Ensure subvolume snapshots is mounted to list snapshots

Signed-off-by: David Cassany <dcassany@suse.com>

pkg/snapshotter/btrfs.go

@@ -68,6 +68,7 @@ type Btrfs struct {
 	installing        bool
 	snapperArgs       []string
 	snapshotsUmount   func() error
+	snapshotsMount    func() error
 }
 
 type btrfsSubvol struct {
@@ -130,6 +131,7 @@ func newBtrfsSnapshotter(cfg types.Config, snapCfg types.SnapshotterConfig, boot
 	return &Btrfs{
 		cfg: cfg, snapshotterCfg: snapCfg, btrfsCfg: *btrfsCfg,
 		bootloader: bootloader, snapshotsUmount: func() error { return nil },
+		snapshotsMount: func() error { return nil },
 	}, nil
 }
 
@@ -381,17 +383,34 @@ func (b *Btrfs) DeleteSnapshot(id int) error {
 	return nil
 }
 
-func (b *Btrfs) GetSnapshots() ([]int, error) {
-	if ok, err := b.isInitiated(b.rootDir); ok {
-		snapshots, err := b.loadSnapshots()
+func (b *Btrfs) GetSnapshots() (snapshots []int, err error) {
+	var ok bool
+
+	if ok, err = b.isInitiated(b.rootDir); ok {
+		// Check if snapshots subvolume is mounted
+		snapshotsSubolume := filepath.Join(b.rootDir, fmt.Sprintf(snapshotPathTmpl, b.activeSnapshotID), snapshotsPath)
+		if notMnt, _ := b.cfg.Mounter.IsLikelyNotMountPoint(snapshotsSubolume); notMnt {
+			err = b.snapshotsMount()
+			if err != nil {
+				return nil, err
+			}
+			defer func() {
+				nErr := b.snapshotsUmount()
+				if err == nil && nErr != nil {
+					err = nErr
+					snapshots = nil
+				}
+			}()
+		}
+		snapshots, err = b.loadSnapshots()
 		if err != nil {
 			return nil, err
 		}
-		return snapshots, nil
+		return snapshots, err
 	} else if err != nil {
 		return nil, err
 	}
-	return []int{}, nil
+	return []int{}, err
 }
 
 func (b *Btrfs) loadSnapshots() ([]int, error) {
@@ -695,10 +714,15 @@ func (b *Btrfs) remountStatePartition(state *types.Partition) error {
 }
 
 func (b *Btrfs) mountSnapshotsSubvolumeInSnapshot(root, device string, snapshotID int) error {
-	b.cfg.Logger.Debugf("Mount snapshots subvolume in active snapshot %d", snapshotID)
-	mountpoint := filepath.Join(filepath.Join(root, fmt.Sprintf(snapshotPathTmpl, snapshotID)), snapshotsPath)
-	subvol := fmt.Sprintf("subvol=%s", filepath.Join(rootSubvol, snapshotsPath))
-	err := b.cfg.Mounter.Mount(device, mountpoint, "btrfs", []string{"rw", subvol})
+	var mountpoint, subvol string
+
+	b.snapshotsMount = func() error {
+		b.cfg.Logger.Debugf("Mount snapshots subvolume in active snapshot %d", snapshotID)
+		mountpoint = filepath.Join(filepath.Join(root, fmt.Sprintf(snapshotPathTmpl, snapshotID)), snapshotsPath)
+		subvol = fmt.Sprintf("subvol=%s", filepath.Join(rootSubvol, snapshotsPath))
+		return b.cfg.Mounter.Mount(device, mountpoint, "btrfs", []string{"rw", subvol})
+	}
+	err := b.snapshotsMount()
 	if err != nil {
 		b.cfg.Logger.Errorf("failed mounting subvolume %s at %s", subvol, mountpoint)
 		return err