internal/app: build container state in shim

This significantly decreases ipc overhead.

Closes #3.

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

cmd/hakurei/command.go

@@ -2,10 +2,13 @@ package main
 
 import (
 	"context"
+	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"log"
 	"os"
+	"os/exec"
 	"os/user"
 	"strconv"
 	"sync"
@@ -13,36 +16,52 @@ import (
 
 	"hakurei.app/command"
 	"hakurei.app/container"
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 	"hakurei.app/hst"
 	"hakurei.app/internal"
 	"hakurei.app/internal/app"
 	"hakurei.app/internal/app/state"
-	"hakurei.app/internal/hlog"
-	"hakurei.app/system"
 	"hakurei.app/system/dbus"
 )
 
-func buildCommand(ctx context.Context, out io.Writer) command.Command {
+func buildCommand(ctx context.Context, msg container.Msg, early *earlyHardeningErrs, out io.Writer) command.Command {
 	var (
 		flagVerbose bool
 		flagJSON    bool
 	)
-	c := command.New(out, log.Printf, "hakurei", func([]string) error { internal.InstallOutput(flagVerbose); return nil }).
+	c := command.New(out, log.Printf, "hakurei", func([]string) error {
+		msg.SwapVerbose(flagVerbose)
+
+		if early.yamaLSM != nil {
+			msg.Verbosef("cannot enable ptrace protection via Yama LSM: %v", early.yamaLSM)
+			// not fatal
+		}
+
+		if early.dumpable != nil {
+			log.Printf("cannot set SUID_DUMP_DISABLE: %s", early.dumpable)
+			// not fatal
+		}
+
+		return nil
+	}).
 		Flag(&flagVerbose, "v", command.BoolFlag(false), "Increase log verbosity").
 		Flag(&flagJSON, "json", command.BoolFlag(false), "Serialise output in JSON when applicable")
 
 	c.Command("shim", command.UsageInternal, func([]string) error { app.ShimMain(); return errSuccess })
 
-	c.Command("app", "Load app from configuration file", func(args []string) error {
+	c.Command("app", "Load and start container from configuration file", func(args []string) error {
 		if len(args) < 1 {
 			log.Fatal("app requires at least 1 argument")
 		}
 
 		// config extraArgs...
-		config := tryPath(args[0])
-		config.Args = append(config.Args, args[1:]...)
+		config := tryPath(msg, args[0])
+		if config != nil && config.Container != nil {
+			config.Container.Args = append(config.Container.Args, args[1:]...)
+		}
 
-		app.Main(ctx, config)
+		app.Main(ctx, msg, config)
 		panic("unreachable")
 	})
 
@@ -62,14 +81,8 @@ func buildCommand(ctx context.Context, out io.Writer) command.Command {
 			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:   flagID,
-				Args: args,
-			}
-
-			if flagIdentity < 0 || flagIdentity > 9999 {
+		c.NewCommand("run", "Configure and start a permissive container", func(args []string) error {
+			if flagIdentity < hst.IdentityMin || flagIdentity > hst.IdentityMax {
 				log.Fatalf("identity %d out of range", flagIdentity)
 			}
 
@@ -78,15 +91,15 @@ func buildCommand(ctx context.Context, out io.Writer) command.Command {
 				passwd     *user.User
 				passwdOnce sync.Once
 				passwdFunc = func() {
-					us := strconv.Itoa(app.HsuUid(new(app.Hsu).MustID(), flagIdentity))
+					us := strconv.Itoa(app.HsuUid(new(app.Hsu).MustIDMsg(msg), flagIdentity))
 					if u, err := user.LookupId(us); err != nil {
-						hlog.Verbosef("cannot look up uid %s", us)
+						msg.Verbosef("cannot look up uid %s", us)
 						passwd = &user.User{
 							Uid:      us,
 							Gid:      us,
 							Username: "chronos",
 							Name:     "Hakurei Permissive Default",
-							HomeDir:  container.FHSVarEmpty,
+							HomeDir:  fhs.VarEmpty,
 						}
 					} else {
 						passwd = u
@@ -94,60 +107,128 @@ func buildCommand(ctx context.Context, out io.Writer) command.Command {
 				}
 			)
 
-			if flagHomeDir == "os" {
-				passwdOnce.Do(passwdFunc)
-				flagHomeDir = passwd.HomeDir
+			// paths are identical, resolve inner shell and program path
+			shell := fhs.AbsRoot.Append("bin", "sh")
+			if a, err := check.NewAbs(os.Getenv("SHELL")); err == nil {
+				shell = a
+			}
+			progPath := shell
+			if len(args) > 0 {
+				if p, err := exec.LookPath(args[0]); err != nil {
+					log.Fatal(errors.Unwrap(err))
+					return err
+				} else if progPath, err = check.NewAbs(p); err != nil {
+					log.Fatal(err.Error())
+					return err
+				}
 			}
 
-			if flagUserName == "chronos" {
-				passwdOnce.Do(passwdFunc)
-				flagUserName = passwd.Username
-			}
-
-			config.Identity = flagIdentity
-			config.Groups = flagGroups
-			config.Username = flagUserName
-
-			if a, err := container.NewAbs(flagHomeDir); err != nil {
-				log.Fatal(err.Error())
-				return err
-			} else {
-				config.Home = a
-			}
-
-			var e system.Enablement
+			var et hst.Enablement
 			if flagWayland {
-				e |= system.EWayland
+				et |= hst.EWayland
 			}
 			if flagX11 {
-				e |= system.EX11
+				et |= hst.EX11
 			}
 			if flagDBus {
-				e |= system.EDBus
+				et |= hst.EDBus
 			}
 			if flagPulse {
-				e |= system.EPulse
+				et |= hst.EPulse
+			}
+
+			config := &hst.Config{
+				ID:          flagID,
+				Identity:    flagIdentity,
+				Groups:      flagGroups,
+				Enablements: hst.NewEnablements(et),
+
+				Container: &hst.ContainerConfig{
+					Userns:       true,
+					HostNet:      true,
+					Tty:          true,
+					HostAbstract: true,
+
+					Filesystem: []hst.FilesystemConfigJSON{
+						// autoroot, includes the home directory
+						{FilesystemConfig: &hst.FSBind{
+							Target:  fhs.AbsRoot,
+							Source:  fhs.AbsRoot,
+							Write:   true,
+							Special: true,
+						}},
+					},
+
+					Username: flagUserName,
+					Shell:    shell,
+
+					Path: progPath,
+					Args: args,
+				},
+			}
+
+			// bind GPU stuff
+			if et&(hst.EX11|hst.EWayland) != 0 {
+				config.Container.Filesystem = append(config.Container.Filesystem, hst.FilesystemConfigJSON{FilesystemConfig: &hst.FSBind{
+					Source:   fhs.AbsDev.Append("dri"),
+					Device:   true,
+					Optional: true,
+				}})
+			}
+
+			config.Container.Filesystem = append(config.Container.Filesystem,
+				// opportunistically bind kvm
+				hst.FilesystemConfigJSON{FilesystemConfig: &hst.FSBind{
+					Source:   fhs.AbsDev.Append("kvm"),
+					Device:   true,
+					Optional: true,
+				}},
+
+				// do autoetc last
+				hst.FilesystemConfigJSON{FilesystemConfig: &hst.FSBind{
+					Target:  fhs.AbsEtc,
+					Source:  fhs.AbsEtc,
+					Special: true,
+				}},
+			)
+
+			if config.Container.Username == "chronos" {
+				passwdOnce.Do(passwdFunc)
+				config.Container.Username = passwd.Username
+			}
+
+			{
+				homeDir := flagHomeDir
+				if homeDir == "os" {
+					passwdOnce.Do(passwdFunc)
+					homeDir = passwd.HomeDir
+				}
+				if a, err := check.NewAbs(homeDir); err != nil {
+					log.Fatal(err.Error())
+					return err
+				} else {
+					config.Container.Home = a
+				}
 			}
-			config.Enablements = hst.NewEnablements(e)
 
 			// parse D-Bus config file from flags if applicable
 			if flagDBus {
 				if flagDBusConfigSession == "builtin" {
 					config.SessionBus = dbus.NewConfig(flagID, true, flagDBusMpris)
 				} else {
-					if conf, err := dbus.NewConfigFromFile(flagDBusConfigSession); err != nil {
+					if f, err := os.Open(flagDBusConfigSession); err != nil {
+						log.Fatal(err.Error())
+					} else if err = json.NewDecoder(f).Decode(&config.SessionBus); 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 flagDBusConfigSystem != "nil" {
-					if conf, err := dbus.NewConfigFromFile(flagDBusConfigSystem); err != nil {
+					if f, err := os.Open(flagDBusConfigSystem); err != nil {
+						log.Fatal(err.Error())
+					} else if err = json.NewDecoder(f).Decode(&config.SystemBus); err != nil {
 						log.Fatalf("cannot load system bus proxy config from %q: %s", flagDBusConfigSystem, err)
-					} else {
-						config.SystemBus = conf
 					}
 				}
 
@@ -162,7 +243,7 @@ func buildCommand(ctx context.Context, out io.Writer) command.Command {
 				}
 			}
 
-			app.Main(ctx, config)
+			app.Main(ctx, msg, config)
 			panic("unreachable")
 		}).
 			Flag(&flagDBusConfigSession, "dbus-config", command.StringFlag("builtin"),
@@ -202,11 +283,13 @@ func buildCommand(ctx context.Context, out io.Writer) command.Command {
 
 			case 1: // instance
 				name := args[0]
-				config, entry := tryShort(name)
+				config, entry := tryShort(msg, name)
 				if config == nil {
-					config = tryPath(name)
+					config = tryPath(msg, name)
+				}
+				if !printShowInstance(os.Stdout, time.Now().UTC(), entry, config, flagShort, flagJSON) {
+					os.Exit(1)
 				}
-				printShowInstance(os.Stdout, time.Now().UTC(), entry, config, flagShort, flagJSON)
 
 			default:
 				log.Fatal("show requires 1 argument")
@@ -219,31 +302,16 @@ func buildCommand(ctx context.Context, out io.Writer) command.Command {
 		var flagShort bool
 		c.NewCommand("ps", "List active instances", func(args []string) error {
 			var sc hst.Paths
-			app.CopyPaths(&sc, new(app.Hsu).MustID())
-			printPs(os.Stdout, time.Now().UTC(), state.NewMulti(sc.RunDirPath.String()), flagShort, flagJSON)
+			app.CopyPaths().Copy(&sc, new(app.Hsu).MustID())
+			printPs(os.Stdout, time.Now().UTC(), state.NewMulti(msg, sc.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())
-		return errSuccess
-	})
-
-	c.Command("license", "Show full license text", func(args []string) error {
-		fmt.Println(license)
-		return errSuccess
-	})
-
-	c.Command("template", "Produce a config template", func(args []string) error {
-		printJSON(os.Stdout, false, hst.Template())
-		return errSuccess
-	})
-
-	c.Command("help", "Show this help message", func([]string) error {
-		c.PrintHelp()
-		return errSuccess
-	})
+	c.Command("version", "Display version information", func(args []string) error { fmt.Println(internal.Version()); return errSuccess })
+	c.Command("license", "Show full license text", func(args []string) error { fmt.Println(license); return errSuccess })
+	c.Command("template", "Produce a config template", func(args []string) error { printJSON(os.Stdout, false, hst.Template()); return errSuccess })
+	c.Command("help", "Show this help message", func([]string) error { c.PrintHelp(); return errSuccess })
 
 	return c
 }

cmd/hakurei/command_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 
 	"hakurei.app/command"
+	"hakurei.app/container"
 )
 
 func TestHelp(t *testing.T) {
@@ -20,8 +21,8 @@ func TestHelp(t *testing.T) {
 Usage:	hakurei [-h | --help] [-v] [--json] COMMAND [OPTIONS]
 
 Commands:
-    app         Load app from configuration file
-    run         Configure and start a permissive default sandbox
+    app         Load and start container from configuration file
+    run         Configure and start a permissive container
     show        Show live or local app configuration
     ps          List active instances
     version     Display version information
@@ -68,7 +69,7 @@ Flags:
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
 			out := new(bytes.Buffer)
-			c := buildCommand(t.Context(), out)
+			c := buildCommand(t.Context(), container.NewMsg(nil), new(earlyHardeningErrs), 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

@@ -13,8 +13,6 @@ import (
 	"syscall"
 
 	"hakurei.app/container"
-	"hakurei.app/internal"
-	"hakurei.app/internal/hlog"
 )
 
 var (
@@ -24,20 +22,20 @@ var (
 	license string
 )
 
-func init() { hlog.Prepare("hakurei") }
+// earlyHardeningErrs are errors collected while setting up early hardening feature.
+type earlyHardeningErrs struct{ yamaLSM, dumpable error }
 
 func main() {
 	// early init path, skips root check and duplicate PR_SET_DUMPABLE
-	container.TryArgv0(hlog.Output{}, hlog.Prepare, internal.InstallOutput)
+	container.TryArgv0(nil)
 
-	if err := container.SetPtracer(0); err != nil {
-		hlog.Verbosef("cannot enable ptrace protection via Yama LSM: %v", err)
-		// not fatal: this program runs as the privileged user
-	}
+	log.SetPrefix("hakurei: ")
+	log.SetFlags(0)
+	msg := container.NewMsg(log.Default())
 
-	if err := container.SetDumpable(container.SUID_DUMP_DISABLE); err != nil {
-		log.Printf("cannot set SUID_DUMP_DISABLE: %s", err)
-		// not fatal: this program runs as the privileged user
+	early := earlyHardeningErrs{
+		yamaLSM:  container.SetPtracer(0),
+		dumpable: container.SetDumpable(container.SUID_DUMP_DISABLE),
 	}
 
 	if os.Geteuid() == 0 {
@@ -48,10 +46,10 @@ func main() {
 		syscall.SIGINT, syscall.SIGTERM)
 	defer stop() // unreachable
 
-	buildCommand(ctx, os.Stderr).MustParse(os.Args[1:], func(err error) {
-		hlog.Verbosef("command returned %v", err)
+	buildCommand(ctx, msg, &early, os.Stderr).MustParse(os.Args[1:], func(err error) {
+		msg.Verbosef("command returned %v", err)
 		if errors.Is(err, errSuccess) {
-			hlog.BeforeExit()
+			msg.BeforeExit()
 			os.Exit(0)
 		}
 		// this catches faulty command handlers that fail to return before this point

cmd/hakurei/parse.go

@@ -10,20 +10,20 @@ import (
 	"strings"
 	"syscall"
 
+	"hakurei.app/container"
 	"hakurei.app/hst"
 	"hakurei.app/internal/app"
 	"hakurei.app/internal/app/state"
-	"hakurei.app/internal/hlog"
 )
 
-func tryPath(name string) (config *hst.Config) {
+func tryPath(msg container.Msg, name string) (config *hst.Config) {
 	var r io.Reader
 	config = new(hst.Config)
 
 	if name != "-" {
-		r = tryFd(name)
+		r = tryFd(msg, name)
 		if r == nil {
-			hlog.Verbose("load configuration from file")
+			msg.Verbose("load configuration from file")
 
 			if f, err := os.Open(name); err != nil {
 				log.Fatalf("cannot access configuration file %q: %s", name, err)
@@ -49,14 +49,14 @@ func tryPath(name string) (config *hst.Config) {
 	return
 }
 
-func tryFd(name string) io.ReadCloser {
+func tryFd(msg container.Msg, name string) io.ReadCloser {
 	if v, err := strconv.Atoi(name); err != nil {
 		if !errors.Is(err, strconv.ErrSyntax) {
-			hlog.Verbosef("name cannot be interpreted as int64: %v", err)
+			msg.Verbosef("name cannot be interpreted as int64: %v", err)
 		}
 		return nil
 	} else {
-		hlog.Verbosef("trying config stream from %d", v)
+		msg.Verbosef("trying config stream from %d", v)
 		fd := uintptr(v)
 		if _, _, errno := syscall.Syscall(syscall.SYS_FCNTL, fd, syscall.F_GETFD, 0); errno != 0 {
 			if errors.Is(errno, syscall.EBADF) {
@@ -68,7 +68,7 @@ func tryFd(name string) io.ReadCloser {
 	}
 }
 
-func tryShort(name string) (config *hst.Config, entry *state.State) {
+func tryShort(msg container.Msg, name string) (config *hst.Config, entry *state.State) {
 	likePrefix := false
 	if len(name) <= 32 {
 		likePrefix = true
@@ -86,11 +86,11 @@ func tryShort(name string) (config *hst.Config, entry *state.State) {
 
 	// try to match from state store
 	if likePrefix && len(name) >= 8 {
-		hlog.Verbose("argument looks like prefix")
+		msg.Verbose("argument looks like prefix")
 
 		var sc hst.Paths
-		app.CopyPaths(&sc, new(app.Hsu).MustID())
-		s := state.NewMulti(sc.RunDirPath.String())
+		app.CopyPaths().Copy(&sc, new(app.Hsu).MustID())
+		s := state.NewMulti(msg, sc.RunDirPath.String())
 		if entries, err := state.Join(s); err != nil {
 			log.Printf("cannot join store: %v", err)
 			// drop to fetch from file
@@ -104,7 +104,7 @@ func tryShort(name string) (config *hst.Config, entry *state.State) {
 					break
 				}
 
-				hlog.Verbosef("instance %s skipped", v)
+				msg.Verbosef("instance %s skipped", v)
 			}
 		}
 	}

cmd/hakurei/print.go

@@ -11,10 +11,10 @@ import (
 	"text/tabwriter"
 	"time"
 
+	"hakurei.app/container"
 	"hakurei.app/hst"
 	"hakurei.app/internal/app"
 	"hakurei.app/internal/app/state"
-	"hakurei.app/system/dbus"
 )
 
 func printShowSystem(output io.Writer, short, flagJSON bool) {
@@ -22,7 +22,7 @@ func printShowSystem(output io.Writer, short, flagJSON bool) {
 	defer t.MustFlush()
 
 	info := &hst.Info{User: new(app.Hsu).MustID()}
-	app.CopyPaths(&info.Paths, info.User)
+	app.CopyPaths().Copy(&info.Paths, info.User)
 
 	if flagJSON {
 		printJSON(output, short, info)
@@ -39,7 +39,9 @@ func printShowSystem(output io.Writer, short, flagJSON bool) {
 func printShowInstance(
 	output io.Writer, now time.Time,
 	instance *state.State, config *hst.Config,
-	short, flagJSON bool) {
+	short, flagJSON bool) (valid bool) {
+	valid = true
+
 	if flagJSON {
 		if instance != nil {
 			printJSON(output, short, instance)
@@ -52,8 +54,11 @@ func printShowInstance(
 	t := newPrinter(output)
 	defer t.MustFlush()
 
-	if config.Container == nil {
-		mustPrint(output, "Warning: this configuration uses permissive defaults!\n\n")
+	if err := config.Validate(); err != nil {
+		valid = false
+		if m, ok := container.GetErrorMessage(err); ok {
+			mustPrint(output, "Error: "+m+"!\n\n")
+		}
 	}
 
 	if instance != nil {
@@ -73,11 +78,11 @@ func printShowInstance(
 	if len(config.Groups) > 0 {
 		t.Printf(" Groups:\t%s\n", strings.Join(config.Groups, ", "))
 	}
-	if config.Home != nil {
-		t.Printf(" Home:\t%s\n", config.Home)
-	}
 	if config.Container != nil {
 		params := config.Container
+		if params.Home != nil {
+			t.Printf(" Home:\t%s\n", params.Home)
+		}
 		if params.Hostname != "" {
 			t.Printf(" Hostname:\t%s\n", params.Hostname)
 		}
@@ -100,12 +105,12 @@ func printShowInstance(
 		}
 		t.Printf(" Flags:\t%s\n", strings.Join(flags, " "))
 
-		if config.Path != nil {
-			t.Printf(" Path:\t%s\n", config.Path)
+		if params.Path != nil {
+			t.Printf(" Path:\t%s\n", params.Path)
+		}
+		if len(params.Args) > 0 {
+			t.Printf(" Arguments:\t%s\n", strings.Join(params.Args, " "))
 		}
-	}
-	if len(config.Args) > 0 {
-		t.Printf(" Arguments:\t%s\n", strings.Join(config.Args, " "))
 	}
 	t.Printf("\n")
 
@@ -114,6 +119,7 @@ func printShowInstance(
 			t.Printf("Filesystem\n")
 			for _, f := range config.Container.Filesystem {
 				if !f.Valid() {
+					valid = false
 					t.Println(" <invalid>")
 					continue
 				}
@@ -133,7 +139,7 @@ func printShowInstance(
 		}
 	}
 
-	printDBus := func(c *dbus.Config) {
+	printDBus := func(c *hst.BusConfig) {
 		t.Printf(" Filter:\t%v\n", c.Filter)
 		if len(c.See) > 0 {
 			t.Printf(" See:\t%q\n", c.See)
@@ -161,6 +167,8 @@ func printShowInstance(
 		printDBus(config.SystemBus)
 		t.Printf("\n")
 	}
+
+	return
 }
 
 func printPs(output io.Writer, now time.Time, s state.Store, short, flagJSON bool) {

cmd/hakurei/print_test.go

@@ -7,7 +7,6 @@ import (
 
 	"hakurei.app/hst"
 	"hakurei.app/internal/app/state"
-	"hakurei.app/system/dbus"
 )
 
 var (
@@ -27,13 +26,14 @@ var (
 	testAppTime = time.Unix(0, 9).UTC()
 )
 
-func Test_printShowInstance(t *testing.T) {
+func TestPrintShowInstance(t *testing.T) {
 	testCases := []struct {
 		name        string
 		instance    *state.State
 		config      *hst.Config
 		short, json bool
 		want        string
+		valid       bool
 	}{
 		{"config", nil, hst.Template(), false, false, `App
  Identity:       9 (org.chromium.Chromium)
@@ -71,21 +71,25 @@ System bus
  Filter:    true
  Talk:      ["org.bluez" "org.freedesktop.Avahi" "org.freedesktop.UPower"]
 
-`},
-		{"config pd", nil, new(hst.Config), false, false, `Warning: this configuration uses permissive defaults!
+`, true},
+		{"config pd", nil, new(hst.Config), false, false, `Error: configuration missing container state!
 
 App
  Identity:       0
  Enablements:    (no enablements)
 
-`},
-		{"config flag none", nil, &hst.Config{Container: new(hst.ContainerConfig)}, false, false, `App
+`, false},
+		{"config flag none", nil, &hst.Config{Container: new(hst.ContainerConfig)}, false, false, `Error: container configuration missing path to home directory!
+
+App
  Identity:       0
  Enablements:    (no enablements)
  Flags:          none
 
-`},
-		{"config nil entries", nil, &hst.Config{Container: &hst.ContainerConfig{Filesystem: make([]hst.FilesystemConfigJSON, 1)}, ExtraPerms: make([]*hst.ExtraPermConfig, 1)}, false, false, `App
+`, false},
+		{"config nil entries", nil, &hst.Config{Container: &hst.ContainerConfig{Filesystem: make([]hst.FilesystemConfigJSON, 1)}, ExtraPerms: make([]*hst.ExtraPermConfig, 1)}, false, false, `Error: container configuration missing path to home directory!
+
+App
  Identity:       0
  Enablements:    (no enablements)
  Flags:          none
@@ -95,8 +99,8 @@ Filesystem
 
 Extra ACL
 
-`},
-		{"config pd dbus see", nil, &hst.Config{SessionBus: &dbus.Config{See: []string{"org.example.test"}}}, false, false, `Warning: this configuration uses permissive defaults!
+`, false},
+		{"config pd dbus see", nil, &hst.Config{SessionBus: &hst.BusConfig{See: []string{"org.example.test"}}}, false, false, `Error: configuration missing container state!
 
 App
  Identity:       0
@@ -106,7 +110,7 @@ Session bus
  Filter:    false
  See:       ["org.example.test"]
 
-`},
+`, false},
 
 		{"instance", testState, hst.Template(), false, false, `State
  Instance:    8e2c76b066dabe574cf073bdb46eb5c1 (3735928559)
@@ -148,8 +152,8 @@ System bus
  Filter:    true
  Talk:      ["org.bluez" "org.freedesktop.Avahi" "org.freedesktop.UPower"]
 
-`},
-		{"instance pd", testState, new(hst.Config), false, false, `Warning: this configuration uses permissive defaults!
+`, true},
+		{"instance pd", testState, new(hst.Config), false, false, `Error: configuration missing container state!
 
 State
  Instance:    8e2c76b066dabe574cf073bdb46eb5c1 (3735928559)
@@ -159,10 +163,10 @@ App
  Identity:       0
  Enablements:    (no enablements)
 
-`},
+`, false},
 
 		{"json nil", nil, nil, false, true, `null
-`},
+`, true},
 		{"json instance", testState, nil, false, true, `{
   "instance": [
     142,
@@ -185,14 +189,6 @@ App
   "pid": 3735928559,
   "config": {
     "id": "org.chromium.Chromium",
-    "path": "/run/current-system/sw/bin/chromium",
-    "args": [
-      "chromium",
-      "--ignore-gpu-blocklist",
-      "--disable-smooth-scrolling",
-      "--enable-features=UseOzonePlatform",
-      "--ozone-platform=wayland"
-    ],
     "enablements": {
       "wayland": true,
       "dbus": true,
@@ -234,9 +230,6 @@ App
       "broadcast": null,
       "filter": true
     },
-    "username": "chronos",
-    "shell": "/run/current-system/sw/bin/zsh",
-    "home": "/data/data/org.chromium.Chromium",
     "extra_perms": [
       {
         "ensure": true,
@@ -259,8 +252,6 @@ App
     "container": {
       "hostname": "localhost",
       "wait_delay": -1,
-      "seccomp_flags": 1,
-      "seccomp_presets": 1,
       "seccomp_compat": true,
       "devel": true,
       "userns": true,
@@ -333,22 +324,25 @@ App
           "dev": true,
           "optional": true
         }
+      ],
+      "username": "chronos",
+      "shell": "/run/current-system/sw/bin/zsh",
+      "home": "/data/data/org.chromium.Chromium",
+      "path": "/run/current-system/sw/bin/chromium",
+      "args": [
+        "chromium",
+        "--ignore-gpu-blocklist",
+        "--disable-smooth-scrolling",
+        "--enable-features=UseOzonePlatform",
+        "--ozone-platform=wayland"
       ]
     }
   },
   "time": "1970-01-01T00:00:00.000000009Z"
 }
-`},
+`, true},
 		{"json config", nil, hst.Template(), false, true, `{
   "id": "org.chromium.Chromium",
-  "path": "/run/current-system/sw/bin/chromium",
-  "args": [
-    "chromium",
-    "--ignore-gpu-blocklist",
-    "--disable-smooth-scrolling",
-    "--enable-features=UseOzonePlatform",
-    "--ozone-platform=wayland"
-  ],
   "enablements": {
     "wayland": true,
     "dbus": true,
@@ -390,9 +384,6 @@ App
     "broadcast": null,
     "filter": true
   },
-  "username": "chronos",
-  "shell": "/run/current-system/sw/bin/zsh",
-  "home": "/data/data/org.chromium.Chromium",
   "extra_perms": [
     {
       "ensure": true,
@@ -415,8 +406,6 @@ App
   "container": {
     "hostname": "localhost",
     "wait_delay": -1,
-    "seccomp_flags": 1,
-    "seccomp_presets": 1,
     "seccomp_compat": true,
     "devel": true,
     "userns": true,
@@ -489,26 +478,39 @@ App
         "dev": true,
         "optional": true
       }
+    ],
+    "username": "chronos",
+    "shell": "/run/current-system/sw/bin/zsh",
+    "home": "/data/data/org.chromium.Chromium",
+    "path": "/run/current-system/sw/bin/chromium",
+    "args": [
+      "chromium",
+      "--ignore-gpu-blocklist",
+      "--disable-smooth-scrolling",
+      "--enable-features=UseOzonePlatform",
+      "--ozone-platform=wayland"
     ]
   }
 }
-`},
+`, true},
 	}
 
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
 			output := new(strings.Builder)
-			printShowInstance(output, testTime, tc.instance, tc.config, tc.short, tc.json)
+			gotValid := printShowInstance(output, testTime, tc.instance, tc.config, tc.short, tc.json)
 			if got := output.String(); got != tc.want {
-				t.Errorf("printShowInstance: got\n%s\nwant\n%s",
-					got, tc.want)
+				t.Errorf("printShowInstance: \n%s\nwant\n%s", got, tc.want)
 				return
 			}
+			if gotValid != tc.valid {
+				t.Errorf("printShowInstance: valid = %v, want %v", gotValid, tc.valid)
+			}
 		})
 	}
 }
 
-func Test_printPs(t *testing.T) {
+func TestPrintPs(t *testing.T) {
 	testCases := []struct {
 		name        string
 		entries     state.Entries
@@ -551,14 +553,6 @@ func Test_printPs(t *testing.T) {
     "pid": 3735928559,
     "config": {
       "id": "org.chromium.Chromium",
-      "path": "/run/current-system/sw/bin/chromium",
-      "args": [
-        "chromium",
-        "--ignore-gpu-blocklist",
-        "--disable-smooth-scrolling",
-        "--enable-features=UseOzonePlatform",
-        "--ozone-platform=wayland"
-      ],
       "enablements": {
         "wayland": true,
         "dbus": true,
@@ -600,9 +594,6 @@ func Test_printPs(t *testing.T) {
         "broadcast": null,
         "filter": true
       },
-      "username": "chronos",
-      "shell": "/run/current-system/sw/bin/zsh",
-      "home": "/data/data/org.chromium.Chromium",
       "extra_perms": [
         {
           "ensure": true,
@@ -625,8 +616,6 @@ func Test_printPs(t *testing.T) {
       "container": {
         "hostname": "localhost",
         "wait_delay": -1,
-        "seccomp_flags": 1,
-        "seccomp_presets": 1,
         "seccomp_compat": true,
         "devel": true,
         "userns": true,
@@ -699,6 +688,17 @@ func Test_printPs(t *testing.T) {
             "dev": true,
             "optional": true
           }
+        ],
+        "username": "chronos",
+        "shell": "/run/current-system/sw/bin/zsh",
+        "home": "/data/data/org.chromium.Chromium",
+        "path": "/run/current-system/sw/bin/chromium",
+        "args": [
+          "chromium",
+          "--ignore-gpu-blocklist",
+          "--disable-smooth-scrolling",
+          "--enable-features=UseOzonePlatform",
+          "--ozone-platform=wayland"
         ]
       }
     },

cmd/hpkg/app.go

@@ -5,10 +5,9 @@ import (
 	"log"
 	"os"
 
-	"hakurei.app/container"
-	"hakurei.app/container/seccomp"
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 	"hakurei.app/hst"
-	"hakurei.app/system/dbus"
 )
 
 type appInfo struct {
@@ -38,9 +37,9 @@ type appInfo struct {
 	// passed through to [hst.Config]
 	DirectWayland bool `json:"direct_wayland,omitempty"`
 	// passed through to [hst.Config]
-	SystemBus *dbus.Config `json:"system_bus,omitempty"`
+	SystemBus *hst.BusConfig `json:"system_bus,omitempty"`
 	// passed through to [hst.Config]
-	SessionBus *dbus.Config `json:"session_bus,omitempty"`
+	SessionBus *hst.BusConfig `json:"session_bus,omitempty"`
 	// passed through to [hst.Config]
 	Enablements *hst.Enablements `json:"enablements,omitempty"`
 
@@ -56,30 +55,23 @@ type appInfo struct {
 	// store path to nixGL source
 	NixGL string `json:"nix_gl,omitempty"`
 	// store path to activate-and-exec script
-	Launcher *container.Absolute `json:"launcher"`
+	Launcher *check.Absolute `json:"launcher"`
 	// store path to /run/current-system
-	CurrentSystem *container.Absolute `json:"current_system"`
+	CurrentSystem *check.Absolute `json:"current_system"`
 	// store path to home-manager activation package
 	ActivationPackage string `json:"activation_package"`
 }
 
-func (app *appInfo) toHst(pathSet *appPathSet, pathname *container.Absolute, argv []string, flagDropShell bool) *hst.Config {
+func (app *appInfo) toHst(pathSet *appPathSet, pathname *check.Absolute, argv []string, flagDropShell bool) *hst.Config {
 	config := &hst.Config{
 		ID: app.ID,
 
-		Path: pathname,
-		Args: argv,
-
 		Enablements: app.Enablements,
 
 		SystemBus:     app.SystemBus,
 		SessionBus:    app.SessionBus,
 		DirectWayland: app.DirectWayland,
 
-		Username: "hakurei",
-		Shell:    pathShell,
-		Home:     pathDataData.Append(app.ID),
-
 		Identity: app.Identity,
 		Groups:   app.Groups,
 
@@ -92,33 +84,35 @@ func (app *appInfo) toHst(pathSet *appPathSet, pathname *container.Absolute, arg
 			Device:       app.Device,
 			Tty:          app.Tty || flagDropShell,
 			MapRealUID:   app.MapRealUID,
+			Multiarch:    app.Multiarch,
 			Filesystem: []hst.FilesystemConfigJSON{
-				{FilesystemConfig: &hst.FSBind{Target: container.AbsFHSEtc, Source: pathSet.cacheDir.Append("etc"), Special: true}},
+				{FilesystemConfig: &hst.FSBind{Target: fhs.AbsEtc, Source: pathSet.cacheDir.Append("etc"), Special: true}},
 				{FilesystemConfig: &hst.FSBind{Source: pathSet.nixPath.Append("store"), Target: pathNixStore}},
 				{FilesystemConfig: &hst.FSLink{Target: pathCurrentSystem, Linkname: app.CurrentSystem.String()}},
 				{FilesystemConfig: &hst.FSLink{Target: pathBin, Linkname: pathSwBin.String()}},
-				{FilesystemConfig: &hst.FSLink{Target: container.AbsFHSUsrBin, Linkname: pathSwBin.String()}},
+				{FilesystemConfig: &hst.FSLink{Target: fhs.AbsUsrBin, Linkname: pathSwBin.String()}},
 				{FilesystemConfig: &hst.FSBind{Source: pathSet.metaPath, Target: hst.AbsTmp.Append("app")}},
-				{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSEtc.Append("resolv.conf"), Optional: true}},
-				{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSSys.Append("block"), Optional: true}},
-				{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSSys.Append("bus"), Optional: true}},
-				{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSSys.Append("class"), Optional: true}},
-				{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSSys.Append("dev"), Optional: true}},
-				{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSSys.Append("devices"), Optional: true}},
+				{FilesystemConfig: &hst.FSBind{Source: fhs.AbsEtc.Append("resolv.conf"), Optional: true}},
+				{FilesystemConfig: &hst.FSBind{Source: fhs.AbsSys.Append("block"), Optional: true}},
+				{FilesystemConfig: &hst.FSBind{Source: fhs.AbsSys.Append("bus"), Optional: true}},
+				{FilesystemConfig: &hst.FSBind{Source: fhs.AbsSys.Append("class"), Optional: true}},
+				{FilesystemConfig: &hst.FSBind{Source: fhs.AbsSys.Append("dev"), Optional: true}},
+				{FilesystemConfig: &hst.FSBind{Source: fhs.AbsSys.Append("devices"), Optional: true}},
 				{FilesystemConfig: &hst.FSBind{Target: pathDataData.Append(app.ID), Source: pathSet.homeDir, Write: true, Ensure: true}},
 			},
+
+			Username: "hakurei",
+			Shell:    pathShell,
+			Home:     pathDataData.Append(app.ID),
+
+			Path: pathname,
+			Args: argv,
 		},
 		ExtraPerms: []*hst.ExtraPermConfig{
 			{Path: dataHome, Execute: true},
 			{Ensure: true, Path: pathSet.baseDir, Read: true, Write: true, Execute: true},
 		},
 	}
-	if app.Multiarch {
-		config.Container.SeccompFlags |= seccomp.AllowMultiarch
-	}
-	if app.Bluetooth {
-		config.Container.SeccompFlags |= seccomp.AllowBluetooth
-	}
 	return config
 }
 

cmd/hpkg/main.go

@@ -12,23 +12,24 @@ import (
 
 	"hakurei.app/command"
 	"hakurei.app/container"
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 	"hakurei.app/hst"
-	"hakurei.app/internal"
-	"hakurei.app/internal/hlog"
 )
 
 var (
 	errSuccess = errors.New("success")
 )
 
-func init() {
-	hlog.Prepare("hpkg")
+func main() {
+	log.SetPrefix("hpkg: ")
+	log.SetFlags(0)
+	msg := container.NewMsg(log.Default())
+
 	if err := os.Setenv("SHELL", pathShell.String()); err != nil {
 		log.Fatalf("cannot set $SHELL: %v", err)
 	}
-}
 
-func main() {
 	if os.Geteuid() == 0 {
 		log.Fatal("this program must not run as root")
 	}
@@ -41,7 +42,7 @@ func main() {
 		flagVerbose   bool
 		flagDropShell bool
 	)
-	c := command.New(os.Stderr, log.Printf, "hpkg", func([]string) error { internal.InstallOutput(flagVerbose); return nil }).
+	c := command.New(os.Stderr, log.Printf, "hpkg", func([]string) error { msg.SwapVerbose(flagVerbose); return nil }).
 		Flag(&flagVerbose, "v", command.BoolFlag(false), "Print debug messages to the console").
 		Flag(&flagDropShell, "s", command.BoolFlag(false), "Drop to a shell in place of next hakurei action")
 
@@ -80,22 +81,22 @@ func main() {
 				Extract package and set up for cleanup.
 			*/
 
-			var workDir *container.Absolute
+			var workDir *check.Absolute
 			if p, err := os.MkdirTemp("", "hpkg.*"); err != nil {
 				log.Printf("cannot create temporary directory: %v", err)
 				return err
-			} else if workDir, err = container.NewAbs(p); err != nil {
+			} else if workDir, err = check.NewAbs(p); err != nil {
 				log.Printf("invalid temporary directory: %v", err)
 				return err
 			}
 			cleanup := func() {
 				// should be faster than a native implementation
-				mustRun(chmod, "-R", "+w", workDir.String())
-				mustRun(rm, "-rf", workDir.String())
+				mustRun(msg, chmod, "-R", "+w", workDir.String())
+				mustRun(msg, rm, "-rf", workDir.String())
 			}
 			beforeRunFail.Store(&cleanup)
 
-			mustRun(tar, "-C", workDir.String(), "-xf", pkgPath)
+			mustRun(msg, tar, "-C", workDir.String(), "-xf", pkgPath)
 
 			/*
 				Parse bundle and app metadata, do pre-install checks.
@@ -148,10 +149,10 @@ func main() {
 				}
 
 				// sec: should compare version string
-				hlog.Verbosef("installing application %q version %q over local %q",
+				msg.Verbosef("installing application %q version %q over local %q",
 					bundle.ID, bundle.Version, a.Version)
 			} else {
-				hlog.Verbosef("application %q clean installation", bundle.ID)
+				msg.Verbosef("application %q clean installation", bundle.ID)
 				// sec: should install credentials
 			}
 
@@ -159,7 +160,7 @@ func main() {
 				Setup steps for files owned by the target user.
 			*/
 
-			withCacheDir(ctx, "install", []string{
+			withCacheDir(ctx, msg, "install", []string{
 				// export inner bundle path in the environment
 				"export BUNDLE=" + hst.Tmp + "/bundle",
 				// replace inner /etc
@@ -181,7 +182,7 @@ func main() {
 			}, workDir, bundle, pathSet, flagDropShell, cleanup)
 
 			if bundle.GPU {
-				withCacheDir(ctx, "mesa-wrappers", []string{
+				withCacheDir(ctx, msg, "mesa-wrappers", []string{
 					// link nixGL mesa wrappers
 					"mkdir -p nix/.nixGL",
 					"ln -s " + bundle.Mesa + "/bin/nixGLIntel nix/.nixGL/nixGL",
@@ -193,7 +194,7 @@ func main() {
 				Activate home-manager generation.
 			*/
 
-			withNixDaemon(ctx, "activate", []string{
+			withNixDaemon(ctx, msg, "activate", []string{
 				// clean up broken links
 				"mkdir -p .local/state/{nix,home-manager}",
 				"chmod -R +w .local/state/{nix,home-manager}",
@@ -261,7 +262,7 @@ func main() {
 			*/
 
 			if a.GPU && flagAutoDrivers {
-				withNixDaemon(ctx, "nix-gl", []string{
+				withNixDaemon(ctx, msg, "nix-gl", []string{
 					"mkdir -p /nix/.nixGL/auto",
 					"rm -rf /nix/.nixGL/auto",
 					"export NIXPKGS_ALLOW_UNFREE=1",
@@ -275,12 +276,12 @@ func main() {
 						"path:" + a.NixGL + "#nixVulkanNvidia",
 				}, true, func(config *hst.Config) *hst.Config {
 					config.Container.Filesystem = append(config.Container.Filesystem, []hst.FilesystemConfigJSON{
-						{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSEtc.Append("resolv.conf"), Optional: true}},
-						{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSSys.Append("block"), Optional: true}},
-						{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSSys.Append("bus"), Optional: true}},
-						{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSSys.Append("class"), Optional: true}},
-						{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSSys.Append("dev"), Optional: true}},
-						{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSSys.Append("devices"), Optional: true}},
+						{FilesystemConfig: &hst.FSBind{Source: fhs.AbsEtc.Append("resolv.conf"), Optional: true}},
+						{FilesystemConfig: &hst.FSBind{Source: fhs.AbsSys.Append("block"), Optional: true}},
+						{FilesystemConfig: &hst.FSBind{Source: fhs.AbsSys.Append("bus"), Optional: true}},
+						{FilesystemConfig: &hst.FSBind{Source: fhs.AbsSys.Append("class"), Optional: true}},
+						{FilesystemConfig: &hst.FSBind{Source: fhs.AbsSys.Append("dev"), Optional: true}},
+						{FilesystemConfig: &hst.FSBind{Source: fhs.AbsSys.Append("devices"), Optional: true}},
 					}...)
 					appendGPUFilesystem(config)
 					return config
@@ -316,7 +317,7 @@ func main() {
 				Spawn app.
 			*/
 
-			mustRunApp(ctx, config, func() {})
+			mustRunApp(ctx, msg, config, func() {})
 			return errSuccess
 		}).
 			Flag(&flagDropShellNixGL, "s", command.BoolFlag(false), "Drop to a shell on nixGL build").
@@ -324,9 +325,9 @@ func main() {
 	}
 
 	c.MustParse(os.Args[1:], func(err error) {
-		hlog.Verbosef("command returned %v", err)
+		msg.Verbosef("command returned %v", err)
 		if errors.Is(err, errSuccess) {
-			hlog.BeforeExit()
+			msg.BeforeExit()
 			os.Exit(0)
 		}
 	})

cmd/hpkg/paths.go

@@ -8,35 +8,36 @@ import (
 	"sync/atomic"
 
 	"hakurei.app/container"
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 	"hakurei.app/hst"
-	"hakurei.app/internal/hlog"
 )
 
 const bash = "bash"
 
 var (
-	dataHome *container.Absolute
+	dataHome *check.Absolute
 )
 
 func init() {
 	// dataHome
-	if a, err := container.NewAbs(os.Getenv("HAKUREI_DATA_HOME")); err == nil {
+	if a, err := check.NewAbs(os.Getenv("HAKUREI_DATA_HOME")); err == nil {
 		dataHome = a
 	} else {
-		dataHome = container.AbsFHSVarLib.Append("hakurei/" + strconv.Itoa(os.Getuid()))
+		dataHome = fhs.AbsVarLib.Append("hakurei/" + strconv.Itoa(os.Getuid()))
 	}
 }
 
 var (
-	pathBin = container.AbsFHSRoot.Append("bin")
+	pathBin = fhs.AbsRoot.Append("bin")
 
-	pathNix           = container.MustAbs("/nix/")
+	pathNix           = check.MustAbs("/nix/")
 	pathNixStore      = pathNix.Append("store/")
-	pathCurrentSystem = container.AbsFHSRun.Append("current-system")
+	pathCurrentSystem = fhs.AbsRun.Append("current-system")
 	pathSwBin         = pathCurrentSystem.Append("sw/bin/")
 	pathShell         = pathSwBin.Append(bash)
 
-	pathData     = container.MustAbs("/data")
+	pathData     = check.MustAbs("/data")
 	pathDataData = pathData.Append("data")
 )
 
@@ -51,8 +52,8 @@ func lookPath(file string) string {
 
 var beforeRunFail = new(atomic.Pointer[func()])
 
-func mustRun(name string, arg ...string) {
-	hlog.Verbosef("spawning process: %q %q", name, arg)
+func mustRun(msg container.Msg, name string, arg ...string) {
+	msg.Verbosef("spawning process: %q %q", name, arg)
 	cmd := exec.Command(name, arg...)
 	cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
 	if err := cmd.Run(); err != nil {
@@ -65,15 +66,15 @@ func mustRun(name string, arg ...string) {
 
 type appPathSet struct {
 	// ${dataHome}/${id}
-	baseDir *container.Absolute
+	baseDir *check.Absolute
 	// ${baseDir}/app
-	metaPath *container.Absolute
+	metaPath *check.Absolute
 	// ${baseDir}/files
-	homeDir *container.Absolute
+	homeDir *check.Absolute
 	// ${baseDir}/cache
-	cacheDir *container.Absolute
+	cacheDir *check.Absolute
 	// ${baseDir}/cache/nix
-	nixPath *container.Absolute
+	nixPath *check.Absolute
 }
 
 func pathSetByApp(id string) *appPathSet {
@@ -89,28 +90,28 @@ func pathSetByApp(id string) *appPathSet {
 func appendGPUFilesystem(config *hst.Config) {
 	config.Container.Filesystem = append(config.Container.Filesystem, []hst.FilesystemConfigJSON{
 		// flatpak commit 763a686d874dd668f0236f911de00b80766ffe79
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("dri"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("dri"), Device: true, Optional: true}},
 		// mali
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("mali"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("mali0"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("umplock"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("mali"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("mali0"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("umplock"), Device: true, Optional: true}},
 		// nvidia
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidiactl"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia-modeset"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidiactl"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia-modeset"), Device: true, Optional: true}},
 		// nvidia OpenCL/CUDA
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia-uvm"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia-uvm-tools"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia-uvm"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia-uvm-tools"), Device: true, Optional: true}},
 
 		// flatpak commit d2dff2875bb3b7e2cd92d8204088d743fd07f3ff
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia0"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia1"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia2"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia3"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia4"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia5"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia6"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia7"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia8"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia9"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia10"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia11"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia12"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia13"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia14"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia15"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia16"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia17"), Device: true, Optional: true}},
-		{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia18"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("nvidia19"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia0"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia1"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia2"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia3"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia4"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia5"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia6"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia7"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia8"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia9"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia10"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia11"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia12"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia13"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia14"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia15"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia16"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia17"), Device: true, Optional: true}},
+		{FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia18"), Device: true, Optional: true}}, {FilesystemConfig: &hst.FSBind{Source: fhs.AbsDev.Append("nvidia19"), Device: true, Optional: true}},
 	}...)
 }

cmd/hpkg/proc.go

@@ -9,14 +9,14 @@ import (
 	"os"
 	"os/exec"
 
+	"hakurei.app/container"
 	"hakurei.app/hst"
 	"hakurei.app/internal"
-	"hakurei.app/internal/hlog"
 )
 
 var hakureiPath = internal.MustHakureiPath()
 
-func mustRunApp(ctx context.Context, config *hst.Config, beforeFail func()) {
+func mustRunApp(ctx context.Context, msg container.Msg, config *hst.Config, beforeFail func()) {
 	var (
 		cmd *exec.Cmd
 		st  io.WriteCloser
@@ -26,10 +26,10 @@ func mustRunApp(ctx context.Context, config *hst.Config, beforeFail func()) {
 		beforeFail()
 		log.Fatalf("cannot pipe: %v", err)
 	} else {
-		if hlog.Load() {
-			cmd = exec.CommandContext(ctx, hakureiPath, "-v", "app", "3")
+		if msg.IsVerbose() {
+			cmd = exec.CommandContext(ctx, hakureiPath.String(), "-v", "app", "3")
 		} else {
-			cmd = exec.CommandContext(ctx, hakureiPath, "app", "3")
+			cmd = exec.CommandContext(ctx, hakureiPath.String(), "app", "3")
 		}
 		cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
 		cmd.ExtraFiles = []*os.File{r}
@@ -51,7 +51,8 @@ func mustRunApp(ctx context.Context, config *hst.Config, beforeFail func()) {
 		var exitError *exec.ExitError
 		if errors.As(err, &exitError) {
 			beforeFail()
-			internal.Exit(exitError.ExitCode())
+			msg.BeforeExit()
+			os.Exit(exitError.ExitCode())
 		} else {
 			beforeFail()
 			log.Fatalf("cannot wait: %v", err)

cmd/hpkg/test/test.py

@@ -62,11 +62,11 @@ def check_state(name, enablements):
 
     config = instance['config']
 
-    if len(config['args']) != 1 or not (config['args'][0].startswith("/nix/store/")) or f"hakurei-{name}-" not in (config['args'][0]):
-        raise Exception(f"unexpected args {instance['config']['args']}")
+    if len(config['container']['args']) != 1 or not (config['container']['args'][0].startswith("/nix/store/")) or f"hakurei-{name}-" not in (config['container']['args'][0]):
+        raise Exception(f"unexpected args {config['container']['args']}")
 
     if config['enablements'] != enablements:
-        raise Exception(f"unexpected enablements {instance['config']['enablements']}")
+        raise Exception(f"unexpected enablements {config['enablements']}")
 
 
 start_all()

cmd/hpkg/with.go

@@ -2,38 +2,24 @@ package main
 
 import (
 	"context"
+	"os"
 	"strings"
 
 	"hakurei.app/container"
-	"hakurei.app/container/seccomp"
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 	"hakurei.app/hst"
-	"hakurei.app/internal"
 )
 
 func withNixDaemon(
 	ctx context.Context,
+	msg container.Msg,
 	action string, command []string, net bool, updateConfig func(config *hst.Config) *hst.Config,
 	app *appInfo, pathSet *appPathSet, dropShell bool, beforeFail func(),
 ) {
-	mustRunAppDropShell(ctx, updateConfig(&hst.Config{
+	mustRunAppDropShell(ctx, msg, updateConfig(&hst.Config{
 		ID: app.ID,
 
-		Path: pathShell,
-		Args: []string{bash, "-lc", "rm -f /nix/var/nix/daemon-socket/socket && " +
-			// start nix-daemon
-			"nix-daemon --store / & " +
-			// wait for socket to appear
-			"(while [ ! -S /nix/var/nix/daemon-socket/socket ]; do sleep 0.01; done) && " +
-			// create directory so nix stops complaining
-			"mkdir -p /nix/var/nix/profiles/per-user/root/channels && " +
-			strings.Join(command, " && ") +
-			// terminate nix-daemon
-			" && pkill nix-daemon",
-		},
-
-		Username: "hakurei",
-		Shell:    pathShell,
-		Home:     pathDataData.Append(app.ID),
 		ExtraPerms: []*hst.ExtraPermConfig{
 			{Path: dataHome, Execute: true},
 			{Ensure: true, Path: pathSet.baseDir, Read: true, Write: true, Execute: true},
@@ -42,36 +28,48 @@ func withNixDaemon(
 		Identity: app.Identity,
 
