Add Cleanup to snapshot API

Cleanup is an optional method a snapshotter may implement.
Cleanup can be used to cleanup resources after a snapshot
has been removed. This function allows a snapshotter to defer
longer resource cleanup until after snapshot removals are
completed. Adding this to the API allows proxy snapshotters
to leverage this enhancement.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

api/next.pb.txt

@@ -3446,6 +3446,16 @@ file {
       json_name: "inodes"
     }
   }
+  message_type {
+    name: "CleanupRequest"
+    field {
+      name: "snapshotter"
+      number: 1
+      label: LABEL_OPTIONAL
+      type: TYPE_STRING
+      json_name: "snapshotter"
+    }
+  }
   enum_type {
     name: "Kind"
     value {
@@ -3529,6 +3539,11 @@ file {
       input_type: ".containerd.services.snapshots.v1.UsageRequest"
       output_type: ".containerd.services.snapshots.v1.UsageResponse"
     }
+    method {
+      name: "Cleanup"
+      input_type: ".containerd.services.snapshots.v1.CleanupRequest"
+      output_type: ".google.protobuf.Empty"
+    }
   }
   options {
     go_package: "github.com/containerd/containerd/api/services/snapshots/v1;snapshots"

api/services/snapshots/v1/snapshots.proto

@@ -21,6 +21,7 @@ service Snapshots {
 	rpc Update(UpdateSnapshotRequest) returns (UpdateSnapshotResponse);
 	rpc List(ListSnapshotsRequest) returns (stream ListSnapshotsResponse);
 	rpc Usage(UsageRequest) returns (UsageResponse);
+	rpc Cleanup(CleanupRequest) returns (google.protobuf.Empty);
 }
 
 message PrepareSnapshotRequest {
@@ -160,3 +161,7 @@ message UsageResponse {
 	int64 size = 1;
 	int64 inodes = 2;
 }
+
+message CleanupRequest {
+	string snapshotter = 1;
+}

contrib/snapshotservice/service.go

@@ -163,6 +163,19 @@ func (s service) Usage(ctx context.Context, ur *snapshotsapi.UsageRequest) (*sna
 	}, nil
 }
 
+func (s service) Cleanup(ctx context.Context, cr *snapshotsapi.CleanupRequest) (*ptypes.Empty, error) {
+	c, ok := s.sn.(snapshots.Cleaner)
+	if !ok {
+		return nil, errdefs.ToGRPCf(errdefs.ErrNotImplemented, "snapshotter does not implement Cleanup method")
+	}
+
+	if err := c.Cleanup(ctx); err != nil {
+		return nil, errdefs.ToGRPC(err)
+	}
+
+	return empty, nil
+}
+
 func fromKind(kind snapshots.Kind) snapshotsapi.Kind {
 	if kind == snapshots.KindActive {
 		return snapshotsapi.KindActive

metadata/snapshot.go

@@ -791,18 +791,17 @@ func validateSnapshot(info *snapshots.Info) error {
 	return nil
 }
 
-type cleaner interface {
-	Cleanup(ctx context.Context) error
-}
-
 func (s *snapshotter) garbageCollect(ctx context.Context) (d time.Duration, err error) {
 	s.l.Lock()
 	t1 := time.Now()
 	defer func() {
 		s.l.Unlock()
 		if err == nil {
-			if c, ok := s.Snapshotter.(cleaner); ok {
+			if c, ok := s.Snapshotter.(snapshots.Cleaner); ok {
 				err = c.Cleanup(ctx)
+				if errdefs.IsNotImplemented(err) {
+					err = nil
+				}
 			}
 		}
 		if err == nil {

services/snapshots/service.go

@@ -255,6 +255,25 @@ func (s *service) Usage(ctx context.Context, ur *snapshotsapi.UsageRequest) (*sn
 	return fromUsage(usage), nil
 }
 
+func (s *service) Cleanup(ctx context.Context, cr *snapshotsapi.CleanupRequest) (*ptypes.Empty, error) {
+	sn, err := s.getSnapshotter(cr.Snapshotter)
+	if err != nil {
+		return nil, err
+	}
+
+	c, ok := sn.(snapshots.Cleaner)
+	if !ok {
+		return nil, errdefs.ToGRPCf(errdefs.ErrNotImplemented, "snapshotter does not implement Cleanup method")
+	}
+
+	err = c.Cleanup(ctx)
+	if err != nil {
+		return nil, errdefs.ToGRPC(err)
+	}
+
+	return empty, nil
+}
+
 func fromKind(kind snapshots.Kind) snapshotsapi.Kind {
 	if kind == snapshots.KindActive {
 		return snapshotsapi.KindActive

snapshots/proxy/proxy.go

@@ -184,6 +184,13 @@ func (p *proxySnapshotter) Close() error {
 	return nil
 }
 
+func (p *proxySnapshotter) Cleanup(ctx context.Context) error {
+	_, err := p.client.Cleanup(ctx, &snapshotsapi.CleanupRequest{
+		Snapshotter: p.snapshotterName,
+	})
+	return errdefs.FromGRPC(err)
+}
+
 func toKind(kind snapshotsapi.Kind) snapshots.Kind {
 	if kind == snapshotsapi.KindActive {
 		return snapshots.KindActive

snapshots/snapshotter.go

@@ -341,6 +341,17 @@ type Snapshotter interface {
 	Close() error
 }
 
+// Cleaner defines a type capable of performing asynchronous resource cleanup.
+// The Cleaner interface should be used by snapshotters which implement fast
+// removal and deferred resource cleanup. This prevents snapshots from needing
+// to perform lengthy resource cleanup before acknowledging a snapshot key
+// has been removed and available for re-use. This is also useful when
+// performing multi-key removal with the intent of cleaning up all the
+// resources after each snapshot key has been removed.
+type Cleaner interface {
+	Cleanup(ctx context.Context) error
+}
+
 // Opt allows setting mutable snapshot properties on creation
 type Opt func(info *Info) error