CRI: use (snapshotter_id, snapshot_key) to uniquely identify snapshots

Before snapshotter per runtime, CRI only supports a global snapshotter.
So a snapshot can be uniquely identified by `snapshot_key`. With snapshotter
per runtime enabled, there may be multiple snapshotters used by CRI. So only
(snapshotter_id, snapshot_key) can uniquely identify a snapshot.
Also extends CRI/store/snapshot/Store to support multiple snapshotters.

Signed-off-by: Jiang Liu <gerry@linux.alibaba.com>

pkg/cri/store/snapshot/snapshot.go

@@ -23,10 +23,17 @@ import (
 	snapshot "github.com/containerd/containerd/snapshots"
 )
 
+type Key struct {
+	// Key is the key of the snapshot
+	Key string
+	// Snapshotter is the name of the snapshotter managing the snapshot
+	Snapshotter string
+}
+
 // Snapshot contains the information about the snapshot.
 type Snapshot struct {
 	// Key is the key of the snapshot
-	Key string
+	Key Key
 	// Kind is the kind of the snapshot (active, committed, view)
 	Kind snapshot.Kind
 	// Size is the size of the snapshot in bytes.
@@ -41,12 +48,12 @@ type Snapshot struct {
 // Store stores all snapshots.
 type Store struct {
 	lock      sync.RWMutex
-	snapshots map[string]Snapshot
+	snapshots map[Key]Snapshot
 }
 
 // NewStore creates a snapshot store.
 func NewStore() *Store {
-	return &Store{snapshots: make(map[string]Snapshot)}
+	return &Store{snapshots: make(map[Key]Snapshot)}
 }
 
 // Add a snapshot into the store.
@@ -58,7 +65,7 @@ func (s *Store) Add(snapshot Snapshot) {
 
 // Get returns the snapshot with specified key. Returns errdefs.ErrNotFound if the
 // snapshot doesn't exist.
-func (s *Store) Get(key string) (Snapshot, error) {
+func (s *Store) Get(key Key) (Snapshot, error) {
 	s.lock.RLock()
 	defer s.lock.RUnlock()
 	if sn, ok := s.snapshots[key]; ok {
@@ -79,7 +86,7 @@ func (s *Store) List() []Snapshot {
 }
 
 // Delete deletes the snapshot with specified key.
-func (s *Store) Delete(key string) {
+func (s *Store) Delete(key Key) {
 	s.lock.Lock()
 	defer s.lock.Unlock()
 	delete(s.snapshots, key)

pkg/cri/store/snapshot/snapshot_test.go

@@ -27,23 +27,35 @@ import (
 )
 
 func TestSnapshotStore(t *testing.T) {
-	snapshots := map[string]Snapshot{
-		"key1": {
-			Key:       "key1",
+	key1 := Key{
+		Key:         "key1",
+		Snapshotter: "snapshotter1",
+	}
+	key2 := Key{
+		Key:         "key2",
+		Snapshotter: "snapshotter1",
+	}
+	key3 := Key{
+		Key:         "key1",
+		Snapshotter: "snapshotter2",
+	}
+	snapshots := map[Key]Snapshot{
+		key1: {
+			Key:       key1,
 			Kind:      snapshot.KindActive,
 			Size:      10,
 			Inodes:    100,
 			Timestamp: time.Now().UnixNano(),
 		},
-		"key2": {
-			Key:       "key2",
+		key2: {
+			Key:       key2,
 			Kind:      snapshot.KindCommitted,
 			Size:      20,
 			Inodes:    200,
 			Timestamp: time.Now().UnixNano(),
 		},
-		"key3": {
-			Key:       "key3",
+		key3: {
+			Key:       key3,
 			Kind:      snapshot.KindView,
 			Size:      0,
 			Inodes:    0,
@@ -70,7 +82,19 @@ func TestSnapshotStore(t *testing.T) {
 	sns := s.List()
 	assert.Len(sns, 3)
 
-	testKey := "key2"
+	invalidKey := Key{
+		Key:         "key2",
+		Snapshotter: "snapshotter2",
+	}
+	t.Logf("should not delete snapshot with invalid key")
+	s.Delete(invalidKey)
+	sns = s.List()
+	assert.Len(sns, 3)
+
+	testKey := Key{
+		Key:         "key2",
+		Snapshotter: "snapshotter1",
+	}
 
 	t.Logf("should be able to delete snapshot")
 	s.Delete(testKey)