 		Container: &hst.ContainerConfig{
-			Hostname:     formatHostname(app.Name) + "-" + action,
-			Userns:       true, // nix sandbox requires userns
-			HostNet:      net,
-			SeccompFlags: seccomp.AllowMultiarch,
-			Tty:          dropShell,
+			Hostname:  formatHostname(app.Name) + "-" + action,
+			Userns:    true, // nix sandbox requires userns
+			HostNet:   net,
+			Multiarch: true,
+			Tty:       dropShell,
 			Filesystem: []hst.FilesystemConfigJSON{
-				{FilesystemConfig: &hst.FSBind{Target: container.AbsFHSEtc, Source: pathSet.cacheDir.Append("etc"), Special: true}},
+				{FilesystemConfig: &hst.FSBind{Target: fhs.AbsEtc, Source: pathSet.cacheDir.Append("etc"), Special: true}},
 				{FilesystemConfig: &hst.FSBind{Source: pathSet.nixPath, Target: pathNix, Write: true}},
 				{FilesystemConfig: &hst.FSLink{Target: pathCurrentSystem, Linkname: app.CurrentSystem.String()}},
 				{FilesystemConfig: &hst.FSLink{Target: pathBin, Linkname: pathSwBin.String()}},
-				{FilesystemConfig: &hst.FSLink{Target: container.AbsFHSUsrBin, Linkname: pathSwBin.String()}},
+				{FilesystemConfig: &hst.FSLink{Target: fhs.AbsUsrBin, Linkname: pathSwBin.String()}},
 				{FilesystemConfig: &hst.FSBind{Target: pathDataData.Append(app.ID), Source: pathSet.homeDir, Write: true, Ensure: true}},
 			},
+
+			Username: "hakurei",
+			Shell:    pathShell,
+			Home:     pathDataData.Append(app.ID),
+
+			Path: pathShell,
+			Args: []string{bash, "-lc", "rm -f /nix/var/nix/daemon-socket/socket && " +
+				// start nix-daemon
+				"nix-daemon --store / & " +
+				// wait for socket to appear
+				"(while [ ! -S /nix/var/nix/daemon-socket/socket ]; do sleep 0.01; done) && " +
+				// create directory so nix stops complaining
+				"mkdir -p /nix/var/nix/profiles/per-user/root/channels && " +
+				strings.Join(command, " && ") +
+				// terminate nix-daemon
+				" && pkill nix-daemon",
+			},
 		},
 	}), dropShell, beforeFail)
 }
 
 func withCacheDir(
 	ctx context.Context,
-	action string, command []string, workDir *container.Absolute,
+	msg container.Msg,
+	action string, command []string, workDir *check.Absolute,
 	app *appInfo, pathSet *appPathSet, dropShell bool, beforeFail func()) {
-	mustRunAppDropShell(ctx, &hst.Config{
+	mustRunAppDropShell(ctx, msg, &hst.Config{
 		ID: app.ID,
 
-		Path: pathShell,
-		Args: []string{bash, "-lc", strings.Join(command, " && ")},
-
-		Username: "nixos",
-		Shell:    pathShell,
-		Home:     pathDataData.Append(app.ID, "cache"),
 		ExtraPerms: []*hst.ExtraPermConfig{
 			{Path: dataHome, Execute: true},
 			{Ensure: true, Path: pathSet.baseDir, Read: true, Write: true, Execute: true},
@@ -81,28 +79,38 @@ func withCacheDir(
 		Identity: app.Identity,
 
 		Container: &hst.ContainerConfig{
-			Hostname:     formatHostname(app.Name) + "-" + action,
-			SeccompFlags: seccomp.AllowMultiarch,
-			Tty:          dropShell,
+			Hostname:  formatHostname(app.Name) + "-" + action,
+			Multiarch: true,
+			Tty:       dropShell,
 			Filesystem: []hst.FilesystemConfigJSON{
-				{FilesystemConfig: &hst.FSBind{Target: container.AbsFHSEtc, Source: workDir.Append(container.FHSEtc), Special: true}},
+				{FilesystemConfig: &hst.FSBind{Target: fhs.AbsEtc, Source: workDir.Append(fhs.Etc), Special: true}},
 				{FilesystemConfig: &hst.FSBind{Source: workDir.Append("nix"), Target: pathNix}},
 				{FilesystemConfig: &hst.FSLink{Target: pathCurrentSystem, Linkname: app.CurrentSystem.String()}},
 				{FilesystemConfig: &hst.FSLink{Target: pathBin, Linkname: pathSwBin.String()}},
-				{FilesystemConfig: &hst.FSLink{Target: container.AbsFHSUsrBin, Linkname: pathSwBin.String()}},
+				{FilesystemConfig: &hst.FSLink{Target: fhs.AbsUsrBin, Linkname: pathSwBin.String()}},
 				{FilesystemConfig: &hst.FSBind{Source: workDir, Target: hst.AbsTmp.Append("bundle")}},
 				{FilesystemConfig: &hst.FSBind{Target: pathDataData.Append(app.ID, "cache"), Source: pathSet.cacheDir, Write: true, Ensure: true}},
 			},
+
+			Username: "nixos",
+			Shell:    pathShell,
+			Home:     pathDataData.Append(app.ID, "cache"),
+
+			Path: pathShell,
+			Args: []string{bash, "-lc", strings.Join(command, " && ")},
 		},
 	}, dropShell, beforeFail)
 }
 
-func mustRunAppDropShell(ctx context.Context, config *hst.Config, dropShell bool, beforeFail func()) {
+func mustRunAppDropShell(ctx context.Context, msg container.Msg, config *hst.Config, dropShell bool, beforeFail func()) {
 	if dropShell {
-		config.Args = []string{bash, "-l"}
-		mustRunApp(ctx, config, beforeFail)
+		if config.Container != nil {
+			config.Container.Args = []string{bash, "-l"}
+		}
+		mustRunApp(ctx, msg, config, beforeFail)
 		beforeFail()
-		internal.Exit(0)
+		msg.BeforeExit()
+		os.Exit(0)
 	}
-	mustRunApp(ctx, config, beforeFail)
+	mustRunApp(ctx, msg, config, beforeFail)
 }

cmd/hsu/main.go

@@ -1,5 +1,7 @@
 package main
 
+// minimise imports to avoid inadvertently calling init or global variable functions
+
 import (
 	"bytes"
 	"fmt"
@@ -19,6 +21,9 @@ const (
 	envGroups   = "HAKUREI_GROUPS"
 
 	PR_SET_NO_NEW_PRIVS = 0x26
+
+	identityMin = 0
+	identityMax = 9999
 )
 
 func main() {
@@ -29,6 +34,9 @@ func main() {
 	if os.Geteuid() != 0 {
 		log.Fatal("this program must be owned by uid 0 and have the setuid bit set")
 	}
+	if os.Getegid() != os.Getgid() {
+		log.Fatal("this program must not have the setgid bit set")
+	}
 
 	puid := os.Getuid()
 	if puid == 0 {
@@ -91,7 +99,7 @@ func main() {
 	// allowed identity range 0 to 9999
 	if as, ok := os.LookupEnv(envIdentity); !ok {
 		log.Fatal("HAKUREI_IDENTITY not set")
-	} else if identity, err := parseUint32Fast(as); err != nil || identity < 0 || identity > 9999 {
+	} else if identity, err := parseUint32Fast(as); err != nil || identity < identityMin || identity > identityMax {
 		log.Fatal("invalid identity")
 	} else {
 		uid += identity

container/autoetc.go

@@ -3,15 +3,18 @@ package container
 import (
 	"encoding/gob"
 	"fmt"
+
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 )
 
 func init() { gob.Register(new(AutoEtcOp)) }
 
 // Etc appends an [Op] that expands host /etc into a toplevel symlink mirror with /etc semantics.
 // This is not a generic setup op. It is implemented here to reduce ipc overhead.
-func (f *Ops) Etc(host *Absolute, prefix string) *Ops {
+func (f *Ops) Etc(host *check.Absolute, prefix string) *Ops {
 	e := &AutoEtcOp{prefix}
-	f.Mkdir(AbsFHSEtc, 0755)
+	f.Mkdir(fhs.AbsEtc, 0755)
 	f.Bind(host, e.hostPath(), 0)
 	*f = append(*f, e)
 	return f
@@ -27,7 +30,7 @@ func (e *AutoEtcOp) apply(state *setupState, k syscallDispatcher) error {
 	}
 	state.nonrepeatable |= nrAutoEtc
 
-	const target = sysrootPath + FHSEtc
+	const target = sysrootPath + fhs.Etc
 	rel := e.hostRel() + "/"
 
 	if err := k.mkdirAll(target, 0755); err != nil {
@@ -42,7 +45,7 @@ func (e *AutoEtcOp) apply(state *setupState, k syscallDispatcher) error {
 			case ".host", "passwd", "group":
 
 			case "mtab":
-				if err = k.symlink(FHSProc+"mounts", target+n); err != nil {
+				if err = k.symlink(fhs.Proc+"mounts", target+n); err != nil {
 					return err
 				}
 
@@ -57,8 +60,8 @@ func (e *AutoEtcOp) apply(state *setupState, k syscallDispatcher) error {
 	return nil
 }
 
-func (e *AutoEtcOp) hostPath() *Absolute { return AbsFHSEtc.Append(e.hostRel()) }
-func (e *AutoEtcOp) hostRel() string     { return ".host/" + e.Prefix }
+func (e *AutoEtcOp) hostPath() *check.Absolute { return fhs.AbsEtc.Append(e.hostRel()) }
+func (e *AutoEtcOp) hostRel() string           { return ".host/" + e.Prefix }
 
 func (e *AutoEtcOp) Is(op Op) bool {
 	ve, ok := op.(*AutoEtcOp)

container/autoetc_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"testing"
 
+	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
 )
 
@@ -256,11 +257,11 @@ func TestAutoEtcOp(t *testing.T) {
 	})
 
 	checkOpsBuilder(t, []opsBuilderTestCase{
-		{"pd", new(Ops).Etc(MustAbs("/etc/"), "048090b6ed8f9ebb10e275ff5d8c0659"), Ops{
-			&MkdirOp{Path: MustAbs("/etc/"), Perm: 0755},
+		{"pd", new(Ops).Etc(check.MustAbs("/etc/"), "048090b6ed8f9ebb10e275ff5d8c0659"), Ops{
+			&MkdirOp{Path: check.MustAbs("/etc/"), Perm: 0755},
 			&BindMountOp{
-				Source: MustAbs("/etc/"),
-				Target: MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+				Source: check.MustAbs("/etc/"),
+				Target: check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
 			},
 			&AutoEtcOp{Prefix: "048090b6ed8f9ebb10e275ff5d8c0659"},
 		}},

container/autoroot.go

@@ -3,19 +3,22 @@ package container
 import (
 	"encoding/gob"
 	"fmt"
+
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 )
 
 func init() { gob.Register(new(AutoRootOp)) }
 
 // Root appends an [Op] that expands a directory into a toplevel bind mount mirror on container root.
 // This is not a generic setup op. It is implemented here to reduce ipc overhead.
-func (f *Ops) Root(host *Absolute, flags int) *Ops {
+func (f *Ops) Root(host *check.Absolute, flags int) *Ops {
 	*f = append(*f, &AutoRootOp{host, flags, nil})
 	return f
 }
 
 type AutoRootOp struct {
-	Host *Absolute
+	Host *check.Absolute
 	// passed through to bindMount
 	Flags int
 
@@ -34,11 +37,11 @@ func (r *AutoRootOp) early(state *setupState, k syscallDispatcher) error {
 		r.resolved = make([]*BindMountOp, 0, len(d))
 		for _, ent := range d {
 			name := ent.Name()
-			if IsAutoRootBindable(name) {
+			if IsAutoRootBindable(state, name) {
 				// careful: the Valid method is skipped, make sure this is always valid
 				op := &BindMountOp{
 					Source: r.Host.Append(name),
-					Target: AbsFHSRoot.Append(name),
+					Target: fhs.AbsRoot.Append(name),
 					Flags:  r.Flags,
 				}
 				if err = op.early(state, k); err != nil {
@@ -78,7 +81,7 @@ func (r *AutoRootOp) String() string {
 }
 
 // IsAutoRootBindable returns whether a dir entry name is selected for AutoRoot.
-func IsAutoRootBindable(name string) bool {
+func IsAutoRootBindable(msg Msg, name string) bool {
 	switch name {
 	case "proc", "dev", "tmp", "mnt", "etc":
 

container/autoroot_test.go

@@ -5,6 +5,8 @@ import (
 	"os"
 	"testing"
 
+	"hakurei.app/container/bits"
+	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
 )
 
@@ -18,15 +20,15 @@ func TestAutoRootOp(t *testing.T) {
 
 	checkOpBehaviour(t, []opBehaviourTestCase{
 		{"readdir", &Params{ParentPerm: 0750}, &AutoRootOp{
-			Host:  MustAbs("/"),
-			Flags: BindWritable,
+			Host:  check.MustAbs("/"),
+			Flags: bits.BindWritable,
 		}, []stub.Call{
 			call("readdir", stub.ExpectArgs{"/"}, stubDir(), stub.UniqueError(2)),
 		}, stub.UniqueError(2), nil, nil},
 
 		{"early", &Params{ParentPerm: 0750}, &AutoRootOp{
-			Host:  MustAbs("/"),
-			Flags: BindWritable,
+			Host:  check.MustAbs("/"),
+			Flags: bits.BindWritable,
 		}, []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),
@@ -34,8 +36,8 @@ func TestAutoRootOp(t *testing.T) {
 		}, stub.UniqueError(1), nil, nil},
 
 		{"apply", &Params{ParentPerm: 0750}, &AutoRootOp{
-			Host:  MustAbs("/"),
-			Flags: BindWritable,
+			Host:  check.MustAbs("/"),
+			Flags: bits.BindWritable,
 		}, []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),
@@ -55,8 +57,8 @@ func TestAutoRootOp(t *testing.T) {
 		}, stub.UniqueError(0)},
 
 		{"success pd", &Params{ParentPerm: 0750}, &AutoRootOp{
-			Host:  MustAbs("/"),
-			Flags: BindWritable,
+			Host:  check.MustAbs("/"),
+			Flags: bits.BindWritable,
 		}, []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),
@@ -86,7 +88,7 @@ func TestAutoRootOp(t *testing.T) {
 		}, nil},
 
 		{"success", &Params{ParentPerm: 0750}, &AutoRootOp{
-			Host: MustAbs("/var/lib/planterette/base/debian:f92c9052"),
+			Host: check.MustAbs("/var/lib/planterette/base/debian:f92c9052"),
 		}, []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),
@@ -119,14 +121,14 @@ func TestAutoRootOp(t *testing.T) {
 	checkOpsValid(t, []opValidTestCase{
 		{"nil", (*AutoRootOp)(nil), false},
 		{"zero", new(AutoRootOp), false},
-		{"valid", &AutoRootOp{Host: MustAbs("/")}, true},
+		{"valid", &AutoRootOp{Host: check.MustAbs("/")}, true},
 	})
 
 	checkOpsBuilder(t, []opsBuilderTestCase{
-		{"pd", new(Ops).Root(MustAbs("/"), BindWritable), Ops{
+		{"pd", new(Ops).Root(check.MustAbs("/"), bits.BindWritable), Ops{
 			&AutoRootOp{
-				Host:  MustAbs("/"),
-				Flags: BindWritable,
+				Host:  check.MustAbs("/"),
+				Flags: bits.BindWritable,
 			},
 		}},
 	})
@@ -135,43 +137,43 @@ func TestAutoRootOp(t *testing.T) {
 		{"zero", new(AutoRootOp), new(AutoRootOp), false},
 
 		{"internal ne", &AutoRootOp{
-			Host:  MustAbs("/"),
-			Flags: BindWritable,
+			Host:  check.MustAbs("/"),
+			Flags: bits.BindWritable,
 		}, &AutoRootOp{
-			Host:     MustAbs("/"),
-			Flags:    BindWritable,
+			Host:     check.MustAbs("/"),
+			Flags:    bits.BindWritable,
 			resolved: []*BindMountOp{new(BindMountOp)},
 		}, true},
 
 		{"flags differs", &AutoRootOp{
-			Host:  MustAbs("/"),
-			Flags: BindWritable | BindDevice,
+			Host:  check.MustAbs("/"),
+			Flags: bits.BindWritable | bits.BindDevice,
 		}, &AutoRootOp{
-			Host:  MustAbs("/"),
-			Flags: BindWritable,
+			Host:  check.MustAbs("/"),
+			Flags: bits.BindWritable,
 		}, false},
 
 		{"host differs", &AutoRootOp{
-			Host:  MustAbs("/tmp/"),
-			Flags: BindWritable,
+			Host:  check.MustAbs("/tmp/"),
+			Flags: bits.BindWritable,
 		}, &AutoRootOp{
-			Host:  MustAbs("/"),
-			Flags: BindWritable,
+			Host:  check.MustAbs("/"),
+			Flags: bits.BindWritable,
 		}, false},
 
 		{"equals", &AutoRootOp{
-			Host:  MustAbs("/"),
-			Flags: BindWritable,
+			Host:  check.MustAbs("/"),
+			Flags: bits.BindWritable,
 		}, &AutoRootOp{
-			Host:  MustAbs("/"),
-			Flags: BindWritable,
+			Host:  check.MustAbs("/"),
+			Flags: bits.BindWritable,
 		}, true},
 	})
 
 	checkOpMeta(t, []opMetaTestCase{
 		{"root", &AutoRootOp{
-			Host:  MustAbs("/"),
-			Flags: BindWritable,
+			Host:  check.MustAbs("/"),
+			Flags: bits.BindWritable,
 		}, "setting up", `auto root "/" flags 0x2`},
 	})
 }
@@ -180,19 +182,26 @@ func TestIsAutoRootBindable(t *testing.T) {
 	testCases := []struct {
 		name string
 		want bool
+		log  bool
 	}{
-		{"proc", false},
-		{"dev", false},
-		{"tmp", false},
-		{"mnt", false},
-		{"etc", false},
-		{"", false},
+		{"proc", false, false},
+		{"dev", false, false},
+		{"tmp", false, false},
+		{"mnt", false, false},
+		{"etc", false, false},
+		{"", false, true},
 
-		{"var", true},
+		{"var", true, false},
 	}
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
-			if got := IsAutoRootBindable(tc.name); got != tc.want {
+			var msg Msg
+			if tc.log {
+				msg = &kstub{nil, stub.New(t, func(s *stub.Stub[syscallDispatcher]) syscallDispatcher { panic("unreachable") }, stub.Expect{Calls: []stub.Call{
+					call("verbose", stub.ExpectArgs{[]any{"got unexpected root entry"}}, nil, nil),
+				}})}
+			}
+			if got := IsAutoRootBindable(msg, tc.name); got != tc.want {
 				t.Errorf("IsAutoRootBindable: %v, want %v", got, tc.want)
 			}
 		})

container/bits/bits.go

@@ -0,0 +1,13 @@
+// Package bits contains constants for configuring the container.
+package bits
+
+const (
+	// BindOptional skips nonexistent host paths.
+	BindOptional = 1 << iota
+	// BindWritable mounts filesystem read-write.
+	BindWritable
+	// BindDevice allows access to devices (special files) on this filesystem.
+	BindDevice
+	// BindEnsure attempts to create the host path if it does not exist.
+	BindEnsure
+)

container/bits/seccomp.go

@@ -0,0 +1,20 @@
+package bits
+
+// FilterPreset specifies parts of the syscall filter preset to enable.
+type FilterPreset int
+
+const (
+	// PresetExt are project-specific extensions.
+	PresetExt FilterPreset = 1 << iota
+	// PresetDenyNS denies namespace setup syscalls.
+	PresetDenyNS
+	// PresetDenyTTY denies faking input.
+	PresetDenyTTY
+	// PresetDenyDevel denies development-related syscalls.
+	PresetDenyDevel
+	// PresetLinux32 sets PER_LINUX32.
+	PresetLinux32
+
+	// PresetStrict is a strict preset useful as a default value.
+	PresetStrict = PresetExt | PresetDenyNS | PresetDenyTTY | PresetDenyDevel
+)

container/check/absolute.go

@@ -1,4 +1,5 @@
-package container
+// Package check provides types yielding values checked to meet a condition.
+package check
 
 import (
 	"encoding/json"
@@ -11,9 +12,7 @@ import (
 )
 
 // AbsoluteError is returned by [NewAbs] and holds the invalid pathname.
-type AbsoluteError struct {
-	Pathname string
-}
+type AbsoluteError struct{ Pathname string }
 
 func (e *AbsoluteError) Error() string { return fmt.Sprintf("path %q is not absolute", e.Pathname) }
 func (e *AbsoluteError) Is(target error) bool {
@@ -25,15 +24,13 @@ func (e *AbsoluteError) Is(target error) bool {
 }
 
 // Absolute holds a pathname checked to be absolute.
-type Absolute struct {
-	pathname string
-}
+type Absolute struct{ pathname string }
 
-// isAbs wraps [path.IsAbs] in case additional checks are added in the future.
-func isAbs(pathname string) bool { return path.IsAbs(pathname) }
+// unsafeAbs returns [check.Absolute] on any string value.
+func unsafeAbs(pathname string) *Absolute { return &Absolute{pathname} }
 
 func (a *Absolute) String() string {
-	if a.pathname == zeroString {
+	if a.pathname == "" {
 		panic("attempted use of zero Absolute")
 	}
 	return a.pathname
@@ -44,16 +41,16 @@ func (a *Absolute) Is(v *Absolute) bool {
 		return true
 	}
 	return a != nil && v != nil &&
-		a.pathname != zeroString && v.pathname != zeroString &&
+		a.pathname != "" && v.pathname != "" &&
 		a.pathname == v.pathname
 }
 
 // NewAbs checks pathname and returns a new [Absolute] if pathname is absolute.
 func NewAbs(pathname string) (*Absolute, error) {
-	if !isAbs(pathname) {
+	if !path.IsAbs(pathname) {
 		return nil, &AbsoluteError{pathname}
 	}
-	return &Absolute{pathname}, nil
+	return unsafeAbs(pathname), nil
 }
 
 // MustAbs calls [NewAbs] and panics on error.
@@ -67,16 +64,16 @@ func MustAbs(pathname string) *Absolute {
 
 // Append calls [path.Join] with [Absolute] as the first element.
 func (a *Absolute) Append(elem ...string) *Absolute {
-	return &Absolute{path.Join(append([]string{a.String()}, elem...)...)}
+	return unsafeAbs(path.Join(append([]string{a.String()}, elem...)...))
 }
 
 // Dir calls [path.Dir] with [Absolute] as its argument.
-func (a *Absolute) Dir() *Absolute { return &Absolute{path.Dir(a.String())} }
+func (a *Absolute) Dir() *Absolute { return unsafeAbs(path.Dir(a.String())) }
 
 func (a *Absolute) GobEncode() ([]byte, error) { return []byte(a.String()), nil }
 func (a *Absolute) GobDecode(data []byte) error {
 	pathname := string(data)
-	if !isAbs(pathname) {
+	if !path.IsAbs(pathname) {
 		return &AbsoluteError{pathname}
 	}
 	a.pathname = pathname
@@ -89,7 +86,7 @@ func (a *Absolute) UnmarshalJSON(data []byte) error {
 	if err := json.Unmarshal(data, &pathname); err != nil {
 		return err
 	}
-	if !isAbs(pathname) {
+	if !path.IsAbs(pathname) {
 		return &AbsoluteError{pathname}
 	}
 	a.pathname = pathname

container/check/absolute_test.go

@@ -1,4 +1,4 @@
-package container
+package check_test
 
 import (
 	"bytes"
@@ -9,8 +9,14 @@ import (
 	"strings"
 	"syscall"
 	"testing"
+	_ "unsafe"
+
+	. "hakurei.app/container/check"
 )
 
+//go:linkname unsafeAbs hakurei.app/container/check.unsafeAbs
+func unsafeAbs(_ string) *Absolute
+
 func TestAbsoluteError(t *testing.T) {
 	testCases := []struct {
 		name string
@@ -80,7 +86,7 @@ func TestNewAbs(t *testing.T) {
 func TestAbsoluteString(t *testing.T) {
 	t.Run("passthrough", func(t *testing.T) {
 		pathname := "/etc"
-		if got := (&Absolute{pathname}).String(); got != pathname {
+		if got := unsafeAbs(pathname).String(); got != pathname {
 			t.Errorf("String: %q, want %q", got, pathname)
 		}
 	})

container/check/overlay.go

@@ -0,0 +1,29 @@
+package check
+
+import "strings"
+
+const (
+	// SpecialOverlayEscape is the escape string for overlay mount options.
+	SpecialOverlayEscape = `\`
+	// SpecialOverlayOption is the separator string between overlay mount options.
+	SpecialOverlayOption = ","
+	// SpecialOverlayPath is the separator string between overlay paths.
+	SpecialOverlayPath = ":"
+)
+
+// EscapeOverlayDataSegment escapes a string for formatting into the data argument of an overlay mount call.
+func EscapeOverlayDataSegment(s string) string {
+	if s == "" {
+		return ""
+	}
+
+	if f := strings.SplitN(s, "\x00", 2); len(f) > 0 {
+		s = f[0]
+	}
+
+	return strings.NewReplacer(
+		SpecialOverlayEscape, SpecialOverlayEscape+SpecialOverlayEscape,
+		SpecialOverlayOption, SpecialOverlayEscape+SpecialOverlayOption,
+		SpecialOverlayPath, SpecialOverlayEscape+SpecialOverlayPath,
+	).Replace(s)
+}

container/check/overlay_test.go

@@ -0,0 +1,27 @@
+package check_test
+
+import (
+	"testing"
+
+	"hakurei.app/container/check"
+)
+
+func TestEscapeOverlayDataSegment(t *testing.T) {
+	testCases := []struct {
+		name string
+		s    string
+		want string
+	}{
+		{"zero", "", ""},
+		{"multi", `\\\:,:,\\\`, `\\\\\\\:\,\:\,\\\\\\`},
+		{"bwrap", `/path :,\`, `/path \:\,\\`},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := check.EscapeOverlayDataSegment(tc.s); got != tc.want {
+				t.Errorf("escapeOverlayDataSegment: %s, want %s", got, tc.want)
+			}
+		})
+	}
+}

container/container.go

@@ -14,6 +14,9 @@ import (
 	. "syscall"
 	"time"
 
+	"hakurei.app/container/bits"
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 	"hakurei.app/container/seccomp"
 )
 
@@ -49,17 +52,18 @@ type (
 
 		cmd *exec.Cmd
 		ctx context.Context
+		msg Msg
 		Params
 	}
 
 	// Params holds container configuration and is safe to serialise.
 	Params struct {
 		// Working directory in the container.
-		Dir *Absolute
+		Dir *check.Absolute
 		// Initial process environment.
 		Env []string
 		// Pathname of initial process in the container.
-		Path *Absolute
+		Path *check.Absolute
 		// Initial process argv.
 		Args []string
 		// Deliver SIGINT to the initial process on context cancellation.
@@ -81,7 +85,7 @@ type (
 		// Extra seccomp flags.
 		SeccompFlags seccomp.ExportFlag
 		// Seccomp presets. Has no effect unless SeccompRules is zero-length.
-		SeccompPresets seccomp.FilterPreset
+		SeccompPresets bits.FilterPreset
 		// Do not load seccomp program.
 		SeccompDisable bool
 
@@ -162,14 +166,14 @@ func (p *Container) Start() error {
 
 	// map to overflow id to work around ownership checks
 	if p.Uid < 1 {
-		p.Uid = OverflowUid()
+		p.Uid = OverflowUid(p.msg)
 	}
 	if p.Gid < 1 {
-		p.Gid = OverflowGid()
+		p.Gid = OverflowGid(p.msg)
 	}
 
 	if !p.RetainSession {
-		p.SeccompPresets |= seccomp.PresetDenyTTY
+		p.SeccompPresets |= bits.PresetDenyTTY
 	}
 
 	if p.AdoptWaitDelay == 0 {
@@ -197,7 +201,7 @@ func (p *Container) Start() error {
 	} else {
 		p.cmd.Cancel = func() error { return p.cmd.Process.Signal(CancelSignal) }
 	}
-	p.cmd.Dir = FHSRoot
+	p.cmd.Dir = fhs.Root
 	p.cmd.SysProcAttr = &SysProcAttr{
 		Setsid:    !p.RetainSession,
 		Pdeathsig: SIGKILL,
@@ -263,19 +267,19 @@ func (p *Container) Start() error {
 					}
 					return &StartError{false, "kernel version too old for LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET", ENOSYS, true, false}
 				} else {
-					msg.Verbosef("landlock abi version %d", abi)
+					p.msg.Verbosef("landlock abi version %d", abi)
 				}
 
 				if rulesetFd, err := rulesetAttr.Create(0); err != nil {
 					return &StartError{true, "create landlock ruleset", err, false, false}
 				} else {
-					msg.Verbosef("enforcing landlock ruleset %s", rulesetAttr)
+					p.msg.Verbosef("enforcing landlock ruleset %s", rulesetAttr)
 					if err = LandlockRestrictSelf(rulesetFd, 0); err != nil {
 						_ = Close(rulesetFd)
 						return &StartError{true, "enforce landlock ruleset", err, false, false}
 					}
 					if err = Close(rulesetFd); err != nil {
-						msg.Verbosef("cannot close landlock ruleset: %v", err)
+						p.msg.Verbosef("cannot close landlock ruleset: %v", err)
 						// not fatal
 					}
 				}
@@ -283,7 +287,7 @@ func (p *Container) Start() error {
 			landlockOut:
 			}
 
-			msg.Verbose("starting container init")
+			p.msg.Verbose("starting container init")
 			if err := p.cmd.Start(); err != nil {
 				return &StartError{false, "start container init", err, false, true}
 			}
@@ -313,7 +317,7 @@ func (p *Container) Serve() error {
 
 	// do not transmit nil
 	if p.Dir == nil {
-		p.Dir = AbsFHSRoot
+		p.Dir = fhs.AbsRoot
 	}
 	if p.SeccompRules == nil {
 		p.SeccompRules = make([]seccomp.NativeRule, 0)
@@ -325,7 +329,7 @@ func (p *Container) Serve() error {
 			Getuid(),
 			Getgid(),
 			len(p.ExtraFiles),
-			msg.IsVerbose(),
+			p.msg.IsVerbose(),
 		},
 	)
 	if err != nil {
@@ -392,17 +396,21 @@ 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 {
-	p := &Container{ctx: ctx, Params: Params{Ops: new(Ops)}}
+func New(ctx context.Context, msg Msg) *Container {
+	if msg == nil {
+		msg = NewMsg(nil)
+	}
+
+	p := &Container{ctx: ctx, msg: msg, Params: Params{Ops: new(Ops)}}
 	c, cancel := context.WithCancel(ctx)
 	p.cancel = cancel
-	p.cmd = exec.CommandContext(c, MustExecutable())
+	p.cmd = exec.CommandContext(c, MustExecutable(msg))
 	return p
 }
 
 // NewCommand calls [New] and initialises the [Params.Path] and [Params.Args] fields.
-func NewCommand(ctx context.Context, pathname *Absolute, name string, args ...string) *Container {
-	z := New(ctx)
+func NewCommand(ctx context.Context, msg Msg, pathname *check.Absolute, name string, args ...string) *Container {
+	z := New(ctx, msg)
 	z.Path = pathname
 	z.Args = append([]string{name}, args...)
 	return z

container/container_test.go

@@ -20,11 +20,11 @@ import (
 
 	"hakurei.app/command"
 	"hakurei.app/container"
+	"hakurei.app/container/bits"
+	"hakurei.app/container/check"
 	"hakurei.app/container/seccomp"
 	"hakurei.app/container/vfs"
 	"hakurei.app/hst"
-	"hakurei.app/internal"
-	"hakurei.app/internal/hlog"
 	"hakurei.app/ldd"
 )
 
@@ -201,20 +201,20 @@ var containerTestCases = []struct {
 
 	rules   []seccomp.NativeRule
 	flags   seccomp.ExportFlag
-	presets seccomp.FilterPreset
+	presets bits.FilterPreset
 }{
 	{"minimal", true, false, false, true,
 		emptyOps, emptyMnt,
-		1000, 100, nil, 0, seccomp.PresetStrict},
+		1000, 100, nil, 0, bits.PresetStrict},
 	{"allow", true, true, true, false,
 		emptyOps, emptyMnt,
-		1000, 100, nil, 0, seccomp.PresetExt | seccomp.PresetDenyDevel},
+		1000, 100, nil, 0, bits.PresetExt | bits.PresetDenyDevel},
 	{"no filter", false, true, true, true,
 		emptyOps, emptyMnt,
-		1000, 100, nil, 0, seccomp.PresetExt},
+		1000, 100, nil, 0, bits.PresetExt},
 	{"custom rules", true, true, true, false,
 		emptyOps, emptyMnt,
-		1, 31, []seccomp.NativeRule{{Syscall: seccomp.ScmpSyscall(syscall.SYS_SETUID), Errno: seccomp.ScmpErrno(syscall.EPERM)}}, 0, seccomp.PresetExt},
+		1, 31, []seccomp.NativeRule{{Syscall: seccomp.ScmpSyscall(syscall.SYS_SETUID), Errno: seccomp.ScmpErrno(syscall.EPERM)}}, 0, bits.PresetExt},
 
 	{"tmpfs", true, false, false, true,
 		earlyOps(new(container.Ops).
@@ -223,11 +223,11 @@ var containerTestCases = []struct {
 		earlyMnt(
 			ent("/", hst.Tmp, "rw,nosuid,nodev,relatime", "tmpfs", "ephemeral", ignore),
 		),
-		9, 9, nil, 0, seccomp.PresetStrict},
+		9, 9, nil, 0, bits.PresetStrict},
 
 	{"dev", true, true /* go test output is not a tty */, false, false,
 		earlyOps(new(container.Ops).
-			Dev(container.MustAbs("/dev"), true),
+			Dev(check.MustAbs("/dev"), true),
 		),
 		earlyMnt(
 			ent("/", "/dev", "ro,nosuid,nodev,relatime", "tmpfs", "devtmpfs", ignore),
@@ -241,11 +241,11 @@ var containerTestCases = []struct {
 			ent("/", "/dev/mqueue", "rw,nosuid,nodev,noexec,relatime", "mqueue", "mqueue", "rw"),
 			ent("/", "/dev/shm", "rw,nosuid,nodev,relatime", "tmpfs", "tmpfs", ignore),
 		),
-		1971, 100, nil, 0, seccomp.PresetStrict},
+		1971, 100, nil, 0, bits.PresetStrict},
 
 	{"dev no mqueue", true, true /* go test output is not a tty */, false, false,
 		earlyOps(new(container.Ops).
-			Dev(container.MustAbs("/dev"), false),
+			Dev(check.MustAbs("/dev"), false),
 		),
 		earlyMnt(
 			ent("/", "/dev", "ro,nosuid,nodev,relatime", "tmpfs", "devtmpfs", ignore),
@@ -258,17 +258,17 @@ var containerTestCases = []struct {
 			ent("/", "/dev/pts", "rw,nosuid,noexec,relatime", "devpts", "devpts", "rw,mode=620,ptmxmode=666"),
 			ent("/", "/dev/shm", "rw,nosuid,nodev,relatime", "tmpfs", "tmpfs", ignore),
 		),
-		1971, 100, nil, 0, seccomp.PresetStrict},
+		1971, 100, nil, 0, bits.PresetStrict},
 
 	{"overlay", true, false, false, true,
 		func(t *testing.T) (*container.Ops, context.Context) {
-			tempDir := container.MustAbs(t.TempDir())
+			tempDir := check.MustAbs(t.TempDir())
 			lower0, lower1, upper, work :=
 				tempDir.Append("lower0"),
 				tempDir.Append("lower1"),
 				tempDir.Append("upper"),
 				tempDir.Append("work")
-			for _, a := range []*container.Absolute{lower0, lower1, upper, work} {
+			for _, a := range []*check.Absolute{lower0, lower1, upper, work} {
 				if err := os.Mkdir(a.String(), 0755); err != nil {
 					t.Fatalf("Mkdir: error = %v", err)
 				}
@@ -286,24 +286,24 @@ var containerTestCases = []struct {
 			return []*vfs.MountInfoEntry{
 				ent("/", hst.Tmp, "rw", "overlay", "overlay",
 					"rw,lowerdir="+
-						container.InternalToHostOvlEscape(ctx.Value(testVal("lower0")).(*container.Absolute).String())+":"+
-						container.InternalToHostOvlEscape(ctx.Value(testVal("lower1")).(*container.Absolute).String())+
+						container.InternalToHostOvlEscape(ctx.Value(testVal("lower0")).(*check.Absolute).String())+":"+
+						container.InternalToHostOvlEscape(ctx.Value(testVal("lower1")).(*check.Absolute).String())+
 						",upperdir="+
-						container.InternalToHostOvlEscape(ctx.Value(testVal("upper")).(*container.Absolute).String())+
+						container.InternalToHostOvlEscape(ctx.Value(testVal("upper")).(*check.Absolute).String())+
 						",workdir="+
-						container.InternalToHostOvlEscape(ctx.Value(testVal("work")).(*container.Absolute).String())+
+						container.InternalToHostOvlEscape(ctx.Value(testVal("work")).(*check.Absolute).String())+
 						",redirect_dir=nofollow,uuid=on,userxattr"),
 			}
 		},
-		1 << 3, 1 << 14, nil, 0, seccomp.PresetStrict},
+		1 << 3, 1 << 14, nil, 0, bits.PresetStrict},
 
 	{"overlay ephemeral", true, false, false, true,
 		func(t *testing.T) (*container.Ops, context.Context) {
-			tempDir := container.MustAbs(t.TempDir())
+			tempDir := check.MustAbs(t.TempDir())
 			lower0, lower1 :=
 				tempDir.Append("lower0"),
 				tempDir.Append("lower1")
-			for _, a := range []*container.Absolute{lower0, lower1} {
+			for _, a := range []*check.Absolute{lower0, lower1} {
 				if err := os.Mkdir(a.String(), 0755); err != nil {
 					t.Fatalf("Mkdir: error = %v", err)
 				}
@@ -319,15 +319,15 @@ var containerTestCases = []struct {
 				ent("/", hst.Tmp, "rw", "overlay", "overlay", ignore),
 			}
 		},
-		1 << 3, 1 << 14, nil, 0, seccomp.PresetStrict},
+		1 << 3, 1 << 14, nil, 0, bits.PresetStrict},
 
 	{"overlay readonly", true, false, false, true,
 		func(t *testing.T) (*container.Ops, context.Context) {
-			tempDir := container.MustAbs(t.TempDir())
+			tempDir := check.MustAbs(t.TempDir())
 			lower0, lower1 :=
 				tempDir.Append("lower0"),
 				tempDir.Append("lower1")
-			for _, a := range []*container.Absolute{lower0, lower1} {
+			for _, a := range []*check.Absolute{lower0, lower1} {
 				if err := os.Mkdir(a.String(), 0755); err != nil {
 					t.Fatalf("Mkdir: error = %v", err)
 				}
@@ -342,17 +342,15 @@ var containerTestCases = []struct {
 			return []*vfs.MountInfoEntry{
 				ent("/", hst.Tmp, "rw", "overlay", "overlay",
 					"ro,lowerdir="+
-						container.InternalToHostOvlEscape(ctx.Value(testVal("lower0")).(*container.Absolute).String())+":"+
-						container.InternalToHostOvlEscape(ctx.Value(testVal("lower1")).(*container.Absolute).String())+
+						container.InternalToHostOvlEscape(ctx.Value(testVal("lower0")).(*check.Absolute).String())+":"+
+						container.InternalToHostOvlEscape(ctx.Value(testVal("lower1")).(*check.Absolute).String())+
 						",redirect_dir=nofollow,userxattr"),
 			}
 		},
-		1 << 3, 1 << 14, nil, 0, seccomp.PresetStrict},
+		1 << 3, 1 << 14, nil, 0, bits.PresetStrict},
 }
 
 func TestContainer(t *testing.T) {
-	replaceOutput(t)
-
 	t.Run("cancel", testContainerCancel(nil, func(t *testing.T, c *container.Container) {
 		wantErr := context.Canceled
 		wantExitCode := 0
@@ -392,7 +390,7 @@ func TestContainer(t *testing.T) {
 			ctx, cancel := context.WithTimeout(t.Context(), helperDefaultTimeout)
 			defer cancel()
 
-			var libPaths []*container.Absolute
+			var libPaths []*check.Absolute
 			c := helperNewContainerLibPaths(ctx, &libPaths, "container", strconv.Itoa(i))
 			c.Uid = tc.uid
 			c.Gid = tc.gid
@@ -413,11 +411,11 @@ func TestContainer(t *testing.T) {
 			c.HostNet = tc.net
 
 			c.
-				Readonly(container.MustAbs(pathReadonly), 0755).
-				Tmpfs(container.MustAbs("/tmp"), 0, 0755).
-				Place(container.MustAbs("/etc/hostname"), []byte(c.Hostname))
+				Readonly(check.MustAbs(pathReadonly), 0755).
+				Tmpfs(check.MustAbs("/tmp"), 0, 0755).
+				Place(check.MustAbs("/etc/hostname"), []byte(c.Hostname))
 			// needs /proc to check mountinfo
-			c.Proc(container.MustAbs("/proc"))
+			c.Proc(check.MustAbs("/proc"))
 
 			// mountinfo cannot be resolved directly by helper due to libPaths nondeterminism
 			mnt := make([]*vfs.MountInfoEntry, 0, 3+len(libPaths))
@@ -448,10 +446,10 @@ func TestContainer(t *testing.T) {
 				_, _ = output.WriteTo(os.Stdout)
 				t.Fatalf("cannot serialise expected mount points: %v", err)
 			}
-			c.Place(container.MustAbs(pathWantMnt), want.Bytes())
+			c.Place(check.MustAbs(pathWantMnt), want.Bytes())
 
 			if tc.ro {
-				c.Remount(container.MustAbs("/"), syscall.MS_RDONLY)
+				c.Remount(check.MustAbs("/"), syscall.MS_RDONLY)
 			}
 
 			if err := c.Start(); err != nil {
@@ -547,12 +545,13 @@ func testContainerCancel(
 }
 
 func TestContainerString(t *testing.T) {
-	c := container.NewCommand(t.Context(), container.MustAbs("/run/current-system/sw/bin/ldd"), "ldd", "/usr/bin/env")
+	msg := container.NewMsg(nil)
+	c := container.NewCommand(t.Context(), msg, check.MustAbs("/run/current-system/sw/bin/ldd"), "ldd", "/usr/bin/env")
 	c.SeccompFlags |= seccomp.AllowMultiarch
 	c.SeccompRules = seccomp.Preset(
-		seccomp.PresetExt|seccomp.PresetDenyNS|seccomp.PresetDenyTTY,
+		bits.PresetExt|bits.PresetDenyNS|bits.PresetDenyTTY,
 		c.SeccompFlags)
-	c.SeccompPresets = seccomp.PresetStrict
+	c.SeccompPresets = bits.PresetStrict
 	want := `argv: ["ldd" "/usr/bin/env"], filter: true, rules: 65, flags: 0x1, presets: 0xf`
 	if got := c.String(); got != want {
 		t.Errorf("String: %s, want %s", got, want)
@@ -683,13 +682,13 @@ const (
 )
 
 var (
-	absHelperInnerPath = container.MustAbs(helperInnerPath)
+	absHelperInnerPath = check.MustAbs(helperInnerPath)
 )
 
 var helperCommands []func(c command.Command)
 
 func TestMain(m *testing.M) {
-	container.TryArgv0(hlog.Output{}, hlog.Prepare, internal.InstallOutput)
+	container.TryArgv0(nil)
 
 	if os.Getenv(envDoCheck) == "1" {
 		c := command.New(os.Stderr, log.Printf, "helper", func(args []string) error {
@@ -711,13 +710,14 @@ func TestMain(m *testing.M) {
 	os.Exit(m.Run())
 }
 
-func helperNewContainerLibPaths(ctx context.Context, libPaths *[]*container.Absolute, args ...string) (c *container.Container) {
-	c = container.NewCommand(ctx, absHelperInnerPath, "helper", args...)
+func helperNewContainerLibPaths(ctx context.Context, libPaths *[]*check.Absolute, args ...string) (c *container.Container) {
+	msg := container.NewMsg(nil)
+	c = container.NewCommand(ctx, msg, absHelperInnerPath, "helper", args...)
 	c.Env = append(c.Env, envDoCheck+"=1")
-	c.Bind(container.MustAbs(os.Args[0]), absHelperInnerPath, 0)
+	c.Bind(check.MustAbs(os.Args[0]), absHelperInnerPath, 0)
 
 	// in case test has cgo enabled
-	if entries, err := ldd.Exec(ctx, os.Args[0]); err != nil {
+	if entries, err := ldd.Exec(ctx, msg, os.Args[0]); err != nil {
 		log.Fatalf("ldd: %v", err)
 	} else {
 		*libPaths = ldd.Path(entries)
@@ -730,5 +730,5 @@ func helperNewContainerLibPaths(ctx context.Context, libPaths *[]*container.Abso
 }
 
 func helperNewContainer(ctx context.Context, args ...string) (c *container.Container) {
-	return helperNewContainerLibPaths(ctx, new([]*container.Absolute), args...)
+	return helperNewContainerLibPaths(ctx, new([]*check.Absolute), args...)
 }

container/dispatcher.go

@@ -3,7 +3,6 @@ package container
 import (
 	"io"
 	"io/fs"
-	"log"
 	"os"
 	"os/exec"
 	"os/signal"
@@ -38,7 +37,7 @@ type syscallDispatcher interface {
 	setNoNewPrivs() error
 
 	// lastcap provides [LastCap].
-	lastcap() uintptr
+	lastcap(msg Msg) uintptr
 	// capset provides capset.
 	capset(hdrp *capHeader, datap *[2]capData) error
 	// capBoundingSetDrop provides capBoundingSetDrop.
@@ -53,9 +52,9 @@ type syscallDispatcher interface {
 	receive(key string, e any, fdp *uintptr) (closeFunc func() error, err error)
 
 	// bindMount provides procPaths.bindMount.
-	bindMount(source, target string, flags uintptr) error
+	bindMount(msg Msg, source, target string, flags uintptr) error
 	// remount provides procPaths.remount.
-	remount(target string, flags uintptr) error
+	remount(msg Msg, target string, flags uintptr) error
 	// mountTmpfs provides mountTmpfs.
 	mountTmpfs(fsname, target string, flags uintptr, size int, perm os.FileMode) error
 	// ensureFile provides ensureFile.
@@ -122,22 +121,12 @@ type syscallDispatcher interface {
 	// wait4 provides syscall.Wait4
 	wait4(pid int, wstatus *syscall.WaitStatus, options int, rusage *syscall.Rusage) (wpid int, err error)
 
-	// printf provides [log.Printf].
-	printf(format string, v ...any)
-	// fatal provides [log.Fatal]
-	fatal(v ...any)
-	// fatalf provides [log.Fatalf]
-	fatalf(format string, v ...any)
-	// verbose provides [Msg.Verbose].
-	verbose(v ...any)
-	// verbosef provides [Msg.Verbosef].
-	verbosef(format string, v ...any)
-	// suspend provides [Msg.Suspend].
-	suspend()
-	// resume provides [Msg.Resume].
-	resume() bool
-	// beforeExit provides [Msg.BeforeExit].
-	beforeExit()
+	// printf provides the Printf method of [log.Logger].
+	printf(msg Msg, format string, v ...any)
+	// fatal provides the Fatal method of [log.Logger]
+	fatal(msg Msg, v ...any)
+	// fatalf provides the Fatalf method of [log.Logger]
+	fatalf(msg Msg, format string, v ...any)
 }
 
 // direct implements syscallDispatcher on the current kernel.
@@ -151,7 +140,7 @@ func (direct) setPtracer(pid uintptr) error       { return SetPtracer(pid) }
 func (direct) setDumpable(dumpable uintptr) error { return SetDumpable(dumpable) }
 func (direct) setNoNewPrivs() error               { return SetNoNewPrivs() }
 
-func (direct) lastcap() uintptr                                { return LastCap() }
+func (direct) lastcap(msg Msg) uintptr                         { return LastCap(msg) }
 func (direct) capset(hdrp *capHeader, datap *[2]capData) error { return capset(hdrp, datap) }
 func (direct) capBoundingSetDrop(cap uintptr) error            { return capBoundingSetDrop(cap) }
 func (direct) capAmbientClearAll() error                       { return capAmbientClearAll() }
@@ -161,11 +150,11 @@ func (direct) receive(key string, e any, fdp *uintptr) (func() error, error) {
 	return Receive(key, e, fdp)
 }
 
-func (direct) bindMount(source, target string, flags uintptr) error {
-	return hostProc.bindMount(source, target, flags)
+func (direct) bindMount(msg Msg, source, target string, flags uintptr) error {
+	return hostProc.bindMount(msg, source, target, flags)
 }
-func (direct) remount(target string, flags uintptr) error {
-	return hostProc.remount(target, flags)
+func (direct) remount(msg Msg, target string, flags uintptr) error {
+	return hostProc.remount(msg, target, flags)
 }
 func (k direct) mountTmpfs(fsname, target string, flags uintptr, size int, perm os.FileMode) error {
 	return mountTmpfs(k, fsname, target, flags, size, perm)
@@ -232,11 +221,6 @@ 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) printf(msg Msg, format string, v ...any) { msg.GetLogger().Printf(format, v...) }
+func (direct) fatal(msg Msg, v ...any)                 { msg.GetLogger().Fatal(v...) }
+func (direct) fatalf(msg Msg, format string, v ...any) { msg.GetLogger().Fatalf(format, v...) }

container/dispatcher_test.go

@@ -2,8 +2,10 @@ package container
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 	"io/fs"
+	"log"
 	"os"
 	"os/exec"
 	"reflect"
@@ -136,7 +138,7 @@ func call(name string, args stub.ExpectArgs, ret any, err error) stub.Call {
 
 type simpleTestCase struct {
 	name    string
-	f       func(k syscallDispatcher) error
+	f       func(k *kstub) error
 	want    stub.Expect
 	wantErr error
 }
@@ -185,11 +187,11 @@ func checkOpBehaviour(t *testing.T, testCases []opBehaviourTestCase) {
 			t.Run(tc.name, func(t *testing.T) {
 				t.Helper()
 
-				state := &setupState{Params: tc.params}
 				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)},
 				)}
+				state := &setupState{Params: tc.params, Msg: k}
 				defer stub.HandleExit(t)
 				errEarly := tc.op.early(state, k)
 				k.Expects(stub.CallSeparator)
@@ -327,7 +329,11 @@ func (k *kstub) setDumpable(dumpable uintptr) error {
 }
 
