Roll back partial macOS storage clones without removing existing files

Author: chruffins

lib/instances/macos_darwin.go

@@ -12,12 +12,25 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-func cloneMacOSStorage(root, disk, aux string) error {
-	for src, dst := range map[string]string{root: disk, filepath.Join(filepath.Dir(root), "aux.img"): aux} {
-		if err := unix.Clonefile(src, dst, unix.CLONE_NOFOLLOW|unix.CLONE_NOOWNERCOPY); err != nil {
+func cloneMacOSStorage(root, disk, aux string) (err error) {
+	var created []string
+	defer func() {
+		if err != nil {
+			// Only remove files this operation created, never pre-existing storage.
+			for _, path := range created {
+				os.Remove(path)
+			}
+		}
+	}()
+	for _, file := range []struct{ src, dst string }{
+		{root, disk},
+		{filepath.Join(filepath.Dir(root), "aux.img"), aux},
+	} {
+		if err = unix.Clonefile(file.src, file.dst, unix.CLONE_NOFOLLOW|unix.CLONE_NOOWNERCOPY); err != nil {
 			return err
 		}
-		if err := os.Chmod(dst, 0600); err != nil {
+		created = append(created, file.dst)
+		if err = os.Chmod(file.dst, 0600); err != nil {
 			return err
 		}
 	}

lib/instances/macos_darwin_test.go

@@ -3,11 +3,75 @@
 package instances
 
 import (
-	"github.com/stretchr/testify/require"
+	"errors"
 	"net"
+	"os"
+	"path/filepath"
 	"testing"
+
+	"github.com/stretchr/testify/require"
+	"golang.org/x/sys/unix"
 )
 
+func TestMacOSStorageClone(t *testing.T) {
+	root := t.TempDir()
+	source := filepath.Join(root, "rootfs.raw")
+	auxSource := filepath.Join(root, "aux.img")
+	require.NoError(t, os.WriteFile(source, []byte("template disk"), 0644))
+	require.NoError(t, os.WriteFile(auxSource, []byte("template aux"), 0644))
+	probe := filepath.Join(root, "probe")
+	err := unix.Clonefile(source, probe, unix.CLONE_NOFOLLOW|unix.CLONE_NOOWNERCOPY)
+	if errors.Is(err, unix.ENOTSUP) || errors.Is(err, unix.EXDEV) {
+		t.Skip("test filesystem does not support clonefile")
+	}
+	require.NoError(t, err)
+	require.NoError(t, os.Remove(probe))
+
+	t.Run("private writable copies", func(t *testing.T) {
+		dest := t.TempDir()
+		disk, aux := filepath.Join(dest, "disk"), filepath.Join(dest, "aux")
+		require.NoError(t, cloneMacOSStorage(source, disk, aux))
+		for path, expected := range map[string]string{disk: "template disk", aux: "template aux"} {
+			data, err := os.ReadFile(path)
+			require.NoError(t, err)
+			require.Equal(t, expected, string(data))
+			info, err := os.Stat(path)
+			require.NoError(t, err)
+			require.Equal(t, os.FileMode(0600), info.Mode().Perm())
+			require.NoError(t, os.WriteFile(path, []byte("instance changes"), 0600))
+		}
+		for path, expected := range map[string]string{source: "template disk", auxSource: "template aux"} {
+			data, err := os.ReadFile(path)
+			require.NoError(t, err)
+			require.Equal(t, expected, string(data))
+		}
+	})
+
+	t.Run("aux failure rolls back only new disk", func(t *testing.T) {
+		dest := t.TempDir()
+		disk, aux := filepath.Join(dest, "disk"), filepath.Join(dest, "aux")
+		require.NoError(t, os.WriteFile(aux, []byte("existing aux"), 0600))
+		require.Error(t, cloneMacOSStorage(source, disk, aux))
+		_, err := os.Stat(disk)
+		require.ErrorIs(t, err, os.ErrNotExist)
+		data, err := os.ReadFile(aux)
+		require.NoError(t, err)
+		require.Equal(t, "existing aux", string(data))
+	})
+
+	t.Run("existing disk is preserved", func(t *testing.T) {
+		dest := t.TempDir()
+		disk, aux := filepath.Join(dest, "disk"), filepath.Join(dest, "aux")
+		require.NoError(t, os.WriteFile(disk, []byte("existing disk"), 0600))
+		require.Error(t, cloneMacOSStorage(source, disk, aux))
+		data, err := os.ReadFile(disk)
+		require.NoError(t, err)
+		require.Equal(t, "existing disk", string(data))
+		_, err = os.Stat(aux)
+		require.ErrorIs(t, err, os.ErrNotExist)
+	})
+}
+
 func TestMacOSLeaseNormalization(t *testing.T) {
 	mac, err := net.ParseMAC("02:00:01:0a:0b:ff")
 	require.NoError(t, err)