Do not migrate legacy images if snapshots are already present (#1990)

* Do not migrate legacy images if snapshots are already present

This commit prevents executing the legacy images migration logic
if snapshotter already finds available snapshots. This mostly
means the migration was already executed and legacy images
had already a chance to be converted into snapshots.

* Fix btrfs snapshotter image variable

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

pkg/features/embedded/grub-config/etc/elemental/grub.cfg

@@ -63,8 +63,8 @@ function set_volume {
     set btrfs_relative_path="y"
     set volume="${root}"
     if [ -n "${1}" ]; then
-      set img=${1}
-      btrfs-mount-subvol ($root) / @/.snapshots/${1}/snapshot
+      set img=@/.snapshots/${1}/snapshot
+      btrfs-mount-subvol ($root) / ${img}
     fi
   elif [ -z "${1}" ]; then
     set_loopdevice /.snapshots/active

pkg/snapshotter/loopdevice.go

@@ -543,6 +543,10 @@ func (l *LoopDevice) legacyImageToSnapsot(image string) error {
 			l.cfg.Logger.Errorf("failed setting the snaphsot ID for legacy images: %v", err)
 			return err
 		}
+		if id > 1 {
+			l.cfg.Logger.Debugf("Skipping legacy image migration, some snapshot already found in the system")
+			return nil
+		}
 		l.cfg.Logger.Debugf("Migrating image %s to snapshot %d", image, id)
 
 		snapPath := filepath.Join(l.rootDir, loopDeviceSnapsPath, strconv.FormatInt(int64(id), 10))