 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) lastcap(msg Msg) uintptr {
+	k.Helper()
+	k.checkMsg(msg)
+	return k.Expects("lastcap").Ret.(uintptr)
+}
 
 func (k *kstub) capset(hdrp *capHeader, datap *[2]capData) error {
 	k.Helper()
@@ -403,16 +409,18 @@ func (k *kstub) receive(key string, e any, fdp *uintptr) (closeFunc func() error
 	return
 }
 
-func (k *kstub) bindMount(source, target string, flags uintptr) error {
+func (k *kstub) bindMount(msg Msg, source, target string, flags uintptr) error {
 	k.Helper()
+	k.checkMsg(msg)
 	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))
 }
 
-func (k *kstub) remount(target string, flags uintptr) error {
+func (k *kstub) remount(msg Msg, target string, flags uintptr) error {
 	k.Helper()
+	k.checkMsg(msg)
 	return k.Expects("remount").Error(
 		stub.CheckArg(k.Stub, "target", target, 0),
 		stub.CheckArg(k.Stub, "flags", flags, 1))
@@ -694,7 +702,7 @@ func (k *kstub) wait4(pid int, wstatus *syscall.WaitStatus, options int, rusage
 	return
 }
 
-func (k *kstub) printf(format string, v ...any) {
+func (k *kstub) printf(_ Msg, format string, v ...any) {
 	k.Helper()
 	if k.Expects("printf").Error(
 		stub.CheckArg(k.Stub, "format", format, 0),
@@ -703,7 +711,7 @@ func (k *kstub) printf(format string, v ...any) {
 	}
 }
 
-func (k *kstub) fatal(v ...any) {
+func (k *kstub) fatal(_ Msg, v ...any) {
 	k.Helper()
 	if k.Expects("fatal").Error(
 		stub.CheckArgReflect(k.Stub, "v", v, 0)) != nil {
@@ -712,7 +720,7 @@ func (k *kstub) fatal(v ...any) {
 	panic(stub.PanicExit)
 }
 
-func (k *kstub) fatalf(format string, v ...any) {
+func (k *kstub) fatalf(_ Msg, format string, v ...any) {
 	k.Helper()
 	if k.Expects("fatalf").Error(
 		stub.CheckArg(k.Stub, "format", format, 0),
@@ -722,7 +730,35 @@ func (k *kstub) fatalf(format string, v ...any) {
 	panic(stub.PanicExit)
 }
 
-func (k *kstub) verbose(v ...any) {
+func (k *kstub) checkMsg(msg Msg) {
+	k.Helper()
+	var target *kstub
+
+	if state, ok := msg.(*setupState); ok {
+		target = state.Msg.(*kstub)
+	} else {
+		target = msg.(*kstub)
+	}
+
+	if k != target {
+		panic(fmt.Sprintf("unexpected Msg: %#v", msg))
+	}
+}
+
+func (k *kstub) GetLogger() *log.Logger { panic("unreachable") }
+func (k *kstub) IsVerbose() bool        { panic("unreachable") }
+
+func (k *kstub) SwapVerbose(verbose bool) bool {
+	k.Helper()
+	expect := k.Expects("swapVerbose")
+	if expect.Error(
+		stub.CheckArg(k.Stub, "verbose", verbose, 0)) != nil {
+		k.FailNow()
+	}
+	return expect.Ret.(bool)
+}
+
+func (k *kstub) Verbose(v ...any) {
 	k.Helper()
 	if k.Expects("verbose").Error(
 		stub.CheckArgReflect(k.Stub, "v", v, 0)) != nil {
@@ -730,7 +766,7 @@ func (k *kstub) verbose(v ...any) {
 	}
 }
 
-func (k *kstub) verbosef(format string, v ...any) {
+func (k *kstub) Verbosef(format string, v ...any) {
 	k.Helper()
 	if k.Expects("verbosef").Error(
 		stub.CheckArg(k.Stub, "format", format, 0),
@@ -739,6 +775,6 @@ func (k *kstub) verbosef(format string, v ...any) {
 	}
 }
 
-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") }
+func (k *kstub) Suspend() bool { k.Helper(); return k.Expects("suspend").Ret.(bool) }
+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

@@ -5,6 +5,7 @@ import (
 	"os"
 	"syscall"
 
+	"hakurei.app/container/check"
 	"hakurei.app/container/vfs"
 )
 
@@ -16,7 +17,7 @@ func messageFromError(err error) (string, bool) {
 	if m, ok := messagePrefixP[os.PathError]("cannot ", err); ok {
 		return m, ok
 	}
-	if m, ok := messagePrefixP[AbsoluteError]("", err); ok {
+	if m, ok := messagePrefixP[check.AbsoluteError]("", err); ok {
 		return m, ok
 	}
 	if m, ok := messagePrefix[OpRepeatError]("", err); ok {

container/errors_test.go

@@ -8,6 +8,7 @@ import (
 	"syscall"
 	"testing"
 
+	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
 	"hakurei.app/container/vfs"
 )
@@ -34,7 +35,7 @@ func TestMessageFromError(t *testing.T) {
 			Err:  stub.UniqueError(0xdeadbeef),
 		}, "cannot mount /sysroot: unique error 3735928559 injected by the test suite", true},
 
-		{"absolute", &AbsoluteError{"etc/mtab"},
+		{"absolute", &check.AbsoluteError{Pathname: "etc/mtab"},
 			`path "etc/mtab" is not absolute`, true},
 
 		{"repeat", OpRepeatError("autoetc"),

container/executable.go

@@ -1,7 +1,6 @@
 package container
 
 import (
-	"log"
 	"os"
 	"sync"
 )
@@ -11,16 +10,16 @@ var (
 	executableOnce sync.Once
 )
 
-func copyExecutable() {
+func copyExecutable(msg Msg) {
 	if name, err := os.Executable(); err != nil {
 		msg.BeforeExit()
-		log.Fatalf("cannot read executable path: %v", err)
+		msg.GetLogger().Fatalf("cannot read executable path: %v", err)
 	} else {
 		executable = name
 	}
 }
 
-func MustExecutable() string {
-	executableOnce.Do(copyExecutable)
+func MustExecutable(msg Msg) string {
+	executableOnce.Do(func() { copyExecutable(msg) })
 	return executable
 }

container/executable_test.go

@@ -9,7 +9,7 @@ import (
 
 func TestExecutable(t *testing.T) {
 	for i := 0; i < 16; i++ {
-		if got := container.MustExecutable(); got != os.Args[0] {
+		if got := container.MustExecutable(container.NewMsg(nil)); got != os.Args[0] {
 			t.Errorf("MustExecutable: %q, want %q",
 				got, os.Args[0])
 		}

container/fhs/abs.go

@@ -0,0 +1,41 @@
+package fhs
+
+import (
+	_ "unsafe"
+
+	"hakurei.app/container/check"
+)
+
+/* constants in this file bypass abs check, be extremely careful when changing them! */
+
+//go:linkname unsafeAbs hakurei.app/container/check.unsafeAbs
+func unsafeAbs(_ string) *check.Absolute
+
+var (
+	// AbsRoot is [Root] as [check.Absolute].
+	AbsRoot = unsafeAbs(Root)
+	// AbsEtc is [Etc] as [check.Absolute].
+	AbsEtc = unsafeAbs(Etc)
+	// AbsTmp is [Tmp] as [check.Absolute].
+	AbsTmp = unsafeAbs(Tmp)
+
+	// AbsRun is [Run] as [check.Absolute].
+	AbsRun = unsafeAbs(Run)
+	// AbsRunUser is [RunUser] as [check.Absolute].
+	AbsRunUser = unsafeAbs(RunUser)
+
+	// AbsUsrBin is [UsrBin] as [check.Absolute].
+	AbsUsrBin = unsafeAbs(UsrBin)
+
+	// AbsVar is [Var] as [check.Absolute].
+	AbsVar = unsafeAbs(Var)
+	// AbsVarLib is [VarLib] as [check.Absolute].
+	AbsVarLib = unsafeAbs(VarLib)
+
+	// AbsDev is [Dev] as [check.Absolute].
+	AbsDev = unsafeAbs(Dev)
+	// AbsProc is [Proc] as [check.Absolute].
+	AbsProc = unsafeAbs(Proc)
+	// AbsSys is [Sys] as [check.Absolute].
+	AbsSys = unsafeAbs(Sys)
+)

container/fhs/fhs.go

@@ -0,0 +1,38 @@
+// Package fhs provides constant and checked pathname values for common FHS paths.
+package fhs
+
+const (
+	// Root points to the file system root.
+	Root = "/"
+	// Etc points to the directory for system-specific configuration.
+	Etc = "/etc/"
+	// Tmp points to the place for small temporary files.
+	Tmp = "/tmp/"
+
+	// Run points to a "tmpfs" file system for system packages to place runtime data, socket files, and similar.
+	Run = "/run/"
+	// RunUser points to a directory containing per-user runtime directories,
+	// each usually individually mounted "tmpfs" instances.
+	RunUser = Run + "user/"
+
+	// Usr points to vendor-supplied operating system resources.
+	Usr = "/usr/"
+	// UsrBin points to binaries and executables for user commands that shall appear in the $PATH search path.
+	UsrBin = Usr + "bin/"
+
+	// Var points to persistent, variable system data. Writable during normal system operation.
+	Var = "/var/"
+	// VarLib points to persistent system data.
+	VarLib = Var + "lib/"
+	// VarEmpty points to a nonstandard directory that is usually empty.
+	VarEmpty = Var + "empty/"
+
+	// Dev points to the root directory for device nodes.
+	Dev = "/dev/"
+	// Proc points to a virtual kernel file system exposing the process list and other functionality.
+	Proc = "/proc/"
+	// ProcSys points to a hierarchy below /proc/ that exposes a number of kernel tunables.
+	ProcSys = Proc + "sys/"
+	// Sys points to a virtual kernel file system exposing discovered devices and other functionality.
+	Sys = "/sys/"
+)

container/init.go

@@ -3,6 +3,7 @@ package container
 import (
 	"errors"
 	"fmt"
+	"log"
 	"os"
 	"os/exec"
 	"path"
@@ -11,6 +12,7 @@ import (
 	. "syscall"
 	"time"
 
+	"hakurei.app/container/fhs"
 	"hakurei.app/container/seccomp"
 )
 
@@ -29,7 +31,7 @@ const (
 
 	it should be noted that none of this should become relevant at any point since the resulting
 	intermediate root tmpfs should be effectively anonymous */
-	intermediateHostPath = FHSProc + "self/fd"
+	intermediateHostPath = fhs.Proc + "self/fd"
 
 	// setup params file descriptor
 	setupEnv = "HAKUREI_SETUP"
@@ -59,6 +61,7 @@ type (
 	setupState struct {
 		nonrepeatable uintptr
 		*Params
+		Msg
 	}
 )
 
@@ -91,20 +94,23 @@ type initParams struct {
 	Verbose bool
 }
 
-func Init(prepareLogger func(prefix string), setVerbose func(verbose bool)) {
-	initEntrypoint(direct{}, prepareLogger, setVerbose)
+// Init is called by [TryArgv0] if the current process is the container init.
+func Init(msg Msg) {
+	if msg == nil {
+		panic("attempting to call initEntrypoint with nil msg")
+	}
+	initEntrypoint(direct{}, msg)
 }
 
-func initEntrypoint(k syscallDispatcher, prepareLogger func(prefix string), setVerbose func(verbose bool)) {
+func initEntrypoint(k syscallDispatcher, msg Msg) {
 	k.lockOSThread()
-	prepareLogger("init")
 
 	if k.getpid() != 1 {
-		k.fatal("this process must run as pid 1")
+		k.fatal(msg, "this process must run as pid 1")
 	}
 
 	if err := k.setPtracer(0); err != nil {
-		k.verbosef("cannot enable ptrace protection via Yama LSM: %v", err)
+		msg.Verbosef("cannot enable ptrace protection via Yama LSM: %v", err)
 		// not fatal: this program has no additional privileges at initial program start
 	}
 
@@ -116,65 +122,65 @@ func initEntrypoint(k syscallDispatcher, prepareLogger func(prefix string), setV
 	)
 	if f, err := k.receive(setupEnv, &params, &setupFd); err != nil {
 		if errors.Is(err, EBADF) {
-			k.fatal("invalid setup descriptor")
+			k.fatal(msg, "invalid setup descriptor")
 		}
 		if errors.Is(err, ErrReceiveEnv) {
-			k.fatal("HAKUREI_SETUP not set")
+			k.fatal(msg, "HAKUREI_SETUP not set")
 		}
 
-		k.fatalf("cannot decode init setup payload: %v", err)
+		k.fatalf(msg, "cannot decode init setup payload: %v", err)
 	} else {
 		if params.Ops == nil {
-			k.fatal("invalid setup parameters")
+			k.fatal(msg, "invalid setup parameters")
 		}
 		if params.ParentPerm == 0 {
 			params.ParentPerm = 0755
 		}
 
-		setVerbose(params.Verbose)
-		k.verbose("received setup parameters")
+		msg.SwapVerbose(params.Verbose)
+		msg.Verbose("received setup parameters")
 		closeSetup = f
 		offsetSetup = int(setupFd + 1)
 	}
 
 	// write uid/gid map here so parent does not need to set dumpable
 	if err := k.setDumpable(SUID_DUMP_USER); err != nil {
-		k.fatalf("cannot set SUID_DUMP_USER: %v", err)
+		k.fatalf(msg, "cannot set SUID_DUMP_USER: %v", err)
 	}
-	if err := k.writeFile(FHSProc+"self/uid_map",
+	if err := k.writeFile(fhs.Proc+"self/uid_map",
 		append([]byte{}, strconv.Itoa(params.Uid)+" "+strconv.Itoa(params.HostUid)+" 1\n"...),
 		0); err != nil {
-		k.fatalf("%v", err)
+		k.fatalf(msg, "%v", err)
 	}
-	if err := k.writeFile(FHSProc+"self/setgroups",
+	if err := k.writeFile(fhs.Proc+"self/setgroups",
 		[]byte("deny\n"),
 		0); err != nil && !os.IsNotExist(err) {
-		k.fatalf("%v", err)
+		k.fatalf(msg, "%v", err)
 	}
-	if err := k.writeFile(FHSProc+"self/gid_map",
+	if err := k.writeFile(fhs.Proc+"self/gid_map",
 		append([]byte{}, strconv.Itoa(params.Gid)+" "+strconv.Itoa(params.HostGid)+" 1\n"...),
 		0); err != nil {
-		k.fatalf("%v", err)
+		k.fatalf(msg, "%v", err)
 	}
 	if err := k.setDumpable(SUID_DUMP_DISABLE); err != nil {
-		k.fatalf("cannot set SUID_DUMP_DISABLE: %v", err)
+		k.fatalf(msg, "cannot set SUID_DUMP_DISABLE: %v", err)
 	}
 
 	oldmask := k.umask(0)
 	if params.Hostname != "" {
 		if err := k.sethostname([]byte(params.Hostname)); err != nil {
-			k.fatalf("cannot set hostname: %v", err)
+			k.fatalf(msg, "cannot set hostname: %v", err)
 		}
 	}
 
 	// cache sysctl before pivot_root
-	lastcap := k.lastcap()
+	lastcap := k.lastcap(msg)
 
-	if err := k.mount(zeroString, FHSRoot, zeroString, MS_SILENT|MS_SLAVE|MS_REC, zeroString); err != nil {
-		k.fatalf("cannot make / rslave: %v", err)
+	if err := k.mount(zeroString, fhs.Root, zeroString, MS_SILENT|MS_SLAVE|MS_REC, zeroString); err != nil {
+		k.fatalf(msg, "cannot make / rslave: %v", err)
 	}
 
-	state := &setupState{Params: &params.Params}
+	state := &setupState{Params: &params.Params, Msg: msg}
 
 	/* early is called right before pivot_root into intermediate root;
 	this step is mostly for gathering information that would otherwise be difficult to obtain
@@ -182,41 +188,41 @@ func initEntrypoint(k syscallDispatcher, prepareLogger func(prefix string), setV
 	the state of the mount namespace */
 	for i, op := range *params.Ops {
 		if op == nil || !op.Valid() {
-			k.fatalf("invalid op at index %d", i)
+			k.fatalf(msg, "invalid op at index %d", i)
 		}
 
 		if err := op.early(state, k); err != nil {
 			if m, ok := messageFromError(err); ok {
-				k.fatal(m)
+				k.fatal(msg, m)
 			} else {
-				k.fatalf("cannot prepare op at index %d: %v", i, err)
+				k.fatalf(msg, "cannot prepare op at index %d: %v", i, err)
 			}
 		}
 	}
 
 	if err := k.mount(SourceTmpfsRootfs, intermediateHostPath, FstypeTmpfs, MS_NODEV|MS_NOSUID, zeroString); err != nil {
-		k.fatalf("cannot mount intermediate root: %v", err)
+		k.fatalf(msg, "cannot mount intermediate root: %v", err)
 	}
 	if err := k.chdir(intermediateHostPath); err != nil {
-		k.fatalf("cannot enter intermediate host path: %v", err)
+		k.fatalf(msg, "cannot enter intermediate host path: %v", err)
 	}
 
 	if err := k.mkdir(sysrootDir, 0755); err != nil {
-		k.fatalf("%v", err)
+		k.fatalf(msg, "%v", err)
 	}
 	if err := k.mount(sysrootDir, sysrootDir, zeroString, MS_SILENT|MS_BIND|MS_REC, zeroString); err != nil {
-		k.fatalf("cannot bind sysroot: %v", err)
+		k.fatalf(msg, "cannot bind sysroot: %v", err)
 	}
 
 	if err := k.mkdir(hostDir, 0755); err != nil {
-		k.fatalf("%v", err)
+		k.fatalf(msg, "%v", err)
 	}
 	// pivot_root uncovers intermediateHostPath in hostDir
 	if err := k.pivotRoot(intermediateHostPath, hostDir); err != nil {
-		k.fatalf("cannot pivot into intermediate root: %v", err)
+		k.fatalf(msg, "cannot pivot into intermediate root: %v", err)
 	}
-	if err := k.chdir(FHSRoot); err != nil {
-		k.fatalf("cannot enter intermediate root: %v", err)
+	if err := k.chdir(fhs.Root); err != nil {
+		k.fatalf(msg, "cannot enter intermediate root: %v", err)
 	}
 
 	/* apply is called right after pivot_root and entering the new root;
@@ -226,64 +232,64 @@ func initEntrypoint(k syscallDispatcher, prepareLogger func(prefix string), setV
 	for i, op := range *params.Ops {
 		// ops already checked during early setup
 		if prefix, ok := op.prefix(); ok {
-			k.verbosef("%s %s", prefix, op)
+			msg.Verbosef("%s %s", prefix, op)
 		}
 		if err := op.apply(state, k); err != nil {
 			if m, ok := messageFromError(err); ok {
-				k.fatal(m)
+				k.fatal(msg, m)
 			} else {
-				k.fatalf("cannot apply op at index %d: %v", i, err)
+				k.fatalf(msg, "cannot apply op at index %d: %v", i, err)
 			}
 		}
 	}
 
 	// setup requiring host root complete at this point
 	if err := k.mount(hostDir, hostDir, zeroString, MS_SILENT|MS_REC|MS_PRIVATE, zeroString); err != nil {
-		k.fatalf("cannot make host root rprivate: %v", err)
+		k.fatalf(msg, "cannot make host root rprivate: %v", err)
 	}
 	if err := k.unmount(hostDir, MNT_DETACH); err != nil {
-		k.fatalf("cannot unmount host root: %v", err)
+		k.fatalf(msg, "cannot unmount host root: %v", err)
 	}
 
 	{
 		var fd int
 		if err := IgnoringEINTR(func() (err error) {
-			fd, err = k.open(FHSRoot, O_DIRECTORY|O_RDONLY, 0)
+			fd, err = k.open(fhs.Root, O_DIRECTORY|O_RDONLY, 0)
 			return
 		}); err != nil {
-			k.fatalf("cannot open intermediate root: %v", err)
+			k.fatalf(msg, "cannot open intermediate root: %v", err)
 		}
 		if err := k.chdir(sysrootPath); err != nil {
-			k.fatalf("cannot enter sysroot: %v", err)
+			k.fatalf(msg, "cannot enter sysroot: %v", err)
 		}
 
 		if err := k.pivotRoot(".", "."); err != nil {
-			k.fatalf("cannot pivot into sysroot: %v", err)
+			k.fatalf(msg, "cannot pivot into sysroot: %v", err)
 		}
 		if err := k.fchdir(fd); err != nil {
-			k.fatalf("cannot re-enter intermediate root: %v", err)
+			k.fatalf(msg, "cannot re-enter intermediate root: %v", err)
 		}
 		if err := k.unmount(".", MNT_DETACH); err != nil {
-			k.fatalf("cannot unmount intermediate root: %v", err)
+			k.fatalf(msg, "cannot unmount intermediate root: %v", err)
 		}
-		if err := k.chdir(FHSRoot); err != nil {
-			k.fatalf("cannot enter root: %v", err)
+		if err := k.chdir(fhs.Root); err != nil {
+			k.fatalf(msg, "cannot enter root: %v", err)
 		}
 
 		if err := k.close(fd); err != nil {
-			k.fatalf("cannot close intermediate root: %v", err)
+			k.fatalf(msg, "cannot close intermediate root: %v", err)
 		}
 	}
 
 	if err := k.capAmbientClearAll(); err != nil {
-		k.fatalf("cannot clear the ambient capability set: %v", err)
+		k.fatalf(msg, "cannot clear the ambient capability set: %v", err)
 	}
 	for i := uintptr(0); i <= lastcap; i++ {
 		if params.Privileged && i == CAP_SYS_ADMIN {
 			continue
 		}
 		if err := k.capBoundingSetDrop(i); err != nil {
-			k.fatalf("cannot drop capability from bounding set: %v", err)
+			k.fatalf(msg, "cannot drop capability from bounding set: %v", err)
 		}
 	}
 
@@ -292,29 +298,29 @@ func initEntrypoint(k syscallDispatcher, prepareLogger func(prefix string), setV
 		keep[capToIndex(CAP_SYS_ADMIN)] |= capToMask(CAP_SYS_ADMIN)
 
 		if err := k.capAmbientRaise(CAP_SYS_ADMIN); err != nil {
-			k.fatalf("cannot raise CAP_SYS_ADMIN: %v", err)
+			k.fatalf(msg, "cannot raise CAP_SYS_ADMIN: %v", err)
 		}
 	}
 	if err := k.capset(
 		&capHeader{_LINUX_CAPABILITY_VERSION_3, 0},
 		&[2]capData{{0, keep[0], keep[0]}, {0, keep[1], keep[1]}},
 	); err != nil {
-		k.fatalf("cannot capset: %v", err)
+		k.fatalf(msg, "cannot capset: %v", err)
 	}
 
 	if !params.SeccompDisable {
 		rules := params.SeccompRules
 		if len(rules) == 0 { // non-empty rules slice always overrides presets
-			k.verbosef("resolving presets %#x", params.SeccompPresets)
+			msg.Verbosef("resolving presets %#x", params.SeccompPresets)
 			rules = seccomp.Preset(params.SeccompPresets, params.SeccompFlags)
 		}
 		if err := k.seccompLoad(rules, params.SeccompFlags); err != nil {
 			// this also indirectly asserts PR_SET_NO_NEW_PRIVS
-			k.fatalf("cannot load syscall filter: %v", err)
+			k.fatalf(msg, "cannot load syscall filter: %v", err)
 		}
-		k.verbosef("%d filter rules loaded", len(rules))
+		msg.Verbosef("%d filter rules loaded", len(rules))
 	} else {
-		k.verbose("syscall filter not configured")
+		msg.Verbose("syscall filter not configured")
 	}
 
 	extraFiles := make([]*os.File, params.Count)
@@ -331,14 +337,14 @@ func initEntrypoint(k syscallDispatcher, prepareLogger func(prefix string), setV
 	cmd.ExtraFiles = extraFiles
 	cmd.Dir = params.Dir.String()
 
-	k.verbosef("starting initial program %s", params.Path)
+	msg.Verbosef("starting initial program %s", params.Path)
 	if err := k.start(cmd); err != nil {
-		k.fatalf("%v", err)
+		k.fatalf(msg, "%v", err)
 	}
-	k.suspend()
+	msg.Suspend()
 
 	if err := closeSetup(); err != nil {
-		k.printf("cannot close setup pipe: %v", err)
+		k.printf(msg, "cannot close setup pipe: %v", err)
 		// not fatal
 	}
 
@@ -372,7 +378,7 @@ func initEntrypoint(k syscallDispatcher, prepareLogger func(prefix string), setV
 			}
 		}
 		if !errors.Is(err, ECHILD) {
-			k.printf("unexpected wait4 response: %v", err)
+			k.printf(msg, "unexpected wait4 response: %v", err)
 		}
 
 		close(done)
@@ -389,50 +395,50 @@ func initEntrypoint(k syscallDispatcher, prepareLogger func(prefix string), setV
 	for {
 		select {
 		case s := <-sig:
-			if k.resume() {
-				k.verbosef("%s after process start", s.String())
+			if msg.Resume() {
+				msg.Verbosef("%s after process start", s.String())
 			} else {
-				k.verbosef("got %s", s.String())
+				msg.Verbosef("got %s", s.String())
 			}
 			if s == CancelSignal && params.ForwardCancel && cmd.Process != nil {
-				k.verbose("forwarding context cancellation")
+				msg.Verbose("forwarding context cancellation")
 				if err := k.signal(cmd, os.Interrupt); err != nil {
-					k.printf("cannot forward cancellation: %v", err)
+					k.printf(msg, "cannot forward cancellation: %v", err)
 				}
 				continue
 			}
-			k.beforeExit()
+			msg.BeforeExit()
 			k.exit(0)
 
 		case w := <-info:
 			if w.wpid == cmd.Process.Pid {
 				// initial process exited, output is most likely available again
-				k.resume()
+				msg.Resume()
 
 				switch {
 				case w.wstatus.Exited():
 					r = w.wstatus.ExitStatus()
-					k.verbosef("initial process exited with code %d", w.wstatus.ExitStatus())
+					msg.Verbosef("initial process exited with code %d", w.wstatus.ExitStatus())
 
 				case w.wstatus.Signaled():
 					r = 128 + int(w.wstatus.Signal())
-					k.verbosef("initial process exited with signal %s", w.wstatus.Signal())
+					msg.Verbosef("initial process exited with signal %s", w.wstatus.Signal())
 
 				default:
 					r = 255
-					k.verbosef("initial process exited with status %#x", w.wstatus)
+					msg.Verbosef("initial process exited with status %#x", w.wstatus)
 				}
 
 				go func() { time.Sleep(params.AdoptWaitDelay); close(timeout) }()
 			}
 
 		case <-done:
-			k.beforeExit()
+			msg.BeforeExit()
 			k.exit(r)
 
 		case <-timeout:
-			k.printf("timeout exceeded waiting for lingering processes")
-			k.beforeExit()
+			k.printf(msg, "timeout exceeded waiting for lingering processes")
+			msg.BeforeExit()
 			k.exit(r)
 		}
 	}
@@ -441,10 +447,16 @@ func initEntrypoint(k syscallDispatcher, prepareLogger func(prefix string), setV
 const initName = "init"
 
 // TryArgv0 calls [Init] if the last element of argv0 is "init".
-func TryArgv0(v Msg, prepare func(prefix string), setVerbose func(verbose bool)) {
+// If a nil msg is passed, the system logger is used instead.
+func TryArgv0(msg Msg) {
+	if msg == nil {
+		log.SetPrefix(initName + ": ")
+		log.SetFlags(0)
+		msg = NewMsg(log.Default())
+	}
+
 	if len(os.Args) > 0 && path.Base(os.Args[0]) == initName {
-		msg = v
-		Init(prepare, setVerbose)
+		Init(msg)
 		msg.BeforeExit()
 		os.Exit(0)
 	}

container/initbind.go

@@ -5,12 +5,15 @@ import (
 	"fmt"
 	"os"
 	"syscall"
+
+	"hakurei.app/container/bits"
+	"hakurei.app/container/check"
 )
 
 func init() { gob.Register(new(BindMountOp)) }
 
 // Bind appends an [Op] that bind mounts host path [BindMountOp.Source] on container path [BindMountOp.Target].
-func (f *Ops) Bind(source, target *Absolute, flags int) *Ops {
+func (f *Ops) Bind(source, target *check.Absolute, flags int) *Ops {
 	*f = append(*f, &BindMountOp{nil, source, target, flags})
 	return f
 }
@@ -18,50 +21,39 @@ func (f *Ops) Bind(source, target *Absolute, flags int) *Ops {
 // BindMountOp bind mounts host path Source on container path Target.
 // Note that Flags uses bits declared in this package and should not be set with constants in [syscall].
 type BindMountOp struct {
-	sourceFinal, Source, Target *Absolute
+	sourceFinal, Source, Target *check.Absolute
 
 	Flags int
 }
 
-const (
-	// BindOptional skips nonexistent host paths.
-	BindOptional = 1 << iota
-	// BindWritable mounts filesystem read-write.
-	BindWritable
-	// BindDevice allows access to devices (special files) on this filesystem.
-	BindDevice
-	// BindEnsure attempts to create the host path if it does not exist.
-	BindEnsure
-)
-
 func (b *BindMountOp) Valid() bool {
 	return b != nil &&
 		b.Source != nil && b.Target != nil &&
-		b.Flags&(BindOptional|BindEnsure) != (BindOptional|BindEnsure)
+		b.Flags&(bits.BindOptional|bits.BindEnsure) != (bits.BindOptional|bits.BindEnsure)
 }
 
 func (b *BindMountOp) early(_ *setupState, k syscallDispatcher) error {
-	if b.Flags&BindEnsure != 0 {
+	if b.Flags&bits.BindEnsure != 0 {
 		if err := k.mkdirAll(b.Source.String(), 0700); err != nil {
 			return err
 		}
 	}
 
 	if pathname, err := k.evalSymlinks(b.Source.String()); err != nil {
-		if os.IsNotExist(err) && b.Flags&BindOptional != 0 {
+		if os.IsNotExist(err) && b.Flags&bits.BindOptional != 0 {
 			// leave sourceFinal as nil
 			return nil
 		}
 		return err
 	} else {
-		b.sourceFinal, err = NewAbs(pathname)
+		b.sourceFinal, err = check.NewAbs(pathname)
 		return err
 	}
 }
 
-func (b *BindMountOp) apply(_ *setupState, k syscallDispatcher) error {
+func (b *BindMountOp) apply(state *setupState, k syscallDispatcher) error {
 	if b.sourceFinal == nil {
-		if b.Flags&BindOptional == 0 {
+		if b.Flags&bits.BindOptional == 0 {
 			// unreachable
 			return OpStateError("bind")
 		}
@@ -84,19 +76,19 @@ func (b *BindMountOp) apply(_ *setupState, k syscallDispatcher) error {
 	}
 
 	var flags uintptr = syscall.MS_REC
-	if b.Flags&BindWritable == 0 {
+	if b.Flags&bits.BindWritable == 0 {
 		flags |= syscall.MS_RDONLY
 	}
-	if b.Flags&BindDevice == 0 {
+	if b.Flags&bits.BindDevice == 0 {
 		flags |= syscall.MS_NODEV
 	}
 
 	if b.sourceFinal.String() == b.Target.String() {
-		k.verbosef("mounting %q flags %#x", target, flags)
+		state.Verbosef("mounting %q flags %#x", target, flags)
 	} else {
-		k.verbosef("mounting %q on %q flags %#x", source, target, flags)
+		state.Verbosef("mounting %q on %q flags %#x", source, target, flags)
 	}
-	return k.bindMount(source, target, flags)
+	return k.bindMount(state, source, target, flags)
 }
 
 func (b *BindMountOp) Is(op Op) bool {

container/initbind_test.go

@@ -6,30 +6,32 @@ import (
 	"syscall"
 	"testing"
 
+	"hakurei.app/container/bits"
+	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
 )
 
 func TestBindMountOp(t *testing.T) {
 	checkOpBehaviour(t, []opBehaviourTestCase{
 		{"ENOENT not optional", new(Params), &BindMountOp{
-			Source: MustAbs("/bin/"),
-			Target: MustAbs("/bin/"),
+			Source: check.MustAbs("/bin/"),
+			Target: check.MustAbs("/bin/"),
 		}, []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,
+			Source: check.MustAbs("/bin/"),
+			Target: check.MustAbs("/bin/"),
+			Flags:  bits.BindOptional,
 		}, []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,
+			Source: check.MustAbs("/bin/"),
+			Target: check.MustAbs("/bin/"),
+			Flags:  bits.BindOptional,
 		}, []stub.Call{
 			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", nil),
 		}, nil, []stub.Call{
@@ -40,9 +42,9 @@ func TestBindMountOp(t *testing.T) {
 		}, nil},
 
 		{"ensureFile device", new(Params), &BindMountOp{
-			Source: MustAbs("/dev/null"),
-			Target: MustAbs("/dev/null"),
-			Flags:  BindWritable | BindDevice,
+			Source: check.MustAbs("/dev/null"),
+			Target: check.MustAbs("/dev/null"),
+			Flags:  bits.BindWritable | bits.BindDevice,
 		}, []stub.Call{
 			call("evalSymlinks", stub.ExpectArgs{"/dev/null"}, "/dev/null", nil),
 		}, nil, []stub.Call{
@@ -51,17 +53,17 @@ func TestBindMountOp(t *testing.T) {
 		}, stub.UniqueError(5)},
 
 		{"mkdirAll ensure", new(Params), &BindMountOp{
-			Source: MustAbs("/bin/"),
-			Target: MustAbs("/bin/"),
-			Flags:  BindEnsure,
+			Source: check.MustAbs("/bin/"),
+			Target: check.MustAbs("/bin/"),
+			Flags:  bits.BindEnsure,
 		}, []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,
+			Source: check.MustAbs("/bin/"),
+			Target: check.MustAbs("/usr/bin/"),
+			Flags:  bits.BindEnsure,
 		}, []stub.Call{
 			call("mkdirAll", stub.ExpectArgs{"/bin/", os.FileMode(0700)}, nil, nil),
 			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", nil),
@@ -73,9 +75,9 @@ func TestBindMountOp(t *testing.T) {
 		}, nil},
 
 		{"success device ro", new(Params), &BindMountOp{
-			Source: MustAbs("/dev/null"),
-			Target: MustAbs("/dev/null"),
-			Flags:  BindDevice,
+			Source: check.MustAbs("/dev/null"),
+			Target: check.MustAbs("/dev/null"),
+			Flags:  bits.BindDevice,
 		}, []stub.Call{
 			call("evalSymlinks", stub.ExpectArgs{"/dev/null"}, "/dev/null", nil),
 		}, nil, []stub.Call{
@@ -86,9 +88,9 @@ func TestBindMountOp(t *testing.T) {
 		}, nil},
 
 		{"success device", new(Params), &BindMountOp{
-			Source: MustAbs("/dev/null"),
-			Target: MustAbs("/dev/null"),
-			Flags:  BindWritable | BindDevice,
+			Source: check.MustAbs("/dev/null"),
+			Target: check.MustAbs("/dev/null"),
+			Flags:  bits.BindWritable | bits.BindDevice,
 		}, []stub.Call{
 			call("evalSymlinks", stub.ExpectArgs{"/dev/null"}, "/dev/null", nil),
 		}, nil, []stub.Call{
@@ -99,15 +101,15 @@ func TestBindMountOp(t *testing.T) {
 		}, nil},
 
 		{"evalSymlinks", new(Params), &BindMountOp{
-			Source: MustAbs("/bin/"),
-			Target: MustAbs("/bin/"),
+			Source: check.MustAbs("/bin/"),
+			Target: check.MustAbs("/bin/"),
 		}, []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/"),
+			Source: check.MustAbs("/bin/"),
+			Target: check.MustAbs("/bin/"),
 		}, []stub.Call{
 			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", nil),
 		}, nil, []stub.Call{
@@ -115,8 +117,8 @@ func TestBindMountOp(t *testing.T) {
 		}, stub.UniqueError(2)},
 
 		{"mkdirAll", new(Params), &BindMountOp{
-			Source: MustAbs("/bin/"),
-			Target: MustAbs("/bin/"),
+			Source: check.MustAbs("/bin/"),
+			Target: check.MustAbs("/bin/"),
 		}, []stub.Call{
 			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", nil),
 		}, nil, []stub.Call{
@@ -125,8 +127,8 @@ func TestBindMountOp(t *testing.T) {
 		}, stub.UniqueError(1)},
 
 		{"bindMount", new(Params), &BindMountOp{
-			Source: MustAbs("/bin/"),
-			Target: MustAbs("/bin/"),
+			Source: check.MustAbs("/bin/"),
+			Target: check.MustAbs("/bin/"),
 		}, []stub.Call{
 			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", nil),
 		}, nil, []stub.Call{
@@ -137,8 +139,8 @@ func TestBindMountOp(t *testing.T) {
 		}, stub.UniqueError(0)},
 
 		{"success eval equals", new(Params), &BindMountOp{
-			Source: MustAbs("/bin/"),
-			Target: MustAbs("/bin/"),
+			Source: check.MustAbs("/bin/"),
+			Target: check.MustAbs("/bin/"),
 		}, []stub.Call{
 			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/bin", nil),
 		}, nil, []stub.Call{
@@ -149,8 +151,8 @@ func TestBindMountOp(t *testing.T) {
 		}, nil},
 
 		{"success", new(Params), &BindMountOp{
-			Source: MustAbs("/bin/"),
-			Target: MustAbs("/bin/"),
+			Source: check.MustAbs("/bin/"),
+			Target: check.MustAbs("/bin/"),
 		}, []stub.Call{
 			call("evalSymlinks", stub.ExpectArgs{"/bin/"}, "/usr/bin", nil),
 		}, nil, []stub.Call{
@@ -173,21 +175,21 @@ func TestBindMountOp(t *testing.T) {
 	checkOpsValid(t, []opValidTestCase{
 		{"nil", (*BindMountOp)(nil), false},
 		{"zero", new(BindMountOp), false},
-		{"nil source", &BindMountOp{Target: MustAbs("/")}, false},
-		{"nil target", &BindMountOp{Source: MustAbs("/")}, false},
-		{"flag optional ensure", &BindMountOp{Source: MustAbs("/"), Target: MustAbs("/"), Flags: BindOptional | BindEnsure}, false},
-		{"valid", &BindMountOp{Source: MustAbs("/"), Target: MustAbs("/")}, true},
+		{"nil source", &BindMountOp{Target: check.MustAbs("/")}, false},
+		{"nil target", &BindMountOp{Source: check.MustAbs("/")}, false},
+		{"flag optional ensure", &BindMountOp{Source: check.MustAbs("/"), Target: check.MustAbs("/"), Flags: bits.BindOptional | bits.BindEnsure}, false},
+		{"valid", &BindMountOp{Source: check.MustAbs("/"), Target: check.MustAbs("/")}, true},
 	})
 
 	checkOpsBuilder(t, []opsBuilderTestCase{
 		{"autoetc", new(Ops).Bind(
-			MustAbs("/etc/"),
-			MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+			check.MustAbs("/etc/"),
+			check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
 			0,
 		), Ops{
 			&BindMountOp{
-				Source: MustAbs("/etc/"),
-				Target: MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+				Source: check.MustAbs("/etc/"),
+				Target: check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
 			},
 		}},
 	})
@@ -196,45 +198,45 @@ func TestBindMountOp(t *testing.T) {
 		{"zero", new(BindMountOp), new(BindMountOp), false},
 
 		{"internal ne", &BindMountOp{
-			Source: MustAbs("/etc/"),
-			Target: MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+			Source: check.MustAbs("/etc/"),
+			Target: check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
 		}, &BindMountOp{
-			Source:      MustAbs("/etc/"),
-			Target:      MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
-			sourceFinal: MustAbs("/etc/"),
+			Source:      check.MustAbs("/etc/"),
+			Target:      check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+			sourceFinal: check.MustAbs("/etc/"),
 		}, true},
 
 		{"flags differs", &BindMountOp{
-			Source: MustAbs("/etc/"),
-			Target: MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+			Source: check.MustAbs("/etc/"),
+			Target: check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
 		}, &BindMountOp{
-			Source: MustAbs("/etc/"),
-			Target: MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
-			Flags:  BindOptional,
+			Source: check.MustAbs("/etc/"),
+			Target: check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+			Flags:  bits.BindOptional,
 		}, false},
 
 		{"source differs", &BindMountOp{
-			Source: MustAbs("/.hakurei/etc/"),
-			Target: MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+			Source: check.MustAbs("/.hakurei/etc/"),
+			Target: check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
 		}, &BindMountOp{
-			Source: MustAbs("/etc/"),
-			Target: MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+			Source: check.MustAbs("/etc/"),
+			Target: check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
 		}, false},
 
 		{"target differs", &BindMountOp{
-			Source: MustAbs("/etc/"),
-			Target: MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+			Source: check.MustAbs("/etc/"),
+			Target: check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
 		}, &BindMountOp{
-			Source: MustAbs("/etc/"),
-			Target: MustAbs("/etc/"),
+			Source: check.MustAbs("/etc/"),
+			Target: check.MustAbs("/etc/"),
 		}, false},
 
 		{"equals", &BindMountOp{
-			Source: MustAbs("/etc/"),
-			Target: MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+			Source: check.MustAbs("/etc/"),
+			Target: check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
 		}, &BindMountOp{
-			Source: MustAbs("/etc/"),
-			Target: MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+			Source: check.MustAbs("/etc/"),
+			Target: check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
 		}, true},
 	})
 
@@ -242,14 +244,14 @@ func TestBindMountOp(t *testing.T) {
 		{"invalid", new(BindMountOp), "mounting", "<invalid>"},
 
 		{"autoetc", &BindMountOp{
-			Source: MustAbs("/etc/"),
-			Target: MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
+			Source: check.MustAbs("/etc/"),
+			Target: check.MustAbs("/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659"),
 		}, "mounting", `"/etc/" on "/etc/.host/048090b6ed8f9ebb10e275ff5d8c0659" flags 0x0`},
 
 		{"hostdev", &BindMountOp{
-			Source: MustAbs("/dev/"),
-			Target: MustAbs("/dev/"),
-			Flags:  BindWritable | BindDevice,
+			Source: check.MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
+			Flags:  bits.BindWritable | bits.BindDevice,
 		}, "mounting", `"/dev/" flags 0x6`},
 	})
 }

container/initdev.go

@@ -5,19 +5,22 @@ import (
 	"fmt"
 	"path"
 	. "syscall"
+
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 )
 
 func init() { gob.Register(new(MountDevOp)) }
 
 // Dev appends an [Op] that mounts a subset of host /dev.
-func (f *Ops) Dev(target *Absolute, mqueue bool) *Ops {
+func (f *Ops) Dev(target *check.Absolute, mqueue bool) *Ops {
 	*f = append(*f, &MountDevOp{target, mqueue, false})
 	return f
 }
 
 // DevWritable appends an [Op] that mounts a writable subset of host /dev.
 // There is usually no good reason to write to /dev, so this should always be followed by a [RemountOp].
-func (f *Ops) DevWritable(target *Absolute, mqueue bool) *Ops {
+func (f *Ops) DevWritable(target *check.Absolute, mqueue bool) *Ops {
 	*f = append(*f, &MountDevOp{target, mqueue, true})
 	return f
 }
@@ -26,7 +29,7 @@ func (f *Ops) DevWritable(target *Absolute, mqueue bool) *Ops {
 // If Mqueue is true, a private instance of [FstypeMqueue] is mounted.
 // If Write is true, the resulting mount point is left writable.
 type MountDevOp struct {
-	Target *Absolute
+	Target *check.Absolute
 	Mqueue bool
 	Write  bool
 }
@@ -46,7 +49,8 @@ func (d *MountDevOp) apply(state *setupState, k syscallDispatcher) error {
 			return err
 		}
 		if err := k.bindMount(
-			toHost(FHSDev+name),
+			state,
+			toHost(fhs.Dev+name),
 			targetPath,
 			0,
 		); err != nil {
@@ -55,15 +59,15 @@ func (d *MountDevOp) apply(state *setupState, k syscallDispatcher) error {
 	}
 	for i, name := range []string{"stdin", "stdout", "stderr"} {
 		if err := k.symlink(
-			FHSProc+"self/fd/"+string(rune(i+'0')),
+			fhs.Proc+"self/fd/"+string(rune(i+'0')),
 			path.Join(target, name),
 		); err != nil {
 			return err
 		}
 	}
 	for _, pair := range [][2]string{
-		{FHSProc + "self/fd", "fd"},
-		{FHSProc + "kcore", "core"},
+		{fhs.Proc + "self/fd", "fd"},
+		{fhs.Proc + "kcore", "core"},
 		{"pts/ptmx", "ptmx"},
 	} {
 		if err := k.symlink(pair[0], path.Join(target, pair[1])); err != nil {
@@ -93,6 +97,7 @@ func (d *MountDevOp) apply(state *setupState, k syscallDispatcher) error {
 			if name, err := k.readlink(hostProc.stdout()); err != nil {
 				return err
 			} else if err = k.bindMount(
+				state,
 				toHost(name),
 				consolePath,
 				0,
@@ -116,7 +121,7 @@ func (d *MountDevOp) apply(state *setupState, k syscallDispatcher) error {
 		return nil
 	}
 
-	if err := k.remount(target, MS_RDONLY); err != nil {
+	if err := k.remount(state, target, MS_RDONLY); err != nil {
 		return err
 	}
 	return k.mountTmpfs(SourceTmpfs, devShmPath, MS_NOSUID|MS_NODEV, 0, 01777)

container/initdev_test.go

@@ -4,20 +4,21 @@ import (
 	"os"
 	"testing"
 
+	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
 )
 
 func TestMountDevOp(t *testing.T) {
 	checkOpBehaviour(t, []opBehaviourTestCase{
 		{"mountTmpfs", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, stub.UniqueError(27)),
 		}, stub.UniqueError(27)},
 
 		{"ensureFile null", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -25,7 +26,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(26)},
 
 		{"bindMount null", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -34,7 +35,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(25)},
 
 		{"ensureFile zero", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -44,7 +45,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(24)},
 
 		{"bindMount zero", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -55,7 +56,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(23)},
 
 		{"ensureFile full", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -67,7 +68,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(22)},
 
 		{"bindMount full", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -80,7 +81,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(21)},
 
 		{"ensureFile random", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -94,7 +95,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(20)},
 
 		{"bindMount random", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -109,7 +110,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(19)},
 
 		{"ensureFile urandom", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -125,7 +126,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(18)},
 
 		{"bindMount urandom", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -142,7 +143,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(17)},
 
 		{"ensureFile tty", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -160,7 +161,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(16)},
 
 		{"bindMount tty", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -179,7 +180,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(15)},
 
 		{"symlink stdin", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -199,7 +200,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(14)},
 
 		{"symlink stdout", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -220,7 +221,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(13)},
 
 		{"symlink stderr", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -242,7 +243,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(12)},
 
 		{"symlink fd", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -265,7 +266,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(11)},
 
 		{"symlink kcore", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -289,7 +290,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(10)},
 
 		{"symlink ptmx", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -314,7 +315,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(9)},
 
 		{"mkdir shm", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -340,7 +341,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(8)},
 
 		{"mkdir devpts", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -367,7 +368,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(7)},
 
 		{"mount devpts", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -395,7 +396,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(6)},
 
 		{"ensureFile stdout", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -425,7 +426,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(5)},
 
 		{"readlink stdout", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -456,7 +457,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(4)},
 
 		{"bindMount stdout", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -488,7 +489,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(3)},
 
 		{"mkdir mqueue", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -521,7 +522,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(2)},
 
 		{"mount mqueue", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -555,7 +556,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(1)},
 
 		{"success no session", &Params{ParentPerm: 0755}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 			Write:  true,
 		}, nil, nil, []stub.Call{
@@ -586,7 +587,7 @@ func TestMountDevOp(t *testing.T) {
 		}, nil},
 
 		{"success no tty", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 			Write:  true,
 		}, nil, nil, []stub.Call{
@@ -618,7 +619,7 @@ func TestMountDevOp(t *testing.T) {
 		}, nil},
 
 		{"remount", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
 			call("ensureFile", stub.ExpectArgs{"/sysroot/dev/null", os.FileMode(0444), os.FileMode(0750)}, nil, nil),
@@ -650,7 +651,7 @@ func TestMountDevOp(t *testing.T) {
 		}, stub.UniqueError(0)},
 
 		{"success no mqueue", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
 			call("ensureFile", stub.ExpectArgs{"/sysroot/dev/null", os.FileMode(0444), os.FileMode(0750)}, nil, nil),
@@ -683,7 +684,7 @@ func TestMountDevOp(t *testing.T) {
 		}, nil},
 
 		{"success rw", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 			Write:  true,
 		}, nil, nil, []stub.Call{
@@ -718,7 +719,7 @@ func TestMountDevOp(t *testing.T) {
 		}, nil},
 
 		{"success", &Params{ParentPerm: 0750, RetainSession: true}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, nil, nil, []stub.Call{
 			call("mountTmpfs", stub.ExpectArgs{"devtmpfs", "/sysroot/dev", uintptr(0x6), 0, os.FileMode(0750)}, nil, nil),
@@ -757,20 +758,20 @@ func TestMountDevOp(t *testing.T) {
 	checkOpsValid(t, []opValidTestCase{
 		{"nil", (*MountDevOp)(nil), false},
 		{"zero", new(MountDevOp), false},
-		{"valid", &MountDevOp{Target: MustAbs("/dev/")}, true},
+		{"valid", &MountDevOp{Target: check.MustAbs("/dev/")}, true},
 	})
 
 	checkOpsBuilder(t, []opsBuilderTestCase{
-		{"dev", new(Ops).Dev(MustAbs("/dev/"), true), Ops{
+		{"dev", new(Ops).Dev(check.MustAbs("/dev/"), true), Ops{
 			&MountDevOp{
-				Target: MustAbs("/dev/"),
+				Target: check.MustAbs("/dev/"),
 				Mqueue: true,
 			},
 		}},
 
-		{"dev writable", new(Ops).DevWritable(MustAbs("/.hakurei/dev/"), false), Ops{
+		{"dev writable", new(Ops).DevWritable(check.MustAbs("/.hakurei/dev/"), false), Ops{
 			&MountDevOp{
-				Target: MustAbs("/.hakurei/dev/"),
+				Target: check.MustAbs("/.hakurei/dev/"),
 				Write:  true,
 			},
 		}},
@@ -780,46 +781,46 @@ func TestMountDevOp(t *testing.T) {
 		{"zero", new(MountDevOp), new(MountDevOp), false},
 
 		{"write differs", &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 			Write:  true,
 		}, false},
 
 		{"mqueue differs", &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 		}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, false},
 
 		{"target differs", &MountDevOp{
-			Target: MustAbs("/"),
+			Target: check.MustAbs("/"),
 			Mqueue: true,
 		}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, false},
 
