cmd/earlyinit: mount system device

This currently relies on a trusted bootloader to determine the boot device.

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

cmd/earlyinit/main.go

@@ -5,17 +5,89 @@
 package main
 
 import (
+	"context"
+	"crypto/rand"
 	"log"
 	"os"
+	"os/exec"
+	"os/signal"
 	"runtime"
+	"runtime/pprof"
+	"slices"
 	"strings"
 	. "syscall"
+
+	"hakurei.app/internal/kobject"
+	"hakurei.app/internal/report"
+	"hakurei.app/internal/uevent"
+)
+
+var r report.Reporter
+
+func init() {
+	log.SetFlags(0)
+	log.SetPrefix("earlyinit: ")
+	r.SetOutput(log.Default())
+
+	// this handles SIGQUIT to provide useful debugging information without
+	// terminating, and prevents the runtime from throwing on the must family
+	// of early error reporting functions, DO NOT REMOVE
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, SIGQUIT)
+	go func() {
+		for {
+			<-c
+			if p := pprof.Lookup("goroutine"); p == nil {
+				log.Println("initial built-in goroutine profile does not exist")
+			} else if err := p.WriteTo(os.Stderr, 2); err != nil {
+				log.Println(err)
+			}
+		}
+	}()
+}
+
+// fatal calls [log.Println] with v and blocks forever. Must be called from
+// main. Must not be used after error reporting is set up.
+func fatal(v ...any) {
+	log.Println(v...)
+	log.Println("unable to continue, please reboot and resolve the problem manually")
+	select {}
+}
+
+// must calls fatal with err if it is non-nil.
+func must(err error) {
+	if err != nil {
+		log.Println(err)
+		select {}
+	}
+}
+
+// mustSyscall is like must, but with an additional action name.
+func mustSyscall(action string, err error) {
+	if err != nil {
+		fatal("cannot "+action+":", err)
+		select {}
+	}
+}
+
+// must1 is like must, but with an additional passed through value.
+func must1[T any](v T, err error) T {
+	must(err)
+	return v
+}
+
+const (
+	// optionSystem specifies devpath of the system device.
+	optionSystem = "system"
+
+	// flagStrict sets [report.DStrict] on r.
+	flagStrict = "strict"
+	// flagNoRecover sets [report.DNoRecover] on r.
+	flagNoRecover = "no_recover"
 )
 
 func main() {
 	runtime.LockOSThread()
-	log.SetFlags(0)
-	log.SetPrefix("earlyinit: ")
 
 	var (
 		option map[string]string
@@ -33,15 +105,33 @@ func main() {
 		}
 	}
 
-	if err := Mount(
+	{
+		var flag uint64
+		if slices.Contains(flags, flagStrict) {
+			flag |= report.DStrict
+		}
+		if slices.Contains(flags, flagNoRecover) {
+			flag |= report.DNoRecover
+		}
+		log.Printf("reporting flags %x", flag)
+		r.SetFlags(flag)
+	}
+
+	mustSyscall("mount devtmpfs", Mount(
 		"devtmpfs",
 		"/dev/",
 		"devtmpfs",
 		MS_NOSUID|MS_NOEXEC,
 		"",
-	); err != nil {
+	))
-		log.Fatalf("cannot mount devtmpfs: %v", err)
+	must(os.Mkdir("/dev/pts/", 0))
-	}
+	mustSyscall("mount devpts", Mount(
+		"devpts",
+		"/dev/pts/",
+		"devpts",
+		MS_NOSUID|MS_NOEXEC,
+		"mode=620,ptmxmode=666",
+	))
 
 	// The kernel might be unable to set up the console. When that happens,
 	// printk is called with "Warning: unable to open an initial console."
@@ -98,6 +188,40 @@ func main() {
 		"",
 	))
 
+	conn := must1(uevent.Dial(-128 * 1024 * 1024))
+	events := make(chan *uevent.Message, 1<<10)
+	var uuid uevent.UUID
+	must1(rand.Read(uuid[:]))
+	ctx, cancel := context.WithCancel(context.Background())
+
+	go consume(ctx, &r, conn, uuid, events)
+	s := kobject.New(uuid, func(o *kobject.Object, env map[string]string) {
+		log.Printf("change %s: %q", o.DevPath, env)
+	}, func(err error) {
+		r.Dispatch(
+			report.Inconsistent,
+			"processed inconsistent uevent",
+			err,
+		)
+	})
+	go func() {
+		s.Consume(ctx, events)
+
+		log.Println("closing NETLINK_KOBJECT_UEVENT socket")
+		cancel()
+		if err := conn.Close(); err != nil {
+			log.Fatal(err) // not reached
+		}
+	}()
+
+	must(os.Mkdir("/system", 0))
+	if devpath := option[optionSystem]; devpath == "" {
+		fatal("system must be nonempty")
+	} else {
+		log.Printf("waiting for devpath pattern %q", devpath)
+		mustMountSystem(ctx, s, devpath)
+	}
+
 	// after top level has been set up
 	mustSyscall("remount root", Mount(
 		"",
@@ -115,17 +239,3 @@ func main() {
 	))
 
