snapshot: add Close()

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

snapshot/btrfs/btrfs.go

@@ -370,3 +370,8 @@ func (b *snapshotter) Remove(ctx context.Context, key string) (err error) {
 
 	return nil
 }
+
+// Close closes the snapshotter
+func (b *snapshotter) Close() error {
+	return b.ms.Close()
+}

snapshot/btrfs/btrfs_test.go

@@ -47,6 +47,9 @@ func boltSnapshotter(t *testing.T) func(context.Context, string) (snapshot.Snaps
 		}
 
 		return snapshotter, func() error {
+			if err := snapshotter.Close(); err != nil {
+				return err
+			}
 			err := mount.UnmountAll(root, unix.MNT_DETACH)
 			if cerr := cleanupDevice(); cerr != nil {
 				err = errors.Wrap(cerr, "device cleanup failed")

snapshot/naive/naive.go

@@ -322,3 +322,8 @@ func (o *snapshotter) mounts(s storage.Snapshot) []mount.Mount {
 		},
 	}
 }
+
+// Close closes the snapshotter
+func (o *snapshotter) Close() error {
+	return o.ms.Close()
+}

snapshot/naive/naive_test.go

@@ -15,7 +15,7 @@ func newSnapshotter(ctx context.Context, root string) (snapshot.Snapshotter, fun
 		return nil, nil, err
 	}
 
-	return snapshotter, nil, nil
+	return snapshotter, func() error { return snapshotter.Close() }, nil
 }
 
 func TestNaive(t *testing.T) {

snapshot/overlay/overlay.go

@@ -401,3 +401,8 @@ func (o *snapshotter) upperPath(id string) string {
 func (o *snapshotter) workPath(id string) string {
 	return filepath.Join(o.root, "snapshots", id, "work")
 }
+
+// Close closes the snapshotter
+func (o *snapshotter) Close() error {
+	return o.ms.Close()
+}

snapshot/overlay/overlay_test.go

@@ -24,7 +24,7 @@ func newSnapshotter(ctx context.Context, root string) (snapshot.Snapshotter, fun
 		return nil, nil, err
 	}
 
-	return snapshotter, nil, nil
+	return snapshotter, func() error { return snapshotter.Close() }, nil
 }
 
 func TestOverlay(t *testing.T) {

snapshot/snapshotter.go

@@ -296,6 +296,14 @@ type Snapshotter interface {
 	// Walk all snapshots in the snapshotter. For each snapshot in the
 	// snapshotter, the function will be called.
 	Walk(ctx context.Context, fn func(context.Context, Info) error) error
+
+	// Close releases the internal resources.
+	//
+	// Close is expected to be called on the end of the lifecycle of the snapshotter,
+	// but not mandatory.
+	//
+	// Close returns nil when it is already closed.
+	Close() error
 }
 
 // Opt allows setting mutable snapshot properties on creation

snapshot/testsuite/testsuite.go

@@ -44,6 +44,7 @@ func SnapshotterSuite(t *testing.T, name string, snapshotterFn func(ctx context.
 	t.Run("ViewReadonly", makeTest(name, snapshotterFn, checkSnapshotterViewReadonly))
 
 	t.Run("StatInWalk", makeTest(name, snapshotterFn, checkStatInWalk))
+	t.Run("CloseTwice", makeTest(name, snapshotterFn, closeTwice))
 }
 
 func makeTest(name string, snapshotterFn func(ctx context.Context, root string) (snapshot.Snapshotter, func() error, error), fn func(ctx context.Context, t *testing.T, snapshotter snapshot.Snapshotter, work string)) func(t *testing.T) {
@@ -786,3 +787,22 @@ func checkFileFromLowerLayer(ctx context.Context, t *testing.T, snapshotter snap
 		t.Fatalf("Check snapshots failed: %+v", err)
 	}
 }
+
+func closeTwice(ctx context.Context, t *testing.T, snapshotter snapshot.Snapshotter, work string) {
+	// do some dummy ops to modify the snapshotter internal state
+	if _, err := snapshotter.Prepare(ctx, "dummy", ""); err != nil {
+		t.Fatal(err)
+	}
+	if err := snapshotter.Commit(ctx, "dummy-1", "dummy"); err != nil {
+		t.Fatal(err)
+	}
+	if err := snapshotter.Remove(ctx, "dummy-1"); err != nil {
+		t.Fatal(err)
+	}
+	if err := snapshotter.Close(); err != nil {
+		t.Fatalf("The first close failed: %+v", err)
+	}
+	if err := snapshotter.Close(); err != nil {
+		t.Fatalf("The second close failed: %+v", err)
+	}
+}

snapshot/windows/windows.go

@@ -84,3 +84,8 @@ func (o *snapshotter) Remove(ctx context.Context, key string) error {
 func (o *snapshotter) Walk(ctx context.Context, fn func(context.Context, snapshot.Info) error) error {
 	panic("not implemented")
 }
+
+// Close closes the snapshotter
+func (o *snapshotter) Close() error {
+	panic("not implemented")
+}