 		{"equals", &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, true},
 	})
 
 	checkOpMeta(t, []opMetaTestCase{
 		{"mqueue", &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Mqueue: true,
 		}, "mounting", `dev on "/dev/" with mqueue`},
 
 		{"dev", &MountDevOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 		}, "mounting", `dev on "/dev/"`},
 	})
 }

container/initmkdir.go

@@ -4,19 +4,21 @@ import (
 	"encoding/gob"
 	"fmt"
 	"os"
+
+	"hakurei.app/container/check"
 )
 
 func init() { gob.Register(new(MkdirOp)) }
 
 // Mkdir appends an [Op] that creates a directory in the container filesystem.
-func (f *Ops) Mkdir(name *Absolute, perm os.FileMode) *Ops {
+func (f *Ops) Mkdir(name *check.Absolute, perm os.FileMode) *Ops {
 	*f = append(*f, &MkdirOp{name, perm})
 	return f
 }
 
 // MkdirOp creates a directory at container Path with permission bits set to Perm.
 type MkdirOp struct {
-	Path *Absolute
+	Path *check.Absolute
 	Perm os.FileMode
 }
 

container/initmkdir_test.go

@@ -4,13 +4,14 @@ import (
 	"os"
 	"testing"
 
+	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
 )
 
 func TestMkdirOp(t *testing.T) {
 	checkOpBehaviour(t, []opBehaviourTestCase{
 		{"success", new(Params), &MkdirOp{
-			Path: MustAbs("/.hakurei"),
+			Path: check.MustAbs("/.hakurei"),
 			Perm: 0500,
 		}, nil, nil, []stub.Call{
 			call("mkdirAll", stub.ExpectArgs{"/sysroot/.hakurei", os.FileMode(0500)}, nil, nil),
@@ -20,25 +21,25 @@ func TestMkdirOp(t *testing.T) {
 	checkOpsValid(t, []opValidTestCase{
 		{"nil", (*MkdirOp)(nil), false},
 		{"zero", new(MkdirOp), false},
-		{"valid", &MkdirOp{Path: MustAbs("/.hakurei")}, true},
+		{"valid", &MkdirOp{Path: check.MustAbs("/.hakurei")}, true},
 	})
 
 	checkOpsBuilder(t, []opsBuilderTestCase{
-		{"etc", new(Ops).Mkdir(MustAbs("/etc/"), 0), Ops{
-			&MkdirOp{Path: MustAbs("/etc/")},
+		{"etc", new(Ops).Mkdir(check.MustAbs("/etc/"), 0), Ops{
+			&MkdirOp{Path: check.MustAbs("/etc/")},
 		}},
 	})
 
 	checkOpIs(t, []opIsTestCase{
 		{"zero", new(MkdirOp), new(MkdirOp), false},
-		{"path differs", &MkdirOp{Path: MustAbs("/"), Perm: 0755}, &MkdirOp{Path: MustAbs("/etc/"), Perm: 0755}, false},
-		{"perm differs", &MkdirOp{Path: MustAbs("/")}, &MkdirOp{Path: MustAbs("/"), Perm: 0755}, false},
-		{"equals", &MkdirOp{Path: MustAbs("/")}, &MkdirOp{Path: MustAbs("/")}, true},
+		{"path differs", &MkdirOp{Path: check.MustAbs("/"), Perm: 0755}, &MkdirOp{Path: check.MustAbs("/etc/"), Perm: 0755}, false},
+		{"perm differs", &MkdirOp{Path: check.MustAbs("/")}, &MkdirOp{Path: check.MustAbs("/"), Perm: 0755}, false},
+		{"equals", &MkdirOp{Path: check.MustAbs("/")}, &MkdirOp{Path: check.MustAbs("/")}, true},
 	})
 
 	checkOpMeta(t, []opMetaTestCase{
 		{"etc", &MkdirOp{
-			Path: MustAbs("/etc/"),
+			Path: check.MustAbs("/etc/"),
 		}, "creating", `directory "/etc/" perm ----------`},
 	})
 }

container/initoverlay.go

@@ -5,6 +5,9 @@ import (
 	"fmt"
 	"slices"
 	"strings"
+
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 )
 
 const (
@@ -52,7 +55,7 @@ func (e *OverlayArgumentError) Error() string {
 }
 
 // Overlay appends an [Op] that mounts the overlay pseudo filesystem on [MountOverlayOp.Target].
-func (f *Ops) Overlay(target, state, work *Absolute, layers ...*Absolute) *Ops {
+func (f *Ops) Overlay(target, state, work *check.Absolute, layers ...*check.Absolute) *Ops {
 	*f = append(*f, &MountOverlayOp{
 		Target: target,
 		Lower:  layers,
@@ -64,34 +67,34 @@ func (f *Ops) Overlay(target, state, work *Absolute, layers ...*Absolute) *Ops {
 
 // OverlayEphemeral appends an [Op] that mounts the overlay pseudo filesystem on [MountOverlayOp.Target]
 // with an ephemeral upperdir and workdir.
-func (f *Ops) OverlayEphemeral(target *Absolute, layers ...*Absolute) *Ops {
-	return f.Overlay(target, AbsFHSRoot, nil, layers...)
+func (f *Ops) OverlayEphemeral(target *check.Absolute, layers ...*check.Absolute) *Ops {
+	return f.Overlay(target, fhs.AbsRoot, nil, layers...)
 }
 
 // OverlayReadonly appends an [Op] that mounts the overlay pseudo filesystem readonly on [MountOverlayOp.Target]
-func (f *Ops) OverlayReadonly(target *Absolute, layers ...*Absolute) *Ops {
+func (f *Ops) OverlayReadonly(target *check.Absolute, layers ...*check.Absolute) *Ops {
 	return f.Overlay(target, nil, nil, layers...)
 }
 
 // MountOverlayOp mounts [FstypeOverlay] on container path Target.
 type MountOverlayOp struct {
-	Target *Absolute
+	Target *check.Absolute
 
 	// Any filesystem, does not need to be on a writable filesystem.
-	Lower []*Absolute
+	Lower []*check.Absolute
 	// formatted for [OptionOverlayLowerdir], resolved, prefixed and escaped during early
 	lower []string
 	// The upperdir is normally on a writable filesystem.
 	//
-	// If Work is nil and Upper holds the special value [AbsFHSRoot],
+	// If Work is nil and Upper holds the special value [fhs.AbsRoot],
 	// an ephemeral upperdir and workdir will be set up.
 	//
 	// If both Work and Upper are nil, upperdir and workdir is omitted and the overlay is mounted readonly.
-	Upper *Absolute
+	Upper *check.Absolute
 	// formatted for [OptionOverlayUpperdir], resolved, prefixed and escaped during early
 	upper string
 	// The workdir needs to be an empty directory on the same filesystem as upperdir.
-	Work *Absolute
+	Work *check.Absolute
 	// formatted for [OptionOverlayWorkdir], resolved, prefixed and escaped during early
 	work string
 
@@ -117,7 +120,7 @@ func (o *MountOverlayOp) Valid() bool {
 func (o *MountOverlayOp) early(_ *setupState, k syscallDispatcher) error {
 	if o.Work == nil && o.Upper != nil {
 		switch o.Upper.String() {
-		case FHSRoot: // ephemeral
+		case fhs.Root: // ephemeral
 			o.ephemeral = true // intermediate root not yet available
 
 		default:
@@ -136,7 +139,7 @@ func (o *MountOverlayOp) early(_ *setupState, k syscallDispatcher) error {
 			if v, err := k.evalSymlinks(o.Upper.String()); err != nil {
 				return err
 			} else {
-				o.upper = EscapeOverlayDataSegment(toHost(v))
+				o.upper = check.EscapeOverlayDataSegment(toHost(v))
 			}
 		}
 
@@ -144,7 +147,7 @@ func (o *MountOverlayOp) early(_ *setupState, k syscallDispatcher) error {
 			if v, err := k.evalSymlinks(o.Work.String()); err != nil {
 				return err
 			} else {
-				o.work = EscapeOverlayDataSegment(toHost(v))
+				o.work = check.EscapeOverlayDataSegment(toHost(v))
 			}
 		}
 	}
@@ -154,7 +157,7 @@ func (o *MountOverlayOp) early(_ *setupState, k syscallDispatcher) error {
 		if v, err := k.evalSymlinks(a.String()); err != nil {
 			return err
 		} else {
-			o.lower[i] = EscapeOverlayDataSegment(toHost(v))
+			o.lower[i] = check.EscapeOverlayDataSegment(toHost(v))
 		}
 	}
 	return nil
@@ -172,10 +175,10 @@ func (o *MountOverlayOp) apply(state *setupState, k syscallDispatcher) error {
 	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 {
+		if o.upper, err = k.mkdirTemp(fhs.Root, intermediatePatternOverlayUpper); err != nil {
 			return err
 		}
-		if o.work, err = k.mkdirTemp(FHSRoot, intermediatePatternOverlayWork); err != nil {
+		if o.work, err = k.mkdirTemp(fhs.Root, intermediatePatternOverlayWork); err != nil {
 			return err
 		}
 	}
@@ -196,17 +199,17 @@ func (o *MountOverlayOp) apply(state *setupState, k syscallDispatcher) error {
 			OptionOverlayWorkdir+"="+o.work)
 	}
 	options = append(options,
-		OptionOverlayLowerdir+"="+strings.Join(o.lower, SpecialOverlayPath),
+		OptionOverlayLowerdir+"="+strings.Join(o.lower, check.SpecialOverlayPath),
 		OptionOverlayUserxattr)
 
-	return k.mount(SourceOverlay, target, FstypeOverlay, 0, strings.Join(options, SpecialOverlayOption))
+	return k.mount(SourceOverlay, target, FstypeOverlay, 0, strings.Join(options, check.SpecialOverlayOption))
 }
 
 func (o *MountOverlayOp) Is(op Op) bool {
 	vo, ok := op.(*MountOverlayOp)
 	return ok && o.Valid() && vo.Valid() &&
 		o.Target.Is(vo.Target) &&
-		slices.EqualFunc(o.Lower, vo.Lower, func(a *Absolute, v *Absolute) bool { return a.Is(v) }) &&
+		slices.EqualFunc(o.Lower, vo.Lower, func(a, v *check.Absolute) bool { return a.Is(v) }) &&
 		o.Upper.Is(vo.Upper) && o.Work.Is(vo.Work)
 }
 func (*MountOverlayOp) prefix() (string, bool) { return "mounting", true }

container/initoverlay_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"testing"
 
+	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
 )
 
@@ -38,21 +39,21 @@ func TestMountOverlayOp(t *testing.T) {
 
 	checkOpBehaviour(t, []opBehaviourTestCase{
 		{"mkdirTemp invalid ephemeral", &Params{ParentPerm: 0705}, &MountOverlayOp{
-			Target: MustAbs("/"),
-			Lower: []*Absolute{
-				MustAbs("/var/lib/planterette/base/debian:f92c9052"),
-				MustAbs("/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"),
+			Target: check.MustAbs("/"),
+			Lower: []*check.Absolute{
+				check.MustAbs("/var/lib/planterette/base/debian:f92c9052"),
+				check.MustAbs("/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"),
 			},
-			Upper: MustAbs("/proc/"),
+			Upper: check.MustAbs("/proc/"),
 		}, nil, &OverlayArgumentError{OverlayEphemeralUnexpectedUpper, "/proc/"}, nil, nil},
 
 		{"mkdirTemp upper ephemeral", &Params{ParentPerm: 0705}, &MountOverlayOp{
-			Target: MustAbs("/"),
-			Lower: []*Absolute{
-				MustAbs("/var/lib/planterette/base/debian:f92c9052"),
-				MustAbs("/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"),
+			Target: check.MustAbs("/"),
+			Lower: []*check.Absolute{
+				check.MustAbs("/var/lib/planterette/base/debian:f92c9052"),
+				check.MustAbs("/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"),
 			},
-			Upper: MustAbs("/"),
+			Upper: check.MustAbs("/"),
 		}, []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),
@@ -62,12 +63,12 @@ func TestMountOverlayOp(t *testing.T) {
 		}, stub.UniqueError(6)},
 
 		{"mkdirTemp work ephemeral", &Params{ParentPerm: 0705}, &MountOverlayOp{
-			Target: MustAbs("/"),
-			Lower: []*Absolute{
-				MustAbs("/var/lib/planterette/base/debian:f92c9052"),
-				MustAbs("/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"),
+			Target: check.MustAbs("/"),
+			Lower: []*check.Absolute{
+				check.MustAbs("/var/lib/planterette/base/debian:f92c9052"),
+				check.MustAbs("/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"),
 			},
-			Upper: MustAbs("/"),
+			Upper: check.MustAbs("/"),
 		}, []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),
@@ -78,12 +79,12 @@ func TestMountOverlayOp(t *testing.T) {
 		}, stub.UniqueError(5)},
 
 		{"success ephemeral", &Params{ParentPerm: 0705}, &MountOverlayOp{
-			Target: MustAbs("/"),
-			Lower: []*Absolute{
-				MustAbs("/var/lib/planterette/base/debian:f92c9052"),
-				MustAbs("/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"),
+			Target: check.MustAbs("/"),
+			Lower: []*check.Absolute{
+				check.MustAbs("/var/lib/planterette/base/debian:f92c9052"),
+				check.MustAbs("/var/lib/planterette/app/org.chromium.Chromium@debian:f92c9052"),
 			},
-			Upper: MustAbs("/"),
+			Upper: check.MustAbs("/"),
 		}, []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),
@@ -101,9 +102,9 @@ func TestMountOverlayOp(t *testing.T) {
 		}, nil},
 
 		{"short lower ro", &Params{ParentPerm: 0755}, &MountOverlayOp{
-			Target: MustAbs("/nix/store"),
-			Lower: []*Absolute{
-				MustAbs("/mnt-root/nix/.ro-store"),
+			Target: check.MustAbs("/nix/store"),
+			Lower: []*check.Absolute{
+				check.MustAbs("/mnt-root/nix/.ro-store"),
 			},
 		}, []stub.Call{
 			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/.ro-store", nil),
@@ -112,10 +113,10 @@ func TestMountOverlayOp(t *testing.T) {
 		}, &OverlayArgumentError{OverlayReadonlyLower, zeroString}},
 
 		{"success ro noPrefix", &Params{ParentPerm: 0755}, &MountOverlayOp{
-			Target: MustAbs("/nix/store"),
-			Lower: []*Absolute{
-				MustAbs("/mnt-root/nix/.ro-store"),
-				MustAbs("/mnt-root/nix/.ro-store0"),
+			Target: check.MustAbs("/nix/store"),
+			Lower: []*check.Absolute{
+				check.MustAbs("/mnt-root/nix/.ro-store"),
+				check.MustAbs("/mnt-root/nix/.ro-store0"),
 			},
 			noPrefix: true,
 		}, []stub.Call{
@@ -131,10 +132,10 @@ func TestMountOverlayOp(t *testing.T) {
 		}, nil},
 
 		{"success ro", &Params{ParentPerm: 0755}, &MountOverlayOp{
-			Target: MustAbs("/nix/store"),
-			Lower: []*Absolute{
-				MustAbs("/mnt-root/nix/.ro-store"),
-				MustAbs("/mnt-root/nix/.ro-store0"),
+			Target: check.MustAbs("/nix/store"),
+			Lower: []*check.Absolute{
+				check.MustAbs("/mnt-root/nix/.ro-store"),
+				check.MustAbs("/mnt-root/nix/.ro-store0"),
 			},
 		}, []stub.Call{
 			call("evalSymlinks", stub.ExpectArgs{"/mnt-root/nix/.ro-store"}, "/mnt-root/nix/.ro-store", nil),
@@ -149,9 +150,9 @@ func TestMountOverlayOp(t *testing.T) {
 		}, 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"),
+			Target: check.MustAbs("/nix/store"),
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, []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),
@@ -160,29 +161,29 @@ func TestMountOverlayOp(t *testing.T) {
 		}, &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"),
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, []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"),
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, []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"),
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, []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),
@@ -190,10 +191,10 @@ func TestMountOverlayOp(t *testing.T) {
 		}, 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"),
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, []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),
@@ -203,10 +204,10 @@ func TestMountOverlayOp(t *testing.T) {
 		}, 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"),
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, []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),
@@ -217,10 +218,10 @@ func TestMountOverlayOp(t *testing.T) {
 		}, 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"),
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, []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),
@@ -235,16 +236,16 @@ func TestMountOverlayOp(t *testing.T) {
 		}, nil},
 
 		{"success", &Params{ParentPerm: 0700}, &MountOverlayOp{
-			Target: MustAbs("/nix/store"),
-			Lower: []*Absolute{
-				MustAbs("/mnt-root/nix/.ro-store"),
-				MustAbs("/mnt-root/nix/.ro-store0"),
-				MustAbs("/mnt-root/nix/.ro-store1"),
-				MustAbs("/mnt-root/nix/.ro-store2"),
-				MustAbs("/mnt-root/nix/.ro-store3"),
+			Target: check.MustAbs("/nix/store"),
+			Lower: []*check.Absolute{
+				check.MustAbs("/mnt-root/nix/.ro-store"),
+				check.MustAbs("/mnt-root/nix/.ro-store0"),
+				check.MustAbs("/mnt-root/nix/.ro-store1"),
+				check.MustAbs("/mnt-root/nix/.ro-store2"),
+				check.MustAbs("/mnt-root/nix/.ro-store3"),
 			},
-			Upper: MustAbs("/mnt-root/nix/.rw-store/upper"),
-			Work:  MustAbs("/mnt-root/nix/.rw-store/work"),
+			Upper: check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:  check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, []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),
@@ -272,7 +273,7 @@ func TestMountOverlayOp(t *testing.T) {
 		t.Run("nil Upper non-nil Work not ephemeral", func(t *testing.T) {
 			wantErr := OpStateError("overlay")
 			if err := (&MountOverlayOp{
-				Work: MustAbs("/"),
+				Work: check.MustAbs("/"),
 			}).early(nil, nil); !errors.Is(err, wantErr) {
 				t.Errorf("apply: error = %v, want %v", err, wantErr)
 			}
@@ -282,39 +283,39 @@ func TestMountOverlayOp(t *testing.T) {
 	checkOpsValid(t, []opValidTestCase{
 		{"nil", (*MountOverlayOp)(nil), false},
 		{"zero", new(MountOverlayOp), false},
-		{"nil lower", &MountOverlayOp{Target: MustAbs("/"), Lower: []*Absolute{nil}}, false},
-		{"ro", &MountOverlayOp{Target: MustAbs("/"), Lower: []*Absolute{MustAbs("/")}}, true},
-		{"ro work", &MountOverlayOp{Target: MustAbs("/"), Work: MustAbs("/tmp/")}, false},
-		{"rw", &MountOverlayOp{Target: MustAbs("/"), Lower: []*Absolute{MustAbs("/")}, Upper: MustAbs("/"), Work: MustAbs("/")}, true},
+		{"nil lower", &MountOverlayOp{Target: check.MustAbs("/"), Lower: []*check.Absolute{nil}}, false},
+		{"ro", &MountOverlayOp{Target: check.MustAbs("/"), Lower: []*check.Absolute{check.MustAbs("/")}}, true},
+		{"ro work", &MountOverlayOp{Target: check.MustAbs("/"), Work: check.MustAbs("/tmp/")}, false},
+		{"rw", &MountOverlayOp{Target: check.MustAbs("/"), Lower: []*check.Absolute{check.MustAbs("/")}, Upper: check.MustAbs("/"), Work: check.MustAbs("/")}, true},
 	})
 
 	checkOpsBuilder(t, []opsBuilderTestCase{
 		{"full", new(Ops).Overlay(
-			MustAbs("/nix/store"),
-			MustAbs("/mnt-root/nix/.rw-store/upper"),
-			MustAbs("/mnt-root/nix/.rw-store/work"),
-			MustAbs("/mnt-root/nix/.ro-store"),
+			check.MustAbs("/nix/store"),
+			check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			check.MustAbs("/mnt-root/nix/.rw-store/work"),
+			check.MustAbs("/mnt-root/nix/.ro-store"),
 		), Ops{
 			&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"),
+				Target: check.MustAbs("/nix/store"),
+				Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+				Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+				Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 			},
 		}},
 
-		{"ephemeral", new(Ops).OverlayEphemeral(MustAbs("/nix/store"), MustAbs("/mnt-root/nix/.ro-store")), Ops{
+		{"ephemeral", new(Ops).OverlayEphemeral(check.MustAbs("/nix/store"), check.MustAbs("/mnt-root/nix/.ro-store")), Ops{
 			&MountOverlayOp{
-				Target: MustAbs("/nix/store"),
-				Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
-				Upper:  MustAbs("/"),
+				Target: check.MustAbs("/nix/store"),
+				Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+				Upper:  check.MustAbs("/"),
 			},
 		}},
 
-		{"readonly", new(Ops).OverlayReadonly(MustAbs("/nix/store"), MustAbs("/mnt-root/nix/.ro-store")), Ops{
+		{"readonly", new(Ops).OverlayReadonly(check.MustAbs("/nix/store"), check.MustAbs("/mnt-root/nix/.ro-store")), Ops{
 			&MountOverlayOp{
-				Target: MustAbs("/nix/store"),
-				Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+				Target: check.MustAbs("/nix/store"),
+				Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
 			},
 		}},
 	})
@@ -323,74 +324,74 @@ func TestMountOverlayOp(t *testing.T) {
 		{"zero", new(MountOverlayOp), new(MountOverlayOp), false},
 
 		{"differs target", &MountOverlayOp{
-			Target: MustAbs("/nix/store/differs"),
-			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
-			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
-			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
+			Target: check.MustAbs("/nix/store/differs"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, &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")}, false},
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work")}, false},
 
 		{"differs lower", &MountOverlayOp{
-			Target: MustAbs("/nix/store"),
-			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store/differs")},
-			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
-			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store/differs")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, &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")}, false},
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work")}, false},
 
 		{"differs upper", &MountOverlayOp{
-			Target: MustAbs("/nix/store"),
-			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
-			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper/differs"),
-			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper/differs"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, &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")}, false},
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work")}, false},
 
 		{"differs work", &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/differs"),
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work/differs"),
 		}, &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")}, false},
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work")}, false},
 
 		{"equals ro", &MountOverlayOp{
-			Target: MustAbs("/nix/store"),
-			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
 		}, &MountOverlayOp{
-			Target: MustAbs("/nix/store"),
-			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")}}, true},
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")}}, true},
 
 		{"equals", &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"),
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, &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")}, true},
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work")}, true},
 	})
 
 	checkOpMeta(t, []opMetaTestCase{
 		{"nix", &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"),
+			Target: check.MustAbs("/nix/store"),
+			Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 		}, "mounting", `overlay on "/nix/store" with 1 layers`},
 	})
 }

container/initplace.go

@@ -4,6 +4,9 @@ import (
 	"encoding/gob"
 	"fmt"
 	"syscall"
+
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 )
 
 const (
@@ -14,13 +17,13 @@ const (
 func init() { gob.Register(new(TmpfileOp)) }
 
 // Place appends an [Op] that places a file in container path [TmpfileOp.Path] containing [TmpfileOp.Data].
-func (f *Ops) Place(name *Absolute, data []byte) *Ops {
+func (f *Ops) Place(name *check.Absolute, data []byte) *Ops {
 	*f = append(*f, &TmpfileOp{name, data})
 	return f
 }
 
 // PlaceP is like Place but writes the address of [TmpfileOp.Data] to the pointer dataP points to.
-func (f *Ops) PlaceP(name *Absolute, dataP **[]byte) *Ops {
+func (f *Ops) PlaceP(name *check.Absolute, dataP **[]byte) *Ops {
 	t := &TmpfileOp{Path: name}
 	*dataP = &t.Data
 
@@ -30,7 +33,7 @@ func (f *Ops) PlaceP(name *Absolute, dataP **[]byte) *Ops {
 
 // TmpfileOp places a file on container Path containing Data.
 type TmpfileOp struct {
-	Path *Absolute
+	Path *check.Absolute
 	Data []byte
 }
 
@@ -38,7 +41,7 @@ func (t *TmpfileOp) Valid() bool                                { return t != ni
 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 {
+	if f, err := k.createTemp(fhs.Root, intermediatePatternTmpfile); err != nil {
 		return err
 	} else if _, err = f.Write(t.Data); err != nil {
 		return err
@@ -52,6 +55,7 @@ func (t *TmpfileOp) apply(state *setupState, k syscallDispatcher) error {
 	if err := k.ensureFile(target, 0444, state.ParentPerm); err != nil {
 		return err
 	} else if err = k.bindMount(
+		state,
 		tmpPath,
 		target,
 		syscall.MS_RDONLY|syscall.MS_NODEV,

container/initplace_test.go

@@ -4,13 +4,14 @@ import (
 	"os"
 	"testing"
 
+	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
 )
 
 func TestTmpfileOp(t *testing.T) {
 	const sampleDataString = `chronos:x:65534:65534:Hakurei:/var/empty:/bin/zsh`
 	var (
-		samplePath = MustAbs("/etc/passwd")
+		samplePath = check.MustAbs("/etc/passwd")
 		sampleData = []byte(sampleDataString)
 	)
 
@@ -100,7 +101,7 @@ func TestTmpfileOp(t *testing.T) {
 		{"zero", new(TmpfileOp), new(TmpfileOp), false},
 
 		{"differs path", &TmpfileOp{
-			Path: MustAbs("/etc/group"),
+			Path: check.MustAbs("/etc/group"),
 			Data: sampleData,
 		}, &TmpfileOp{
 			Path: samplePath,

container/initproc.go

@@ -4,18 +4,20 @@ import (
 	"encoding/gob"
 	"fmt"
 	. "syscall"
+
+	"hakurei.app/container/check"
 )
 
 func init() { gob.Register(new(MountProcOp)) }
 
 // Proc appends an [Op] that mounts a private instance of proc.
-func (f *Ops) Proc(target *Absolute) *Ops {
+func (f *Ops) Proc(target *check.Absolute) *Ops {
 	*f = append(*f, &MountProcOp{target})
 	return f
 }
 
 // MountProcOp mounts a new instance of [FstypeProc] on container path Target.
-type MountProcOp struct{ Target *Absolute }
+type MountProcOp struct{ Target *check.Absolute }
 
 func (p *MountProcOp) Valid() bool                                { return p != nil && p.Target != nil }
 func (p *MountProcOp) early(*setupState, syscallDispatcher) error { return nil }

container/initproc_test.go

@@ -4,6 +4,7 @@ import (
 	"os"
 	"testing"
 
+	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
 )
 
@@ -11,14 +12,14 @@ func TestMountProcOp(t *testing.T) {
 	checkOpBehaviour(t, []opBehaviourTestCase{
 		{"mkdir", &Params{ParentPerm: 0755},
 			&MountProcOp{
-				Target: MustAbs("/proc/"),
+				Target: check.MustAbs("/proc/"),
 			}, 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/"),
+				Target: check.MustAbs("/proc/"),
 			}, 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),
@@ -28,12 +29,12 @@ func TestMountProcOp(t *testing.T) {
 	checkOpsValid(t, []opValidTestCase{
 		{"nil", (*MountProcOp)(nil), false},
 		{"zero", new(MountProcOp), false},
-		{"valid", &MountProcOp{Target: MustAbs("/proc/")}, true},
+		{"valid", &MountProcOp{Target: check.MustAbs("/proc/")}, true},
 	})
 
 	checkOpsBuilder(t, []opsBuilderTestCase{
-		{"proc", new(Ops).Proc(MustAbs("/proc/")), Ops{
-			&MountProcOp{Target: MustAbs("/proc/")},
+		{"proc", new(Ops).Proc(check.MustAbs("/proc/")), Ops{
+			&MountProcOp{Target: check.MustAbs("/proc/")},
 		}},
 	})
 
@@ -41,20 +42,20 @@ func TestMountProcOp(t *testing.T) {
 		{"zero", new(MountProcOp), new(MountProcOp), false},
 
 		{"target differs", &MountProcOp{
-			Target: MustAbs("/proc/nonexistent"),
+			Target: check.MustAbs("/proc/nonexistent"),
 		}, &MountProcOp{
-			Target: MustAbs("/proc/"),
+			Target: check.MustAbs("/proc/"),
 		}, false},
 
 		{"equals", &MountProcOp{
-			Target: MustAbs("/proc/"),
+			Target: check.MustAbs("/proc/"),
 		}, &MountProcOp{
-			Target: MustAbs("/proc/"),
+			Target: check.MustAbs("/proc/"),
 		}, true},
 	})
 
 	checkOpMeta(t, []opMetaTestCase{
-		{"proc", &MountProcOp{Target: MustAbs("/proc/")},
+		{"proc", &MountProcOp{Target: check.MustAbs("/proc/")},
 			"mounting", `proc on "/proc/"`},
 	})
 }

container/initremount.go

@@ -3,26 +3,28 @@ package container
 import (
 	"encoding/gob"
 	"fmt"
+
+	"hakurei.app/container/check"
 )
 
 func init() { gob.Register(new(RemountOp)) }
 
 // Remount appends an [Op] that applies [RemountOp.Flags] on container path [RemountOp.Target].
-func (f *Ops) Remount(target *Absolute, flags uintptr) *Ops {
+func (f *Ops) Remount(target *check.Absolute, flags uintptr) *Ops {
 	*f = append(*f, &RemountOp{target, flags})
 	return f
 }
 
 // RemountOp remounts Target with Flags.
 type RemountOp struct {
-	Target *Absolute
+	Target *check.Absolute
 	Flags  uintptr
 }
 
 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 k.remount(toSysroot(r.Target.String()), r.Flags)
+func (r *RemountOp) apply(state *setupState, k syscallDispatcher) error {
+	return k.remount(state, toSysroot(r.Target.String()), r.Flags)
 }
 
 func (r *RemountOp) Is(op Op) bool {

container/initremount_test.go

@@ -4,13 +4,14 @@ import (
 	"syscall"
 	"testing"
 
+	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
 )
 
 func TestRemountOp(t *testing.T) {
 	checkOpBehaviour(t, []opBehaviourTestCase{
 		{"success", new(Params), &RemountOp{
-			Target: MustAbs("/"),
+			Target: check.MustAbs("/"),
 			Flags:  syscall.MS_RDONLY,
 		}, nil, nil, []stub.Call{
 			call("remount", stub.ExpectArgs{"/sysroot", uintptr(1)}, nil, nil),
@@ -20,13 +21,13 @@ func TestRemountOp(t *testing.T) {
 	checkOpsValid(t, []opValidTestCase{
 		{"nil", (*RemountOp)(nil), false},
 		{"zero", new(RemountOp), false},
-		{"valid", &RemountOp{Target: MustAbs("/"), Flags: syscall.MS_RDONLY}, true},
+		{"valid", &RemountOp{Target: check.MustAbs("/"), Flags: syscall.MS_RDONLY}, true},
 	})
 
 	checkOpsBuilder(t, []opsBuilderTestCase{
-		{"root", new(Ops).Remount(MustAbs("/"), syscall.MS_RDONLY), Ops{
+		{"root", new(Ops).Remount(check.MustAbs("/"), syscall.MS_RDONLY), Ops{
 			&RemountOp{
-				Target: MustAbs("/"),
+				Target: check.MustAbs("/"),
 				Flags:  syscall.MS_RDONLY,
 			},
 		}},
@@ -36,33 +37,33 @@ func TestRemountOp(t *testing.T) {
 		{"zero", new(RemountOp), new(RemountOp), false},
 
 		{"target differs", &RemountOp{
-			Target: MustAbs("/dev/"),
+			Target: check.MustAbs("/dev/"),
 			Flags:  syscall.MS_RDONLY,
 		}, &RemountOp{
-			Target: MustAbs("/"),
+			Target: check.MustAbs("/"),
 			Flags:  syscall.MS_RDONLY,
 		}, false},
 
 		{"flags differs", &RemountOp{
-			Target: MustAbs("/"),
+			Target: check.MustAbs("/"),
 			Flags:  syscall.MS_RDONLY | syscall.MS_NODEV,
 		}, &RemountOp{
-			Target: MustAbs("/"),
+			Target: check.MustAbs("/"),
 			Flags:  syscall.MS_RDONLY,
 		}, false},
 
 		{"equals", &RemountOp{
-			Target: MustAbs("/"),
+			Target: check.MustAbs("/"),
 			Flags:  syscall.MS_RDONLY,
 		}, &RemountOp{
-			Target: MustAbs("/"),
+			Target: check.MustAbs("/"),
 			Flags:  syscall.MS_RDONLY,
 		}, true},
 	})
 
 	checkOpMeta(t, []opMetaTestCase{
 		{"root", &RemountOp{
-			Target: MustAbs("/"),
+			Target: check.MustAbs("/"),
 			Flags:  syscall.MS_RDONLY,
 		}, "remounting", `"/" flags 0x1`},
 	})

container/initsymlink.go

@@ -4,19 +4,21 @@ import (
 	"encoding/gob"
 	"fmt"
 	"path"
+
+	"hakurei.app/container/check"
 )
 
 func init() { gob.Register(new(SymlinkOp)) }
 
 // Link appends an [Op] that creates a symlink in the container filesystem.
-func (f *Ops) Link(target *Absolute, linkName string, dereference bool) *Ops {
+func (f *Ops) Link(target *check.Absolute, linkName string, dereference bool) *Ops {
 	*f = append(*f, &SymlinkOp{target, linkName, dereference})
 	return f
 }
 
 // SymlinkOp optionally dereferences LinkName and creates a symlink at container path Target.
 type SymlinkOp struct {
-	Target *Absolute
+	Target *check.Absolute
 	// LinkName is an arbitrary uninterpreted pathname.
 	LinkName string
 
@@ -28,8 +30,8 @@ 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 &AbsoluteError{l.LinkName}
+		if !path.IsAbs(l.LinkName) {
+			return &check.AbsoluteError{Pathname: l.LinkName}
 		}
 		if name, err := k.readlink(l.LinkName); err != nil {
 			return err

container/initsymlink_test.go

@@ -4,26 +4,27 @@ import (
 	"os"
 	"testing"
 
+	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
 )
 
 func TestSymlinkOp(t *testing.T) {
 	checkOpBehaviour(t, []opBehaviourTestCase{
 		{"mkdir", &Params{ParentPerm: 0700}, &SymlinkOp{
-			Target:   MustAbs("/etc/nixos"),
+			Target:   check.MustAbs("/etc/nixos"),
 			LinkName: "/etc/static/nixos",
 		}, 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"),
+			Target:      check.MustAbs("/etc/mtab"),
 			LinkName:    "etc/mtab",
 			Dereference: true,
-		}, nil, &AbsoluteError{"etc/mtab"}, nil, nil},
+		}, nil, &check.AbsoluteError{Pathname: "etc/mtab"}, nil, nil},
 
 		{"readlink", &Params{ParentPerm: 0755}, &SymlinkOp{
-			Target:      MustAbs("/etc/mtab"),
+			Target:      check.MustAbs("/etc/mtab"),
 			LinkName:    "/etc/mtab",
 			Dereference: true,
 		}, []stub.Call{
@@ -31,7 +32,7 @@ func TestSymlinkOp(t *testing.T) {
 		}, stub.UniqueError(0), nil, nil},
 
 		{"success noderef", &Params{ParentPerm: 0700}, &SymlinkOp{
-			Target:   MustAbs("/etc/nixos"),
+			Target:   check.MustAbs("/etc/nixos"),
 			LinkName: "/etc/static/nixos",
 		}, nil, nil, []stub.Call{
 			call("mkdirAll", stub.ExpectArgs{"/sysroot/etc", os.FileMode(0700)}, nil, nil),
@@ -39,7 +40,7 @@ func TestSymlinkOp(t *testing.T) {
 		}, nil},
 
 		{"success", &Params{ParentPerm: 0755}, &SymlinkOp{
-			Target:      MustAbs("/etc/mtab"),
+			Target:      check.MustAbs("/etc/mtab"),
 			LinkName:    "/etc/mtab",
 			Dereference: true,
 		}, []stub.Call{
@@ -54,18 +55,18 @@ func TestSymlinkOp(t *testing.T) {
 		{"nil", (*SymlinkOp)(nil), false},
 		{"zero", new(SymlinkOp), false},
 		{"nil target", &SymlinkOp{LinkName: "/run/current-system"}, false},
-		{"zero linkname", &SymlinkOp{Target: MustAbs("/run/current-system")}, false},
-		{"valid", &SymlinkOp{Target: MustAbs("/run/current-system"), LinkName: "/run/current-system", Dereference: true}, true},
+		{"zero linkname", &SymlinkOp{Target: check.MustAbs("/run/current-system")}, false},
+		{"valid", &SymlinkOp{Target: check.MustAbs("/run/current-system"), LinkName: "/run/current-system", Dereference: true}, true},
 	})
 
 	checkOpsBuilder(t, []opsBuilderTestCase{
 		{"current-system", new(Ops).Link(
-			MustAbs("/run/current-system"),
+			check.MustAbs("/run/current-system"),
 			"/run/current-system",
 			true,
 		), Ops{
 			&SymlinkOp{
-				Target:      MustAbs("/run/current-system"),
+				Target:      check.MustAbs("/run/current-system"),
 				LinkName:    "/run/current-system",
 				Dereference: true,
 			},
@@ -76,40 +77,40 @@ func TestSymlinkOp(t *testing.T) {
 		{"zero", new(SymlinkOp), new(SymlinkOp), false},
 
 		{"target differs", &SymlinkOp{
-			Target:      MustAbs("/run/current-system/differs"),
+			Target:      check.MustAbs("/run/current-system/differs"),
 			LinkName:    "/run/current-system",
 			Dereference: true,
 		}, &SymlinkOp{
-			Target:      MustAbs("/run/current-system"),
+			Target:      check.MustAbs("/run/current-system"),
 			LinkName:    "/run/current-system",
 			Dereference: true,
 		}, false},
 
 		{"linkname differs", &SymlinkOp{
-			Target:      MustAbs("/run/current-system"),
+			Target:      check.MustAbs("/run/current-system"),
 			LinkName:    "/run/current-system/differs",
 			Dereference: true,
 		}, &SymlinkOp{
-			Target:      MustAbs("/run/current-system"),
+			Target:      check.MustAbs("/run/current-system"),
 			LinkName:    "/run/current-system",
 			Dereference: true,
 		}, false},
 
 		{"dereference differs", &SymlinkOp{
-			Target:   MustAbs("/run/current-system"),
+			Target:   check.MustAbs("/run/current-system"),
 			LinkName: "/run/current-system",
 		}, &SymlinkOp{
-			Target:      MustAbs("/run/current-system"),
+			Target:      check.MustAbs("/run/current-system"),
 			LinkName:    "/run/current-system",
 			Dereference: true,
 		}, false},
 
 		{"equals", &SymlinkOp{
-			Target:      MustAbs("/run/current-system"),
+			Target:      check.MustAbs("/run/current-system"),
 			LinkName:    "/run/current-system",
 			Dereference: true,
 		}, &SymlinkOp{
-			Target:      MustAbs("/run/current-system"),
+			Target:      check.MustAbs("/run/current-system"),
 			LinkName:    "/run/current-system",
 			Dereference: true,
 		}, true},
@@ -117,7 +118,7 @@ func TestSymlinkOp(t *testing.T) {
 
 	checkOpMeta(t, []opMetaTestCase{
 		{"current-system", &SymlinkOp{
-			Target:      MustAbs("/run/current-system"),
+			Target:      check.MustAbs("/run/current-system"),
 			LinkName:    "/run/current-system",
 			Dereference: true,
 		}, "creating", `symlink on "/run/current-system" linkname "/run/current-system"`},

container/inittmpfs.go

@@ -7,6 +7,8 @@ import (
 	"os"
 	"strconv"
 	. "syscall"
+
+	"hakurei.app/container/check"
 )
 
 func init() { gob.Register(new(MountTmpfsOp)) }
@@ -18,13 +20,13 @@ func (e TmpfsSizeError) Error() string {
 }
 
 // Tmpfs appends an [Op] that mounts tmpfs on container path [MountTmpfsOp.Path].
-func (f *Ops) Tmpfs(target *Absolute, size int, perm os.FileMode) *Ops {
+func (f *Ops) Tmpfs(target *check.Absolute, size int, perm os.FileMode) *Ops {
 	*f = append(*f, &MountTmpfsOp{SourceTmpfsEphemeral, target, MS_NOSUID | MS_NODEV, size, perm})
 	return f
 }
 
 // Readonly appends an [Op] that mounts read-only tmpfs on container path [MountTmpfsOp.Path].
-func (f *Ops) Readonly(target *Absolute, perm os.FileMode) *Ops {
+func (f *Ops) Readonly(target *check.Absolute, perm os.FileMode) *Ops {
 	*f = append(*f, &MountTmpfsOp{SourceTmpfsReadonly, target, MS_RDONLY | MS_NOSUID | MS_NODEV, 0, perm})
 	return f
 }
@@ -32,7 +34,7 @@ func (f *Ops) Readonly(target *Absolute, perm os.FileMode) *Ops {
 // MountTmpfsOp mounts [FstypeTmpfs] on container Path.
 type MountTmpfsOp struct {
 	FSName string
-	Path   *Absolute
+	Path   *check.Absolute
 	Flags  uintptr
 	Size   int
 	Perm   os.FileMode

container/inittmpfs_test.go

@@ -5,6 +5,7 @@ import (
 	"syscall"
 	"testing"
 
+	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
 )
 
@@ -24,7 +25,7 @@ func TestMountTmpfsOp(t *testing.T) {
 
 		{"success", new(Params), &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user/1000/"),
+			Path:   check.MustAbs("/run/user/1000/"),
 			Size:   1 << 10,
 			Perm:   0700,
 		}, nil, nil, []stub.Call{
@@ -42,19 +43,19 @@ func TestMountTmpfsOp(t *testing.T) {
 		{"nil", (*MountTmpfsOp)(nil), false},
 		{"zero", new(MountTmpfsOp), false},
 		{"nil path", &MountTmpfsOp{FSName: "tmpfs"}, false},
-		{"zero fsname", &MountTmpfsOp{Path: MustAbs("/tmp/")}, false},
-		{"valid", &MountTmpfsOp{FSName: "tmpfs", Path: MustAbs("/tmp/")}, true},
+		{"zero fsname", &MountTmpfsOp{Path: check.MustAbs("/tmp/")}, false},
+		{"valid", &MountTmpfsOp{FSName: "tmpfs", Path: check.MustAbs("/tmp/")}, true},
 	})
 
 	checkOpsBuilder(t, []opsBuilderTestCase{
 		{"runtime", new(Ops).Tmpfs(
-			MustAbs("/run/user"),
+			check.MustAbs("/run/user"),
 			1<<10,
 			0755,
 		), Ops{
 			&MountTmpfsOp{
 				FSName: "ephemeral",
-				Path:   MustAbs("/run/user"),
+				Path:   check.MustAbs("/run/user"),
 				Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 				Size:   1 << 10,
 				Perm:   0755,
@@ -62,12 +63,12 @@ func TestMountTmpfsOp(t *testing.T) {
 		}},
 
 		{"nscd", new(Ops).Readonly(
-			MustAbs("/var/run/nscd"),
+			check.MustAbs("/var/run/nscd"),
 			0755,
 		), Ops{
 			&MountTmpfsOp{
 				FSName: "readonly",
-				Path:   MustAbs("/var/run/nscd"),
+				Path:   check.MustAbs("/var/run/nscd"),
 				Flags:  syscall.MS_NOSUID | syscall.MS_NODEV | syscall.MS_RDONLY,
 				Perm:   0755,
 			},
@@ -79,13 +80,13 @@ func TestMountTmpfsOp(t *testing.T) {
 
 		{"fsname differs", &MountTmpfsOp{
 			FSName: "readonly",
-			Path:   MustAbs("/run/user"),
+			Path:   check.MustAbs("/run/user"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 			Size:   1 << 10,
 			Perm:   0755,
 		}, &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user"),
+			Path:   check.MustAbs("/run/user"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 			Size:   1 << 10,
 			Perm:   0755,
@@ -93,13 +94,13 @@ func TestMountTmpfsOp(t *testing.T) {
 
 		{"path differs", &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user/differs"),
+			Path:   check.MustAbs("/run/user/differs"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 			Size:   1 << 10,
 			Perm:   0755,
 		}, &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user"),
+			Path:   check.MustAbs("/run/user"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 			Size:   1 << 10,
 			Perm:   0755,
@@ -107,13 +108,13 @@ func TestMountTmpfsOp(t *testing.T) {
 
 		{"flags differs", &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user"),
+			Path:   check.MustAbs("/run/user"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV | syscall.MS_RDONLY,
 			Size:   1 << 10,
 			Perm:   0755,
 		}, &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user"),
+			Path:   check.MustAbs("/run/user"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 			Size:   1 << 10,
 			Perm:   0755,
@@ -121,13 +122,13 @@ func TestMountTmpfsOp(t *testing.T) {
 
 		{"size differs", &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user"),
+			Path:   check.MustAbs("/run/user"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 			Size:   1,
 			Perm:   0755,
 		}, &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user"),
+			Path:   check.MustAbs("/run/user"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 			Size:   1 << 10,
 			Perm:   0755,
@@ -135,13 +136,13 @@ func TestMountTmpfsOp(t *testing.T) {
 
 		{"perm differs", &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user"),
+			Path:   check.MustAbs("/run/user"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 			Size:   1 << 10,
 			Perm:   0700,
 		}, &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user"),
+			Path:   check.MustAbs("/run/user"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 			Size:   1 << 10,
 			Perm:   0755,
@@ -149,13 +150,13 @@ func TestMountTmpfsOp(t *testing.T) {
 
 		{"equals", &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user"),
+			Path:   check.MustAbs("/run/user"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 			Size:   1 << 10,
 			Perm:   0755,
 		}, &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user"),
+			Path:   check.MustAbs("/run/user"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 			Size:   1 << 10,
 			Perm:   0755,
@@ -165,7 +166,7 @@ func TestMountTmpfsOp(t *testing.T) {
 	checkOpMeta(t, []opMetaTestCase{
 		{"runtime", &MountTmpfsOp{
 			FSName: "ephemeral",
-			Path:   MustAbs("/run/user"),
+			Path:   check.MustAbs("/run/user"),
 			Flags:  syscall.MS_NOSUID | syscall.MS_NODEV,
 			Size:   1 << 10,
 			Perm:   0755,

container/mount.go

@@ -4,7 +4,6 @@ import (
 	"errors"
 	"fmt"
 	"os"
-	"strings"
 	. "syscall"
 
 	"hakurei.app/container/vfs"
@@ -59,7 +58,6 @@ const (
 	FstypeNULL = zeroString
 	// FstypeProc represents the proc pseudo-filesystem.
 	// A fully visible instance of proc must be available in the mount namespace for proc to be mounted.
-	// This filesystem type is usually mounted on [FHSProc].
 	FstypeProc = "proc"
 	// FstypeDevpts represents the devpts pseudo-filesystem.
 	// This type of filesystem is usually mounted on /dev/pts.
@@ -86,28 +84,20 @@ const (
 	// OptionOverlayUserxattr represents the userxattr option of the overlay pseudo-filesystem.
 	// Use the "user.overlay." xattr namespace instead of "trusted.overlay.".
 	OptionOverlayUserxattr = "userxattr"
-
-	// SpecialOverlayEscape is the escape string for overlay mount options.
-	SpecialOverlayEscape = `\`
-	// SpecialOverlayOption is the separator string between overlay mount options.
-	SpecialOverlayOption = ","
-	// SpecialOverlayPath is the separator string between overlay paths.
-	SpecialOverlayPath = ":"
 )
 
 // bindMount mounts source on target and recursively applies flags if MS_REC is set.
-func (p *procPaths) bindMount(source, target string, flags uintptr) error {
+func (p *procPaths) bindMount(msg Msg, source, target string, flags uintptr) error {
 	// syscallDispatcher.bindMount and procPaths.remount must not be called from this function
 
 	if err := p.k.mount(source, target, FstypeNULL, MS_SILENT|MS_BIND|flags&MS_REC, zeroString); err != nil {
 		return err
 	}
-
-	return p.k.remount(target, flags)
+	return p.k.remount(msg, target, flags)
 }
 
 // remount applies flags on target, recursively if MS_REC is set.
-func (p *procPaths) remount(target string, flags uintptr) error {
+func (p *procPaths) remount(msg Msg, target string, flags uintptr) error {
 	// syscallDispatcher methods bindMount, remount must not be called from this function
 
 	var targetFinal string
@@ -116,7 +106,7 @@ func (p *procPaths) remount(target string, flags uintptr) error {
 	} else {
 		targetFinal = v
 		if targetFinal != target {
-			p.k.verbosef("target resolves to %q", targetFinal)
+			msg.Verbosef("target resolves to %q", targetFinal)
 		}
 	}
 
@@ -146,7 +136,7 @@ func (p *procPaths) remount(target string, flags uintptr) error {
 			return err
 		}
 
-		if err = remountWithFlags(p.k, n, mf); err != nil {
+		if err = remountWithFlags(p.k, msg, n, mf); err != nil {
 			return err
 		}
 		if flags&MS_REC == 0 {
@@ -159,7 +149,7 @@ func (p *procPaths) remount(target string, flags uintptr) error {
 				continue
 			}
 
-			if err = remountWithFlags(p.k, cur, mf); err != nil && !errors.Is(err, EACCES) {
+			if err = remountWithFlags(p.k, msg, cur, mf); err != nil && !errors.Is(err, EACCES) {
 				return err
 			}
 		}
@@ -169,12 +159,12 @@ func (p *procPaths) remount(target string, flags uintptr) error {
 }
 
 // remountWithFlags remounts mount point described by [vfs.MountInfoNode].
-func remountWithFlags(k syscallDispatcher, n *vfs.MountInfoNode, mf uintptr) error {
+func remountWithFlags(k syscallDispatcher, msg Msg, n *vfs.MountInfoNode, mf uintptr) error {
 	// syscallDispatcher methods bindMount, remount must not be called from this function
 
 	kf, unmatched := n.Flags()
 	if len(unmatched) != 0 {
-		k.verbosef("unmatched vfs options: %q", unmatched)
+		msg.Verbosef("unmatched vfs options: %q", unmatched)
 	}
 
 	if kf&mf != mf {
@@ -208,20 +198,3 @@ func parentPerm(perm os.FileMode) os.FileMode {
 	}
 	return os.FileMode(pperm)
 }
-
-// EscapeOverlayDataSegment escapes a string for formatting into the data argument of an overlay mount call.
-func EscapeOverlayDataSegment(s string) string {
-	if s == zeroString {
-		return zeroString
-	}
-
-	if f := strings.SplitN(s, "\x00", 2); len(f) > 0 {
-		s = f[0]
-	}
-
-	return strings.NewReplacer(
-		SpecialOverlayEscape, SpecialOverlayEscape+SpecialOverlayEscape,
-		SpecialOverlayOption, SpecialOverlayEscape+SpecialOverlayOption,
-		SpecialOverlayPath, SpecialOverlayEscape+SpecialOverlayPath,
-	).Replace(s)
-}

container/mount_test.go

@@ -11,21 +11,21 @@ import (
 
 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)
+		{"mount", func(k *kstub) error {
+			return newProcPaths(k, hostPath).bindMount(nil, "/host/nix", "/sysroot/nix", syscall.MS_RDONLY)
 		}, stub.Expect{Calls: []stub.Call{
 			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)
+		{"success ne", func(k *kstub) error {
+			return newProcPaths(k, hostPath).bindMount(k, "/host/nix", "/sysroot/.host-nix", syscall.MS_RDONLY)
 		}, stub.Expect{Calls: []stub.Call{
 			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)
+		{"success", func(k *kstub) error {
+			return newProcPaths(k, hostPath).bindMount(k, "/host/nix", "/sysroot/nix", syscall.MS_RDONLY)
 		}, stub.Expect{Calls: []stub.Call{
 			call("mount", stub.ExpectArgs{"/host/nix", "/sysroot/nix", "", uintptr(0x9000), ""}, nil, nil),
 			call("remount", stub.ExpectArgs{"/sysroot/nix", uintptr(1)}, nil, nil),
@@ -77,29 +77,29 @@ func TestRemount(t *testing.T) {
 416 415 0:30 / /sysroot/nix/store ro,relatime master:5 - overlay overlay rw,lowerdir=/mnt-root/nix/.ro-store,upperdir=/mnt-root/nix/.rw-store/upper,workdir=/mnt-root/nix/.rw-store/work`
 
