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/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)
+		}
+	}
+}