 }
-
-// mustSyscall calls [log.Fatalln] if err is non-nil.
-func mustSyscall(action string, err error) {
-	if err != nil {
-		log.Fatalln("cannot "+action+":", err)
-	}
-}
-
-// must calls [log.Fatal] with err if it is non-nil.
-func must(err error) {
-	if err != nil {
-		log.Fatal(err)
-	}
-}

cmd/earlyinit/mount.go

@@ -0,0 +1,69 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"os"
+	"path/filepath"
+	"strconv"
+	"syscall"
+	"time"
+
+	"hakurei.app/check"
+	"hakurei.app/fhs"
+	"hakurei.app/internal/kobject"
+)
+
+// mustMountSystem waits for and mounts a system device matching pattern.
+func mustMountSystem(
+	ctx context.Context,
+	s *kobject.State,
+	pattern string,
+) {
+	c, stop := context.WithTimeout(ctx, 30*time.Second)
+	defer stop()
+
+	for {
+		var matchErr error
+		var systemPath *check.Absolute
+		s.Range(c, func(o *kobject.Object) bool {
+			if o.Subsystem != "block" ||
+				o.Env["DEVTYPE"] != "disk" {
+				return true
+			}
+
+			if ok, err := filepath.Match(pattern, o.DevPath); err != nil {
+				matchErr = err
+				return false
+			} else if !ok {
+				return true
+			}
+
+			name, ok := o.Env["DEVNAME"]
+			if !ok {
+				return true
+			}
+			systemPath = fhs.AbsDev.Append(name)
+			return false
+		})
+		if c.Err() != nil {
+			fatal("devpath", strconv.Quote(pattern), "never appeared")
+		}
+		if matchErr != nil {
+			fatal("cannot match system devpath:", matchErr)
+		}
+		err := syscall.Mount(
+			systemPath.String(),
+			"/system/",
+			"squashfs",
+			0,
+			"threads=multi",
+		)
+		if err == nil {
+			break
+		}
+		if !errors.Is(err, os.ErrNotExist) {
+			fatal("cannot mount system:", err)
+		}
+	}
+}

cmd/earlyinit/uevent.go

@@ -0,0 +1,103 @@
+package main
+
+import (
+	"context"
+	"log"
+	"time"
+
+	"hakurei.app/fhs"
+	"hakurei.app/internal/report"
+	"hakurei.app/internal/uevent"
+)
+
+// newRejectColdboot returns a function to be called on every subsequent pending
+// coldboot, and returns whether coldboot should proceed. Rejection is sticky.
+func newRejectColdboot() func() bool {
+	// one coldboot per five minutes, two consecutive coldboot
+	const (
+		coldbootInterval = 5 * time.Minute
+		coldbootBurst    = 2
+	)
+
+	done := make(chan struct{})
+	s := make(chan struct{}, coldbootBurst)
+	s <- struct{}{} // for early fault before reporting is ready
+	go func() {
+		t := time.NewTicker(coldbootInterval)
+		for {
+			select {
+			case <-done:
+				return
+
+			case <-t.C:
+				select {
+				case s <- struct{}{}:
+				default:
+				}
+			}
+		}
+	}()
+
+	return func() bool {
+		select {
+		case <-s:
+			return true
+
+		case <-done:
+			return false
+
+		default:
+			close(done)
+			return false
+		}
+	}
+}
+
+// consume continuously consumes events from conn with retries.
+func consume(
+	ctx context.Context,
+	r *report.Reporter,
+	conn *uevent.Conn,
+	uuid uevent.UUID,
+	events chan<- *uevent.Message,
+) {
+	defer close(events)
+
+	nextColdboot := newRejectColdboot()
+	coldboot := true
+retry:
+	if dispatchErr := conn.Consume(ctx, fhs.Sys, &uuid, events, coldboot, func(path string) {
+		log.Println("coldboot visited", path)
+	}, func(err error) bool {
+		if _, ok := err.(uevent.NeedsColdboot); ok && !nextColdboot() {
+			r.Dispatch(
+				report.Degraded,
+				"rejecting coldboot loop",
+				err,
+			)
+			return false
+		}
+		r.Dispatch(
+			report.Inconsistent,
+			"consumed invalid message",
+			err,
+		)
+		return true
+	}, nil); dispatchErr != nil {
+		if _, ok := dispatchErr.(uevent.Recoverable); !ok {
+			r.Dispatch(
+				report.Fatal,
+				"discontinuing uevent processing due to nonrecoverable error",
+				dispatchErr,
+			)
+			return
+		}
+
+		if _, ok := dispatchErr.(uevent.NeedsColdboot); ok {
+			// coldboot loop rejected by handler
+			coldboot = false
+		}
+
+		goto retry
+	}
+}

cmd/earlyinit/uevent_test.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"testing"
+	"testing/synctest"
+	"time"
+)
+
+func TestRejectColdboot(t *testing.T) {
+	t.Parallel()
+
+	synctest.Test(t, func(t *testing.T) {
+		nextColdboot := newRejectColdboot()
+		want := func(want bool) {
+			if got := nextColdboot(); got != want {
+				t.Fatalf("nextColdboot: %v, want %v", got, want)
+			}
+		}
+
+		synctest.Wait()
+		want(true)
+		time.Sleep(time.Hour)
+		synctest.Wait()
+		want(true)
+		want(true)
+		time.Sleep(5 * time.Minute)
+		synctest.Wait()
+		want(true)
+		want(false)
+		time.Sleep(time.Hour)
+		synctest.Wait()
+		want(false)
+		want(false)
+	})
+}