 	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)
+		{"evalSymlinks", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(nil, "/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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)
+		{"open", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(nil, "/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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)
+		{"readlink", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(nil, "/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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)
+		{"close", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(nil, "/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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),
@@ -107,8 +107,8 @@ func TestRemount(t *testing.T) {
 			call("close", stub.ExpectArgs{0xdeadbeef}, nil, stub.UniqueError(3)),
 		}}, &os.PathError{Op: "close", Path: "/sysroot/nix", Err: stub.UniqueError(3)}},
 
-		{"mountinfo no match", func(k syscallDispatcher) error {
-			return newProcPaths(k, hostPath).remount("/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
+		{"mountinfo no match", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(k, "/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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),
@@ -118,8 +118,8 @@ func TestRemount(t *testing.T) {
 			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)
+		{"mountinfo", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(nil, "/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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),
@@ -128,8 +128,8 @@ func TestRemount(t *testing.T) {
 			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)
+		{"mount", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(nil, "/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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),
@@ -139,8 +139,8 @@ func TestRemount(t *testing.T) {
 			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)
+		{"mount propagate", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(nil, "/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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),
@@ -151,8 +151,8 @@ func TestRemount(t *testing.T) {
 			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)
+		{"success toplevel", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(nil, "/sysroot/bin", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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),
@@ -162,8 +162,8 @@ func TestRemount(t *testing.T) {
 			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)
+		{"success EACCES", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(nil, "/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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),
@@ -175,8 +175,8 @@ func TestRemount(t *testing.T) {
 			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)
+		{"success no propagate", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(nil, "/sysroot/nix", syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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),
@@ -186,8 +186,8 @@ func TestRemount(t *testing.T) {
 			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)
+		{"success case sensitive", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(nil, "/sysroot/nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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),
@@ -199,8 +199,8 @@ func TestRemount(t *testing.T) {
 			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)
+		{"success", func(k *kstub) error {
+			return newProcPaths(k, hostPath).remount(k, "/sysroot/.nix", syscall.MS_REC|syscall.MS_RDONLY|syscall.MS_NODEV)
 		}, 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),
@@ -217,18 +217,18 @@ func TestRemount(t *testing.T) {
 
 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)
+		{"noop unmatched", func(k *kstub) error {
+			return remountWithFlags(k, k, &vfs.MountInfoNode{MountInfoEntry: &vfs.MountInfoEntry{VfsOptstr: "rw,relatime,cat"}}, 0)
 		}, 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)
+		{"noop", func(k *kstub) error {
+			return remountWithFlags(k, nil, &vfs.MountInfoNode{MountInfoEntry: &vfs.MountInfoEntry{VfsOptstr: "rw,relatime"}}, 0)
 		}, stub.Expect{}, nil},
 
-		{"success", func(k syscallDispatcher) error {
-			return remountWithFlags(k, &vfs.MountInfoNode{MountInfoEntry: &vfs.MountInfoEntry{VfsOptstr: "rw,relatime"}}, syscall.MS_RDONLY)
+		{"success", func(k *kstub) error {
+			return remountWithFlags(k, nil, &vfs.MountInfoNode{MountInfoEntry: &vfs.MountInfoEntry{VfsOptstr: "rw,relatime"}}, syscall.MS_RDONLY)
 		}, stub.Expect{Calls: []stub.Call{
 			call("mount", stub.ExpectArgs{"none", "", "", uintptr(0x209021), ""}, nil, nil),
 		}}, nil},
@@ -237,20 +237,20 @@ func TestRemountWithFlags(t *testing.T) {
 
 func TestMountTmpfs(t *testing.T) {
 	checkSimple(t, "mountTmpfs", []simpleTestCase{
-		{"mkdirAll", func(k syscallDispatcher) error {
+		{"mkdirAll", func(k *kstub) error {
 			return mountTmpfs(k, "ephemeral", "/sysroot/run/user/1000", 0, 1<<10, 0700)
 		}, 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 {
+		{"success no size", func(k *kstub) error {
 			return mountTmpfs(k, "ephemeral", "/sysroot/run/user/1000", 0, 0, 0710)
 		}, 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 {
+		{"success", func(k *kstub) error {
 			return mountTmpfs(k, "ephemeral", "/sysroot/run/user/1000", 0, 1<<10, 0700)
 		}, stub.Expect{Calls: []stub.Call{
 			call("mkdirAll", stub.ExpectArgs{"/sysroot/run/user/1000", os.FileMode(0700)}, nil, nil),
@@ -281,23 +281,3 @@ func TestParentPerm(t *testing.T) {
 		})
 	}
 }
-
-func TestEscapeOverlayDataSegment(t *testing.T) {
-	testCases := []struct {
-		name string
-		s    string
-		want string
-	}{
-		{"zero", zeroString, zeroString},
-		{"multi", `\\\:,:,\\\`, `\\\\\\\:\,\:\,\\\\\\`},
-		{"bwrap", `/path :,\`, `/path \:\,\\`},
-	}
-
-	for _, tc := range testCases {
-		t.Run(tc.name, func(t *testing.T) {
-			if got := EscapeOverlayDataSegment(tc.s); got != tc.want {
-				t.Errorf("escapeOverlayDataSegment: %s, want %s", got, tc.want)
-			}
-		})
-	}
-}

container/msg.go

@@ -23,45 +23,88 @@ func GetErrorMessage(err error) (string, bool) {
 	return e.Message(), true
 }
 
+// Msg is used for package-wide verbose logging.
 type Msg interface {
+	// GetLogger returns the address of the underlying [log.Logger].
+	GetLogger() *log.Logger
+
+	// IsVerbose atomically loads and returns whether [Msg] has verbose logging enabled.
 	IsVerbose() bool
+	// SwapVerbose atomically stores a new verbose state and returns the previous value held by [Msg].
+	SwapVerbose(verbose bool) bool
+	// Verbose passes its argument to the Println method of the underlying [log.Logger] if IsVerbose returns true.
 	Verbose(v ...any)
+	// Verbosef passes its argument to the Printf method of the underlying [log.Logger] if IsVerbose returns true.
 	Verbosef(format string, v ...any)
 
-	Suspend()
+	// Suspend causes the embedded [Suspendable] to withhold writes to its downstream [io.Writer].
+	// Suspend returns false and is a noop if called between calls to Suspend and Resume.
+	Suspend() bool
+
+	// Resume dumps the entire buffer held by the embedded [Suspendable] and stops withholding future writes.
+	// Resume returns false and is a noop if a call to Suspend does not precede it.
 	Resume() bool
+
+	// BeforeExit runs implementation-specific cleanup code, and optionally prints warnings.
+	// BeforeExit is called before [os.Exit].
 	BeforeExit()
 }
 
-type DefaultMsg struct{ inactive atomic.Bool }
+// defaultMsg is the default implementation of the [Msg] interface.
+// The zero value is not safe for use. Callers should use the [NewMsg] function instead.
+type defaultMsg struct {
+	verbose atomic.Bool
 
-func (msg *DefaultMsg) IsVerbose() bool { return true }
-func (msg *DefaultMsg) Verbose(v ...any) {
-	if !msg.inactive.Load() {
-		log.Println(v...)
+	logger *log.Logger
+	Suspendable
+}
+
+// NewMsg initialises a downstream [log.Logger] for a new [Msg].
+// The [log.Logger] should no longer be configured after NewMsg returns.
+// If downstream is nil, a new logger is initialised in its place.
+func NewMsg(downstream *log.Logger) Msg {
+	if downstream == nil {
+		downstream = log.New(log.Writer(), "container: ", 0)
+	}
+
+	m := defaultMsg{logger: downstream}
+	m.Suspendable.Downstream = downstream.Writer()
+	downstream.SetOutput(&m.Suspendable)
+	return &m
+}
+
+func (msg *defaultMsg) GetLogger() *log.Logger { return msg.logger }
+
+func (msg *defaultMsg) IsVerbose() bool               { return msg.verbose.Load() }
+func (msg *defaultMsg) SwapVerbose(verbose bool) bool { return msg.verbose.Swap(verbose) }
+func (msg *defaultMsg) Verbose(v ...any) {
+	if msg.verbose.Load() {
+		msg.logger.Println(v...)
 	}
 }
-func (msg *DefaultMsg) Verbosef(format string, v ...any) {
-	if !msg.inactive.Load() {
-		log.Printf(format, v...)
+func (msg *defaultMsg) Verbosef(format string, v ...any) {
+	if msg.verbose.Load() {
+		msg.logger.Printf(format, v...)
 	}
 }
 
-func (msg *DefaultMsg) Suspend()     { msg.inactive.Store(true) }
-func (msg *DefaultMsg) Resume() bool { return msg.inactive.CompareAndSwap(true, false) }
-func (msg *DefaultMsg) BeforeExit()  {}
+// Resume calls [Suspendable.Resume] and prints a message if buffer was filled
+// between calls to [Suspendable.Suspend] and Resume.
+func (msg *defaultMsg) Resume() bool {
+	resumed, dropped, _, err := msg.Suspendable.Resume()
+	if err != nil {
+		// probably going to result in an error as well, so this message is as good as unreachable
+		msg.logger.Printf("cannot dump buffer on resume: %v", err)
+	}
+	if resumed && dropped > 0 {
+		msg.logger.Printf("dropped %d bytes while output is suspended", dropped)
+	}
+	return resumed
+}
 
-// msg is the [Msg] implemented used by all exported [container] functions.
-var msg Msg = new(DefaultMsg)
-
-// GetOutput returns the current active [Msg] implementation.
-func GetOutput() Msg { return msg }
-
-// SetOutput replaces the current active [Msg] implementation.
-func SetOutput(v Msg) {
-	if v == nil {
-		msg = new(DefaultMsg)
-	} else {
-		msg = v
+// BeforeExit prints a message if called between calls to [Suspendable.Suspend] and Resume.
+func (msg *defaultMsg) BeforeExit() {
+	if msg.Resume() {
+		msg.logger.Printf("beforeExit reached on suspended output")
 	}
 }

container/msg_test.go

@@ -1,14 +1,16 @@
 package container_test
 
 import (
+	"bytes"
 	"errors"
+	"io"
 	"log"
 	"strings"
-	"sync/atomic"
 	"syscall"
 	"testing"
 
 	"hakurei.app/container"
+	"hakurei.app/container/stub"
 )
 
 func TestMessageError(t *testing.T) {
@@ -39,146 +41,137 @@ func TestMessageError(t *testing.T) {
 }
 
 func TestDefaultMsg(t *testing.T) {
-	{
-		w := log.Writer()
-		f := log.Flags()
-		t.Cleanup(func() { log.SetOutput(w); log.SetFlags(f) })
-	}
-	msg := new(container.DefaultMsg)
+	// copied from output.go
+	const suspendBufMax = 1 << 24
 
-	t.Run("is verbose", func(t *testing.T) {
-		if !msg.IsVerbose() {
-			t.Error("IsVerbose unexpected outcome")
-		}
-	})
+	t.Run("logger", func(t *testing.T) {
+		t.Run("nil", func(t *testing.T) {
+			got := container.NewMsg(nil).GetLogger()
 
-	t.Run("verbose", func(t *testing.T) {
-		log.SetOutput(panicWriter{})
-		msg.Suspend()
-		msg.Verbose()
-		msg.Verbosef("\x00")
-		msg.Resume()
-
-		buf := new(strings.Builder)
-		log.SetOutput(buf)
-		log.SetFlags(0)
-		msg.Verbose()
-		msg.Verbosef("\x00")
-
-		want := "\n\x00\n"
-		if buf.String() != want {
-			t.Errorf("Verbose: %q, want %q", buf.String(), want)
-		}
-	})
-
-	t.Run("inactive", func(t *testing.T) {
-		{
-			inactive := msg.Resume()
-			if inactive {
-				t.Cleanup(func() { msg.Suspend() })
+			if out := got.Writer().(*container.Suspendable).Downstream; out != log.Writer() {
+				t.Errorf("GetLogger: Downstream = %#v", out)
 			}
-		}
 
-		if msg.Resume() {
-			t.Error("Resume unexpected outcome")
-		}
+			if prefix := got.Prefix(); prefix != "container: " {
+				t.Errorf("GetLogger: prefix = %q", prefix)
+			}
+		})
 
-		msg.Suspend()
-		if !msg.Resume() {
-			t.Error("Resume unexpected outcome")
-		}
+		t.Run("takeover", func(t *testing.T) {
+			l := log.New(io.Discard, "\x00", 0xdeadbeef)
+			got := container.NewMsg(l)
+
+			if logger := got.GetLogger(); logger != l {
+				t.Errorf("GetLogger: %#v, want %#v", logger, l)
+			}
+
+			if ds := l.Writer().(*container.Suspendable).Downstream; ds != io.Discard {
+				t.Errorf("GetLogger: Downstream = %#v", ds)
+			}
+		})
 	})
 
-	// the function is a noop
-	t.Run("beforeExit", func(t *testing.T) { msg.BeforeExit() })
-}
+	dw := expectWriter{t: t}
 
-type panicWriter struct{}
+	steps := []struct {
+		name     string
+		pt, next []byte
+		err      error
 
-func (panicWriter) Write([]byte) (int, error) { panic("unreachable") }
+		f func(t *testing.T, msg container.Msg)
+	}{
+		{"zero verbose", nil, nil, nil, func(t *testing.T, msg container.Msg) {
+			if msg.IsVerbose() {
+				t.Error("IsVerbose unexpected true")
+			}
+		}},
 
-func saveRestoreOutput(t *testing.T) {
-	out := container.GetOutput()
-	t.Cleanup(func() { container.SetOutput(out) })
-}
+		{"swap false", nil, nil, nil, func(t *testing.T, msg container.Msg) {
+			if msg.SwapVerbose(false) {
+				t.Error("SwapVerbose unexpected true")
+			}
+		}},
+		{"write discard", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
+			msg.Verbose("\x00")
+			msg.Verbosef("\x00")
+		}},
+		{"verbose false", nil, nil, nil, func(t *testing.T, msg container.Msg) {
+			if msg.IsVerbose() {
+				t.Error("IsVerbose unexpected true")
+			}
+		}},
 
-func replaceOutput(t *testing.T) {
-	saveRestoreOutput(t)
-	container.SetOutput(&testOutput{t: t})
-}
+		{"swap true", nil, nil, nil, func(t *testing.T, msg container.Msg) {
+			if msg.SwapVerbose(true) {
+				t.Error("SwapVerbose unexpected true")
+			}
+		}},
+		{"write verbose", []byte("test: \x00\n"), nil, nil, func(_ *testing.T, msg container.Msg) {
+			msg.Verbose("\x00")
+		}},
+		{"write verbosef", []byte(`test: "\x00"` + "\n"), nil, nil, func(_ *testing.T, msg container.Msg) {
+			msg.Verbosef("%q", "\x00")
+		}},
+		{"verbose true", nil, nil, nil, func(t *testing.T, msg container.Msg) {
+			if !msg.IsVerbose() {
+				t.Error("IsVerbose unexpected false")
+			}
+		}},
 
-type testOutput struct {
-	t         *testing.T
-	suspended atomic.Bool
-}
+		{"resume noop", nil, nil, nil, func(t *testing.T, msg container.Msg) {
+			if msg.Resume() {
+				t.Error("Resume unexpected success")
+			}
+		}},
+		{"beforeExit noop", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
+			msg.BeforeExit()
+		}},
 
-func (out *testOutput) IsVerbose() bool { return testing.Verbose() }
+		{"beforeExit suspend", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
+			msg.Suspend()
+		}},
+		{"beforeExit message", []byte("test: beforeExit reached on suspended output\n"), nil, nil, func(_ *testing.T, msg container.Msg) {
+			msg.BeforeExit()
+		}},
+		{"post beforeExit resume noop", nil, nil, nil, func(t *testing.T, msg container.Msg) {
+			if msg.Resume() {
+				t.Error("Resume unexpected success")
+			}
+		}},
 
-func (out *testOutput) Verbose(v ...any) {
-	if !out.IsVerbose() {
-		return
-	}
-	out.t.Log(v...)
-}
+		{"suspend", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
+			msg.Suspend()
+		}},
+		{"suspend write", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
+			msg.GetLogger().Print("\x00")
+		}},
+		{"resume error", []byte("test: \x00\n"), []byte("test: cannot dump buffer on resume: unique error 0 injected by the test suite\n"), stub.UniqueError(0), func(t *testing.T, msg container.Msg) {
+			if !msg.Resume() {
+				t.Error("Resume unexpected failure")
+			}
+		}},
 
-func (out *testOutput) Verbosef(format string, v ...any) {
-	if !out.IsVerbose() {
-		return
-	}
-	out.t.Logf(format, v...)
-}
-
-func (out *testOutput) Suspend() {
-	if out.suspended.CompareAndSwap(false, true) {
-		out.Verbose("suspend called")
-		return
-	}
-	out.Verbose("suspend called on suspended output")
-}
-
-func (out *testOutput) Resume() bool {
-	if out.suspended.CompareAndSwap(true, false) {
-		out.Verbose("resume called")
-		return true
-	}
-	out.Verbose("resume called on unsuspended output")
-	return false
-}
-
-func (out *testOutput) BeforeExit() { out.Verbose("beforeExit called") }
-
-func TestGetSetOutput(t *testing.T) {
-	{
-		out := container.GetOutput()
-		t.Cleanup(func() { container.SetOutput(out) })
+		{"suspend drop", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
+			msg.Suspend()
+		}},
+		{"suspend write fill", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
+			msg.GetLogger().Print(strings.Repeat("\x00", suspendBufMax))
+		}},
+		{"resume dropped", append([]byte("test: "), bytes.Repeat([]byte{0}, suspendBufMax-6)...), []byte("test: dropped 7 bytes while output is suspended\n"), nil, func(t *testing.T, msg container.Msg) {
+			if !msg.Resume() {
+				t.Error("Resume unexpected failure")
+			}
+		}},
 	}
 
-	t.Run("default", func(t *testing.T) {
-		container.SetOutput(new(stubOutput))
-		if v, ok := container.GetOutput().(*container.DefaultMsg); ok {
-			t.Fatalf("SetOutput: got unexpected output %#v", v)
+	msg := container.NewMsg(log.New(&dw, "test: ", 0))
+	for _, step := range steps {
+		// these share the same writer, so cannot be subtests
+		t.Logf("running step %q", step.name)
+		dw.expect, dw.next, dw.err = step.pt, step.next, step.err
+		step.f(t, msg)
+		if dw.expect != nil {
+			t.Errorf("expect: %q", string(dw.expect))
 		}
-		container.SetOutput(nil)
-		if _, ok := container.GetOutput().(*container.DefaultMsg); !ok {
-			t.Fatalf("SetOutput: got unexpected output %#v", container.GetOutput())
-		}
-	})
-
-	t.Run("stub", func(t *testing.T) {
-		container.SetOutput(new(stubOutput))
-		if _, ok := container.GetOutput().(*stubOutput); !ok {
-			t.Fatalf("SetOutput: got unexpected output %#v", container.GetOutput())
-		}
-	})
+	}
 }
-
-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) Suspend()                { panic("unreachable") }
-func (*stubOutput) Resume() bool            { panic("unreachable") }
-func (*stubOutput) BeforeExit()             { panic("unreachable") }

container/output_test.go

@@ -28,7 +28,7 @@ func TestSuspendable(t *testing.T) {
 	)
 
 	// shares the same writer
-	testCases := []struct {
+	steps := []struct {
 		name    string
 		w, pt   []byte
 		err     error
@@ -75,25 +75,25 @@ func TestSuspendable(t *testing.T) {
 	var dw expectWriter
 
 	w := container.Suspendable{Downstream: &dw}
-	for _, tc := range testCases {
+	for _, step := range steps {
 		// these share the same writer, so cannot be subtests
-		t.Logf("writing step %q", tc.name)
-		dw.expect, dw.err = tc.pt, tc.err
+		t.Logf("writing step %q", step.name)
+		dw.expect, dw.err = step.pt, step.err
 
 		var (
 			gotN   int
 			gotErr error
 		)
 
-		wantN := tc.n
+		wantN := step.n
 		switch wantN {
 		case nSpecialPtEquiv:
-			wantN = len(tc.pt)
-			gotN, gotErr = w.Write(tc.w)
+			wantN = len(step.pt)
+			gotN, gotErr = w.Write(step.w)
 
 		case nSpecialWEquiv:
-			wantN = len(tc.w)
-			gotN, gotErr = w.Write(tc.w)
+			wantN = len(step.w)
+			gotN, gotErr = w.Write(step.w)
 
 		case nSpecialSuspend:
 			s := w.IsSuspended()
@@ -101,8 +101,8 @@ func TestSuspendable(t *testing.T) {
 				t.Fatal("Suspend: unexpected success")
 			}
 
-			wantN = len(tc.w)
-			gotN, gotErr = w.Write(tc.w)
+			wantN = len(step.w)
+			gotN, gotErr = w.Write(step.w)
 
 		default:
 			if wantN <= nSpecialDump {
@@ -118,10 +118,10 @@ func TestSuspendable(t *testing.T) {
 					t.Errorf("Resume: dropped = %d, want %d", dropped, wantDropped)
 				}
 
-				wantN = len(tc.pt)
+				wantN = len(step.pt)
 				gotN, gotErr = int(n), err
 			} else {
-				gotN, gotErr = w.Write(tc.w)
+				gotN, gotErr = w.Write(step.w)
 			}
 		}
 
@@ -129,9 +129,13 @@ func TestSuspendable(t *testing.T) {
 			t.Errorf("Write: n = %d, want %d", gotN, wantN)
 		}
 
-		if !reflect.DeepEqual(gotErr, tc.wantErr) {
+		if !reflect.DeepEqual(gotErr, step.wantErr) {
 			t.Errorf("Write: %v", gotErr)
 		}
+
+		if dw.expect != nil {
+			t.Errorf("expect: %q", string(dw.expect))
+		}
 	}
 }
 
@@ -139,17 +143,31 @@ func TestSuspendable(t *testing.T) {
 type expectWriter struct {
 	expect []byte
 	err    error
+
+	// optional consecutive write
+	next []byte
+
+	// optional, calls Error on failure if not nil
+	t *testing.T
 }
 
 func (w *expectWriter) Write(p []byte) (n int, err error) {
-	defer func() { w.expect = nil }()
+	defer func() { w.expect = w.next; w.next = nil }()
 
 	n, err = len(p), w.err
 	if w.expect == nil {
-		return 0, errors.New("unexpected call to Write: " + strconv.Quote(string(p)))
+		n, err = 0, errors.New("unexpected call to Write: "+strconv.Quote(string(p)))
+		if w.t != nil {
+			w.t.Error(err.Error())
+		}
+		return
 	}
 	if string(p) != string(w.expect) {
-		return 0, errors.New("p = " + strconv.Quote(string(p)) + ", want " + strconv.Quote(string(w.expect)))
+		n, err = 0, errors.New("p = "+strconv.Quote(string(p))+", want "+strconv.Quote(string(w.expect)))
+		if w.t != nil {
+			w.t.Error(err.Error())
+		}
+		return
 	}
 	return
 }

container/path.go

@@ -9,84 +9,18 @@ import (
 	"strings"
 	"syscall"
 
+	"hakurei.app/container/fhs"
 	"hakurei.app/container/vfs"
 )
 
-/* constants in this file bypass abs check, be extremely careful when changing them! */
-
-const (
-	// FHSRoot points to the file system root.
-	FHSRoot = "/"
-	// FHSEtc points to the directory for system-specific configuration.
-	FHSEtc = "/etc/"
-	// FHSTmp points to the place for small temporary files.
-	FHSTmp = "/tmp/"
-
-	// FHSRun points to a "tmpfs" file system for system packages to place runtime data, socket files, and similar.
-	FHSRun = "/run/"
-	// FHSRunUser points to a directory containing per-user runtime directories,
-	// each usually individually mounted "tmpfs" instances.
-	FHSRunUser = FHSRun + "user/"
-
-	// FHSUsr points to vendor-supplied operating system resources.
-	FHSUsr = "/usr/"
-	// FHSUsrBin points to binaries and executables for user commands that shall appear in the $PATH search path.
-	FHSUsrBin = FHSUsr + "bin/"
-
-	// FHSVar points to persistent, variable system data. Writable during normal system operation.
-	FHSVar = "/var/"
-	// FHSVarLib points to persistent system data.
-	FHSVarLib = FHSVar + "lib/"
-	// FHSVarEmpty points to a nonstandard directory that is usually empty.
-	FHSVarEmpty = FHSVar + "empty/"
-
-	// FHSDev points to the root directory for device nodes.
-	FHSDev = "/dev/"
-	// FHSProc points to a virtual kernel file system exposing the process list and other functionality.
-	FHSProc = "/proc/"
-	// FHSProcSys points to a hierarchy below /proc/ that exposes a number of kernel tunables.
-	FHSProcSys = FHSProc + "sys/"
-	// FHSSys points to a virtual kernel file system exposing discovered devices and other functionality.
-	FHSSys = "/sys/"
-)
-
-var (
-	// AbsFHSRoot is [FHSRoot] as [Absolute].
-	AbsFHSRoot = &Absolute{FHSRoot}
-	// AbsFHSEtc is [FHSEtc] as [Absolute].
-	AbsFHSEtc = &Absolute{FHSEtc}
-	// AbsFHSTmp is [FHSTmp] as [Absolute].
-	AbsFHSTmp = &Absolute{FHSTmp}
-
-	// AbsFHSRun is [FHSRun] as [Absolute].
-	AbsFHSRun = &Absolute{FHSRun}
-	// AbsFHSRunUser is [FHSRunUser] as [Absolute].
-	AbsFHSRunUser = &Absolute{FHSRunUser}
-
-	// AbsFHSUsrBin is [FHSUsrBin] as [Absolute].
-	AbsFHSUsrBin = &Absolute{FHSUsrBin}
-
-	// AbsFHSVar is [FHSVar] as [Absolute].
-	AbsFHSVar = &Absolute{FHSVar}
-	// AbsFHSVarLib is [FHSVarLib] as [Absolute].
-	AbsFHSVarLib = &Absolute{FHSVarLib}
-
-	// AbsFHSDev is [FHSDev] as [Absolute].
-	AbsFHSDev = &Absolute{FHSDev}
-	// AbsFHSProc is [FHSProc] as [Absolute].
-	AbsFHSProc = &Absolute{FHSProc}
-	// AbsFHSSys is [FHSSys] as [Absolute].
-	AbsFHSSys = &Absolute{FHSSys}
-)
-
 const (
 	// Nonexistent is a path that cannot exist.
 	// /proc is chosen because a system with covered /proc is unsupported by this package.
-	Nonexistent = FHSProc + "nonexistent"
+	Nonexistent = fhs.Proc + "nonexistent"
 
-	hostPath    = FHSRoot + hostDir
+	hostPath    = fhs.Root + hostDir
 	hostDir     = "host"
-	sysrootPath = FHSRoot + sysrootDir
+	sysrootPath = fhs.Root + sysrootDir
 	sysrootDir  = "sysroot"
 )
 

container/path_test.go

@@ -10,6 +10,7 @@ import (
 	"testing"
 	"unsafe"
 
+	"hakurei.app/container/check"
 	"hakurei.app/container/vfs"
 )
 
@@ -49,8 +50,8 @@ func TestToHost(t *testing.T) {
 	}
 }
 
-// InternalToHostOvlEscape exports toHost passed to EscapeOverlayDataSegment.
-func InternalToHostOvlEscape(s string) string { return EscapeOverlayDataSegment(toHost(s)) }
+// InternalToHostOvlEscape exports toHost passed to [check.EscapeOverlayDataSegment].
+func InternalToHostOvlEscape(s string) string { return check.EscapeOverlayDataSegment(toHost(s)) }
 
 func TestCreateFile(t *testing.T) {
 	t.Run("nonexistent", func(t *testing.T) {

container/seccomp/hash_amd64_test.go

@@ -1,6 +1,9 @@
 package seccomp_test
 
-import . "hakurei.app/container/seccomp"
+import (
+	. "hakurei.app/container/bits"
+	. "hakurei.app/container/seccomp"
+)
 
 var bpfExpected = bpfLookup{
 	{AllowMultiarch | AllowCAN |

container/seccomp/hash_arm64_test.go

@@ -1,6 +1,9 @@
 package seccomp_test
 
-import . "hakurei.app/container/seccomp"
+import (
+	. "hakurei.app/container/bits"
+	. "hakurei.app/container/seccomp"
+)
 
 var bpfExpected = bpfLookup{
 	{AllowMultiarch | AllowCAN |

container/seccomp/hash_test.go

@@ -3,13 +3,14 @@ package seccomp_test
 import (
 	"encoding/hex"
 
+	"hakurei.app/container/bits"
 	"hakurei.app/container/seccomp"
 )
 
 type (
 	bpfPreset = struct {
 		seccomp.ExportFlag
-		seccomp.FilterPreset
+		bits.FilterPreset
 	}
 	bpfLookup map[bpfPreset][]byte
 )

container/seccomp/libseccomp_test.go

@@ -8,6 +8,7 @@ import (
 	"syscall"
 	"testing"
 
+	. "hakurei.app/container/bits"
 	. "hakurei.app/container/seccomp"
 )
 

container/seccomp/presets.go

@@ -4,46 +4,33 @@ package seccomp
 
 import (
 	. "syscall"
+
+	"hakurei.app/container/bits"
 )
 
-type FilterPreset int
-
-const (
-	// PresetExt are project-specific extensions.
-	PresetExt FilterPreset = 1 << iota
-	// PresetDenyNS denies namespace setup syscalls.
-	PresetDenyNS
-	// PresetDenyTTY denies faking input.
-	PresetDenyTTY
-	// PresetDenyDevel denies development-related syscalls.
-	PresetDenyDevel
-	// PresetLinux32 sets PER_LINUX32.
-	PresetLinux32
-)
-
-func Preset(presets FilterPreset, flags ExportFlag) (rules []NativeRule) {
+func Preset(presets bits.FilterPreset, flags ExportFlag) (rules []NativeRule) {
 	allowedPersonality := PER_LINUX
-	if presets&PresetLinux32 != 0 {
+	if presets&bits.PresetLinux32 != 0 {
 		allowedPersonality = PER_LINUX32
 	}
 	presetDevelFinal := presetDevel(ScmpDatum(allowedPersonality))
 
 	l := len(presetCommon)
-	if presets&PresetDenyNS != 0 {
+	if presets&bits.PresetDenyNS != 0 {
 		l += len(presetNamespace)
 	}
-	if presets&PresetDenyTTY != 0 {
+	if presets&bits.PresetDenyTTY != 0 {
 		l += len(presetTTY)
 	}
-	if presets&PresetDenyDevel != 0 {
+	if presets&bits.PresetDenyDevel != 0 {
 		l += len(presetDevelFinal)
 	}
 	if flags&AllowMultiarch == 0 {
 		l += len(presetEmu)
 	}
-	if presets&PresetExt != 0 {
+	if presets&bits.PresetExt != 0 {
 		l += len(presetCommonExt)
-		if presets&PresetDenyNS != 0 {
+		if presets&bits.PresetDenyNS != 0 {
 			l += len(presetNamespaceExt)
 		}
 		if flags&AllowMultiarch == 0 {
@@ -53,21 +40,21 @@ func Preset(presets FilterPreset, flags ExportFlag) (rules []NativeRule) {
 
 	rules = make([]NativeRule, 0, l)
 	rules = append(rules, presetCommon...)
-	if presets&PresetDenyNS != 0 {
+	if presets&bits.PresetDenyNS != 0 {
 		rules = append(rules, presetNamespace...)
 	}
-	if presets&PresetDenyTTY != 0 {
+	if presets&bits.PresetDenyTTY != 0 {
 		rules = append(rules, presetTTY...)
 	}
-	if presets&PresetDenyDevel != 0 {
+	if presets&bits.PresetDenyDevel != 0 {
 		rules = append(rules, presetDevelFinal...)
 	}
 	if flags&AllowMultiarch == 0 {
 		rules = append(rules, presetEmu...)
 	}
-	if presets&PresetExt != 0 {
+	if presets&bits.PresetExt != 0 {
 		rules = append(rules, presetCommonExt...)
-		if presets&PresetDenyNS != 0 {
+		if presets&bits.PresetDenyNS != 0 {
 			rules = append(rules, presetNamespaceExt...)
 		}
 		if flags&AllowMultiarch == 0 {

container/seccomp/proc.go

@@ -8,10 +8,6 @@ import (
 	"hakurei.app/helper/proc"
 )
 
-const (
-	PresetStrict = PresetExt | PresetDenyNS | PresetDenyTTY | PresetDenyDevel
-)
-
 // New returns an inactive Encoder instance.
 func New(rules []NativeRule, flags ExportFlag) *Encoder { return &Encoder{newExporter(rules, flags)} }
 

container/sysctl.go

@@ -2,10 +2,11 @@ package container
 
 import (
 	"bytes"
-	"log"
 	"os"
 	"strconv"
 	"sync"
+
+	"hakurei.app/container/fhs"
 )
 
 var (
@@ -17,31 +18,33 @@ var (
 )
 
 const (
-	kernelOverflowuidPath = FHSProcSys + "kernel/overflowuid"
-	kernelOverflowgidPath = FHSProcSys + "kernel/overflowgid"
-	kernelCapLastCapPath  = FHSProcSys + "kernel/cap_last_cap"
+	kernelOverflowuidPath = fhs.ProcSys + "kernel/overflowuid"
+	kernelOverflowgidPath = fhs.ProcSys + "kernel/overflowgid"
+	kernelCapLastCapPath  = fhs.ProcSys + "kernel/cap_last_cap"
 )
 
-func mustReadSysctl() {
-	if v, err := os.ReadFile(kernelOverflowuidPath); err != nil {
-		log.Fatalf("cannot read %q: %v", kernelOverflowuidPath, err)
-	} else if kernelOverflowuid, err = strconv.Atoi(string(bytes.TrimSpace(v))); err != nil {
-		log.Fatalf("cannot interpret %q: %v", kernelOverflowuidPath, err)
-	}
+func mustReadSysctl(msg Msg) {
+	sysctlOnce.Do(func() {
+		if v, err := os.ReadFile(kernelOverflowuidPath); err != nil {
+			msg.GetLogger().Fatalf("cannot read %q: %v", kernelOverflowuidPath, err)
+		} else if kernelOverflowuid, err = strconv.Atoi(string(bytes.TrimSpace(v))); err != nil {
+			msg.GetLogger().Fatalf("cannot interpret %q: %v", kernelOverflowuidPath, err)
+		}
 
-	if v, err := os.ReadFile(kernelOverflowgidPath); err != nil {
-		log.Fatalf("cannot read %q: %v", kernelOverflowgidPath, err)
-	} else if kernelOverflowgid, err = strconv.Atoi(string(bytes.TrimSpace(v))); err != nil {
-		log.Fatalf("cannot interpret %q: %v", kernelOverflowgidPath, err)
-	}
+		if v, err := os.ReadFile(kernelOverflowgidPath); err != nil {
+			msg.GetLogger().Fatalf("cannot read %q: %v", kernelOverflowgidPath, err)
+		} else if kernelOverflowgid, err = strconv.Atoi(string(bytes.TrimSpace(v))); err != nil {
+			msg.GetLogger().Fatalf("cannot interpret %q: %v", kernelOverflowgidPath, err)
+		}
 
-	if v, err := os.ReadFile(kernelCapLastCapPath); err != nil {
-		log.Fatalf("cannot read %q: %v", kernelCapLastCapPath, err)
-	} else if kernelCapLastCap, err = strconv.Atoi(string(bytes.TrimSpace(v))); err != nil {
-		log.Fatalf("cannot interpret %q: %v", kernelCapLastCapPath, err)
-	}
+		if v, err := os.ReadFile(kernelCapLastCapPath); err != nil {
+			msg.GetLogger().Fatalf("cannot read %q: %v", kernelCapLastCapPath, err)
+		} else if kernelCapLastCap, err = strconv.Atoi(string(bytes.TrimSpace(v))); err != nil {
+			msg.GetLogger().Fatalf("cannot interpret %q: %v", kernelCapLastCapPath, err)
+		}
+	})
 }
 
-func OverflowUid() int { sysctlOnce.Do(mustReadSysctl); return kernelOverflowuid }
-func OverflowGid() int { sysctlOnce.Do(mustReadSysctl); return kernelOverflowgid }
-func LastCap() uintptr { sysctlOnce.Do(mustReadSysctl); return uintptr(kernelCapLastCap) }
+func OverflowUid(msg Msg) int { mustReadSysctl(msg); return kernelOverflowuid }
+func OverflowGid(msg Msg) int { mustReadSysctl(msg); return kernelOverflowgid }
+func LastCap(msg Msg) uintptr { mustReadSysctl(msg); return uintptr(kernelCapLastCap) }

dist/comp/_hakurei

@@ -54,8 +54,8 @@ __hakurei_instances() {
 {
   local -a _hakurei_cmds
   _hakurei_cmds=(
-    "app:Load app from configuration file"
-    "run:Configure and start a permissive default sandbox"
+    "app:Load and start container from configuration file"
+    "run:Configure and start a permissive container"
     "show:Show live or local app configuration"
     "ps:List active instances"
     "version:Display version information"

dist/install.sh

@@ -4,7 +4,7 @@ cd "$(dirname -- "$0")" || exit 1
 install -vDm0755 "bin/hakurei" "${HAKUREI_INSTALL_PREFIX}/usr/bin/hakurei"
 install -vDm0755 "bin/hpkg" "${HAKUREI_INSTALL_PREFIX}/usr/bin/hpkg"
 
-install -vDm6511 "bin/hsu" "${HAKUREI_INSTALL_PREFIX}/usr/bin/hsu"
+install -vDm4511 "bin/hsu" "${HAKUREI_INSTALL_PREFIX}/usr/bin/hsu"
 if [ ! -f "${HAKUREI_INSTALL_PREFIX}/etc/hsurc" ]; then
     install -vDm0400 "hsurc.default" "${HAKUREI_INSTALL_PREFIX}/etc/hsurc"
 fi

helper/container.go

@@ -10,13 +10,15 @@ import (
 	"sync"
 
 	"hakurei.app/container"
+	"hakurei.app/container/check"
 	"hakurei.app/helper/proc"
 )
 
 // New initialises a Helper instance with wt as the null-terminated argument writer.
 func New(
 	ctx context.Context,
-	pathname *container.Absolute, name string,
+	msg container.Msg,
+	pathname *check.Absolute, name string,
 	wt io.WriterTo,
 	stat bool,
 	argF func(argsFd, statFd int) []string,
@@ -26,7 +28,7 @@ func New(
 	var args []string
 	h := new(helperContainer)
 	h.helperFiles, args = newHelperFiles(ctx, wt, stat, argF, extraFiles)
-	h.Container = container.NewCommand(ctx, pathname, name, args...)
+	h.Container = container.NewCommand(ctx, msg, pathname, name, args...)
 	h.WaitDelay = WaitDelay
 	if cmdF != nil {
 		cmdF(h.Container)

helper/container_test.go

@@ -7,12 +7,14 @@ import (
 	"testing"
 
 	"hakurei.app/container"
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 	"hakurei.app/helper"
 )
 
 func TestContainer(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)
+		h := helper.New(t.Context(), nil, check.MustAbs(container.Nonexistent), "hakurei", argsWt, false, argF, nil, nil)
 
 		wantErr := "container: starting an invalid container"
 		if err := h.Start(); err == nil || err.Error() != wantErr {
@@ -22,7 +24,7 @@ func TestContainer(t *testing.T) {
 	})
 
 	t.Run("valid new helper nil check", func(t *testing.T) {
-		if got := helper.New(t.Context(), container.MustAbs(container.Nonexistent), "hakurei", argsWt, false, argF, nil, nil); got == nil {
+		if got := helper.New(t.Context(), nil, check.MustAbs(container.Nonexistent), "hakurei", argsWt, false, argF, nil, nil); got == nil {
 			t.Errorf("New(%q, %q) got nil",
 				argsWt, "hakurei")
 			return
@@ -31,12 +33,12 @@ func TestContainer(t *testing.T) {
 
 	t.Run("implementation compliance", func(t *testing.T) {
 		testHelper(t, func(ctx context.Context, setOutput func(stdoutP, stderrP *io.Writer), stat bool) helper.Helper {
-			return helper.New(ctx, container.MustAbs(os.Args[0]), "helper", argsWt, stat, argF, func(z *container.Container) {
+			return helper.New(ctx, nil, check.MustAbs(os.Args[0]), "helper", argsWt, stat, argF, func(z *container.Container) {
 				setOutput(&z.Stdout, &z.Stderr)
 				z.
-					Bind(container.AbsFHSRoot, container.AbsFHSRoot, 0).
-					Proc(container.AbsFHSProc).
-					Dev(container.AbsFHSDev, true)
+					Bind(fhs.AbsRoot, fhs.AbsRoot, 0).
+					Proc(fhs.AbsProc).
+					Dev(fhs.AbsDev, true)
 			}, nil)
 		})
 	})

helper/proc/files.go

@@ -6,11 +6,18 @@ import (
 	"os/exec"
 	"sync/atomic"
 	"syscall"
+	"testing"
 	"time"
 )
 
 var FulfillmentTimeout = 2 * time.Second
 
+func init() {
+	if testing.Testing() {
+		FulfillmentTimeout *= 10
+	}
+}
+
 // A File is an extra file with deferred initialisation.
 type File interface {
 	// Init initialises File state. Init must not be called more than once.

helper/stub_test.go

@@ -6,12 +6,10 @@ import (
 
 	"hakurei.app/container"
 	"hakurei.app/helper"
-	"hakurei.app/internal"
-	"hakurei.app/internal/hlog"
 )
 
 func TestMain(m *testing.M) {
-	container.TryArgv0(hlog.Output{}, hlog.Prepare, internal.InstallOutput)
+	container.TryArgv0(nil)
 	helper.InternalHelperStub()
 	os.Exit(m.Run())
 }

hst/config.go

@@ -1,112 +1,178 @@
 package hst
 
 import (
+	"errors"
+	"strconv"
 	"time"
 
-	"hakurei.app/container"
-	"hakurei.app/container/seccomp"
-	"hakurei.app/system/dbus"
+	"hakurei.app/container/check"
 )
 
 const Tmp = "/.hakurei"
 
-var AbsTmp = container.MustAbs(Tmp)
+var AbsTmp = check.MustAbs(Tmp)
+
+const (
+	// WaitDelayDefault is used when WaitDelay has its zero value.
+	WaitDelayDefault = 5 * time.Second
+	// WaitDelayMax is used if WaitDelay exceeds its value.
+	WaitDelayMax = 30 * time.Second
+
+	// IdentityMin is the minimum value of [Config.Identity]. This is enforced by cmd/hsu.
+	IdentityMin = 0
+	// IdentityMax is the maximum value of [Config.Identity]. This is enforced by cmd/hsu.
+	IdentityMax = 9999
+
+	// ShimExitRequest is returned when the priv side process requests shim exit.
+	ShimExitRequest = 254
+	// ShimExitOrphan is returned when the shim is orphaned before priv side delivers a signal.
+	ShimExitOrphan = 3
+)
 
-// Config is used to seal an app implementation.
 type (
+	// Config configures an application container, implemented in internal/app.
 	Config struct {
-		// reverse-DNS style arbitrary identifier string from config;
-		// passed to wayland security-context-v1 as application ID
-		// and used as part of defaults in dbus session proxy
+		// Reverse-DNS style configured arbitrary identifier string.
+		// Passed to wayland security-context-v1 and used as part of defaults in dbus session proxy.
 		ID string `json:"id"`
 
-		// absolute path to executable file
-		Path *container.Absolute `json:"path,omitempty"`
-		// final args passed to container init
-		Args []string `json:"args"`
-
-		// system services to make available in the container
+		// System services to make available in the container.
 		Enablements *Enablements `json:"enablements,omitempty"`
 
-		// session D-Bus proxy configuration;
-		// nil makes session bus proxy assume built-in defaults
-		SessionBus *dbus.Config `json:"session_bus,omitempty"`
-		// system D-Bus proxy configuration;
-		// nil disables system bus proxy
-		SystemBus *dbus.Config `json:"system_bus,omitempty"`
-		// direct access to wayland socket; when this gets set no attempt is made to attach security-context-v1
-		// and the bare socket is mounted to the sandbox
+		// Session D-Bus proxy configuration.
+		// If set to nil, session bus proxy assume built-in defaults.
+		SessionBus *BusConfig `json:"session_bus,omitempty"`
+		// System D-Bus proxy configuration.
+		// If set to nil, system bus proxy is disabled.
+		SystemBus *BusConfig `json:"system_bus,omitempty"`
+		// Direct access to wayland socket, no attempt is made to attach security-context-v1
+		// and the bare socket is made available to the container.
 		DirectWayland bool `json:"direct_wayland,omitempty"`
 
-		// passwd username in container, defaults to passwd name of target uid or chronos
-		Username string `json:"username,omitempty"`
-		// absolute path to shell
-		Shell *container.Absolute `json:"shell"`
-		// directory to enter and use as home in the container mount namespace
-		Home *container.Absolute `json:"home"`
-
-		// extra acl ops to perform before setuid
+		// Extra acl update ops to perform before setuid.
 		ExtraPerms []*ExtraPermConfig `json:"extra_perms,omitempty"`
 
-		// numerical application id, used for init user namespace credentials
+		// Numerical application id, passed to hsu, used to derive init user namespace credentials.
 		Identity int `json:"identity"`
-		// list of supplementary groups inherited by container processes
+		// Init user namespace supplementary groups inherited by all container processes.
 		Groups []string `json:"groups"`
 
-		// abstract container configuration baseline
+		// High level configuration applied to the underlying [container.Params].
 		Container *ContainerConfig `json:"container"`
 	}
 
-	// ContainerConfig describes the container configuration baseline to which the app implementation adds upon.
+	// ContainerConfig describes the container configuration to be applied to an underlying [container.Params].
 	ContainerConfig struct {
-		// container hostname
+		// Container UTS namespace hostname.
 		Hostname string `json:"hostname,omitempty"`
 
-		// duration to wait for after interrupting a container's initial process in nanoseconds;
-		// a negative value causes the container to be terminated immediately on cancellation
+		// Duration in nanoseconds to wait for after interrupting the initial process.
+		// Defaults to [WaitDelayDefault] if less than or equals to zero,
+		// or [WaitDelayMax] if greater than [WaitDelayMax].
 		WaitDelay time.Duration `json:"wait_delay,omitempty"`
 
-		// extra seccomp flags
-		SeccompFlags seccomp.ExportFlag `json:"seccomp_flags"`
-		// extra seccomp presets
-		SeccompPresets seccomp.FilterPreset `json:"seccomp_presets"`
-		// disable project-specific filter extensions
+		// Emit Flatpak-compatible seccomp filter programs.
 		SeccompCompat bool `json:"seccomp_compat,omitempty"`
-		// allow ptrace and friends
+		// Allow ptrace and friends.
 		Devel bool `json:"devel,omitempty"`
-		// allow userns creation in container
+		// Allow userns creation and container setup syscalls.
 		Userns bool `json:"userns,omitempty"`
-		// share host net namespace
+		// Share host net namespace.
 		HostNet bool `json:"host_net,omitempty"`
-		// share abstract unix socket scope
+		// Share abstract unix socket scope.
 		HostAbstract bool `json:"host_abstract,omitempty"`
-		// allow dangerous terminal I/O
+		// Allow dangerous terminal I/O (faking input).
 		Tty bool `json:"tty,omitempty"`
-		// allow multiarch
+		// Allow multiarch.
 		Multiarch bool `json:"multiarch,omitempty"`
 
-		// initial process environment variables
+		// Initial process environment variables.
 		Env map[string]string `json:"env"`
-		// 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
+
+		/* Map target user uid to privileged user uid in the container 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
+		// Mount /dev/ from the init mount namespace as-is in the container mount namespace.
 		Device bool `json:"device,omitempty"`
-		// container mount points;
-		// if the first element targets /, it is inserted early and excluded from path hiding
+
+		/* Container mount points.
+
+		If the first element targets /, it is inserted early and excluded from path hiding. */
 		Filesystem []FilesystemConfigJSON `json:"filesystem"`
+
+		// String used as the username of the emulated user, validated against the default NAME_REGEX from adduser.
+		// Defaults to passwd name of target uid or chronos.
+		Username string `json:"username,omitempty"`
+		// Pathname of shell in the container filesystem to use for the emulated user.
+		Shell *check.Absolute `json:"shell"`
+		// Directory in the container filesystem to enter and use as the home directory of the emulated user.
+		Home *check.Absolute `json:"home"`
+
+		// Pathname to executable file in the container filesystem.
+		Path *check.Absolute `json:"path,omitempty"`
+		// Final args passed to the initial program.
+		Args []string `json:"args"`
 	}
 )
 
