lxd-imagebuilder: Export root partition device uuid as variable (from Incus)

doc/examples/ubuntu.yaml

@@ -341,7 +341,7 @@ actions:
     update-grub
     grub-install --uefi-secure-boot --target="${TARGET}-efi" --no-nvram --removable
     update-grub
-    sed -i "s#root=[^ ]*#root=/dev/sda2#g" /boot/grub/grub.cfg
+    sed -i "s#root=[^ ]*#root=${LXD_IMAGEBUILDER_ROOT_UUID}#g" /boot/grub/grub.cfg
   types:
   - vm
 

lxd-imagebuilder/main_lxd.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"context"
 	"errors"
 	"fmt"
 	"io"
@@ -350,6 +351,13 @@ func (c *cmdLXD) run(cmd *cobra.Command, args []string, overlayDir string) error
 			return fmt.Errorf("Failed to mount UEFI partition: %w", err)
 		}
 
+		rootUUID, err := vm.findRootfsDevUUID()
+		if err != nil {
+			return fmt.Errorf("Failed to find rootfs device UUID: %w", err)
+		}
+
+		c.global.ctx = context.WithValue(c.global.ctx, shared.ContextKeyEnviron, []string{fmt.Sprintf("%s=%s", shared.EnvRootUUID, rootUUID)})
+
 		// We cannot use LXD's rsync package as that uses the --delete flag which
 		// causes an issue due to the boot/efi directory being present.
 		err = shared.RsyncLocal(c.global.ctx, overlayDir+"/", vmDir)

lxd-imagebuilder/vm.go

@@ -61,6 +61,32 @@ func (v *vm) getUEFIDevFile() string {
 	return fmt.Sprintf("%sp1", v.loopDevice)
 }
 
+func (v *vm) findRootfsDevUUID() (rootUUID string, err error) {
+	rootfsDevFile := v.getRootfsDevFile()
+	if rootfsDevFile == "" {
+		return "", fmt.Errorf("Failed to get rootfs device name")
+	}
+
+	var out strings.Builder
+	if err = shared.RunCommand(v.ctx, nil, &out, "blkid", "-o", "export", rootfsDevFile); err != nil {
+		return "", fmt.Errorf("Failed to get rootfs device UUID: %w", err)
+	}
+
+	fields := strings.Fields(out.String())
+	for _, field := range fields {
+		if strings.HasPrefix(field, "UUID=") {
+			rootUUID = field
+			break
+		}
+	}
+
+	if rootUUID == "" {
+		return "", fmt.Errorf("No rootfs device UUID found")
+	}
+
+	return rootUUID, nil
+}
+
 func (v *vm) createEmptyDiskImage() error {
 	f, err := os.Create(v.imageFile)
 	if err != nil {

shared/util.go

@@ -23,6 +23,11 @@ import (
 	yaml "gopkg.in/yaml.v2"
 )
 
+const (
+	ContextKeyEnviron = ContextKey("environ")
+	EnvRootUUID       = "LXD_IMAGEBUILDER_ROOT_UUID"
+)
+
 // EnvVariable represents a environment variable.
 type EnvVariable struct {
 	Value string
@@ -32,6 +37,9 @@ type EnvVariable struct {
 // Environment represents a set of environment variables.
 type Environment map[string]EnvVariable
 
+// ContextKey type.
+type ContextKey string
+
 // Copy copies a file.
 func Copy(src, dest string) error {
 	var err error
@@ -61,6 +69,10 @@ func Copy(src, dest string) error {
 // RunCommand runs a command. Stdout is written to the given io.Writer. If nil, it's written to the real stdout. Stderr is always written to the real stderr.
 func RunCommand(ctx context.Context, stdin io.Reader, stdout io.Writer, name string, arg ...string) error {
 	cmd := exec.CommandContext(ctx, name, arg...)
+	env, ok := ctx.Value(ContextKeyEnviron).([]string)
+	if ok && len(env) > 0 {
+		cmd.Env = append(os.Environ(), env...)
+	}
 
 	if stdin != nil {
 		cmd.Stdin = stdin