#v", v)
+					}
+					gotPt = append(gotPt, v[0].(string))
+				},
+				buf: new(strings.Builder),
+			}
+
+			var pos int
+			tc.f(func(s string) {
+				_, err := out.Write([]byte(s))
+				if tc.wantErr != nil {
+					if !reflect.DeepEqual(err, tc.wantErr[pos]) {
+						t.Fatalf("Write: error = %v, want %v", err, tc.wantErr[pos])
+					}
+				} else if err != nil {
+					t.Fatalf("Write: unexpected error: %v", err)
+					return
+				}
+				pos++
+			})
+
+			if !slices.Equal(out.msg, tc.want) {
+				t.Errorf("msg: %#v, want %#v", out.msg, tc.want)
+			}
+
+			if out.buf.String() != tc.wantBuf {
+				t.Errorf("buf: %q, want %q", out.buf, tc.wantBuf)
+			}
+
+			wantPt := make([]string, len(tc.wantPt))
+			for i, m := range tc.wantPt {
+				wantPt[i] = tc.prefix + m
+			}
+			if !slices.Equal(gotPt, wantPt) {
+				t.Errorf("passthrough: %#v, want %#v", gotPt, wantPt)
+			}
+
+			wantDump := make([]string, len(tc.want)+len(tc.wantExt))
+			for i, m := range tc.want {
+				wantDump[i] = tc.prefix + m
+			}
+			for i, m := range tc.wantExt {
+				wantDump[len(tc.want)+i] = m
+			}
+			t.Run("dump", func(t *testing.T) {
+				got := make([]string, 0, len(wantDump))
+				out.println = func(v ...any) {
+					if len(v) != 1 {
+						t.Fatalf("Dump: invalid call to println: %#v", v)
+					}
+					got = append(got, v[0].(string))
+				}
+				out.Dump()
+
+				if !slices.Equal(got, wantDump) {
+					t.Errorf("Dump: %#v, want %#v", got, wantDump)
+				}
+			})
+		})
+	}
+}