+var (
+	// ErrConfigNull is returned by [Config.Validate] for an invalid configuration that contains a null value for any
+	// field that must not be null.
+	ErrConfigNull = errors.New("unexpected null in config")
+
+	// ErrIdentityBounds is returned by [Config.Validate] for an out of bounds [Config.Identity] value.
+	ErrIdentityBounds = errors.New("identity out of bounds")
+)
+
+// Validate checks [Config] and returns [AppError] if an invalid value is encountered.
+func (config *Config) Validate() error {
+	if config == nil {
+		return &AppError{Step: "validate configuration", Err: ErrConfigNull,
+			Msg: "invalid configuration"}
+	}
+
+	// this is checked again in hsu
+	if config.Identity < IdentityMin || config.Identity > IdentityMax {
+		return &AppError{Step: "validate configuration", Err: ErrIdentityBounds,
+			Msg: "identity " + strconv.Itoa(config.Identity) + " out of range"}
+	}
+
+	if err := config.SessionBus.CheckInterfaces("session"); err != nil {
+		return err
+	}
+	if err := config.SystemBus.CheckInterfaces("system"); err != nil {
+		return err
+	}
+
+	if config.Container == nil {
+		return &AppError{Step: "validate configuration", Err: ErrConfigNull,
+			Msg: "configuration missing container state"}
+	}
+	if config.Container.Home == nil {
+		return &AppError{Step: "validate configuration", Err: ErrConfigNull,
+			Msg: "container configuration missing path to home directory"}
+	}
+	if config.Container.Shell == nil {
+		return &AppError{Step: "validate configuration", Err: ErrConfigNull,
+			Msg: "container configuration missing path to shell"}
+	}
+	if config.Container.Path == nil {
+		return &AppError{Step: "validate configuration", Err: ErrConfigNull,
+			Msg: "container configuration missing path to initial program"}
+	}
+	return nil
+}
+
 // ExtraPermConfig describes an acl update op.
 type ExtraPermConfig struct {
-	Ensure  bool                `json:"ensure,omitempty"`
-	Path    *container.Absolute `json:"path"`
-	Read    bool                `json:"r,omitempty"`
-	Write   bool                `json:"w,omitempty"`
-	Execute bool                `json:"x,omitempty"`
+	Ensure  bool            `json:"ensure,omitempty"`
+	Path    *check.Absolute `json:"path"`
+	Read    bool            `json:"r,omitempty"`
+	Write   bool            `json:"w,omitempty"`
+	Execute bool            `json:"x,omitempty"`
 }
 
 func (e *ExtraPermConfig) String() string {

hst/config_test.go

@@ -1,12 +1,57 @@
 package hst_test
 
 import (
+	"reflect"
 	"testing"
 
-	"hakurei.app/container"
+	"hakurei.app/container/fhs"
 	"hakurei.app/hst"
 )
 
+func TestConfigValidate(t *testing.T) {
+	testCases := []struct {
+		name    string
+		config  *hst.Config
+		wantErr error
+	}{
+		{"nil", nil, &hst.AppError{Step: "validate configuration", Err: hst.ErrConfigNull,
+			Msg: "invalid configuration"}},
+		{"identity lower", &hst.Config{Identity: -1}, &hst.AppError{Step: "validate configuration", Err: hst.ErrIdentityBounds,
+			Msg: "identity -1 out of range"}},
+		{"identity upper", &hst.Config{Identity: 10000}, &hst.AppError{Step: "validate configuration", Err: hst.ErrIdentityBounds,
+			Msg: "identity 10000 out of range"}},
+		{"dbus session", &hst.Config{SessionBus: &hst.BusConfig{See: []string{""}}},
+			&hst.BadInterfaceError{Interface: "", Segment: "session"}},
+		{"dbus system", &hst.Config{SystemBus: &hst.BusConfig{See: []string{""}}},
+			&hst.BadInterfaceError{Interface: "", Segment: "system"}},
+		{"container", &hst.Config{}, &hst.AppError{Step: "validate configuration", Err: hst.ErrConfigNull,
+			Msg: "configuration missing container state"}},
+		{"home", &hst.Config{Container: &hst.ContainerConfig{}}, &hst.AppError{Step: "validate configuration", Err: hst.ErrConfigNull,
+			Msg: "container configuration missing path to home directory"}},
+		{"shell", &hst.Config{Container: &hst.ContainerConfig{
+			Home: fhs.AbsTmp,
+		}}, &hst.AppError{Step: "validate configuration", Err: hst.ErrConfigNull,
+			Msg: "container configuration missing path to shell"}},
+		{"path", &hst.Config{Container: &hst.ContainerConfig{
+			Home:  fhs.AbsTmp,
+			Shell: fhs.AbsTmp,
+		}}, &hst.AppError{Step: "validate configuration", Err: hst.ErrConfigNull,
+			Msg: "container configuration missing path to initial program"}},
+		{"valid", &hst.Config{Container: &hst.ContainerConfig{
+			Home:  fhs.AbsTmp,
+			Shell: fhs.AbsTmp,
+			Path:  fhs.AbsTmp,
+		}}, nil},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if err := tc.config.Validate(); !reflect.DeepEqual(err, tc.wantErr) {
+				t.Errorf("Validate: error = %#v, want %#v", err, tc.wantErr)
+			}
+		})
+	}
+}
+
 func TestExtraPermConfig(t *testing.T) {
 	testCases := []struct {
 		name   string
@@ -15,14 +60,14 @@ func TestExtraPermConfig(t *testing.T) {
 	}{
 		{"nil", nil, "<invalid>"},
 		{"nil path", &hst.ExtraPermConfig{Path: nil}, "<invalid>"},
-		{"r", &hst.ExtraPermConfig{Path: container.AbsFHSRoot, Read: true}, "r--:/"},
-		{"r+", &hst.ExtraPermConfig{Ensure: true, Path: container.AbsFHSRoot, Read: true}, "r--+:/"},
+		{"r", &hst.ExtraPermConfig{Path: fhs.AbsRoot, Read: true}, "r--:/"},
+		{"r+", &hst.ExtraPermConfig{Ensure: true, Path: fhs.AbsRoot, Read: true}, "r--+:/"},
 		{"w", &hst.ExtraPermConfig{Path: hst.AbsTmp, Write: true}, "-w-:/.hakurei"},
 		{"w+", &hst.ExtraPermConfig{Ensure: true, Path: hst.AbsTmp, Write: true}, "-w-+:/.hakurei"},
-		{"x", &hst.ExtraPermConfig{Path: container.AbsFHSRunUser, Execute: true}, "--x:/run/user/"},
-		{"x+", &hst.ExtraPermConfig{Ensure: true, Path: container.AbsFHSRunUser, Execute: true}, "--x+:/run/user/"},
-		{"rwx", &hst.ExtraPermConfig{Path: container.AbsFHSTmp, Read: true, Write: true, Execute: true}, "rwx:/tmp/"},
-		{"rwx+", &hst.ExtraPermConfig{Ensure: true, Path: container.AbsFHSTmp, Read: true, Write: true, Execute: true}, "rwx+:/tmp/"},
+		{"x", &hst.ExtraPermConfig{Path: fhs.AbsRunUser, Execute: true}, "--x:/run/user/"},
+		{"x+", &hst.ExtraPermConfig{Ensure: true, Path: fhs.AbsRunUser, Execute: true}, "--x+:/run/user/"},
+		{"rwx", &hst.ExtraPermConfig{Path: fhs.AbsTmp, Read: true, Write: true, Execute: true}, "rwx:/tmp/"},
+		{"rwx+", &hst.ExtraPermConfig{Ensure: true, Path: fhs.AbsTmp, Read: true, Write: true, Execute: true}, "rwx+:/tmp/"},
 	}
 
 	for _, tc := range testCases {

hst/dbus.go

@@ -0,0 +1,109 @@
+package hst
+
+import (
+	"strconv"
+	"strings"
+)
+
+// BadInterfaceError is returned when Interface fails an undocumented check in xdg-dbus-proxy,
+// which would have cause a silent failure.
+type BadInterfaceError struct {
+	// Interface is the offending interface string.
+	Interface string
+	// Segment is passed through from the [BusConfig.CheckInterfaces] argument.
+	Segment string
+}
+
+func (e *BadInterfaceError) Message() string { return e.Error() }
+func (e *BadInterfaceError) Error() string {
+	if e == nil {
+		return "<nil>"
+	}
+	return "bad interface string " + strconv.Quote(e.Interface) + " in " + e.Segment + " bus configuration"
+}
+
+// BusConfig configures the xdg-dbus-proxy process.
+type BusConfig struct {
+	// See set 'see' policy for NAME (--see=NAME)
+	See []string `json:"see"`
+	// Talk set 'talk' policy for NAME (--talk=NAME)
+	Talk []string `json:"talk"`
+	// Own set 'own' policy for NAME (--own=NAME)
+	Own []string `json:"own"`
+
+	// Call set RULE for calls on NAME (--call=NAME=RULE)
+	Call map[string]string `json:"call"`
+	// Broadcast set RULE for broadcasts from NAME (--broadcast=NAME=RULE)
+	Broadcast map[string]string `json:"broadcast"`
+
+	// Log turn on logging (--log)
+	Log bool `json:"log,omitempty"`
+	// Filter enable filtering (--filter)
+	Filter bool `json:"filter"`
+}
+
+// Interfaces iterates over all interface strings specified in [BusConfig].
+func (c *BusConfig) Interfaces(yield func(string) bool) {
+	if c == nil {
+		return
+	}
+
+	for _, iface := range c.See {
+		if !yield(iface) {
+			return
+		}
+	}
+	for _, iface := range c.Talk {
+		if !yield(iface) {
+			return
+		}
+	}
+	for _, iface := range c.Own {
+		if !yield(iface) {
+			return
+		}
+	}
+
+	for iface := range c.Call {
+		if !yield(iface) {
+			return
+		}
+	}
+	for iface := range c.Broadcast {
+		if !yield(iface) {
+			return
+		}
+	}
+}
+
+// CheckInterfaces checks for invalid interface strings based on an undocumented check in xdg-dbus-error,
+// returning [BadInterfaceError] if one is encountered.
+func (c *BusConfig) CheckInterfaces(segment string) error {
+	if c == nil {
+		return nil
+	}
+
+	for iface := range c.Interfaces {
+		/*
+			xdg-dbus-proxy fails without output when this condition is not met:
+				char *dot = strrchr (filter->interface, '.');
+				if (dot != NULL)
+				  {
+				    *dot = 0;
+				    if (strcmp (dot + 1, "*") != 0)
+				      filter->member = g_strdup (dot + 1);
+				  }
+
+			trim ".*" since they are removed before searching for '.':
+				if (g_str_has_suffix (name, ".*"))
+				  {
+				    name[strlen (name) - 2] = 0;
+				    wildcard = TRUE;
+				  }
+		*/
+		if strings.IndexByte(strings.TrimSuffix(iface, ".*"), '.') == -1 {
+			return &BadInterfaceError{iface, segment}
+		}
+	}
+	return nil
+}

hst/dbus_test.go

@@ -0,0 +1,109 @@
+package hst_test
+
+import (
+	"reflect"
+	"slices"
+	"testing"
+
+	"hakurei.app/container"
+	"hakurei.app/hst"
+)
+
+func TestBadInterfaceError(t *testing.T) {
+	testCases := []struct {
+		name string
+		err  error
+		want string
+	}{
+		{"nil", (*hst.BadInterfaceError)(nil), "<nil>"},
+		{"session", &hst.BadInterfaceError{Interface: "\x00", Segment: "session"},
+			`bad interface string "\x00" in session bus configuration`},
+		{"system", &hst.BadInterfaceError{Interface: "\x01", Segment: "system"},
+			`bad interface string "\x01" in system bus configuration`},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if gotError := tc.err.Error(); gotError != tc.want {
+				t.Errorf("Error: %s, want %s", gotError, tc.want)
+			}
+			if gotMessage, ok := container.GetErrorMessage(tc.err); !ok {
+				t.Error("GetErrorMessage: ok = false")
+			} else if gotMessage != tc.want {
+				t.Errorf("GetErrorMessage: %s, want %s", gotMessage, tc.want)
+			}
+		})
+	}
+}
+
+func TestBusConfigInterfaces(t *testing.T) {
+	testCases := []struct {
+		name   string
+		c      *hst.BusConfig
+		cutoff int
+		want   []string
+	}{
+		{"nil", nil, 0, nil},
+		{"all", &hst.BusConfig{
+			See: []string{"see"}, Talk: []string{"talk"}, Own: []string{"own"},
+			Call:      map[string]string{"call": "unreachable"},
+			Broadcast: map[string]string{"broadcast": "unreachable"},
+		}, 0, []string{"see", "talk", "own", "call", "broadcast"}},
+
+		{"all cutoff", &hst.BusConfig{
+			See: []string{"see"}, Talk: []string{"talk"}, Own: []string{"own"},
+			Call:      map[string]string{"call": "unreachable"},
+			Broadcast: map[string]string{"broadcast": "unreachable"},
+		}, 3, []string{"see", "talk", "own"}},
+
+		{"cutoff see", &hst.BusConfig{See: []string{"see"}}, 1, []string{"see"}},
+		{"cutoff talk", &hst.BusConfig{Talk: []string{"talk"}}, 1, []string{"talk"}},
+		{"cutoff own", &hst.BusConfig{Own: []string{"own"}}, 1, []string{"own"}},
+		{"cutoff call", &hst.BusConfig{Call: map[string]string{"call": "unreachable"}}, 1, []string{"call"}},
+		{"cutoff broadcast", &hst.BusConfig{Broadcast: map[string]string{"broadcast": "unreachable"}}, 1, []string{"broadcast"}},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			var got []string
+			if tc.cutoff > 0 {
+				var i int
+				got = make([]string, 0, tc.cutoff)
+				for v := range tc.c.Interfaces {
+					i++
+					got = append(got, v)
+					if i == tc.cutoff {
+						break
+					}
+				}
+			} else {
+				got = slices.Collect(tc.c.Interfaces)
+			}
+
+			if !slices.Equal(got, tc.want) {
+				t.Errorf("Interfaces: %q, want %q", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestBusConfigCheckInterfaces(t *testing.T) {
+	testCases := []struct {
+		name string
+		c    *hst.BusConfig
+		err  error
+	}{
+		{"nil", nil, nil},
+		{"zero", &hst.BusConfig{See: []string{""}},
+			&hst.BadInterfaceError{Interface: "", Segment: "zero"}},
+		{"suffix", &hst.BusConfig{See: []string{".*"}},
+			&hst.BadInterfaceError{Interface: ".*", Segment: "suffix"}},
+		{"valid suffix", &hst.BusConfig{See: []string{"..*"}}, nil},
+		{"valid", &hst.BusConfig{See: []string{"."}}, nil},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if err := tc.c.CheckInterfaces(tc.name); !reflect.DeepEqual(err, tc.err) {
+				t.Errorf("CheckInterfaces: error = %#v, want %#v", err, tc.err)
+			}
+		})
+	}
+}

hst/enablement.go

@@ -2,15 +2,56 @@ package hst
 
 import (
 	"encoding/json"
+	"fmt"
+	"strings"
 	"syscall"
-
-	"hakurei.app/system"
 )
 
-// NewEnablements returns the address of [system.Enablement] as [Enablements].
-func NewEnablements(e system.Enablement) *Enablements { return (*Enablements)(&e) }
+// Enablement represents an optional host service to export to the target user.
+type Enablement byte
 
-// enablementsJSON is the [json] representation of the [system.Enablement] bit field.
+const (
+	EWayland Enablement = 1 << iota
+	EX11
+	EDBus
+	EPulse
+
+	EM
+)
+
+func (e Enablement) String() string {
+	switch e {
+	case 0:
+		return "(no enablements)"
+	case EWayland:
+		return "wayland"
+	case EX11:
+		return "x11"
+	case EDBus:
+		return "dbus"
+	case EPulse:
+		return "pulseaudio"
+	default:
+		buf := new(strings.Builder)
+		buf.Grow(32)
+
+		for i := Enablement(1); i < EM; i <<= 1 {
+			if e&i != 0 {
+				buf.WriteString(", " + i.String())
+			}
+		}
+
+		if buf.Len() == 0 {
+			return fmt.Sprintf("e%x", byte(e))
+		}
+		return strings.TrimPrefix(buf.String(), ", ")
+	}
+}
+
+// NewEnablements returns the address of [Enablement] as [Enablements].
+func NewEnablements(e Enablement) *Enablements { return (*Enablements)(&e) }
+
+// enablementsJSON is the [json] representation of the [Enablement] bit field.
 type enablementsJSON struct {
 	Wayland bool `json:"wayland,omitempty"`
 	X11     bool `json:"x11,omitempty"`
@@ -18,15 +59,15 @@ type enablementsJSON struct {
 	Pulse   bool `json:"pulse,omitempty"`
 }
 
-// Enablements is the [json] adapter for [system.Enablement].
-type Enablements system.Enablement
+// Enablements is the [json] adapter for [Enablement].
+type Enablements Enablement
 
-// Unwrap returns the underlying [system.Enablement].
-func (e *Enablements) Unwrap() system.Enablement {
+// Unwrap returns the underlying [Enablement].
+func (e *Enablements) Unwrap() Enablement {
 	if e == nil {
 		return 0
 	}
-	return system.Enablement(*e)
+	return Enablement(*e)
 }
 
 func (e *Enablements) MarshalJSON() ([]byte, error) {
@@ -34,10 +75,10 @@ func (e *Enablements) MarshalJSON() ([]byte, error) {
 		return nil, syscall.EINVAL
 	}
 	return json.Marshal(&enablementsJSON{
-		Wayland: system.Enablement(*e)&system.EWayland != 0,
-		X11:     system.Enablement(*e)&system.EX11 != 0,
-		DBus:    system.Enablement(*e)&system.EDBus != 0,
-		Pulse:   system.Enablement(*e)&system.EPulse != 0,
+		Wayland: Enablement(*e)&EWayland != 0,
+		X11:     Enablement(*e)&EX11 != 0,
+		DBus:    Enablement(*e)&EDBus != 0,
+		Pulse:   Enablement(*e)&EPulse != 0,
 	})
 }
 
@@ -51,18 +92,18 @@ func (e *Enablements) UnmarshalJSON(data []byte) error {
 		return err
 	}
 
-	var ve system.Enablement
+	var ve Enablement
 	if v.Wayland {
-		ve |= system.EWayland
+		ve |= EWayland
 	}
 	if v.X11 {
-		ve |= system.EX11
+		ve |= EX11
 	}
 	if v.DBus {
-		ve |= system.EDBus
+		ve |= EDBus
 	}
 	if v.Pulse {
-		ve |= system.EPulse
+		ve |= EPulse
 	}
 	*e = Enablements(ve)
 	return nil

hst/enablement_test.go

@@ -7,9 +7,44 @@ import (
 	"testing"
 
 	"hakurei.app/hst"
-	"hakurei.app/system"
 )
 
+func TestEnablementString(t *testing.T) {
+	testCases := []struct {
+		flags hst.Enablement
+		want  string
+	}{
+		{0, "(no enablements)"},
+		{hst.EWayland, "wayland"},
+		{hst.EX11, "x11"},
+		{hst.EDBus, "dbus"},
+		{hst.EPulse, "pulseaudio"},
+		{hst.EWayland | hst.EX11, "wayland, x11"},
+		{hst.EWayland | hst.EDBus, "wayland, dbus"},
+		{hst.EWayland | hst.EPulse, "wayland, pulseaudio"},
+		{hst.EX11 | hst.EDBus, "x11, dbus"},
+		{hst.EX11 | hst.EPulse, "x11, pulseaudio"},
+		{hst.EDBus | hst.EPulse, "dbus, pulseaudio"},
+		{hst.EWayland | hst.EX11 | hst.EDBus, "wayland, x11, dbus"},
+		{hst.EWayland | hst.EX11 | hst.EPulse, "wayland, x11, pulseaudio"},
+		{hst.EWayland | hst.EDBus | hst.EPulse, "wayland, dbus, pulseaudio"},
+		{hst.EX11 | hst.EDBus | hst.EPulse, "x11, dbus, pulseaudio"},
+		{hst.EWayland | hst.EX11 | hst.EDBus | hst.EPulse, "wayland, x11, dbus, pulseaudio"},
+
+		{1 << 5, "e20"},
+		{1 << 6, "e40"},
+		{1 << 7, "e80"},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.want, func(t *testing.T) {
+			if got := tc.flags.String(); got != tc.want {
+				t.Errorf("String: %q, want %q", got, tc.want)
+			}
+		})
+	}
+}
+
 func TestEnablements(t *testing.T) {
 	testCases := []struct {
 		name  string
@@ -19,11 +54,11 @@ func TestEnablements(t *testing.T) {
 	}{
 		{"nil", nil, "null", `{"value":null,"magic":3236757504}`},
 		{"zero", hst.NewEnablements(0), `{}`, `{"value":{},"magic":3236757504}`},
-		{"wayland", hst.NewEnablements(system.EWayland), `{"wayland":true}`, `{"value":{"wayland":true},"magic":3236757504}`},
-		{"x11", hst.NewEnablements(system.EX11), `{"x11":true}`, `{"value":{"x11":true},"magic":3236757504}`},
-		{"dbus", hst.NewEnablements(system.EDBus), `{"dbus":true}`, `{"value":{"dbus":true},"magic":3236757504}`},
-		{"pulse", hst.NewEnablements(system.EPulse), `{"pulse":true}`, `{"value":{"pulse":true},"magic":3236757504}`},
-		{"all", hst.NewEnablements(system.EWayland | system.EX11 | system.EDBus | system.EPulse), `{"wayland":true,"x11":true,"dbus":true,"pulse":true}`, `{"value":{"wayland":true,"x11":true,"dbus":true,"pulse":true},"magic":3236757504}`},
+		{"wayland", hst.NewEnablements(hst.EWayland), `{"wayland":true}`, `{"value":{"wayland":true},"magic":3236757504}`},
+		{"x11", hst.NewEnablements(hst.EX11), `{"x11":true}`, `{"value":{"x11":true},"magic":3236757504}`},
+		{"dbus", hst.NewEnablements(hst.EDBus), `{"dbus":true}`, `{"value":{"dbus":true},"magic":3236757504}`},
+		{"pulse", hst.NewEnablements(hst.EPulse), `{"pulse":true}`, `{"value":{"pulse":true},"magic":3236757504}`},
+		{"all", hst.NewEnablements(hst.EWayland | hst.EX11 | hst.EDBus | hst.EPulse), `{"wayland":true,"x11":true,"dbus":true,"pulse":true}`, `{"value":{"wayland":true,"x11":true,"dbus":true,"pulse":true},"magic":3236757504}`},
 	}
 
 	for _, tc := range testCases {
@@ -88,7 +123,7 @@ func TestEnablements(t *testing.T) {
 		})
 
 		t.Run("val", func(t *testing.T) {
-			if got := hst.NewEnablements(system.EWayland | system.EPulse).Unwrap(); got != system.EWayland|system.EPulse {
+			if got := hst.NewEnablements(hst.EWayland | hst.EPulse).Unwrap(); got != hst.EWayland|hst.EPulse {
 				t.Errorf("Unwrap: %v", got)
 			}
 		})

hst/fs.go

@@ -4,9 +4,10 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"os"
 	"reflect"
 
-	"hakurei.app/container"
+	"hakurei.app/container/check"
 )
 
 // FilesystemConfig is an abstract representation of a mount point.
@@ -14,21 +15,44 @@ type FilesystemConfig interface {
 	// Valid returns whether the configuration is valid.
 	Valid() bool
 	// Path returns the target path in the container.
-	Path() *container.Absolute
+	Path() *check.Absolute
 	// Host returns a slice of all host paths used by this operation.
-	Host() []*container.Absolute
+	Host() []*check.Absolute
 	// Apply appends the [container.Op] implementing this operation.
 	Apply(z *ApplyState)
 
 	fmt.Stringer
 }
 
+// The Ops interface enables [FilesystemConfig] to queue container ops without depending on the container package.
+type Ops interface {
+	// Tmpfs appends an op that mounts tmpfs on a container path.
+	Tmpfs(target *check.Absolute, size int, perm os.FileMode) Ops
+	// Readonly appends an op that mounts read-only tmpfs on a container path.
+	Readonly(target *check.Absolute, perm os.FileMode) Ops
+
+	// Bind appends an op that bind mounts a host path on a container path.
+	Bind(source, target *check.Absolute, flags int) Ops
+	// Overlay appends an op that mounts the overlay pseudo filesystem.
+	Overlay(target, state, work *check.Absolute, layers ...*check.Absolute) Ops
+	// OverlayReadonly appends an op that mounts the overlay pseudo filesystem readonly.
+	OverlayReadonly(target *check.Absolute, layers ...*check.Absolute) Ops
+
+	// Link appends an op that creates a symlink in the container filesystem.
+	Link(target *check.Absolute, linkName string, dereference bool) Ops
+
+	// Root appends an op that expands a directory into a toplevel bind mount mirror on container root.
+	Root(host *check.Absolute, flags int) Ops
+	// Etc appends an op that expands host /etc into a toplevel symlink mirror with /etc semantics.
+	Etc(host *check.Absolute, prefix string) Ops
+}
+
 // ApplyState holds the address of [container.Ops] and any relevant application state.
 type ApplyState struct {
 	// AutoEtcPrefix is the prefix for [container.AutoEtcOp].
 	AutoEtcPrefix string
 
-	*container.Ops
+	Ops
 }
 
 var (

hst/fs_test.go

@@ -3,12 +3,14 @@ package hst_test
 import (
 	"encoding/json"
 	"errors"
+	"os"
 	"reflect"
 	"strings"
 	"syscall"
 	"testing"
 
 	"hakurei.app/container"
+	"hakurei.app/container/check"
 	"hakurei.app/hst"
 )
 
@@ -216,11 +218,11 @@ type stubFS struct {
 	typeName string
 }
 
-func (s stubFS) Valid() bool                 { return false }
-func (s stubFS) Path() *container.Absolute   { panic("unreachable") }
-func (s stubFS) Host() []*container.Absolute { panic("unreachable") }
-func (s stubFS) Apply(*hst.ApplyState)       { panic("unreachable") }
-func (s stubFS) String() string              { return "<invalid " + s.typeName + ">" }
+func (s stubFS) Valid() bool             { return false }
+func (s stubFS) Path() *check.Absolute   { panic("unreachable") }
+func (s stubFS) Host() []*check.Absolute { panic("unreachable") }
+func (s stubFS) Apply(*hst.ApplyState)   { panic("unreachable") }
+func (s stubFS) String() string          { return "<invalid " + s.typeName + ">" }
 
 type sCheck struct {
 	FS    hst.FilesystemConfigJSON `json:"fs"`
@@ -232,8 +234,8 @@ type fsTestCase struct {
 	fs    hst.FilesystemConfig
 	valid bool
 	ops   container.Ops
-	path  *container.Absolute
-	host  []*container.Absolute
+	path  *check.Absolute
+	host  []*check.Absolute
 	str   string
 }
 
@@ -248,7 +250,7 @@ func checkFs(t *testing.T, testCases []fsTestCase) {
 
 			t.Run("ops", func(t *testing.T) {
 				ops := new(container.Ops)
-				tc.fs.Apply(&hst.ApplyState{AutoEtcPrefix: ":3", Ops: ops})
+				tc.fs.Apply(&hst.ApplyState{AutoEtcPrefix: ":3", Ops: opsAdapter{ops}})
 				if !reflect.DeepEqual(ops, &tc.ops) {
 					gotString := new(strings.Builder)
 					for _, op := range *ops {
@@ -287,11 +289,45 @@ func checkFs(t *testing.T, testCases []fsTestCase) {
 	}
 }
 
-func m(pathname string) *container.Absolute { return container.MustAbs(pathname) }
-func ms(pathnames ...string) []*container.Absolute {
-	as := make([]*container.Absolute, len(pathnames))
+type opsAdapter struct{ *container.Ops }
+
+func (p opsAdapter) Tmpfs(target *check.Absolute, size int, perm os.FileMode) hst.Ops {
+	return opsAdapter{p.Ops.Tmpfs(target, size, perm)}
+}
+
+func (p opsAdapter) Readonly(target *check.Absolute, perm os.FileMode) hst.Ops {
+	return opsAdapter{p.Ops.Readonly(target, perm)}
+}
+
+func (p opsAdapter) Bind(source, target *check.Absolute, flags int) hst.Ops {
+	return opsAdapter{p.Ops.Bind(source, target, flags)}
+}
+
+func (p opsAdapter) Overlay(target, state, work *check.Absolute, layers ...*check.Absolute) hst.Ops {
+	return opsAdapter{p.Ops.Overlay(target, state, work, layers...)}
+}
+
+func (p opsAdapter) OverlayReadonly(target *check.Absolute, layers ...*check.Absolute) hst.Ops {
+	return opsAdapter{p.Ops.OverlayReadonly(target, layers...)}
+}
+
+func (p opsAdapter) Link(target *check.Absolute, linkName string, dereference bool) hst.Ops {
+	return opsAdapter{p.Ops.Link(target, linkName, dereference)}
+}
+
+func (p opsAdapter) Root(host *check.Absolute, flags int) hst.Ops {
+	return opsAdapter{p.Ops.Root(host, flags)}
+}
+
+func (p opsAdapter) Etc(host *check.Absolute, prefix string) hst.Ops {
+	return opsAdapter{p.Ops.Etc(host, prefix)}
+}
+
+func m(pathname string) *check.Absolute { return check.MustAbs(pathname) }
+func ms(pathnames ...string) []*check.Absolute {
+	as := make([]*check.Absolute, len(pathnames))
 	for i, pathname := range pathnames {
-		as[i] = container.MustAbs(pathname)
+		as[i] = check.MustAbs(pathname)
 	}
 	return as
 }

hst/fsbind.go

@@ -4,7 +4,9 @@ import (
 	"encoding/gob"
 	"strings"
 
-	"hakurei.app/container"
+	"hakurei.app/container/bits"
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 )
 
 func init() { gob.Register(new(FSBind)) }
@@ -15,9 +17,9 @@ const FilesystemBind = "bind"
 // FSBind represents a host to container bind mount.
 type FSBind struct {
 	// mount point in container, same as Source if empty
-	Target *container.Absolute `json:"dst,omitempty"`
+	Target *check.Absolute `json:"dst,omitempty"`
 	// host filesystem path to make available to the container
-	Source *container.Absolute `json:"src"`
+	Source *check.Absolute `json:"src"`
 	// do not mount Target read-only
 	Write bool `json:"write,omitempty"`
 	// do not disable device files on Target, implies Write
@@ -28,19 +30,19 @@ type FSBind struct {
 	Optional bool `json:"optional,omitempty"`
 
 	// enable special behaviour:
-	// for autoroot, Target must be set to [container.AbsFHSRoot];
-	// for autoetc, Target must be set to [container.AbsFHSEtc]
+	// for autoroot, Target must be set to [fhs.AbsRoot];
+	// for autoetc, Target must be set to [fhs.AbsEtc]
 	Special bool `json:"special,omitempty"`
 }
 
 // IsAutoRoot returns whether this FSBind has autoroot behaviour enabled.
 func (b *FSBind) IsAutoRoot() bool {
-	return b.Valid() && b.Special && b.Target.String() == container.FHSRoot
+	return b.Valid() && b.Special && b.Target.String() == fhs.Root
 }
 
 // IsAutoEtc returns whether this FSBind has autoetc behaviour enabled.
 func (b *FSBind) IsAutoEtc() bool {
-	return b.Valid() && b.Special && b.Target.String() == container.FHSEtc
+	return b.Valid() && b.Special && b.Target.String() == fhs.Etc
 }
 
 func (b *FSBind) Valid() bool {
@@ -55,7 +57,7 @@ func (b *FSBind) Valid() bool {
 			return false
 		} else {
 			switch b.Target.String() {
-			case container.FHSRoot, container.FHSEtc:
+			case fhs.Root, fhs.Etc:
 				break
 
 			default:
@@ -66,7 +68,7 @@ func (b *FSBind) Valid() bool {
 	return true
 }
 
-func (b *FSBind) Path() *container.Absolute {
+func (b *FSBind) Path() *check.Absolute {
 	if !b.Valid() {
 		return nil
 	}
@@ -76,11 +78,11 @@ func (b *FSBind) Path() *container.Absolute {
 	return b.Target
 }
 
-func (b *FSBind) Host() []*container.Absolute {
+func (b *FSBind) Host() []*check.Absolute {
 	if !b.Valid() {
 		return nil
 	}
-	return []*container.Absolute{b.Source}
+	return []*check.Absolute{b.Source}
 }
 
 func (b *FSBind) Apply(z *ApplyState) {
@@ -94,16 +96,16 @@ func (b *FSBind) Apply(z *ApplyState) {
 	}
 	var flags int
 	if b.Write {
-		flags |= container.BindWritable
+		flags |= bits.BindWritable
 	}
 	if b.Device {
-		flags |= container.BindDevice | container.BindWritable
+		flags |= bits.BindDevice | bits.BindWritable
 	}
 	if b.Ensure {
-		flags |= container.BindEnsure
+		flags |= bits.BindEnsure
 	}
 	if b.Optional {
-		flags |= container.BindOptional
+		flags |= bits.BindOptional
 	}
 
 	switch {
@@ -137,7 +139,7 @@ func (b *FSBind) String() string {
 			if flagSym != "" {
 				prefix += ":" + flagSym
 			}
-			if b.Source.String() != container.FHSRoot {
+			if b.Source.String() != fhs.Root {
 				return prefix + ":" + b.Source.String()
 			}
 			return prefix

hst/fsbind_test.go

@@ -4,6 +4,7 @@ import (
 	"testing"
 
 	"hakurei.app/container"
+	"hakurei.app/container/bits"
 	"hakurei.app/hst"
 )
 
@@ -21,7 +22,7 @@ func TestFSBind(t *testing.T) {
 		}, true, container.Ops{&container.BindMountOp{
 			Source: m("/mnt/dev"),
 			Target: m("/dev"),
-			Flags:  container.BindWritable | container.BindDevice | container.BindOptional,
+			Flags:  bits.BindWritable | bits.BindDevice | bits.BindOptional,
 		}}, m("/dev"), ms("/mnt/dev"),
 			"d+/mnt/dev:/dev"},
 
@@ -33,7 +34,7 @@ func TestFSBind(t *testing.T) {
 		}, true, container.Ops{&container.BindMountOp{
 			Source: m("/mnt/dev"),
 			Target: m("/dev"),
-			Flags:  container.BindWritable | container.BindDevice | container.BindEnsure,
+			Flags:  bits.BindWritable | bits.BindDevice | bits.BindEnsure,
 		}}, m("/dev"), ms("/mnt/dev"),
 			"d-/mnt/dev:/dev"},
 
@@ -45,7 +46,7 @@ func TestFSBind(t *testing.T) {
 		}, true, container.Ops{&container.BindMountOp{
 			Source: m("/mnt/dev"),
 			Target: m("/dev"),
-			Flags:  container.BindWritable | container.BindDevice,
+			Flags:  bits.BindWritable | bits.BindDevice,
 		}}, m("/dev"), ms("/mnt/dev"),
 			"d*/mnt/dev:/dev"},
 
@@ -56,7 +57,7 @@ func TestFSBind(t *testing.T) {
 		}, true, container.Ops{&container.BindMountOp{
 			Source: m("/mnt/tmp"),
 			Target: m("/tmp"),
-			Flags:  container.BindWritable,
+			Flags:  bits.BindWritable,
 		}}, m("/tmp"), ms("/mnt/tmp"),
 			"w*/mnt/tmp:/tmp"},
 
@@ -95,7 +96,7 @@ func TestFSBind(t *testing.T) {
 			Special: true,
 		}, true, container.Ops{&container.AutoRootOp{
 			Host:  m("/"),
-			Flags: container.BindWritable,
+			Flags: bits.BindWritable,
 		}}, m("/"), ms("/"), "autoroot:w"},
 
 		{"autoroot silly", &hst.FSBind{
@@ -105,7 +106,7 @@ func TestFSBind(t *testing.T) {
 			Special: true,
 		}, true, container.Ops{&container.AutoRootOp{
 			Host:  m("/etc"),
-			Flags: container.BindWritable,
+			Flags: bits.BindWritable,
 		}}, m("/"), ms("/etc"), "autoroot:w:/etc"},
 
 		{"autoetc", &hst.FSBind{

hst/fsephemeral.go

@@ -5,7 +5,7 @@ import (
 	"os"
 	"strings"
 
-	"hakurei.app/container"
+	"hakurei.app/container/check"
 )
 
 func init() { gob.Register(new(FSEphemeral)) }
@@ -16,7 +16,7 @@ const FilesystemEphemeral = "ephemeral"
 // FSEphemeral represents an ephemeral container mount point.
 type FSEphemeral struct {
 	// mount point in container
-	Target *container.Absolute `json:"dst,omitempty"`
+	Target *check.Absolute `json:"dst,omitempty"`
 	// do not mount filesystem read-only
 	Write bool `json:"write,omitempty"`
 	// upper limit on the size of the filesystem
@@ -27,14 +27,14 @@ type FSEphemeral struct {
 
 func (e *FSEphemeral) Valid() bool { return e != nil && e.Target != nil }
 
-func (e *FSEphemeral) Path() *container.Absolute {
+func (e *FSEphemeral) Path() *check.Absolute {
 	if !e.Valid() {
 		return nil
 	}
 	return e.Target
 }
 
-func (e *FSEphemeral) Host() []*container.Absolute { return nil }
+func (e *FSEphemeral) Host() []*check.Absolute { return nil }
 
 const fsEphemeralDefaultPerm = os.FileMode(0755)
 

hst/fslink.go

@@ -4,7 +4,7 @@ import (
 	"encoding/gob"
 	"path"
 
-	"hakurei.app/container"
+	"hakurei.app/container/check"
 )
 
 func init() { gob.Register(new(FSLink)) }
@@ -15,7 +15,7 @@ const FilesystemLink = "link"
 // FSLink represents a symlink in the container filesystem.
 type FSLink struct {
 	// link path in container
-	Target *container.Absolute `json:"dst"`
+	Target *check.Absolute `json:"dst"`
 	// linkname the symlink points to
 	Linkname string `json:"linkname"`
 	// whether to dereference linkname before creating the link
@@ -29,14 +29,14 @@ func (l *FSLink) Valid() bool {
 	return !l.Dereference || path.IsAbs(l.Linkname)
 }
 
-func (l *FSLink) Path() *container.Absolute {
+func (l *FSLink) Path() *check.Absolute {
 	if !l.Valid() {
 		return nil
 	}
 	return l.Target
 }
 
-func (l *FSLink) Host() []*container.Absolute { return nil }
+func (l *FSLink) Host() []*check.Absolute { return nil }
 
 func (l *FSLink) Apply(z *ApplyState) {
 	if !l.Valid() {

hst/fsoverlay.go

@@ -4,7 +4,7 @@ import (
 	"encoding/gob"
 	"strings"
 
-	"hakurei.app/container"
+	"hakurei.app/container/check"
 )
 
 func init() { gob.Register(new(FSOverlay)) }
@@ -15,14 +15,14 @@ const FilesystemOverlay = "overlay"
 // FSOverlay represents an overlay mount point.
 type FSOverlay struct {
 	// mount point in container
-	Target *container.Absolute `json:"dst"`
+	Target *check.Absolute `json:"dst"`
 
 	// any filesystem, does not need to be on a writable filesystem, must not be nil
-	Lower []*container.Absolute `json:"lower"`
+	Lower []*check.Absolute `json:"lower"`
 	// the upperdir is normally on a writable filesystem, leave as nil to mount Lower readonly
-	Upper *container.Absolute `json:"upper,omitempty"`
+	Upper *check.Absolute `json:"upper,omitempty"`
 	// the workdir needs to be an empty directory on the same filesystem as Upper, must not be nil if Upper is populated
-	Work *container.Absolute `json:"work,omitempty"`
+	Work *check.Absolute `json:"work,omitempty"`
 }
 
 func (o *FSOverlay) Valid() bool {
@@ -43,18 +43,18 @@ func (o *FSOverlay) Valid() bool {
 	}
 }
 
-func (o *FSOverlay) Path() *container.Absolute {
+func (o *FSOverlay) Path() *check.Absolute {
 	if !o.Valid() {
 		return nil
 	}
 	return o.Target
 }
 
-func (o *FSOverlay) Host() []*container.Absolute {
+func (o *FSOverlay) Host() []*check.Absolute {
 	if !o.Valid() {
 		return nil
 	}
-	p := make([]*container.Absolute, 0, 2+len(o.Lower))
+	p := make([]*check.Absolute, 0, 2+len(o.Lower))
 	if o.Upper != nil && o.Work != nil {
 		p = append(p, o.Upper, o.Work)
 	}
@@ -81,18 +81,18 @@ func (o *FSOverlay) String() string {
 
 	lower := make([]string, len(o.Lower))
 	for i, a := range o.Lower {
-		lower[i] = container.EscapeOverlayDataSegment(a.String())
+		lower[i] = check.EscapeOverlayDataSegment(a.String())
 	}
 
 	if o.Upper != nil && o.Work != nil {
 		return "w*" + strings.Join(append([]string{
-			container.EscapeOverlayDataSegment(o.Target.String()),
-			container.EscapeOverlayDataSegment(o.Upper.String()),
-			container.EscapeOverlayDataSegment(o.Work.String())},
-			lower...), container.SpecialOverlayPath)
+			check.EscapeOverlayDataSegment(o.Target.String()),
+			check.EscapeOverlayDataSegment(o.Upper.String()),
+			check.EscapeOverlayDataSegment(o.Work.String())},
+			lower...), check.SpecialOverlayPath)
 	} else {
 		return "*" + strings.Join(append([]string{
-			container.EscapeOverlayDataSegment(o.Target.String())},
-			lower...), container.SpecialOverlayPath)
+			check.EscapeOverlayDataSegment(o.Target.String())},
+			lower...), check.SpecialOverlayPath)
 	}
 }

hst/fsoverlay_test.go

@@ -4,13 +4,14 @@ import (
 	"testing"
 
 	"hakurei.app/container"
+	"hakurei.app/container/check"
 	"hakurei.app/hst"
 )
 
 func TestFSOverlay(t *testing.T) {
 	checkFs(t, []fsTestCase{
 		{"nil", (*hst.FSOverlay)(nil), false, nil, nil, nil, "<invalid>"},
-		{"nil lower", &hst.FSOverlay{Target: m("/etc"), Lower: []*container.Absolute{nil}}, false, nil, nil, nil, "<invalid>"},
+		{"nil lower", &hst.FSOverlay{Target: m("/etc"), Lower: []*check.Absolute{nil}}, false, nil, nil, nil, "<invalid>"},
 		{"zero lower", &hst.FSOverlay{Target: m("/etc"), Upper: m("/"), Work: m("/")}, false, nil, nil, nil, "<invalid>"},
 		{"zero lower ro", &hst.FSOverlay{Target: m("/etc")}, false, nil, nil, nil, "<invalid>"},
 		{"short lower", &hst.FSOverlay{Target: m("/etc"), Lower: ms("/etc")}, false, nil, nil, nil, "<invalid>"},

hst/hst.go

@@ -6,10 +6,8 @@ import (
 	"net"
 	"os"
 
-	"hakurei.app/container"
-	"hakurei.app/container/seccomp"
-	"hakurei.app/system"
-	"hakurei.app/system/dbus"
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 )
 
 // An AppError is returned while starting an app according to [hst.Config].
@@ -41,13 +39,13 @@ func (e *AppError) Message() string {
 // Paths contains environment-dependent paths used by hakurei.
 type Paths struct {
 	// temporary directory returned by [os.TempDir] (usually `/tmp`)
-	TempDir *container.Absolute `json:"temp_dir"`
+	TempDir *check.Absolute `json:"temp_dir"`
 	// path to shared directory (usually `/tmp/hakurei.%d`, [Info.User])
-	SharePath *container.Absolute `json:"share_path"`
+	SharePath *check.Absolute `json:"share_path"`
 	// XDG_RUNTIME_DIR value (usually `/run/user/%d`, uid)
-	RuntimePath *container.Absolute `json:"runtime_path"`
+	RuntimePath *check.Absolute `json:"runtime_path"`
 	// application runtime directory (usually `/run/user/%d/hakurei`)
-	RunDirPath *container.Absolute `json:"run_dir_path"`
+	RunDirPath *check.Absolute `json:"run_dir_path"`
 }
 
 type Info struct {
@@ -62,18 +60,9 @@ func Template() *Config {
 	return &Config{
 		ID: "org.chromium.Chromium",
 
-		Path: container.AbsFHSRun.Append("current-system/sw/bin/chromium"),
-		Args: []string{
-			"chromium",
-			"--ignore-gpu-blocklist",
-			"--disable-smooth-scrolling",
-			"--enable-features=UseOzonePlatform",
-			"--ozone-platform=wayland",
-		},
+		Enablements: NewEnablements(EWayland | EDBus | EPulse),
 
-		Enablements: NewEnablements(system.EWayland | system.EDBus | system.EPulse),
-
-		SessionBus: &dbus.Config{
+		SessionBus: &BusConfig{
 			See: nil,
 			Talk: []string{"org.freedesktop.Notifications", "org.freedesktop.FileManager1", "org.freedesktop.ScreenSaver",
 				"org.freedesktop.secrets", "org.kde.kwalletd5", "org.kde.kwalletd6", "org.gnome.SessionManager"},
@@ -84,7 +73,7 @@ func Template() *Config {
 			Log:       false,
 			Filter:    true,
 		},
-		SystemBus: &dbus.Config{
+		SystemBus: &BusConfig{
 			See:       nil,
 			Talk:      []string{"org.bluez", "org.freedesktop.Avahi", "org.freedesktop.UPower"},
 			Own:       nil,
@@ -95,31 +84,26 @@ func Template() *Config {
 		},
 		DirectWayland: false,
 
-		Username: "chronos",
-		Shell:    container.AbsFHSRun.Append("current-system/sw/bin/zsh"),
-		Home:     container.MustAbs("/data/data/org.chromium.Chromium"),
 		ExtraPerms: []*ExtraPermConfig{
-			{Path: container.AbsFHSVarLib.Append("hakurei/u0"), Ensure: true, Execute: true},
-			{Path: container.AbsFHSVarLib.Append("hakurei/u0/org.chromium.Chromium"), Read: true, Write: true, Execute: true},
+			{Path: fhs.AbsVarLib.Append("hakurei/u0"), Ensure: true, Execute: true},
+			{Path: fhs.AbsVarLib.Append("hakurei/u0/org.chromium.Chromium"), Read: true, Write: true, Execute: true},
 		},
 
 		Identity: 9,
 		Groups:   []string{"video", "dialout", "plugdev"},
 
 		Container: &ContainerConfig{
-			Hostname:       "localhost",
-			Devel:          true,
-			Userns:         true,
-			HostNet:        true,
-			HostAbstract:   true,
-			Device:         true,
-			WaitDelay:      -1,
-			SeccompFlags:   seccomp.AllowMultiarch,
-			SeccompPresets: seccomp.PresetExt,
-			SeccompCompat:  true,
-			Tty:            true,
-			Multiarch:      true,
-			MapRealUID:     true,
+			Hostname:      "localhost",
+			Devel:         true,
+			Userns:        true,
+			HostNet:       true,
+			HostAbstract:  true,
+			Device:        true,
+			WaitDelay:     -1,
+			SeccompCompat: true,
+			Tty:           true,
+			Multiarch:     true,
+			MapRealUID:    true,
 			// example API credentials pulled from Google Chrome
 			// DO NOT USE THESE IN A REAL BROWSER
 			Env: map[string]string{
@@ -128,21 +112,34 @@ func Template() *Config {
 				"GOOGLE_DEFAULT_CLIENT_SECRET": "OTJgUOQcT7lO7GsGZq2G4IlT",
 			},
 			Filesystem: []FilesystemConfigJSON{
-				{&FSBind{Target: container.AbsFHSRoot, Source: container.AbsFHSVarLib.Append("hakurei/base/org.debian"), Write: true, Special: true}},
-				{&FSBind{Target: container.AbsFHSEtc, Source: container.AbsFHSEtc, Special: true}},
-				{&FSEphemeral{Target: container.AbsFHSTmp, Write: true, Perm: 0755}},
+				{&FSBind{Target: fhs.AbsRoot, Source: fhs.AbsVarLib.Append("hakurei/base/org.debian"), Write: true, Special: true}},
+				{&FSBind{Target: fhs.AbsEtc, Source: fhs.AbsEtc, Special: true}},
+				{&FSEphemeral{Target: fhs.AbsTmp, Write: true, Perm: 0755}},
 				{&FSOverlay{
-					Target: container.MustAbs("/nix/store"),
-					Lower:  []*container.Absolute{container.MustAbs("/mnt-root/nix/.ro-store")},
-					Upper:  container.MustAbs("/mnt-root/nix/.rw-store/upper"),
-					Work:   container.MustAbs("/mnt-root/nix/.rw-store/work"),
+					Target: check.MustAbs("/nix/store"),
+					Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
+					Upper:  check.MustAbs("/mnt-root/nix/.rw-store/upper"),
+					Work:   check.MustAbs("/mnt-root/nix/.rw-store/work"),
 				}},
-				{&FSBind{Source: container.MustAbs("/nix/store")}},
-				{&FSLink{Target: container.AbsFHSRun.Append("current-system"), Linkname: "/run/current-system", Dereference: true}},
-				{&FSLink{Target: container.AbsFHSRun.Append("opengl-driver"), Linkname: "/run/opengl-driver", Dereference: true}},
-				{&FSBind{Source: container.AbsFHSVarLib.Append("hakurei/u0/org.chromium.Chromium"),
-					Target: container.MustAbs("/data/data/org.chromium.Chromium"), Write: true, Ensure: true}},
-				{&FSBind{Source: container.AbsFHSDev.Append("dri"), Device: true, Optional: true}},
+				{&FSBind{Source: check.MustAbs("/nix/store")}},
+				{&FSLink{Target: fhs.AbsRun.Append("current-system"), Linkname: "/run/current-system", Dereference: true}},
+				{&FSLink{Target: fhs.AbsRun.Append("opengl-driver"), Linkname: "/run/opengl-driver", Dereference: true}},
+				{&FSBind{Source: fhs.AbsVarLib.Append("hakurei/u0/org.chromium.Chromium"),
+					Target: check.MustAbs("/data/data/org.chromium.Chromium"), Write: true, Ensure: true}},
+				{&FSBind{Source: fhs.AbsDev.Append("dri"), Device: true, Optional: true}},
+			},
+
+			Username: "chronos",
+			Shell:    fhs.AbsRun.Append("current-system/sw/bin/zsh"),
+			Home:     check.MustAbs("/data/data/org.chromium.Chromium"),
+
+			Path: fhs.AbsRun.Append("current-system/sw/bin/chromium"),
+			Args: []string{
+				"chromium",
+				"--ignore-gpu-blocklist",
+				"--disable-smooth-scrolling",
+				"--enable-features=UseOzonePlatform",
+				"--ozone-platform=wayland",
 			},
 		},
 	}

hst/hst_test.go

@@ -92,14 +92,6 @@ func TestAppError(t *testing.T) {
 func TestTemplate(t *testing.T) {
 	const want = `{
 	"id": "org.chromium.Chromium",
-	"path": "/run/current-system/sw/bin/chromium",
-	"args": [
-		"chromium",
-		"--ignore-gpu-blocklist",
-		"--disable-smooth-scrolling",
-		"--enable-features=UseOzonePlatform",
-		"--ozone-platform=wayland"
-	],
 	"enablements": {
 		"wayland": true,
 		"dbus": true,
@@ -141,9 +133,6 @@ func TestTemplate(t *testing.T) {
 		"broadcast": null,
 		"filter": true
 	},
-	"username": "chronos",
-	"shell": "/run/current-system/sw/bin/zsh",
-	"home": "/data/data/org.chromium.Chromium",
 	"extra_perms": [
 		{
 			"ensure": true,
@@ -166,8 +155,6 @@ func TestTemplate(t *testing.T) {
 	"container": {
 		"hostname": "localhost",
 		"wait_delay": -1,
-		"seccomp_flags": 1,
-		"seccomp_presets": 1,
 		"seccomp_compat": true,
 		"devel": true,
 		"userns": true,
@@ -240,6 +227,17 @@ func TestTemplate(t *testing.T) {
 				"dev": true,
 				"optional": true
 			}
+		],
+		"username": "chronos",
+		"shell": "/run/current-system/sw/bin/zsh",
+		"home": "/data/data/org.chromium.Chromium",
+		"path": "/run/current-system/sw/bin/chromium",
+		"args": [
+			"chromium",
+			"--ignore-gpu-blocklist",
+			"--disable-smooth-scrolling",
+			"--enable-features=UseOzonePlatform",
+			"--ozone-platform=wayland"
 		]
 	}
 }`

internal/app/app.go

@@ -6,23 +6,24 @@ import (
 	"log"
 	"os"
 
+	"hakurei.app/container"
 	"hakurei.app/hst"
 	"hakurei.app/internal/app/state"
 )
 
 // Main runs an app according to [hst.Config] and terminates. Main does not return.
-func Main(ctx context.Context, config *hst.Config) {
+func Main(ctx context.Context, msg container.Msg, config *hst.Config) {
 	var id state.ID
 	if err := state.NewAppID(&id); err != nil {
 		log.Fatal(err)
 	}
 
-	seal := outcome{id: &stringPair[state.ID]{id, id.String()}, syscallDispatcher: direct{}}
-	if err := seal.finalise(ctx, config); err != nil {
+	seal := outcome{syscallDispatcher: direct{}}
+	if err := seal.finalise(ctx, msg, &id, config); err != nil {
 		printMessageError("cannot seal app:", err)
 		os.Exit(1)
 	}
 
-	seal.main()
+	seal.main(msg)
 	panic("unreachable")
 }

internal/app/app_stub_test.go

@@ -1,199 +0,0 @@
-package app
-
-import (
-	"fmt"
-	"io/fs"
-	"log"
-	"os/exec"
-	"os/user"
-)
-
-type stubNixOS struct {
-	lookPathErr map[string]error
-	usernameErr map[string]error
-}
-
-func (k *stubNixOS) new(func(k syscallDispatcher)) { panic("not implemented") }
-
-func (k *stubNixOS) getuid() int { return 1971 }
-func (k *stubNixOS) getgid() int { return 100 }
-
-func (k *stubNixOS) lookupEnv(key string) (string, bool) {
-	switch key {
-	case "SHELL":
-		return "/run/current-system/sw/bin/zsh", true
-	case "TERM":
-		return "xterm-256color", true
-	case "WAYLAND_DISPLAY":
-		return "wayland-0", true
-	case "PULSE_COOKIE":
-		return "", false
-	case "HOME":
-		return "/home/ophestra", true
-	case "XDG_RUNTIME_DIR":
-		return "/run/user/1971", true
-	case "XDG_CONFIG_HOME":
-		return "/home/ophestra/xdg/config", true
-	default:
-		panic(fmt.Sprintf("attempted to access unexpected environment variable %q", key))
-	}
-}
-
-func (k *stubNixOS) stat(name string) (fs.FileInfo, error) {
-	switch name {
-	case "/var/run/nscd":
-		return nil, nil
-	case "/run/user/1971/pulse":
-		return nil, nil
-	case "/run/user/1971/pulse/native":
-		return stubFileInfoMode(0666), nil
-	case "/home/ophestra/.pulse-cookie":
-		return stubFileInfoIsDir(true), nil
-	case "/home/ophestra/xdg/config/pulse/cookie":
-		return stubFileInfoIsDir(false), nil
-	default:
-		panic(fmt.Sprintf("attempted to stat unexpected path %q", name))
-	}
-}
-
-func (k *stubNixOS) readdir(name string) ([]fs.DirEntry, error) {
-	switch name {
-	case "/":
-		return stubDirEntries("bin", "boot", "dev", "etc", "home", "lib",
-			"lib64", "nix", "proc", "root", "run", "srv", "sys", "tmp", "usr", "var")
-
-	case "/run":
-		return stubDirEntries("agetty.reload", "binfmt", "booted-system",
-			"credentials", "cryptsetup", "current-system", "dbus", "host", "keys",
-			"libvirt", "libvirtd.pid", "lock", "log", "lvm", "mount", "NetworkManager",
-			"nginx", "nixos", "nscd", "opengl-driver", "pppd", "resolvconf", "sddm",
-			"store", "syncoid", "system", "systemd", "tmpfiles.d", "udev", "udisks2",
-			"user", "utmp", "virtlogd.pid", "wrappers", "zed.pid", "zed.state")
-
-	case "/etc":
-		return stubDirEntries("alsa", "bashrc", "binfmt.d", "dbus-1", "default",
-			"ethertypes", "fonts", "fstab", "fuse.conf", "group", "host.conf", "hostid",
-			"hostname", "hostname.CHECKSUM", "hosts", "inputrc", "ipsec.d", "issue", "kbd",
-			"libblockdev", "locale.conf", "localtime", "login.defs", "lsb-release", "lvm",
-			"machine-id", "man_db.conf", "modprobe.d", "modules-load.d", "mtab", "nanorc",
-			"netgroup", "NetworkManager", "nix", "nixos", "NIXOS", "nscd.conf", "nsswitch.conf",
-			"opensnitchd", "os-release", "pam", "pam.d", "passwd", "pipewire", "pki", "polkit-1",
-			"profile", "protocols", "qemu", "resolv.conf", "resolvconf.conf", "rpc", "samba",
-			"sddm.conf", "secureboot", "services", "set-environment", "shadow", "shells", "ssh",
-			"ssl", "static", "subgid", "subuid", "sudoers", "sysctl.d", "systemd", "terminfo",
-			"tmpfiles.d", "udev", "udisks2", "UPower", "vconsole.conf", "X11", "zfs", "zinputrc",
-			"zoneinfo", "zprofile", "zshenv", "zshrc")
-
-	default:
-		panic(fmt.Sprintf("attempted to read unexpected directory %q", name))
-	}
-}
-
-func (k *stubNixOS) tempdir() string { return "/tmp/" }
-
-func (k *stubNixOS) evalSymlinks(path string) (string, error) {
-	switch path {
-	case "/run/user/1971":
-		return "/run/user/1971", nil
-	case "/tmp/hakurei.0":
-		return "/tmp/hakurei.0", nil
-	case "/run/dbus":
-		return "/run/dbus", nil
-	case "/dev/kvm":
-		return "/dev/kvm", nil
-	case "/etc/":
-		return "/etc/", nil
-	case "/bin":
-		return "/bin", nil
-	case "/boot":
-		return "/boot", nil
-	case "/home":
-		return "/home", nil
-	case "/lib":
-		return "/lib", nil
-	case "/lib64":
-		return "/lib64", nil
-	case "/nix":
-		return "/nix", nil
-	case "/root":
-		return "/root", nil
-	case "/run":
-		return "/run", nil
-	case "/srv":
-		return "/srv", nil
-	case "/sys":
-		return "/sys", nil
-	case "/usr":
-		return "/usr", nil
-	case "/var":
-		return "/var", nil
-	case "/dev/dri":
-		return "/dev/dri", nil
-	case "/usr/bin/":
-		return "/usr/bin/", nil
-	case "/nix/store":
-		return "/nix/store", nil
-	case "/run/current-system":
-		return "/nix/store/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-nixos-system-satori-25.05.99999999.aaaaaaa", nil
-	case "/sys/block":
-		return "/sys/block", nil
-	case "/sys/bus":
-		return "/sys/bus", nil
-	case "/sys/class":
-		return "/sys/class", nil
-	case "/sys/dev":
-		return "/sys/dev", nil
-	case "/sys/devices":
-		return "/sys/devices", nil
-	case "/run/opengl-driver":
-		return "/nix/store/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-graphics-drivers", nil
-	case "/var/lib/persist/module/hakurei/0/1":
-		return "/var/lib/persist/module/hakurei/0/1", nil
-	default:
-		panic(fmt.Sprintf("attempted to evaluate unexpected path %q", path))
-	}
-}
-
-func (k *stubNixOS) lookPath(file string) (string, error) {
-	if k.lookPathErr != nil {
-		if err, ok := k.lookPathErr[file]; ok {
-			return "", err
-		}
-	}
-
-	switch file {
-	case "zsh":
-		return "/run/current-system/sw/bin/zsh", nil
-	default:
-		panic(fmt.Sprintf("attempted to look up unexpected executable %q", file))
-	}
-}
-
-func (k *stubNixOS) lookupGroupId(name string) (string, error) {
-	switch name {
-	case "video":
-		return "26", nil
-	default:
-		return "", user.UnknownGroupError(name)
-	}
-}
-
-func (k *stubNixOS) cmdOutput(cmd *exec.Cmd) ([]byte, error) {
-	switch cmd.Path {
-	case "/proc/nonexistent/hsu":
-		return []byte{'0'}, nil
-	default:
-		panic(fmt.Sprintf("unexpected cmd %#v", cmd))
-	}
-}
-
-func (k *stubNixOS) overflowUid() int { return 65534 }
-func (k *stubNixOS) overflowGid() int { return 65534 }
-
-func (k *stubNixOS) mustHsuPath() string { return "/proc/nonexistent/hsu" }
-
-func (k *stubNixOS) fatalf(format string, v ...any) { panic(fmt.Sprintf(format, v...)) }
-
-func (k *stubNixOS) isVerbose() bool                  { return true }
-func (k *stubNixOS) verbose(v ...any)                 { log.Print(v...) }
-func (k *stubNixOS) verbosef(format string, v ...any) { log.Printf(format, v...) }

internal/app/app_test.go

@@ -1,25 +1,36 @@
 package app
 
 import (
-	"context"
+	"bytes"
+	"encoding/gob"
 	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
 	"io/fs"
-	"os"
+	"log"
+	"maps"
+	"os/exec"
+	"os/user"
 	"reflect"
 	"syscall"
 	"testing"
 	"time"
 
 	"hakurei.app/container"
-	"hakurei.app/container/seccomp"
+	"hakurei.app/container/bits"
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 	"hakurei.app/hst"
 	"hakurei.app/internal/app/state"
 	"hakurei.app/system"
 	"hakurei.app/system/acl"
-	"hakurei.app/system/dbus"
 )
 
 func TestApp(t *testing.T) {
+	msg := container.NewMsg(nil)
+	msg.SwapVerbose(testing.Verbose())
+
 	testCases := []struct {
 		name       string
 		k          syscallDispatcher
@@ -30,19 +41,47 @@ func TestApp(t *testing.T) {
 	}{
 		{
 			"nixos permissive defaults no enablements", new(stubNixOS),
-			&hst.Config{Username: "chronos", Home: m("/home/chronos")},
+			&hst.Config{Container: &hst.ContainerConfig{
+				Userns: true, HostNet: true, HostAbstract: true, Tty: true,
+
+				Filesystem: []hst.FilesystemConfigJSON{
+					{FilesystemConfig: &hst.FSBind{
+						Target:  fhs.AbsRoot,
+						Source:  fhs.AbsRoot,
+						Write:   true,
+						Special: true,
+					}},
+					{FilesystemConfig: &hst.FSBind{
+						Source:   fhs.AbsDev.Append("kvm"),
+						Device:   true,
+						Optional: true,
+					}},
+					{FilesystemConfig: &hst.FSBind{
+						Target:  fhs.AbsEtc,
+						Source:  fhs.AbsEtc,
+						Special: true,
+					}},
+				},
+
+				Username: "chronos",
+				Shell:    m("/run/current-system/sw/bin/zsh"),
+				Home:     m("/home/chronos"),
+
+				Path: m("/run/current-system/sw/bin/zsh"),
+				Args: []string{"/run/current-system/sw/bin/zsh"},
+			}},
 			state.ID{
 				0x4a, 0x45, 0x0b, 0x65,
 				0x96, 0xd7, 0xbc, 0x15,
 				0xbd, 0x01, 0x78, 0x0e,
 				0xb9, 0xa6, 0x07, 0xac,
 			},
-			system.New(context.TODO(), 1000000).
-				Ensure("/tmp/hakurei.0", 0711).
-				Ensure("/tmp/hakurei.0/runtime", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/runtime", acl.Execute).
-				Ensure("/tmp/hakurei.0/runtime/0", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/runtime/0", acl.Read, acl.Write, acl.Execute).
-				Ensure("/tmp/hakurei.0/tmpdir", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/tmpdir", acl.Execute).
-				Ensure("/tmp/hakurei.0/tmpdir/0", 01700).UpdatePermType(system.User, "/tmp/hakurei.0/tmpdir/0", acl.Read, acl.Write, acl.Execute),
+			system.New(t.Context(), msg, 1000000).
+				Ensure(m("/tmp/hakurei.0"), 0711).
+				Ensure(m("/tmp/hakurei.0/runtime"), 0700).UpdatePermType(system.User, m("/tmp/hakurei.0/runtime"), acl.Execute).
+				Ensure(m("/tmp/hakurei.0/runtime/0"), 0700).UpdatePermType(system.User, m("/tmp/hakurei.0/runtime/0"), acl.Read, acl.Write, acl.Execute).
+				Ensure(m("/tmp/hakurei.0/tmpdir"), 0700).UpdatePermType(system.User, m("/tmp/hakurei.0/tmpdir"), acl.Execute).
+				Ensure(m("/tmp/hakurei.0/tmpdir/0"), 01700).UpdatePermType(system.User, m("/tmp/hakurei.0/tmpdir/0"), acl.Read, acl.Write, acl.Execute),
 			&container.Params{
 				Dir:  m("/home/chronos"),
 				Path: m("/run/current-system/sw/bin/zsh"),
@@ -57,24 +96,24 @@ func TestApp(t *testing.T) {
 					"XDG_SESSION_TYPE=tty",
 				},
 				Ops: new(container.Ops).
-					Root(m("/"), container.BindWritable).
+					Root(m("/"), bits.BindWritable).
 					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).
+					Bind(m("/dev/kvm"), m("/dev/kvm"), bits.BindWritable|bits.BindDevice|bits.BindOptional).
 					Etc(m("/etc/"), "4a450b6596d7bc15bd01780eb9a607ac").
 					Tmpfs(m("/run/user/1971"), 8192, 0755).
+					Tmpfs(m("/run/nscd"), 8192, 0755).
 					Tmpfs(m("/run/dbus"), 8192, 0755).
 					Remount(m("/dev/"), syscall.MS_RDONLY).
 					Tmpfs(m("/run/user/"), 4096, 0755).
-					Bind(m("/tmp/hakurei.0/runtime/0"), m("/run/user/65534"), container.BindWritable).
-					Bind(m("/tmp/hakurei.0/tmpdir/0"), m("/tmp/"), container.BindWritable).
+					Bind(m("/tmp/hakurei.0/runtime/0"), m("/run/user/65534"), bits.BindWritable).
+					Bind(m("/tmp/hakurei.0/tmpdir/0"), m("/tmp/"), bits.BindWritable).
 					Place(m("/etc/passwd"), []byte("chronos:x:65534:65534:Hakurei:/home/chronos:/run/current-system/sw/bin/zsh\n")).
 					Place(m("/etc/group"), []byte("hakurei:x:65534:\n")).
 					Remount(m("/"), syscall.MS_RDONLY),
-				SeccompPresets: seccomp.PresetExt | seccomp.PresetDenyDevel,
+				SeccompPresets: bits.PresetExt | bits.PresetDenyDevel,
 				HostNet:        true,
 				HostAbstract:   true,
 				RetainSession:  true,
@@ -85,12 +124,9 @@ func TestApp(t *testing.T) {
 			"nixos permissive defaults chromium", new(stubNixOS),
 			&hst.Config{
 				ID:       "org.chromium.Chromium",
-				Args:     []string{"zsh", "-c", "exec chromium "},
 				Identity: 9,
 				Groups:   []string{"video"},
-				Username: "chronos",
-				Home:     m("/home/chronos"),
-				SessionBus: &dbus.Config{
+				SessionBus: &hst.BusConfig{
 					Talk: []string{
 						"org.freedesktop.Notifications",
 						"org.freedesktop.FileManager1",
@@ -113,7 +149,7 @@ func TestApp(t *testing.T) {
 					},
 					Filter: true,
 				},
-				SystemBus: &dbus.Config{
+				SystemBus: &hst.BusConfig{
 					Talk: []string{
 						"org.bluez",
 						"org.freedesktop.Avahi",
@@ -121,7 +157,42 @@ func TestApp(t *testing.T) {
 					},
 					Filter: true,
 				},
-				Enablements: hst.NewEnablements(system.EWayland | system.EDBus | system.EPulse),
+				Enablements: hst.NewEnablements(hst.EWayland | hst.EDBus | hst.EPulse),
+
+				Container: &hst.ContainerConfig{
+					Userns: true, HostNet: true, HostAbstract: true, Tty: true,
+
+					Filesystem: []hst.FilesystemConfigJSON{
+						{FilesystemConfig: &hst.FSBind{
+							Target:  fhs.AbsRoot,
+							Source:  fhs.AbsRoot,
+							Write:   true,
+							Special: true,
+						}},
+						{FilesystemConfig: &hst.FSBind{
+							Source:   fhs.AbsDev.Append("dri"),
+							Device:   true,
+							Optional: true,
+						}},
+						{FilesystemConfig: &hst.FSBind{
+							Source:   fhs.AbsDev.Append("kvm"),
+							Device:   true,
+							Optional: true,
+						}},
+						{FilesystemConfig: &hst.FSBind{
+							Target:  fhs.AbsEtc,
+							Source:  fhs.AbsEtc,
+							Special: true,
+						}},
+					},
+
+					Username: "chronos",
+					Shell:    m("/run/current-system/sw/bin/zsh"),
+					Home:     m("/home/chronos"),
+
+					Path: m("/run/current-system/sw/bin/zsh"),
+					Args: []string{"zsh", "-c", "exec chromium "},
+				},
 			},
 			state.ID{
 				0xeb, 0xf0, 0x83, 0xd1,
@@ -129,20 +200,19 @@ func TestApp(t *testing.T) {
 				0x82, 0xd4, 0x13, 0x36,
 				0x9b, 0x64, 0xce, 0x7c,
 			},
-			system.New(context.TODO(), 1000009).
-				Ensure("/tmp/hakurei.0", 0711).
-				Ensure("/tmp/hakurei.0/runtime", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/runtime", acl.Execute).
-				Ensure("/tmp/hakurei.0/runtime/9", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/runtime/9", acl.Read, acl.Write, acl.Execute).
-				Ensure("/tmp/hakurei.0/tmpdir", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/tmpdir", acl.Execute).
-				Ensure("/tmp/hakurei.0/tmpdir/9", 01700).UpdatePermType(system.User, "/tmp/hakurei.0/tmpdir/9", acl.Read, acl.Write, acl.Execute).
-				Ephemeral(system.Process, "/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c", 0711).
-				Wayland(new(*os.File), "/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/wayland", "/run/user/1971/wayland-0", "org.chromium.Chromium", "ebf083d1b175911782d413369b64ce7c").
-				Ensure("/run/user/1971/hakurei", 0700).UpdatePermType(system.User, "/run/user/1971/hakurei", acl.Execute).
-				Ensure("/run/user/1971", 0700).UpdatePermType(system.User, "/run/user/1971", acl.Execute). // this is ordered as is because the previous Ensure only calls mkdir if XDG_RUNTIME_DIR is unset
-				Ephemeral(system.Process, "/run/user/1971/hakurei/ebf083d1b175911782d413369b64ce7c", 0700).UpdatePermType(system.Process, "/run/user/1971/hakurei/ebf083d1b175911782d413369b64ce7c", acl.Execute).
-				Link("/run/user/1971/pulse/native", "/run/user/1971/hakurei/ebf083d1b175911782d413369b64ce7c/pulse").
-				CopyFile(new([]byte), "/home/ophestra/xdg/config/pulse/cookie", 256, 256).
-				MustProxyDBus("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/bus", &dbus.Config{
+			system.New(t.Context(), msg, 1000009).
+				Ensure(m("/tmp/hakurei.0"), 0711).
+				Ensure(m("/tmp/hakurei.0/runtime"), 0700).UpdatePermType(system.User, m("/tmp/hakurei.0/runtime"), acl.Execute).
+				Ensure(m("/tmp/hakurei.0/runtime/9"), 0700).UpdatePermType(system.User, m("/tmp/hakurei.0/runtime/9"), acl.Read, acl.Write, acl.Execute).
+				Ensure(m("/tmp/hakurei.0/tmpdir"), 0700).UpdatePermType(system.User, m("/tmp/hakurei.0/tmpdir"), acl.Execute).
+				Ensure(m("/tmp/hakurei.0/tmpdir/9"), 01700).UpdatePermType(system.User, m("/tmp/hakurei.0/tmpdir/9"), acl.Read, acl.Write, acl.Execute).
+				Ephemeral(system.Process, m("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c"), 0711).
+				Wayland(m("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/wayland"), m("/run/user/1971/wayland-0"), "org.chromium.Chromium", "ebf083d1b175911782d413369b64ce7c").
+				Ensure(m("/run/user/1971/hakurei"), 0700).UpdatePermType(system.User, m("/run/user/1971/hakurei"), acl.Execute).
+				Ensure(m("/run/user/1971"), 0700).UpdatePermType(system.User, m("/run/user/1971"), acl.Execute). // this is ordered as is because the previous Ensure only calls mkdir if XDG_RUNTIME_DIR is unset
+				Ephemeral(system.Process, m("/run/user/1971/hakurei/ebf083d1b175911782d413369b64ce7c"), 0700).UpdatePermType(system.Process, m("/run/user/1971/hakurei/ebf083d1b175911782d413369b64ce7c"), acl.Execute).
+				Link(m("/run/user/1971/pulse/native"), m("/run/user/1971/hakurei/ebf083d1b175911782d413369b64ce7c/pulse")).
+				MustProxyDBus(m("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/bus"), &hst.BusConfig{
 					Talk: []string{
 						"org.freedesktop.Notifications",
 						"org.freedesktop.FileManager1",
@@ -164,7 +234,7 @@ func TestApp(t *testing.T) {
 						"org.freedesktop.portal.*": "@/org/freedesktop/portal/*",
 					},
 					Filter: true,
-				}, "/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/system_bus_socket", &dbus.Config{
+				}, m("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/system_bus_socket"), &hst.BusConfig{
 					Talk: []string{
 						"org.bluez",
 						"org.freedesktop.Avahi",
@@ -172,8 +242,8 @@ func TestApp(t *testing.T) {
 					},
 					Filter: true,
 				}).
-				UpdatePerm("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/bus", acl.Read, acl.Write).
-				UpdatePerm("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/system_bus_socket", acl.Read, acl.Write),
+				UpdatePerm(m("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/bus"), acl.Read, acl.Write).
+				UpdatePerm(m("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/system_bus_socket"), acl.Read, acl.Write),
 			&container.Params{
 				Dir:  m("/home/chronos"),
 				Path: m("/run/current-system/sw/bin/zsh"),
@@ -193,30 +263,30 @@ func TestApp(t *testing.T) {
 					"XDG_SESSION_TYPE=tty",
 				},
 				Ops: new(container.Ops).
-					Root(m("/"), container.BindWritable).
+					Root(m("/"), bits.BindWritable).
 					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).
+					Bind(m("/dev/dri"), m("/dev/dri"), bits.BindWritable|bits.BindDevice|bits.BindOptional).
+					Bind(m("/dev/kvm"), m("/dev/kvm"), bits.BindWritable|bits.BindDevice|bits.BindOptional).
 					Etc(m("/etc/"), "ebf083d1b175911782d413369b64ce7c").
 					Tmpfs(m("/run/user/1971"), 8192, 0755).
+					Tmpfs(m("/run/nscd"), 8192, 0755).
 					Tmpfs(m("/run/dbus"), 8192, 0755).
 					Remount(m("/dev/"), syscall.MS_RDONLY).
 					Tmpfs(m("/run/user/"), 4096, 0755).
-					Bind(m("/tmp/hakurei.0/runtime/9"), m("/run/user/65534"), container.BindWritable).
-					Bind(m("/tmp/hakurei.0/tmpdir/9"), m("/tmp/"), container.BindWritable).
+					Bind(m("/tmp/hakurei.0/runtime/9"), m("/run/user/65534"), bits.BindWritable).
+					Bind(m("/tmp/hakurei.0/tmpdir/9"), m("/tmp/"), bits.BindWritable).
 					Place(m("/etc/passwd"), []byte("chronos:x:65534:65534:Hakurei:/home/chronos:/run/current-system/sw/bin/zsh\n")).
 					Place(m("/etc/group"), []byte("hakurei:x:65534:\n")).
 					Bind(m("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/wayland"), m("/run/user/65534/wayland-0"), 0).
 					Bind(m("/run/user/1971/hakurei/ebf083d1b175911782d413369b64ce7c/pulse"), m("/run/user/65534/pulse/native"), 0).
-					Place(m(hst.Tmp+"/pulse-cookie"), nil).
+					Place(m(hst.Tmp+"/pulse-cookie"), bytes.Repeat([]byte{0}, pulseCookieSizeMax)).
 					Bind(m("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/bus"), m("/run/user/65534/bus"), 0).
 					Bind(m("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/system_bus_socket"), m("/run/dbus/system_bus_socket"), 0).
 					Remount(m("/"), syscall.MS_RDONLY),
-				SeccompPresets: seccomp.PresetExt | seccomp.PresetDenyDevel,
+				SeccompPresets: bits.PresetExt | bits.PresetDenyDevel,
 				HostNet:        true,
 				HostAbstract:   true,
 				RetainSession:  true,
@@ -228,10 +298,7 @@ func TestApp(t *testing.T) {
 			"nixos chromium direct wayland", new(stubNixOS),
 			&hst.Config{
 				ID:          "org.chromium.Chromium",
-				Path:        m("/nix/store/yqivzpzzn7z5x0lq9hmbzygh45d8rhqd-chromium-start"),
-				Enablements: hst.NewEnablements(system.EWayland | system.EDBus | system.EPulse),
-				Shell:       m("/run/current-system/sw/bin/zsh"),
-
+				Enablements: hst.NewEnablements(hst.EWayland | hst.EDBus | hst.EPulse),
 				Container: &hst.ContainerConfig{
 					Userns: true, HostNet: true, MapRealUID: true, Env: nil,
 					Filesystem: []hst.FilesystemConfigJSON{
@@ -249,12 +316,18 @@ func TestApp(t *testing.T) {
 						f(&hst.FSBind{Source: m("/etc/"), Target: m("/etc/"), Special: true}),
 						f(&hst.FSBind{Source: m("/var/lib/persist/module/hakurei/0/1"), Write: true, Ensure: true}),
 					},
+
+					Username: "u0_a1",
+					Shell:    m("/run/current-system/sw/bin/zsh"),
+					Home:     m("/var/lib/persist/module/hakurei/0/1"),
+
+					Path: m("/nix/store/yqivzpzzn7z5x0lq9hmbzygh45d8rhqd-chromium-start"),
 				},
-				SystemBus: &dbus.Config{
+				SystemBus: &hst.BusConfig{
 					Talk:   []string{"org.bluez", "org.freedesktop.Avahi", "org.freedesktop.UPower"},
 					Filter: true,
 				},
-				SessionBus: &dbus.Config{
+				SessionBus: &hst.BusConfig{
 					Talk: []string{
 						"org.freedesktop.FileManager1", "org.freedesktop.Notifications",
 						"org.freedesktop.ScreenSaver", "org.freedesktop.secrets",
@@ -270,8 +343,6 @@ func TestApp(t *testing.T) {
 				},
 				DirectWayland: true,
 
-				Username: "u0_a1",
-				Home:     m("/var/lib/persist/module/hakurei/0/1"),
 				Identity: 1, Groups: []string{},
 			},
 			state.ID{
@@ -280,20 +351,19 @@ func TestApp(t *testing.T) {
 				0x4c, 0xf0, 0x73, 0xbd,
 				0xb4, 0x6e, 0xb5, 0xc1,
 			},
-			system.New(context.TODO(), 1000001).
-				Ensure("/tmp/hakurei.0", 0711).
-				Ensure("/tmp/hakurei.0/runtime", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/runtime", acl.Execute).
-				Ensure("/tmp/hakurei.0/runtime/1", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/runtime/1", acl.Read, acl.Write, acl.Execute).
-				Ensure("/tmp/hakurei.0/tmpdir", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/tmpdir", acl.Execute).
-				Ensure("/tmp/hakurei.0/tmpdir/1", 01700).UpdatePermType(system.User, "/tmp/hakurei.0/tmpdir/1", acl.Read, acl.Write, acl.Execute).
-				Ensure("/run/user/1971/hakurei", 0700).UpdatePermType(system.User, "/run/user/1971/hakurei", acl.Execute).
-				Ensure("/run/user/1971", 0700).UpdatePermType(system.User, "/run/user/1971", acl.Execute). // this is ordered as is because the previous Ensure only calls mkdir if XDG_RUNTIME_DIR is unset
-				UpdatePermType(system.EWayland, "/run/user/1971/wayland-0", acl.Read, acl.Write, acl.Execute).
-				Ephemeral(system.Process, "/run/user/1971/hakurei/8e2c76b066dabe574cf073bdb46eb5c1", 0700).UpdatePermType(system.Process, "/run/user/1971/hakurei/8e2c76b066dabe574cf073bdb46eb5c1", acl.Execute).
-				Link("/run/user/1971/pulse/native", "/run/user/1971/hakurei/8e2c76b066dabe574cf073bdb46eb5c1/pulse").
-				CopyFile(nil, "/home/ophestra/xdg/config/pulse/cookie", 256, 256).
-				Ephemeral(system.Process, "/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1", 0711).
-				MustProxyDBus("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/bus", &dbus.Config{
+			system.New(t.Context(), msg, 1000001).
+				Ensure(m("/tmp/hakurei.0"), 0711).
+				Ensure(m("/tmp/hakurei.0/runtime"), 0700).UpdatePermType(system.User, m("/tmp/hakurei.0/runtime"), acl.Execute).
+				Ensure(m("/tmp/hakurei.0/runtime/1"), 0700).UpdatePermType(system.User, m("/tmp/hakurei.0/runtime/1"), acl.Read, acl.Write, acl.Execute).
+				Ensure(m("/tmp/hakurei.0/tmpdir"), 0700).UpdatePermType(system.User, m("/tmp/hakurei.0/tmpdir"), acl.Execute).
+				Ensure(m("/tmp/hakurei.0/tmpdir/1"), 01700).UpdatePermType(system.User, m("/tmp/hakurei.0/tmpdir/1"), acl.Read, acl.Write, acl.Execute).
+				Ensure(m("/run/user/1971/hakurei"), 0700).UpdatePermType(system.User, m("/run/user/1971/hakurei"), acl.Execute).
+				Ensure(m("/run/user/1971"), 0700).UpdatePermType(system.User, m("/run/user/1971"), acl.Execute). // this is ordered as is because the previous Ensure only calls mkdir if XDG_RUNTIME_DIR is unset
+				UpdatePermType(hst.EWayland, m("/run/user/1971/wayland-0"), acl.Read, acl.Write, acl.Execute).
+				Ephemeral(system.Process, m("/run/user/1971/hakurei/8e2c76b066dabe574cf073bdb46eb5c1"), 0700).UpdatePermType(system.Process, m("/run/user/1971/hakurei/8e2c76b066dabe574cf073bdb46eb5c1"), acl.Execute).
+				Link(m("/run/user/1971/pulse/native"), m("/run/user/1971/hakurei/8e2c76b066dabe574cf073bdb46eb5c1/pulse")).
+				Ephemeral(system.Process, m("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1"), 0711).
+				MustProxyDBus(m("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/bus"), &hst.BusConfig{
 					Talk: []string{
 						"org.freedesktop.FileManager1", "org.freedesktop.Notifications",
 						"org.freedesktop.ScreenSaver", "org.freedesktop.secrets",
@@ -306,7 +376,7 @@ func TestApp(t *testing.T) {
 					},
 					Call: map[string]string{}, Broadcast: map[string]string{},
 					Filter: true,
-				}, "/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/system_bus_socket", &dbus.Config{
+				}, m("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/system_bus_socket"), &hst.BusConfig{
 					Talk: []string{
 						"org.bluez",
 						"org.freedesktop.Avahi",
@@ -314,8 +384,8 @@ func TestApp(t *testing.T) {
 					},
 					Filter: true,
 				}).
-				UpdatePerm("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/bus", acl.Read, acl.Write).
-				UpdatePerm("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/system_bus_socket", acl.Read, acl.Write),
+				UpdatePerm(m("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/bus"), acl.Read, acl.Write).
+				UpdatePerm(m("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/system_bus_socket"), acl.Read, acl.Write),
 			&container.Params{
 				Uid:  1971,
 				Gid:  100,
@@ -345,28 +415,28 @@ func TestApp(t *testing.T) {
 					Bind(m("/usr/bin/"), m("/usr/bin/"), 0).
 					Bind(m("/nix/store"), m("/nix/store"), 0).
 					Bind(m("/run/current-system"), m("/run/current-system"), 0).
-					Bind(m("/sys/block"), m("/sys/block"), container.BindOptional).
-					Bind(m("/sys/bus"), m("/sys/bus"), container.BindOptional).
-					Bind(m("/sys/class"), m("/sys/class"), container.BindOptional).
-					Bind(m("/sys/dev"), m("/sys/dev"), container.BindOptional).
-					Bind(m("/sys/devices"), m("/sys/devices"), container.BindOptional).
+					Bind(m("/sys/block"), m("/sys/block"), bits.BindOptional).
+					Bind(m("/sys/bus"), m("/sys/bus"), bits.BindOptional).
+					Bind(m("/sys/class"), m("/sys/class"), bits.BindOptional).
+					Bind(m("/sys/dev"), m("/sys/dev"), bits.BindOptional).
+					Bind(m("/sys/devices"), m("/sys/devices"), bits.BindOptional).
 					Bind(m("/run/opengl-driver"), m("/run/opengl-driver"), 0).
-					Bind(m("/dev/dri"), m("/dev/dri"), container.BindDevice|container.BindWritable|container.BindOptional).
+					Bind(m("/dev/dri"), m("/dev/dri"), bits.BindDevice|bits.BindWritable|bits.BindOptional).
 					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).
+					Bind(m("/var/lib/persist/module/hakurei/0/1"), m("/var/lib/persist/module/hakurei/0/1"), bits.BindWritable|bits.BindEnsure).
 					Remount(m("/dev/"), syscall.MS_RDONLY).
 					Tmpfs(m("/run/user/"), 4096, 0755).
-					Bind(m("/tmp/hakurei.0/runtime/1"), m("/run/user/1971"), container.BindWritable).
-					Bind(m("/tmp/hakurei.0/tmpdir/1"), m("/tmp/"), container.BindWritable).
+					Bind(m("/tmp/hakurei.0/runtime/1"), m("/run/user/1971"), bits.BindWritable).
+					Bind(m("/tmp/hakurei.0/tmpdir/1"), m("/tmp/"), bits.BindWritable).
 					Place(m("/etc/passwd"), []byte("u0_a1:x:1971:100:Hakurei:/var/lib/persist/module/hakurei/0/1:/run/current-system/sw/bin/zsh\n")).
 					Place(m("/etc/group"), []byte("hakurei:x:100:\n")).
 					Bind(m("/run/user/1971/wayland-0"), m("/run/user/1971/wayland-0"), 0).
 					Bind(m("/run/user/1971/hakurei/8e2c76b066dabe574cf073bdb46eb5c1/pulse"), m("/run/user/1971/pulse/native"), 0).
-					Place(m(hst.Tmp+"/pulse-cookie"), nil).
+					Place(m(hst.Tmp+"/pulse-cookie"), bytes.Repeat([]byte{0}, pulseCookieSizeMax)).
 					Bind(m("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/bus"), m("/run/user/1971/bus"), 0).
 					Bind(m("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/system_bus_socket"), m("/run/dbus/system_bus_socket"), 0).
 					Remount(m("/"), syscall.MS_RDONLY),
-				SeccompPresets: seccomp.PresetExt | seccomp.PresetDenyTTY | seccomp.PresetDenyDevel,
+				SeccompPresets: bits.PresetExt | bits.PresetDenyTTY | bits.PresetDenyDevel,
 				HostNet:        true,
 				ForwardCancel:  true,
 			},
@@ -375,28 +445,75 @@ func TestApp(t *testing.T) {
 
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
-			t.Run("finalise", func(t *testing.T) {
-				seal := outcome{syscallDispatcher: tc.k, id: &stringPair[state.ID]{tc.id, tc.id.String()}}
-				err := seal.finalise(t.Context(), tc.config)
-				if err != nil {
-					if s, ok := container.GetErrorMessage(err); !ok {
-						t.Fatalf("Seal: error = %v", err)
-					} else {
-						t.Fatalf("Seal: %s", s)
+			gr, gw := io.Pipe()
+
+			var gotSys *system.I
+			{
+				sPriv := outcomeState{
+					ID:        &tc.id,
+					Identity:  tc.config.Identity,
+					UserID:    (&Hsu{k: tc.k}).MustIDMsg(msg),
+					EnvPaths:  copyPaths(tc.k),
+					Container: tc.config.Container,
+				}
+
+				sPriv.populateEarly(tc.k, msg, tc.config)
+				if err := sPriv.populateLocal(tc.k, msg); err != nil {
+					t.Fatalf("populateLocal: error = %#v", err)
+				}
+
+				gotSys = system.New(t.Context(), msg, sPriv.uid.unwrap())
+				stateSys := outcomeStateSys{sys: gotSys, outcomeState: &sPriv}
+				for _, op := range sPriv.Shim.Ops {
+					if err := op.toSystem(&stateSys, tc.config); err != nil {
+						t.Fatalf("toSystem: error = %#v", err)
 					}
 				}
 
-				t.Run("sys", func(t *testing.T) {
-					if !seal.sys.Equal(tc.wantSys) {
-						t.Errorf("Seal: sys = %#v, want %#v", seal.sys, tc.wantSys)
+				go func() {
+					e := gob.NewEncoder(gw)
+					if err := errors.Join(e.Encode(&sPriv)); err != nil {
+						t.Errorf("Encode: error = %v", err)
+						panic("unexpected encode fault")
 					}
-				})
+				}()
+			}
 
-				t.Run("params", func(t *testing.T) {
-					if !reflect.DeepEqual(seal.container, tc.wantParams) {
-						t.Errorf("seal: container =\n%s\n, want\n%s", mustMarshal(seal.container), mustMarshal(tc.wantParams))
+			var gotParams container.Params
+			{
+				var sShim outcomeState
+
+				d := gob.NewDecoder(gr)
+				if err := errors.Join(d.Decode(&sShim)); err != nil {
+					t.Fatalf("Decode: error = %v", err)
+				}
+				if err := sShim.populateLocal(tc.k, msg); err != nil {
+					t.Fatalf("populateLocal: error = %#v", err)
+				}
+
+				stateParams := outcomeStateParams{params: &gotParams, outcomeState: &sShim}
+				if sShim.Container.Env == nil {
+					stateParams.env = make(map[string]string, envAllocSize)
+				} else {
+					stateParams.env = maps.Clone(sShim.Container.Env)
+				}
+				for _, op := range sShim.Shim.Ops {
+					if err := op.toContainer(&stateParams); err != nil {
+						t.Fatalf("toContainer: error = %#v", err)
 					}
-				})
+				}
+			}
+
+			t.Run("sys", func(t *testing.T) {
+				if !gotSys.Equal(tc.wantSys) {
+					t.Errorf("toSystem: sys = %#v, want %#v", gotSys, tc.wantSys)
+				}
+			})
+
+			t.Run("params", func(t *testing.T) {
+				if !reflect.DeepEqual(&gotParams, tc.wantParams) {
+					t.Errorf("toContainer: params =\n%s\n, want\n%s", mustMarshal(&gotParams), mustMarshal(tc.wantParams))
+				}
 			})
 		})
 	}
@@ -443,8 +560,203 @@ func (s stubFileInfoIsDir) ModTime() time.Time { panic("attempted to call ModTim
 func (s stubFileInfoIsDir) IsDir() bool        { return bool(s) }
 func (s stubFileInfoIsDir) Sys() any           { panic("attempted to call Sys") }
 
-func m(pathname string) *container.Absolute {
-	return container.MustAbs(pathname)
+type stubFileInfoPulseCookie struct{ stubFileInfoIsDir }
+
+func (s stubFileInfoPulseCookie) Size() int64 { return pulseCookieSizeMax }
+
+type stubOsFileReadCloser struct{ io.ReadCloser }
+
+func (s stubOsFileReadCloser) Name() string               { panic("attempting to call Name") }
+func (s stubOsFileReadCloser) Write([]byte) (int, error)  { panic("attempting to call Write") }
+func (s stubOsFileReadCloser) Stat() (fs.FileInfo, error) { panic("attempting to call Stat") }
+
+type stubNixOS struct {
+	usernameErr map[string]error
+}
+
+func (k *stubNixOS) new(func(k syscallDispatcher)) { panic("not implemented") }
+
+func (k *stubNixOS) getuid() int { return 1971 }
+func (k *stubNixOS) getgid() int { return 100 }
+
+func (k *stubNixOS) lookupEnv(key string) (string, bool) {
+	switch key {
+	case "SHELL":
+		return "/run/current-system/sw/bin/zsh", true
+	case "TERM":
+		return "xterm-256color", true
+	case "WAYLAND_DISPLAY":
+		return "wayland-0", true
+	case "PULSE_COOKIE":
+		return "", false
+	case "HOME":
+		return "/home/ophestra", true
+	case "XDG_RUNTIME_DIR":
+		return "/run/user/1971", true
+	case "XDG_CONFIG_HOME":
+		return "/home/ophestra/xdg/config", true
+	default:
+		panic(fmt.Sprintf("attempted to access unexpected environment variable %q", key))
+	}
+}
+
+func (k *stubNixOS) stat(name string) (fs.FileInfo, error) {
+	switch name {
+	case "/var/run/nscd":
+		return nil, nil
+	case "/run/user/1971/pulse":
+		return nil, nil
+	case "/run/user/1971/pulse/native":
+		return stubFileInfoMode(0666), nil
+	case "/home/ophestra/.pulse-cookie":
+		return stubFileInfoIsDir(true), nil
+	case "/home/ophestra/xdg/config/pulse/cookie":
+		return stubFileInfoPulseCookie{false}, nil
+	default:
+		panic(fmt.Sprintf("attempted to stat unexpected path %q", name))
+	}
+}
+
+func (k *stubNixOS) open(name string) (osFile, error) {
+	switch name {
+	case "/home/ophestra/xdg/config/pulse/cookie":
+		return stubOsFileReadCloser{io.NopCloser(bytes.NewReader(bytes.Repeat([]byte{0}, pulseCookieSizeMax)))}, nil
+	default:
+		panic(fmt.Sprintf("attempted to open unexpected path %q", name))
+	}
+}
+
+func (k *stubNixOS) readdir(name string) ([]fs.DirEntry, error) {
+	switch name {
+	case "/":
+		return stubDirEntries("bin", "boot", "dev", "etc", "home", "lib",
+			"lib64", "nix", "proc", "root", "run", "srv", "sys", "tmp", "usr", "var")
+
+	case "/run":
+		return stubDirEntries("agetty.reload", "binfmt", "booted-system",
+			"credentials", "cryptsetup", "current-system", "dbus", "host", "keys",
+			"libvirt", "libvirtd.pid", "lock", "log", "lvm", "mount", "NetworkManager",
+			"nginx", "nixos", "nscd", "opengl-driver", "pppd", "resolvconf", "sddm",
+			"store", "syncoid", "system", "systemd", "tmpfiles.d", "udev", "udisks2",
+			"user", "utmp", "virtlogd.pid", "wrappers", "zed.pid", "zed.state")
+
+	case "/etc":
+		return stubDirEntries("alsa", "bashrc", "binfmt.d", "dbus-1", "default",
+			"ethertypes", "fonts", "fstab", "fuse.conf", "group", "host.conf", "hostid",
+			"hostname", "hostname.CHECKSUM", "hosts", "inputrc", "ipsec.d", "issue", "kbd",
+			"libblockdev", "locale.conf", "localtime", "login.defs", "lsb-release", "lvm",
+			"machine-id", "man_db.conf", "modprobe.d", "modules-load.d", "mtab", "nanorc",
+			"netgroup", "NetworkManager", "nix", "nixos", "NIXOS", "nscd.conf", "nsswitch.conf",
+			"opensnitchd", "os-release", "pam", "pam.d", "passwd", "pipewire", "pki", "polkit-1",
+			"profile", "protocols", "qemu", "resolv.conf", "resolvconf.conf", "rpc", "samba",
+			"sddm.conf", "secureboot", "services", "set-environment", "shadow", "shells", "ssh",
+			"ssl", "static", "subgid", "subuid", "sudoers", "sysctl.d", "systemd", "terminfo",
+			"tmpfiles.d", "udev", "udisks2", "UPower", "vconsole.conf", "X11", "zfs", "zinputrc",
+			"zoneinfo", "zprofile", "zshenv", "zshrc")
+
+	default:
+		panic(fmt.Sprintf("attempted to read unexpected directory %q", name))
+	}
+}
+
+func (k *stubNixOS) tempdir() string { return "/tmp/" }
+
+func (k *stubNixOS) evalSymlinks(path string) (string, error) {
+	switch path {
+	case "/var/run/nscd":
+		return "/run/nscd", nil
+	case "/run/user/1971":
+		return "/run/user/1971", nil
+	case "/tmp/hakurei.0":
+		return "/tmp/hakurei.0", nil
+	case "/run/dbus":
+		return "/run/dbus", nil
+	case "/dev/kvm":
+		return "/dev/kvm", nil
+	case "/etc/":
+		return "/etc/", nil
+	case "/bin":
+		return "/bin", nil
+	case "/boot":
+		return "/boot", nil
+	case "/home":
+		return "/home", nil
+	case "/lib":
+		return "/lib", nil
+	case "/lib64":
+		return "/lib64", nil
+	case "/nix":
+		return "/nix", nil
+	case "/root":
+		return "/root", nil
+	case "/run":
+		return "/run", nil
+	case "/srv":
+		return "/srv", nil
+	case "/sys":
+		return "/sys", nil
+	case "/usr":
+		return "/usr", nil
+	case "/var":
+		return "/var", nil
+	case "/dev/dri":
+		return "/dev/dri", nil
+	case "/usr/bin/":
+		return "/usr/bin/", nil
+	case "/nix/store":
+		return "/nix/store", nil
+	case "/run/current-system":
+		return "/nix/store/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-nixos-system-satori-25.05.99999999.aaaaaaa", nil
+	case "/sys/block":
+		return "/sys/block", nil
+	case "/sys/bus":
+		return "/sys/bus", nil
+	case "/sys/class":
+		return "/sys/class", nil
+	case "/sys/dev":
+		return "/sys/dev", nil
+	case "/sys/devices":
+		return "/sys/devices", nil
+	case "/run/opengl-driver":
+		return "/nix/store/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-graphics-drivers", nil
+	case "/var/lib/persist/module/hakurei/0/1":
+		return "/var/lib/persist/module/hakurei/0/1", nil
+	default:
+		panic(fmt.Sprintf("attempted to evaluate unexpected path %q", path))
+	}
+}
+
+func (k *stubNixOS) lookupGroupId(name string) (string, error) {
+	switch name {
+	case "video":
+		return "26", nil
+	default:
+		return "", user.UnknownGroupError(name)
+	}
+}
+
+func (k *stubNixOS) cmdOutput(cmd *exec.Cmd) ([]byte, error) {
+	switch cmd.Path {
+	case "/proc/nonexistent/hsu":
+		return []byte{'0'}, nil
+	default:
+		panic(fmt.Sprintf("unexpected cmd %#v", cmd))
+	}
+}
+
+func (k *stubNixOS) overflowUid(container.Msg) int { return 65534 }
+func (k *stubNixOS) overflowGid(container.Msg) int { return 65534 }
+
+func (k *stubNixOS) mustHsuPath() *check.Absolute { return m("/proc/nonexistent/hsu") }
+
+func (k *stubNixOS) fatalf(format string, v ...any) { panic(fmt.Sprintf(format, v...)) }
+
+func (k *stubNixOS) isVerbose() bool                  { return true }
+func (k *stubNixOS) verbose(v ...any)                 { log.Print(v...) }
+func (k *stubNixOS) verbosef(format string, v ...any) { log.Printf(format, v...) }
+
+func m(pathname string) *check.Absolute {
+	return check.MustAbs(pathname)
 }
 
 func f(c hst.FilesystemConfig) hst.FilesystemConfigJSON {

internal/app/container.go

@@ -1,254 +0,0 @@
-package app
-
-import (
-	"errors"
-	"fmt"
-	"io/fs"
-	"maps"
-	"path"
-	"syscall"
-
-	"hakurei.app/container"
-	"hakurei.app/container/seccomp"
-	"hakurei.app/hst"
-	"hakurei.app/system/dbus"
-)
-
-// 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(
-	k syscallDispatcher,
-	s *hst.ContainerConfig,
-	prefix string,
-	sc *hst.Paths,
-	uid, gid *int,
-) (*container.Params, map[string]string, error) {
-	if s == nil {
-		return nil, nil, newWithMessage("invalid container configuration")
-	}
-
-	params := &container.Params{
-		Hostname:       s.Hostname,
-		SeccompFlags:   s.SeccompFlags,
-		SeccompPresets: s.SeccompPresets,
-		RetainSession:  s.Tty,
-		HostNet:        s.HostNet,
-		HostAbstract:   s.HostAbstract,
-
-		// the container is canceled when shim is requested to exit or receives an interrupt or termination signal;
-		// this behaviour is implemented in the shim
-		ForwardCancel: s.WaitDelay >= 0,
-	}
-
-	as := &hst.ApplyState{AutoEtcPrefix: prefix}
-	{
-		ops := make(container.Ops, 0, preallocateOpsCount+len(s.Filesystem))
-		params.Ops = &ops
-		as.Ops = &ops
-	}
-
-	if s.Multiarch {
-		params.SeccompFlags |= seccomp.AllowMultiarch
-	}
-
-	if !s.SeccompCompat {
-		params.SeccompPresets |= seccomp.PresetExt
-	}
-	if !s.Devel {
-		params.SeccompPresets |= seccomp.PresetDenyDevel
-	}
-	if !s.Userns {
-		params.SeccompPresets |= seccomp.PresetDenyNS
-	}
-	if !s.Tty {
-		params.SeccompPresets |= seccomp.PresetDenyTTY
-	}
-
-	if s.MapRealUID {
-		params.Uid = k.getuid()
-		*uid = params.Uid
-		params.Gid = k.getgid()
-		*gid = params.Gid
-	} else {
-		*uid = k.overflowUid()
-		*gid = k.overflowGid()
-	}
-
-	filesystem := s.Filesystem
-	var autoroot *hst.FSBind
-	// valid happens late, so root mount gets it here
-	if len(filesystem) > 0 && filesystem[0].Valid() && filesystem[0].Path().String() == container.FHSRoot {
-		// if the first element targets /, it is inserted early and excluded from path hiding
-		rootfs := filesystem[0].FilesystemConfig
-		filesystem = filesystem[1:]
-		rootfs.Apply(as)
-
-		// autoroot requires special handling during path hiding
-		if b, ok := rootfs.(*hst.FSBind); ok && b.IsAutoRoot() {
-			autoroot = b
-		}
-	}
-
-	params.
-		Proc(container.AbsFHSProc).
-		Tmpfs(hst.AbsTmp, 1<<12, 0755)
-
-	if !s.Device {
-		params.DevWritable(container.AbsFHSDev, true)
-	} 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 */
-	var hidePaths []string
-	hidePaths = append(hidePaths, sc.RuntimePath.String(), sc.SharePath.String())
-	_, systemBusAddr := dbus.Address()
-	if entries, err := dbus.Parse([]byte(systemBusAddr)); err != nil {
-		return nil, nil, err
-	} else {
-		// there is usually only one, do not preallocate
-		for _, entry := range entries {
-			if entry.Method != "unix" {
-				continue
-			}
-			for _, pair := range entry.Values {
-				if pair[0] == "path" {
-					if path.IsAbs(pair[1]) {
-						// get parent dir of socket
-						dir := path.Dir(pair[1])
-						if dir == "." || dir == container.FHSRoot {
-							k.verbosef("dbus socket %q is in an unusual location", pair[1])
-						}
-						hidePaths = append(hidePaths, dir)
-					} else {
-						k.verbosef("dbus socket %q is not absolute", pair[1])
-					}
-				}
-			}
-		}
-	}
-	hidePathMatch := make([]bool, len(hidePaths))
-	for i := range hidePaths {
-		if err := evalSymlinks(k, &hidePaths[i]); err != nil {
-			return nil, nil, err
-		}
-	}
-
-	var hidePathSourceCount int
-	for i, c := range filesystem {
-		if !c.Valid() {
-			return nil, nil, fmt.Errorf("invalid filesystem at index %d", i)
-		}
-		c.Apply(as)
-
-		// fs counter
-		hidePathSourceCount += len(c.Host())
-	}
-
-	// AutoRootOp is a collection of many BindMountOp internally
-	var autoRootEntries []fs.DirEntry
-	if autoroot != nil {
-		if d, err := k.readdir(autoroot.Source.String()); err != nil {
-			return nil, nil, err
-		} else {
-			// autoroot counter
-			hidePathSourceCount += len(d)
-			autoRootEntries = d
-		}
-	}
-
-	hidePathSource := make([]*container.Absolute, 0, hidePathSourceCount)
-
-	// fs append
-	for _, c := range filesystem {
-		// all entries already checked above
-		hidePathSource = append(hidePathSource, c.Host()...)
-	}
-
-	// autoroot append
-	if autoroot != nil {
-		for _, ent := range autoRootEntries {
-			name := ent.Name()
-			if container.IsAutoRootBindable(name) {
-				hidePathSource = append(hidePathSource, autoroot.Source.Append(name))
-			}
-		}
-	}
-
-	// evaluated path, input path
-	hidePathSourceEval := make([][2]string, len(hidePathSource))
-	for i, a := range hidePathSource {
-		if a == nil {
-			// unreachable
-			return nil, nil, syscall.ENOTRECOVERABLE
-		}
-
-		hidePathSourceEval[i] = [2]string{a.String(), a.String()}
-		if err := evalSymlinks(k, &hidePathSourceEval[i][0]); err != nil {
-			return nil, nil, err
-		}
-	}
-
-	for _, p := range hidePathSourceEval {
-		for i := range hidePaths {
-			// skip matched entries
-			if hidePathMatch[i] {
-				continue
-			}
-
-			if ok, err := deepContainsH(p[0], hidePaths[i]); err != nil {
-				return nil, nil, err
-			} else if ok {
-				hidePathMatch[i] = true
-				k.verbosef("hiding path %q from %q", hidePaths[i], p[1])
-			}
-		}
-	}
-
-	// cover matched paths
-	for i, ok := range hidePathMatch {
-		if ok {
-			if a, err := container.NewAbs(hidePaths[i]); err != nil {
-				var absoluteError *container.AbsoluteError
-				if !errors.As(err, &absoluteError) {
-					return nil, nil, err
-				}
-				if absoluteError == nil {
-					return nil, nil, syscall.ENOTRECOVERABLE
-				}
-				return nil, nil, fmt.Errorf("invalid path hiding candidate %q", absoluteError.Pathname)
-			} else {
-				params.Tmpfs(a, 1<<13, 0755)
-			}
-		}
-	}
-
-	// no more ContainerConfig paths beyond this point
-	if !s.Device {
-		params.Remount(container.AbsFHSDev, syscall.MS_RDONLY)
-	}
-
-	return params, maps.Clone(s.Env), nil
-}
-
-// evalSymlinks calls syscallDispatcher.evalSymlinks but discards errors unwrapping to [fs.ErrNotExist].
-func evalSymlinks(k syscallDispatcher, v *string) error {
-	if p, err := k.evalSymlinks(*v); err != nil {
-		if !errors.Is(err, fs.ErrNotExist) {
-			return err
-		}
-		k.verbosef("path %q does not yet exist", *v)
-	} else {
-		*v = p
-	}
-	return nil
-}

internal/app/dispatcher.go

@@ -1,6 +1,8 @@
 package app
 
 import (
+	"io"
+	"io/fs"
 	"log"
 	"os"
 	"os/exec"
@@ -8,10 +10,17 @@ import (
 	"path/filepath"
 
 	"hakurei.app/container"
+	"hakurei.app/container/check"
 	"hakurei.app/internal"
-	"hakurei.app/internal/hlog"
 )
 
+// osFile represents [os.File].
+type osFile interface {
+	Name() string
+	io.Writer
+	fs.File
+}
+
 // syscallDispatcher provides methods that make state-dependent system calls as part of their behaviour.
 type syscallDispatcher interface {
 	// new starts a goroutine with a new instance of syscallDispatcher.
@@ -27,6 +36,8 @@ type syscallDispatcher interface {
 	lookupEnv(key string) (string, bool)
 	// stat provides [os.Stat].
 	stat(name string) (os.FileInfo, error)
+	// open provides [os.Open].
+	open(name string) (osFile, error)
 	// readdir provides [os.ReadDir].
 	readdir(name string) ([]os.DirEntry, error)
 	// tempdir provides [os.TempDir].
@@ -35,9 +46,6 @@ type syscallDispatcher interface {
 	// evalSymlinks provides [filepath.EvalSymlinks].
 	evalSymlinks(path string) (string, error)
 
-	// lookPath provides exec.LookPath.
-	lookPath(file string) (string, error)
-
 	// lookupGroupId calls [user.LookupGroup] and returns the Gid field of the resulting [user.Group] struct.
 	lookupGroupId(name string) (string, error)
 
@@ -45,19 +53,15 @@ type syscallDispatcher interface {
 	cmdOutput(cmd *exec.Cmd) ([]byte, error)
 
 	// overflowUid provides [container.OverflowUid].
-	overflowUid() int
+	overflowUid(msg container.Msg) int
 	// overflowGid provides [container.OverflowGid].
-	overflowGid() int
+	overflowGid(msg container.Msg) int
 
 	// mustHsuPath provides [internal.MustHsuPath].
-	mustHsuPath() string
+	mustHsuPath() *check.Absolute
 
 	// fatalf provides [log.Fatalf].
 	fatalf(format string, v ...any)
-
-	isVerbose() bool
-	verbose(v ...any)
-	verbosef(format string, v ...any)
 }
 
 // direct implements syscallDispatcher on the current kernel.
@@ -69,13 +73,12 @@ func (direct) getuid() int                                { return os.Getuid() }
 func (direct) getgid() int                                { return os.Getgid() }
 func (direct) lookupEnv(key string) (string, bool)        { return os.LookupEnv(key) }
 func (direct) stat(name string) (os.FileInfo, error)      { return os.Stat(name) }
+func (direct) open(name string) (osFile, error)           { return os.Open(name) }
 func (direct) readdir(name string) ([]os.DirEntry, error) { return os.ReadDir(name) }
 func (direct) tempdir() string                            { return os.TempDir() }
 
 func (direct) evalSymlinks(path string) (string, error) { return filepath.EvalSymlinks(path) }
 
-func (direct) lookPath(file string) (string, error) { return exec.LookPath(file) }
-
 func (direct) lookupGroupId(name string) (gid string, err error) {
 	var group *user.Group
 	group, err = user.LookupGroup(name)
@@ -87,13 +90,9 @@ func (direct) lookupGroupId(name string) (gid string, err error) {
 
 func (direct) cmdOutput(cmd *exec.Cmd) ([]byte, error) { return cmd.Output() }
 
-func (direct) overflowUid() int { return container.OverflowUid() }
-func (direct) overflowGid() int { return container.OverflowGid() }
+func (direct) overflowUid(msg container.Msg) int { return container.OverflowUid(msg) }
+func (direct) overflowGid(msg container.Msg) int { return container.OverflowGid(msg) }
 
-func (direct) mustHsuPath() string { return internal.MustHsuPath() }
+func (direct) mustHsuPath() *check.Absolute { return internal.MustHsuPath() }
 
 func (direct) fatalf(format string, v ...any) { log.Fatalf(format, v...) }
-
-func (k direct) isVerbose() bool                { return hlog.Load() }
-func (direct) verbose(v ...any)                 { hlog.Verbose(v...) }
-func (direct) verbosef(format string, v ...any) { hlog.Verbosef(format, v...) }

internal/app/dispatcher_test.go

@@ -0,0 +1,27 @@
+package app
+
+import (
+	"os"
+	"os/exec"
+
+	"hakurei.app/container"
+	"hakurei.app/container/check"
+)
+
+type panicDispatcher struct{}
+
+func (panicDispatcher) new(func(k syscallDispatcher))         { panic("unreachable") }
+func (panicDispatcher) getuid() int                           { panic("unreachable") }
+func (panicDispatcher) getgid() int                           { panic("unreachable") }
+func (panicDispatcher) lookupEnv(string) (string, bool)       { panic("unreachable") }
+func (panicDispatcher) stat(string) (os.FileInfo, error)      { panic("unreachable") }
+func (panicDispatcher) open(string) (osFile, error)           { panic("unreachable") }
+func (panicDispatcher) readdir(string) ([]os.DirEntry, error) { panic("unreachable") }
+func (panicDispatcher) tempdir() string                       { panic("unreachable") }
+func (panicDispatcher) evalSymlinks(string) (string, error)   { panic("unreachable") }
+func (panicDispatcher) lookupGroupId(string) (string, error)  { panic("unreachable") }
+func (panicDispatcher) cmdOutput(*exec.Cmd) ([]byte, error)   { panic("unreachable") }
+func (panicDispatcher) overflowUid(container.Msg) int         { panic("unreachable") }
+func (panicDispatcher) overflowGid(container.Msg) int         { panic("unreachable") }
+func (panicDispatcher) mustHsuPath() *check.Absolute          { panic("unreachable") }
+func (panicDispatcher) fatalf(string, ...any)                 { panic("unreachable") }

internal/app/env.go

@@ -0,0 +1,59 @@
+package app
+
+import (
+	"strconv"
+
+	"hakurei.app/container/check"
+	"hakurei.app/hst"
+)
+
+// EnvPaths holds paths copied from the environment and is used to create [hst.Paths].
+type EnvPaths struct {
+	// TempDir is returned by [os.TempDir].
+	TempDir *check.Absolute
+	// RuntimePath is copied from $XDG_RUNTIME_DIR.
+	RuntimePath *check.Absolute
+}
+
+// Copy expands [EnvPaths] into [hst.Paths].
+func (env *EnvPaths) Copy(v *hst.Paths, userid int) {
+	if env == nil || env.TempDir == nil || v == nil {
+		panic("attempting to use an invalid EnvPaths")
+	}
+
+	v.TempDir = env.TempDir
+	v.SharePath = env.TempDir.Append("hakurei." + strconv.Itoa(userid))
+
+	if env.RuntimePath == nil {
+		// fall back to path in share since hakurei has no hard XDG dependency
+		v.RunDirPath = v.SharePath.Append("run")
+		v.RuntimePath = v.RunDirPath.Append("compat")
+	} else {
+		v.RuntimePath = env.RuntimePath
+		v.RunDirPath = env.RuntimePath.Append("hakurei")
+	}
+}
+
+// CopyPaths returns a populated [EnvPaths].
+func CopyPaths() *EnvPaths { return copyPaths(direct{}) }
+
+// copyPaths returns a populated [EnvPaths].
+func copyPaths(k syscallDispatcher) *EnvPaths {
+	const xdgRuntimeDir = "XDG_RUNTIME_DIR"
+
+	var env EnvPaths
+
+	if tempDir, err := check.NewAbs(k.tempdir()); err != nil {
+		k.fatalf("invalid TMPDIR: %v", err)
+		panic("unreachable")
+	} else {
+		env.TempDir = tempDir
+	}
+
+	r, _ := k.lookupEnv(xdgRuntimeDir)
+	if a, err := check.NewAbs(r); err == nil {
+		env.RuntimePath = a
+	}
+
+	return &env
+}

internal/app/env_test.go

@@ -0,0 +1,131 @@
+package app
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+
+	"hakurei.app/container"
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
+	"hakurei.app/container/stub"
+	"hakurei.app/hst"
+)
+
+func TestEnvPaths(t *testing.T) {
+	testCases := []struct {
+		name string
+		env  *EnvPaths
+		want hst.Paths
+
+		wantPanic string
+	}{
+		{"nil", nil, hst.Paths{}, "attempting to use an invalid EnvPaths"},
+		{"zero", new(EnvPaths), hst.Paths{}, "attempting to use an invalid EnvPaths"},
+
+		{"nil tempdir", &EnvPaths{
+			RuntimePath: fhs.AbsTmp,
+		}, hst.Paths{}, "attempting to use an invalid EnvPaths"},
+
+		{"nil runtime", &EnvPaths{
+			TempDir: fhs.AbsTmp,
+		}, hst.Paths{
+			TempDir:     fhs.AbsTmp,
+			SharePath:   fhs.AbsTmp.Append("hakurei.3735928559"),
+			RuntimePath: fhs.AbsTmp.Append("hakurei.3735928559/run/compat"),
+			RunDirPath:  fhs.AbsTmp.Append("hakurei.3735928559/run"),
+		}, ""},
+
+		{"full", &EnvPaths{
+			TempDir:     fhs.AbsTmp,
+			RuntimePath: fhs.AbsRunUser.Append("1000"),
+		}, hst.Paths{
+			TempDir:     fhs.AbsTmp,
+			SharePath:   fhs.AbsTmp.Append("hakurei.3735928559"),
+			RuntimePath: fhs.AbsRunUser.Append("1000"),
+			RunDirPath:  fhs.AbsRunUser.Append("1000/hakurei"),
+		}, ""},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if tc.wantPanic != "" {
+				defer func() {
+					if r := recover(); r != tc.wantPanic {
+						t.Errorf("Copy: panic = %#v, want %q", r, tc.wantPanic)
+					}
+				}()
+			}
+
+			var sc hst.Paths
+			tc.env.Copy(&sc, 0xdeadbeef)
+			if !reflect.DeepEqual(&sc, &tc.want) {
+				t.Errorf("Copy: %#v, want %#v", sc, tc.want)
+			}
+		})
+	}
+}
+
+func TestCopyPaths(t *testing.T) {
+	testCases := []struct {
+		name  string
+		env   map[string]string
+		tmp   string
+		fatal string
+		want  EnvPaths
+	}{
+		{"invalid tempdir", nil, "\x00",
+			"invalid TMPDIR: path \"\\x00\" is not absolute", EnvPaths{}},
+		{"empty environment", make(map[string]string), container.Nonexistent,
+			"", EnvPaths{TempDir: check.MustAbs(container.Nonexistent)}},
+		{"invalid XDG_RUNTIME_DIR", map[string]string{"XDG_RUNTIME_DIR": "\x00"}, container.Nonexistent,
+			"", EnvPaths{TempDir: check.MustAbs(container.Nonexistent)}},
+		{"full", map[string]string{"XDG_RUNTIME_DIR": "/\x00"}, container.Nonexistent,
+			"", EnvPaths{TempDir: check.MustAbs(container.Nonexistent), RuntimePath: check.MustAbs("/\x00")}},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if tc.fatal != "" {
+				defer stub.HandleExit(t)
+			}
+
+			k := copyPathsDispatcher{t: t, env: tc.env, tmp: tc.tmp, expectsFatal: tc.fatal}
+			got := copyPaths(k)
+
+			if tc.fatal != "" {
+				t.Fatalf("copyPaths: expected fatal %q", tc.fatal)
+			}
+
+			if !reflect.DeepEqual(got, &tc.want) {
+				t.Errorf("copyPaths: %#v, want %#v", got, &tc.want)
+			}
+		})
+	}
+}
+
+// copyPathsDispatcher implements enough of syscallDispatcher for all copyPaths code paths.
+type copyPathsDispatcher struct {
+	env map[string]string
+	tmp string
+
+	// must be checked at the conclusion of the test
+	expectsFatal string
+
+	t *testing.T
+	panicDispatcher
+}
+
+func (k copyPathsDispatcher) tempdir() string { return k.tmp }
+func (k copyPathsDispatcher) lookupEnv(key string) (value string, ok bool) {
+	value, ok = k.env[key]
+	return
+}
+func (k copyPathsDispatcher) fatalf(format string, v ...any) {
+	if k.expectsFatal == "" {
+		k.t.Fatalf("unexpected call to fatalf: format = %q, v = %#v", format, v)
+	}
+
+	if got := fmt.Sprintf(format, v...); got != k.expectsFatal {
+		k.t.Fatalf("fatalf: %q, want %q", got, k.expectsFatal)
+	}
+	panic(stub.PanicExit)
+}

internal/app/finalise.go

@@ -7,24 +7,14 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/fs"
 	"os"
 	"os/user"
-	"slices"
-	"strconv"
-	"strings"
 	"sync/atomic"
-	"syscall"
-	"time"
 
 	"hakurei.app/container"
 	"hakurei.app/hst"
 	"hakurei.app/internal/app/state"
-	"hakurei.app/internal/hlog"
 	"hakurei.app/system"
-	"hakurei.app/system/acl"
-	"hakurei.app/system/dbus"
-	"hakurei.app/system/wayland"
 )
 
 func newWithMessage(msg string) error { return newWithMessageError(msg, os.ErrInvalid) }
@@ -34,129 +24,40 @@ func newWithMessageError(msg string, err error) error {
 
 // An outcome is the runnable state of a hakurei container via [hst.Config].
 type outcome struct {
-	// copied from initialising [app]
-	id *stringPair[state.ID]
-	// copied from [sys.State]
-	runDirPath *container.Absolute
-
 	// initial [hst.Config] gob stream for state data;
 	// this is prepared ahead of time as config is clobbered during seal creation
 	ct io.WriterTo
-	// dump dbus proxy message buffer
-	dbusMsg func()
 
-	user hsuUser
-	sys  *system.I
-	ctx  context.Context
+	// Supplementary group ids. Populated during finalise.
+	supp []string
+	// Resolved priv side operating system interactions. Populated during finalise.
+	sys *system.I
+	// Transmitted to shim. Populated during finalise.
+	state *outcomeState
 
-	waitDelay time.Duration
-	container *container.Params
-	env       map[string]string
-	sync      *os.File
-	active    atomic.Bool
+	// Whether the current process is in outcome.main.
+	active atomic.Bool
 
+	ctx context.Context
 	syscallDispatcher
 }
 
-// shareHost holds optional share directory state that must not be accessed directly
-type shareHost struct {
-	// whether XDG_RUNTIME_DIR is used post hsu
-	useRuntimeDir bool
-	// process-specific directory in tmpdir, empty if unused
-	sharePath *container.Absolute
-	// process-specific directory in XDG_RUNTIME_DIR, empty if unused
-	runtimeSharePath *container.Absolute
-
-	seal *outcome
-	sc   hst.Paths
-}
-
-// ensureRuntimeDir must be called if direct access to paths within XDG_RUNTIME_DIR is required
-func (share *shareHost) ensureRuntimeDir() {
-	if share.useRuntimeDir {
-		return
-	}
-	share.useRuntimeDir = true
-	share.seal.sys.Ensure(share.sc.RunDirPath.String(), 0700)
-	share.seal.sys.UpdatePermType(system.User, share.sc.RunDirPath.String(), acl.Execute)
-	share.seal.sys.Ensure(share.sc.RuntimePath.String(), 0700) // ensure this dir in case XDG_RUNTIME_DIR is unset
-	share.seal.sys.UpdatePermType(system.User, share.sc.RuntimePath.String(), acl.Execute)
-}
-
-// instance returns a process-specific share path within tmpdir
-func (share *shareHost) instance() *container.Absolute {
-	if share.sharePath != nil {
-		return share.sharePath
-	}
-	share.sharePath = share.sc.SharePath.Append(share.seal.id.String())
-	share.seal.sys.Ephemeral(system.Process, share.sharePath.String(), 0711)
-	return share.sharePath
-}
-
-// runtime returns a process-specific share path within XDG_RUNTIME_DIR
-func (share *shareHost) runtime() *container.Absolute {
-	if share.runtimeSharePath != nil {
-		return share.runtimeSharePath
-	}
-	share.ensureRuntimeDir()
-	share.runtimeSharePath = share.sc.RunDirPath.Append(share.seal.id.String())
-	share.seal.sys.Ephemeral(system.Process, share.runtimeSharePath.String(), 0700)
-	share.seal.sys.UpdatePerm(share.runtimeSharePath.String(), acl.Execute)
-	return share.runtimeSharePath
-}
-
-// hsuUser stores post-hsu credentials and metadata
-type hsuUser struct {
-	identity *stringPair[int]
-	// target uid resolved by hid:aid
-	uid *stringPair[int]
-
-	// supplementary group ids
-	supp []string
-
-	// app user home directory
-	home *container.Absolute
-	// passwd database username
-	username string
-}
-
-func (k *outcome) finalise(ctx context.Context, 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 {
+func (k *outcome) finalise(ctx context.Context, msg container.Msg, id *state.ID, config *hst.Config) error {
+	if ctx == nil || id == nil {
 		// unreachable
 		panic("invalid call to finalise")
 	}
-	if k.ctx != nil {
+	if k.ctx != nil || k.sys != nil || k.state != nil {
 		// unreachable
 		panic("attempting to finalise twice")
 	}
 	k.ctx = ctx
 
-	if config == nil {
-		return newWithMessage("invalid configuration")
-	}
-	if config.Home == nil {
-		return newWithMessage("invalid path to home directory")
+	if err := config.Validate(); err != nil {
+		return err
 	}
 
+	// TODO(ophestra): do not clobber during finalise
 	{
 		// encode initial configuration for state tracking
 		ct := new(bytes.Buffer)
@@ -166,26 +67,8 @@ func (k *outcome) finalise(ctx context.Context, config *hst.Config) error {
 		k.ct = ct
 	}
 
-	// allowed identity range 0 to 9999, this is checked again in hsu
-	if config.Identity < 0 || config.Identity > 9999 {
-		return newWithMessage(fmt.Sprintf("identity %d out of range", config.Identity))
-	}
-
-	k.user = hsuUser{
-		identity: newInt(config.Identity),
-		home:     config.Home,
-		username: config.Username,
-	}
-
-	hsu := Hsu{k: k}
-	if k.user.username == "" {
-		k.user.username = "chronos"
-	} else if !isValidUsername(k.user.username) {
-		return newWithMessage(fmt.Sprintf("invalid user name %q", k.user.username))
-	}
-	k.user.uid = newInt(HsuUid(hsu.MustID(), k.user.identity.unwrap()))
-
-	k.user.supp = make([]string, len(config.Groups))
+	// hsu expects numerical group ids
+	supp := make([]string, len(config.Groups))
 	for i, name := range config.Groups {
 		if gid, err := k.lookupGroupId(name); err != nil {
 			var unknownGroupError user.UnknownGroupError
@@ -195,411 +78,33 @@ func (k *outcome) finalise(ctx context.Context, config *hst.Config) error {
 				return &hst.AppError{Step: "look up group by name", Err: err}
 			}
 		} else {
-			k.user.supp[i] = gid
+			supp[i] = gid
 		}
 	}
 
-	// permissive defaults
-	if config.Container == nil {
-		hlog.Verbose("container configuration not supplied, PROCEED WITH CAUTION")
-
-		if config.Shell == nil {
-			config.Shell = container.AbsFHSRoot.Append("bin", "sh")
-			s, _ := k.lookupEnv(shell)
-			if a, err := container.NewAbs(s); err == nil {
-				config.Shell = a
-			}
-		}
-
-		// hsu clears the environment so resolve paths early
-		if config.Path == nil {
-			if len(config.Args) > 0 {
-				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 newWithMessageError(err.Error(), err)
-				}
-			} else {
-				config.Path = config.Shell
-			}
-		}
-
-		conf := &hst.ContainerConfig{
-			Userns:       true,
-			HostNet:      true,
-			HostAbstract: true,
-			Tty:          true,
-
-			Filesystem: []hst.FilesystemConfigJSON{
-				// autoroot, includes the home directory
-				{FilesystemConfig: &hst.FSBind{
-					Target:  container.AbsFHSRoot,
-					Source:  container.AbsFHSRoot,
-					Write:   true,
-					Special: true,
-				}},
-			},
-		}
-
-		// bind GPU stuff
-		if config.Enablements.Unwrap()&(system.EX11|system.EWayland) != 0 {
-			conf.Filesystem = append(conf.Filesystem, hst.FilesystemConfigJSON{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("dri"), Device: true, Optional: true}})
-		}
-		// opportunistically bind kvm
-		conf.Filesystem = append(conf.Filesystem, hst.FilesystemConfigJSON{FilesystemConfig: &hst.FSBind{Source: container.AbsFHSDev.Append("kvm"), Device: true, Optional: true}})
-
-		// hide nscd from container if present
-		nscd := container.AbsFHSVar.Append("run/nscd")
-		if _, err := k.stat(nscd.String()); !errors.Is(err, fs.ErrNotExist) {
-			conf.Filesystem = append(conf.Filesystem, hst.FilesystemConfigJSON{FilesystemConfig: &hst.FSEphemeral{Target: nscd}})
-		}
-
-		// do autoetc last
-		conf.Filesystem = append(conf.Filesystem,
-			hst.FilesystemConfigJSON{FilesystemConfig: &hst.FSBind{
-				Target:  container.AbsFHSEtc,
-				Source:  container.AbsFHSEtc,
-				Special: true,
-			}},
-		)
-
-		config.Container = conf
+	// early validation complete at this point
+	s := outcomeState{
+		ID:        id,
+		Identity:  config.Identity,
+		UserID:    (&Hsu{k: k}).MustIDMsg(msg),
+		EnvPaths:  copyPaths(k.syscallDispatcher),
+		Container: config.Container,
+	}
+	s.populateEarly(k.syscallDispatcher, msg, config)
+	if err := s.populateLocal(k.syscallDispatcher, msg); err != nil {
+		return err
 	}
 
-	// late nil checks for pd behaviour
-	if config.Shell == nil {
-		return newWithMessage("invalid shell path")
-	}
-	if config.Path == nil {
-		return newWithMessage("invalid program path")
-	}
-
-	// TODO(ophestra): revert this after params to shim
-	share := &shareHost{seal: k}
-	copyPaths(k.syscallDispatcher, &share.sc, hsu.MustID())
-
-	var mapuid, mapgid *stringPair[int]
-	{
-		var uid, gid int
-		var err error
-		k.container, k.env, err = newContainer(k, config.Container, k.id.String(), &share.sc, &uid, &gid)
-		k.waitDelay = config.Container.WaitDelay
-		if err != nil {
-			return &hst.AppError{Step: "initialise container configuration", Err: err}
-		}
-		if len(config.Args) == 0 {
-			config.Args = []string{config.Path.String()}
-		}
-		k.container.Path = config.Path
-		k.container.Args = config.Args
-
-		mapuid = newInt(uid)
-		mapgid = newInt(gid)
-		if k.env == nil {
-			k.env = make(map[string]string, 1<<6)
-		}
-	}
-
-	// inner XDG_RUNTIME_DIR default formatting of `/run/user/%d` as mapped uid
-	innerRuntimeDir := container.AbsFHSRunUser.Append(mapuid.String())
-	k.env[xdgRuntimeDir] = innerRuntimeDir.String()
-	k.env[xdgSessionClass] = "user"
-	k.env[xdgSessionType] = "tty"
-
-	k.runDirPath = share.sc.RunDirPath
-	k.sys = system.New(k.ctx, k.user.uid.unwrap())
-	k.sys.Ensure(share.sc.SharePath.String(), 0711)
-
-	{
-		runtimeDir := share.sc.SharePath.Append("runtime")
-		k.sys.Ensure(runtimeDir.String(), 0700)
-		k.sys.UpdatePermType(system.User, runtimeDir.String(), acl.Execute)
-		runtimeDirInst := runtimeDir.Append(k.user.identity.String())
-		k.sys.Ensure(runtimeDirInst.String(), 0700)
-		k.sys.UpdatePermType(system.User, runtimeDirInst.String(), acl.Read, acl.Write, acl.Execute)
-		k.container.Tmpfs(container.AbsFHSRunUser, 1<<12, 0755)
-		k.container.Bind(runtimeDirInst, innerRuntimeDir, container.BindWritable)
-	}
-
-	{
-		tmpdir := share.sc.SharePath.Append("tmpdir")
-		k.sys.Ensure(tmpdir.String(), 0700)
-		k.sys.UpdatePermType(system.User, tmpdir.String(), acl.Execute)
-		tmpdirInst := tmpdir.Append(k.user.identity.String())
-		k.sys.Ensure(tmpdirInst.String(), 01700)
-		k.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
-		k.container.Bind(tmpdirInst, container.AbsFHSTmp, container.BindWritable)
-	}
-
-	{
-		username := "chronos"
-		if k.user.username != "" {
-			username = k.user.username
-		}
-		k.container.Dir = k.user.home
-		k.env["HOME"] = k.user.home.String()
-		k.env["USER"] = username
-		k.env[shell] = config.Shell.String()
-
-		k.container.Place(container.AbsFHSEtc.Append("passwd"),
-			[]byte(username+":x:"+mapuid.String()+":"+mapgid.String()+":Hakurei:"+k.user.home.String()+":"+config.Shell.String()+"\n"))
-		k.container.Place(container.AbsFHSEtc.Append("group"),
-			[]byte("hakurei:x:"+mapgid.String()+":\n"))
-	}
-
-	// pass TERM for proper terminal I/O in initial process
-	if t, ok := k.lookupEnv(term); ok {
-		k.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 := 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 {
-			socketPath = share.sc.RuntimePath.Append(name)
-		} else {
-			socketPath = a
-		}
-
-		innerPath := innerRuntimeDir.Append(wayland.FallbackName)
-		k.env[wayland.WaylandDisplay] = wayland.FallbackName
-
-		if !config.DirectWayland { // set up security-context-v1
-			appID := config.ID
-			if appID == "" {
-				// use instance ID in case app id is not set
-				appID = "app.hakurei." + k.id.String()
-			}
-			// downstream socket paths
-			outerPath := share.instance().Append("wayland")
-			k.sys.Wayland(&k.sync, outerPath.String(), socketPath.String(), appID, k.id.String())
-			k.container.Bind(outerPath, innerPath, 0)
-		} else { // bind mount wayland socket (insecure)
-			hlog.Verbose("direct wayland access, PROCEED WITH CAUTION")
-			share.ensureRuntimeDir()
-			k.container.Bind(socketPath, innerPath, 0)
-			k.sys.UpdatePermType(system.EWayland, socketPath.String(), acl.Read, acl.Write, acl.Execute)
-		}
-	}
-
-	if config.Enablements.Unwrap()&system.EX11 != 0 {
-		if d, ok := k.lookupEnv(display); !ok {
-			return newWithMessage("DISPLAY is not set")
-		} else {
-			socketDir := container.AbsFHSTmp.Append(".X11-unix")
-
-			// the socket file at `/tmp/.X11-unix/X%d` is typically owned by the priv user
-			// and not accessible by the target user
-			var socketPath *container.Absolute
-			if len(d) > 1 && d[0] == ':' { // `:%d`
-				if n, err := strconv.Atoi(d[1:]); err == nil && n >= 0 {
-					socketPath = socketDir.Append("X" + strconv.Itoa(n))
-				}
-			} else if len(d) > 5 && strings.HasPrefix(d, "unix:") { // `unix:%s`
-				if a, err := container.NewAbs(d[5:]); err == nil {
-					socketPath = a
-				}
-			}
-			if socketPath != nil {
-				if _, err := k.stat(socketPath.String()); err != nil {
-					if !errors.Is(err, fs.ErrNotExist) {
-						return &hst.AppError{Step: fmt.Sprintf("access X11 socket %q", socketPath), Err: err}
-					}
-				} else {
-					k.sys.UpdatePermType(system.EX11, socketPath.String(), acl.Read, acl.Write, acl.Execute)
-					if !config.Container.HostAbstract {
-						d = "unix:" + socketPath.String()
-					}
-				}
-			}
-
-			k.sys.ChangeHosts("#" + k.user.uid.String())
-			k.env[display] = d
-			k.container.Bind(socketDir, socketDir, 0)
-		}
-	}
-
-	if config.Enablements.Unwrap()&system.EPulse != 0 {
-		// PulseAudio runtime directory (usually `/run/user/%d/pulse`)
-		pulseRuntimeDir := share.sc.RuntimePath.Append("pulse")
-		// PulseAudio socket (usually `/run/user/%d/pulse/native`)
-		pulseSocket := pulseRuntimeDir.Append("native")
-
-		if _, err := k.stat(pulseRuntimeDir.String()); err != nil {
-			if !errors.Is(err, fs.ErrNotExist) {
-				return &hst.AppError{Step: fmt.Sprintf("access PulseAudio directory %q", pulseRuntimeDir), Err: err}
-			}
-			return newWithMessage(fmt.Sprintf("PulseAudio directory %q not found", pulseRuntimeDir))
-		}
-
-		if s, err := k.stat(pulseSocket.String()); err != nil {
-			if !errors.Is(err, fs.ErrNotExist) {
-				return &hst.AppError{Step: fmt.Sprintf("access PulseAudio socket %q", pulseSocket), Err: err}
-			}
-			return newWithMessage(fmt.Sprintf("PulseAudio directory %q found but socket does not exist", pulseRuntimeDir))
-		} else {
-			if m := s.Mode(); m&0o006 != 0o006 {
-				return newWithMessage(fmt.Sprintf("unexpected permissions on %q: %s", pulseSocket, m))
-			}
-		}
-
-		// hard link pulse socket into target-executable share
-		innerPulseRuntimeDir := share.runtime().Append("pulse")
-		innerPulseSocket := innerRuntimeDir.Append("pulse", "native")
-		k.sys.Link(pulseSocket.String(), innerPulseRuntimeDir.String())
-		k.container.Bind(innerPulseRuntimeDir, innerPulseSocket, 0)
-		k.env[pulseServer] = "unix:" + innerPulseSocket.String()
-
-		// publish current user's pulse cookie for target user
-		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
-				}
-			}
-
-			// $XDG_CONFIG_HOME/pulse/cookie
-			if p, ok := k.lookupEnv(xdgConfigHome); ok {
-				if a, err := container.NewAbs(p); err != nil {
-					return &hst.AppError{Step: paLocateStep, Err: err}
-				} else {
-					paCookiePath = a.Append("pulse", "cookie")
-				}
-				if s, err := k.stat(paCookiePath.String()); err != nil {
-					paCookiePath = nil
-					if !errors.Is(err, fs.ErrNotExist) {
-						return &hst.AppError{Step: "access PulseAudio cookie", Err: err}
-					}
-					// fallthrough
-				} else if s.IsDir() {
-					paCookiePath = nil
-				} else {
-					goto out
-				}
-			}
-		out:
-		}
-
-		if paCookiePath != nil {
-			innerDst := hst.AbsTmp.Append("/pulse-cookie")
-			k.env[pulseCookie] = innerDst.String()
-			var payload *[]byte
-			k.container.PlaceP(innerDst, &payload)
-			k.sys.CopyFile(payload, paCookiePath.String(), 256, 256)
-		} else {
-			hlog.Verbose("cannot locate PulseAudio cookie (tried " +
-				"$PULSE_COOKIE, " +
-				"$XDG_CONFIG_HOME/pulse/cookie, " +
-				"$HOME/.pulse-cookie)")
-		}
-	}
-
-	if config.Enablements.Unwrap()&system.EDBus != 0 {
-		// ensure dbus session bus defaults
-		if config.SessionBus == nil {
-			config.SessionBus = dbus.NewConfig(config.ID, true, true)
-		}
-
-		// downstream socket paths
-		sessionPath, systemPath := share.instance().Append("bus"), share.instance().Append("system_bus_socket")
-
-		// configure dbus proxy
-		if f, err := k.sys.ProxyDBus(
-			config.SessionBus, config.SystemBus,
-			sessionPath.String(), systemPath.String(),
-		); err != nil {
+	sys := system.New(k.ctx, msg, s.uid.unwrap())
+	stateSys := outcomeStateSys{sys: sys, outcomeState: &s}
+	for _, op := range s.Shim.Ops {
+		if err := op.toSystem(&stateSys, config); err != nil {
 			return err
-		} else {
-			k.dbusMsg = f
-		}
-
-		// share proxy sockets
-		sessionInner := innerRuntimeDir.Append("bus")
-		k.env[dbusSessionBusAddress] = "unix:path=" + sessionInner.String()
-		k.container.Bind(sessionPath, sessionInner, 0)
-		k.sys.UpdatePerm(sessionPath.String(), acl.Read, acl.Write)
-		if config.SystemBus != nil {
-			systemInner := container.AbsFHSRun.Append("dbus/system_bus_socket")
-			k.env[dbusSystemBusAddress] = "unix:path=" + systemInner.String()
-			k.container.Bind(systemPath, systemInner, 0)
-			k.sys.UpdatePerm(systemPath.String(), acl.Read, acl.Write)
 		}
 	}
 
-	// mount root read-only as the final setup Op
-	k.container.Remount(container.AbsFHSRoot, syscall.MS_RDONLY)
-
-	// append ExtraPerms last
-	for _, p := range config.ExtraPerms {
-		if p == nil || p.Path == nil {
-			continue
-		}
-
-		if p.Ensure {
-			k.sys.Ensure(p.Path.String(), 0700)
-		}
-
-		perms := make(acl.Perms, 0, 3)
-		if p.Read {
-			perms = append(perms, acl.Read)
-		}
-		if p.Write {
-			perms = append(perms, acl.Write)
-		}
-		if p.Execute {
-			perms = append(perms, acl.Execute)
-		}
-		k.sys.UpdatePermType(system.User, p.Path.String(), perms...)
-	}
-
-	// flatten and sort env for deterministic behaviour
-	k.container.Env = make([]string, 0, len(k.env))
-	for key, value := range k.env {
-		if strings.IndexByte(key, '=') != -1 {
-			return &hst.AppError{Step: "flatten environment", Err: syscall.EINVAL,
-				Msg: fmt.Sprintf("invalid environment variable %s", key)}
-		}
-		k.container.Env = append(k.container.Env, key+"="+value)
-	}
-	slices.Sort(k.container.Env)
-
-	if hlog.Load() {
-		hlog.Verbosef("created application seal for uid %s (%s) groups: %v, argv: %s, ops: %d",
-			k.user.uid, k.user.username, config.Groups, k.container.Args, len(*k.container.Ops))
-	}
-
+	k.sys = sys
+	k.supp = supp
+	k.state = &s
 	return nil
 }

internal/app/hsu.go

@@ -10,8 +10,8 @@ import (
 	"sync"
 
 	"hakurei.app/container"
+	"hakurei.app/container/fhs"
 	"hakurei.app/hst"
-	"hakurei.app/internal/hlog"
 )
 
 // Hsu caches responses from cmd/hsu.
@@ -40,13 +40,13 @@ func (h *Hsu) ID() (int, error) {
 	h.ensureDispatcher()
 	h.idOnce.Do(func() {
 		h.id = -1
-		hsuPath := h.k.mustHsuPath()
+		hsuPath := h.k.mustHsuPath().String()
 
 		cmd := exec.Command(hsuPath)
 		cmd.Path = hsuPath
 		cmd.Stderr = os.Stderr // pass through fatal messages
 		cmd.Env = make([]string, 0)
-		cmd.Dir = container.FHSRoot
+		cmd.Dir = fhs.Root
 		var (
 			p         []byte
 			exitError *exec.ExitError
@@ -71,7 +71,10 @@ func (h *Hsu) ID() (int, error) {
 }
 
 // MustID calls [Hsu.ID] and terminates on error.
-func (h *Hsu) MustID() int {
+func (h *Hsu) MustID() int { return h.MustIDMsg(nil) }
+
+// MustIDMsg implements MustID with a custom [container.Msg].
+func (h *Hsu) MustIDMsg(msg container.Msg) int {
 	id, err := h.ID()
 	if err == nil {
 		return id
@@ -79,7 +82,9 @@ func (h *Hsu) MustID() int {
 
 	const fallback = "cannot retrieve user id from setuid wrapper:"
 	if errors.Is(err, ErrHsuAccess) {
-		hlog.Verbose("*"+fallback, err)
+		if msg != nil {
+			msg.Verbose("*"+fallback, err)
+		}
 		os.Exit(1)
 		return -0xdeadbeef
 	} else if m, ok := container.GetErrorMessage(err); ok {

internal/app/outcome.go

@@ -0,0 +1,248 @@
+package app
+
+import (
+	"os"
+	"strconv"
+
+	"hakurei.app/container"
+	"hakurei.app/container/check"
+	"hakurei.app/hst"
+	"hakurei.app/internal/app/state"
+	"hakurei.app/system"
+	"hakurei.app/system/acl"
+)
+
+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 {
+	v T
+	s string
+}
+
+func (s *stringPair[T]) unwrap() T      { return s.v }
+func (s *stringPair[T]) String() string { return s.s }
+
+// outcomeState is copied to the shim process and available while applying outcomeOp.
+// This is transmitted from the priv side to the shim, so exported fields should be kept to a minimum.
+type outcomeState struct {
+	// Params only used by the shim process. Populated by populateEarly.
+	Shim *shimParams
+
+	// Generated and accounted for by the caller.
+	ID *state.ID
+	// Copied from ID.
+	id *stringPair[state.ID]
+
+	// Copied from the [hst.Config] field of the same name.
+	Identity int
+	// Copied from Identity.
+	identity *stringPair[int]
+	// Returned by [Hsu.MustIDMsg].
+	UserID int
+	// Target init namespace uid resolved from UserID and identity.
+	uid *stringPair[int]
+
+	// Included as part of [hst.Config], transmitted as-is unless permissive defaults.
+	Container *hst.ContainerConfig
+
+	// Mapped credentials within container user namespace.
+	Mapuid, Mapgid int
+	// Copied from their respective exported values.
+	mapuid, mapgid *stringPair[int]
+
+	// Copied from [EnvPaths] per-process.
+	sc hst.Paths
+	*EnvPaths
+
+	// Matched paths to cover. Populated by spFilesystemOp.
+	HidePaths []*check.Absolute
+
+	// Copied via populateLocal.
+	k syscallDispatcher
+	// Copied via populateLocal.
+	msg container.Msg
+}
+
+// valid checks outcomeState to be safe for use with outcomeOp.
+func (s *outcomeState) valid() bool {
+	return s != nil &&
+		s.Shim.valid() &&
+		s.ID != nil &&
+		s.Container != nil &&
+		s.EnvPaths != nil
+}
+
+// populateEarly populates exported fields via syscallDispatcher.
+// This must only be called from the priv side.
+func (s *outcomeState) populateEarly(k syscallDispatcher, msg container.Msg, config *hst.Config) {
+	s.Shim = &shimParams{PrivPID: os.Getpid(), Verbose: msg.IsVerbose(), Ops: fromConfig(config)}
+
+	// enforce bounds and default early
+	if s.Container.WaitDelay <= 0 {
+		s.Shim.WaitDelay = hst.WaitDelayDefault
+	} else if s.Container.WaitDelay > hst.WaitDelayMax {
+		s.Shim.WaitDelay = hst.WaitDelayMax
+	} else {
+		s.Shim.WaitDelay = s.Container.WaitDelay
+	}
+
+	if s.Container.MapRealUID {
+		s.Mapuid, s.Mapgid = k.getuid(), k.getgid()
+	} else {
+		s.Mapuid, s.Mapgid = k.overflowUid(msg), k.overflowGid(msg)
+	}
+
+	return
+}
+
+// populateLocal populates unexported fields from transmitted exported fields.
+// These fields are cheaper to recompute per-process.
+func (s *outcomeState) populateLocal(k syscallDispatcher, msg container.Msg) error {
+	if !s.valid() || k == nil || msg == nil {
+		return newWithMessage("impossible outcome state reached")
+	}
+
+	if s.k != nil || s.msg != nil {
+		panic("attempting to call populateLocal twice")
+	}
+	s.k = k
+	s.msg = msg
+
+	s.id = &stringPair[state.ID]{*s.ID, s.ID.String()}
+
+	s.Copy(&s.sc, s.UserID)
+	msg.Verbosef("process share directory at %q, runtime directory at %q", s.sc.SharePath, s.sc.RunDirPath)
+
+	s.identity = newInt(s.Identity)
+	s.mapuid, s.mapgid = newInt(s.Mapuid), newInt(s.Mapgid)
+	s.uid = newInt(HsuUid(s.UserID, s.identity.unwrap()))
+
+	return nil
+}
+
+// instancePath returns a path formatted for outcomeStateSys.instance.
+// This method must only be called from outcomeOp.toContainer if
+// outcomeOp.toSystem has already called outcomeStateSys.instance.
+func (s *outcomeState) instancePath() *check.Absolute { return s.sc.SharePath.Append(s.id.String()) }
+
+// runtimePath returns a path formatted for outcomeStateSys.runtime.
+// This method must only be called from outcomeOp.toContainer if
+// outcomeOp.toSystem has already called outcomeStateSys.runtime.
+func (s *outcomeState) runtimePath() *check.Absolute { return s.sc.RunDirPath.Append(s.id.String()) }
+
+// outcomeStateSys wraps outcomeState and [system.I]. Used on the priv side only.
+// Implementations of outcomeOp must not access fields other than sys unless explicitly stated.
+type outcomeStateSys struct {
+	// Whether XDG_RUNTIME_DIR is used post hsu.
+	useRuntimeDir bool
+	// Process-specific directory in TMPDIR, nil if unused.
+	sharePath *check.Absolute
+	// Process-specific directory in XDG_RUNTIME_DIR, nil if unused.
+	runtimeSharePath *check.Absolute
+
+	sys *system.I
+	*outcomeState
+}
+
+// ensureRuntimeDir must be called if access to paths within XDG_RUNTIME_DIR is required.
+func (state *outcomeStateSys) ensureRuntimeDir() {
+	if state.useRuntimeDir {
+		return
+	}
+	state.useRuntimeDir = true
+	state.sys.Ensure(state.sc.RunDirPath, 0700)
+	state.sys.UpdatePermType(system.User, state.sc.RunDirPath, acl.Execute)
+	state.sys.Ensure(state.sc.RuntimePath, 0700) // ensure this dir in case XDG_RUNTIME_DIR is unset
+	state.sys.UpdatePermType(system.User, state.sc.RuntimePath, acl.Execute)
+}
+
+// instance returns the pathname to a process-specific directory within TMPDIR.
+// This directory must only hold entries bound to [system.Process].
+func (state *outcomeStateSys) instance() *check.Absolute {
+	if state.sharePath != nil {
+		return state.sharePath
+	}
+	state.sharePath = state.instancePath()
+	state.sys.Ephemeral(system.Process, state.sharePath, 0711)
+	return state.sharePath
+}
+
+// runtime returns the pathname to a process-specific directory within XDG_RUNTIME_DIR.
+// This directory must only hold entries bound to [system.Process].
+func (state *outcomeStateSys) runtime() *check.Absolute {
+	if state.runtimeSharePath != nil {
+		return state.runtimeSharePath
+	}
+	state.ensureRuntimeDir()
+	state.runtimeSharePath = state.runtimePath()
+	state.sys.Ephemeral(system.Process, state.runtimeSharePath, 0700)
+	state.sys.UpdatePerm(state.runtimeSharePath, acl.Execute)
+	return state.runtimeSharePath
+}
+
+// outcomeStateParams wraps outcomeState and [container.Params]. Used on the shim side only.
+type outcomeStateParams struct {
+	// Overrides the embedded [container.Params] in [container.Container]. The Env field must not be used.
+	params *container.Params
+	// Collapsed into the Env slice in [container.Params] by the final outcomeOp.
+	env map[string]string
+
+	// Filesystems with the optional root sliced off if present. Populated by spParamsOp.
+	// Safe for use by spFilesystemOp.
+	filesystem []hst.FilesystemConfigJSON
+
+	// Inner XDG_RUNTIME_DIR default formatting of `/run/user/%d` via mapped uid.
+	// Populated by spRuntimeOp.
+	runtimeDir *check.Absolute
+
+	as hst.ApplyState
+	*outcomeState
+}
+
+// An outcomeOp inflicts an outcome on [system.I] and contains enough information to
+// inflict it on [container.Params] in a separate process.
+// An implementation of outcomeOp must store cross-process states in exported fields only.
+type outcomeOp interface {
+	// toSystem inflicts the current outcome on [system.I] in the priv side process.
+	toSystem(state *outcomeStateSys, config *hst.Config) error
+
+	// toContainer inflicts the current outcome on [container.Params] in the shim process.
+	// The implementation must not write to the Env field of [container.Params] as it will be overwritten
+	// by flattened env map.
+	toContainer(state *outcomeStateParams) error
+}
+
+// fromConfig returns a corresponding slice of outcomeOp for [hst.Config].
+// This function assumes the caller has already called the Validate method on [hst.Config]
+// and checked that it returns nil.
+func fromConfig(config *hst.Config) (ops []outcomeOp) {
+	ops = []outcomeOp{
+		// must run first
+		&spParamsOp{},
+
+		// TODO(ophestra): move this late for #8 and #9
+		spFilesystemOp{},
+
+		spRuntimeOp{},
+		spTmpdirOp{},
+		spAccountOp{},
+	}
+
+	et := config.Enablements.Unwrap()
+	if et&hst.EWayland != 0 {
+		ops = append(ops, &spWaylandOp{})
+	}
+	if et&hst.EX11 != 0 {
+		ops = append(ops, &spX11Op{})
+	}
+	if et&hst.EPulse != 0 {
+		ops = append(ops, &spPulseOp{})
+	}
+	if et&hst.EDBus != 0 {
+		ops = append(ops, &spDBusOp{})
+	}
+
+	ops = append(ops, spFinal{})
+	return
+}