Update metadata plugin initialization

Updates metadata plugin to require content and
snapshotter plugins be loaded and initializes with
those plugins, keeping the metadata database structure
static after initialization. Service plugins now only
require metadata plugin access snapshotter or content
stores through metadata, which was already required
behavior of the services.

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

metadata/bolt.go

@@ -17,9 +17,14 @@ func WithTransactionContext(ctx context.Context, tx *bolt.Tx) context.Context {
 	return context.WithValue(ctx, transactionKey{}, tx)
 }
 
+type transactor interface {
+	View(fn func(*bolt.Tx) error) error
+	Update(fn func(*bolt.Tx) error) error
+}
+
 // view gets a bolt db transaction either from the context
 // or starts a new one with the provided bolt database.
-func view(ctx context.Context, db *DB, fn func(*bolt.Tx) error) error {
+func view(ctx context.Context, db transactor, fn func(*bolt.Tx) error) error {
 	tx, ok := ctx.Value(transactionKey{}).(*bolt.Tx)
 	if !ok {
 		return db.View(fn)
@@ -29,7 +34,7 @@ func view(ctx context.Context, db *DB, fn func(*bolt.Tx) error) error {
 
 // update gets a writable bolt db transaction either from the context
 // or starts a new one with the provided bolt database.
-func update(ctx context.Context, db *DB, fn func(*bolt.Tx) error) error {
+func update(ctx context.Context, db transactor, fn func(*bolt.Tx) error) error {
 	tx, ok := ctx.Value(transactionKey{}).(*bolt.Tx)
 	if !ok {
 		return db.Update(fn)

metadata/content.go

@@ -19,23 +19,16 @@ import (
 
 type contentStore struct {
 	content.Store
-	db *DB
+	db transactor
 }
 
-// NewContentStore returns a namespaced content store using an existing
+// newContentStore returns a namespaced content store using an existing
 // content store interface.
-func NewContentStore(db *DB, cs content.Store) content.Store {
-	db.storeL.Lock()
-	defer db.storeL.Unlock()
-
-	if db.cs == nil {
-		db.cs = &contentStore{
-			Store: cs,
-			db:    db,
-		}
+func newContentStore(db transactor, cs content.Store) content.Store {
+	return &contentStore{
+		Store: cs,
+		db:    db,
 	}
-	return db.cs
-
 }
 
 func (cs *contentStore) Info(ctx context.Context, dgst digest.Digest) (content.Info, error) {
@@ -360,7 +353,7 @@ type namespacedWriter struct {
 	content.Writer
 	ref       string
 	namespace string
-	db        *DB
+	db        transactor
 }
 
 func (nw *namespacedWriter) Commit(ctx context.Context, size int64, expected digest.Digest, opts ...content.Opt) error {

metadata/content_test.go

@@ -23,7 +23,7 @@ func createContentStore(ctx context.Context, root string) (content.Store, func()
 		return nil, nil, err
 	}
 
-	return NewContentStore(NewDB(db), cs), func() error {
+	return NewDB(db, cs, nil).ContentStore(), func() error {
 		return db.Close()
 	}, nil
 }

metadata/db.go

@@ -1,26 +1,40 @@
 package metadata
 
 import (
-	"sync"
-
 	"github.com/boltdb/bolt"
+	"github.com/containerd/containerd/content"
+	"github.com/containerd/containerd/snapshot"
 )
 
 type DB struct {
 	db *bolt.DB
-
-	storeL sync.Mutex
-	ss     map[string]*snapshotter
-	cs     *contentStore
+	ss map[string]snapshot.Snapshotter
+	cs content.Store
 }
 
-func NewDB(db *bolt.DB) *DB {
+func NewDB(db *bolt.DB, cs content.Store, ss map[string]snapshot.Snapshotter) *DB {
 	return &DB{
 		db: db,
-		ss: map[string]*snapshotter{},
+		ss: ss,
+		cs: cs,
 	}
 }
 
+func (m *DB) ContentStore() content.Store {
+	if m.cs == nil {
+		return nil
+	}
+	return newContentStore(m, m.cs)
+}
+
+func (m *DB) Snapshotter(name string) snapshot.Snapshotter {
+	sn, ok := m.ss[name]
+	if !ok {
+		return nil
+	}
+	return newSnapshotter(m, name, sn)
+}
+
 func (m *DB) View(fn func(*bolt.Tx) error) error {
 	return m.db.View(fn)
 }

metadata/snapshot.go

@@ -19,26 +19,17 @@ import (
 type snapshotter struct {
 	snapshot.Snapshotter
 	name string
-	db   *DB
+	db   transactor
 }
 
-// NewSnapshotter returns a new Snapshotter which namespaces the given snapshot
-// using the provided name and metadata store.
-func NewSnapshotter(db *DB, name string, sn snapshot.Snapshotter) snapshot.Snapshotter {
-	db.storeL.Lock()
-	defer db.storeL.Unlock()
-
-	ss, ok := db.ss[name]
-	if !ok {
-		ss = &snapshotter{
-			Snapshotter: sn,
-			name:        name,
-			db:          db,
-		}
-		db.ss[name] = ss
+// newSnapshotter returns a new Snapshotter which namespaces the given snapshot
+// using the provided name and database.
+func newSnapshotter(db transactor, name string, sn snapshot.Snapshotter) snapshot.Snapshotter {
+	return &snapshotter{
+		Snapshotter: sn,
+		name:        name,
+		db:          db,
 	}
-
-	return ss
 }
 
 func createKey(id uint64, namespace, key string) string {
@@ -466,11 +457,7 @@ func (s *snapshotter) Remove(ctx context.Context, key string) error {
 			}
 		}
 
-		if err := bkt.DeleteBucket([]byte(key)); err != nil {
-			return err
-		}
-
-		return nil
+		return bkt.DeleteBucket([]byte(key))
 	})
 }
 

metadata/snapshot_test.go

@@ -13,7 +13,7 @@ import (
 	"github.com/containerd/containerd/testutil"
 )
 
-func newSnapshotter(ctx context.Context, root string) (snapshot.Snapshotter, func() error, error) {
+func newTestSnapshotter(ctx context.Context, root string) (snapshot.Snapshotter, func() error, error) {
 	naiveRoot := filepath.Join(root, "naive")
 	if err := os.Mkdir(naiveRoot, 0770); err != nil {
 		return nil, nil, err
@@ -28,7 +28,7 @@ func newSnapshotter(ctx context.Context, root string) (snapshot.Snapshotter, fun
 		return nil, nil, err
 	}
 
-	sn := NewSnapshotter(NewDB(db), "naive", snapshotter)
+	sn := NewDB(db, nil, map[string]snapshot.Snapshotter{"naive": snapshotter}).Snapshotter("naive")
 
 	return sn, func() error {
 		return db.Close()
@@ -38,5 +38,5 @@ func newSnapshotter(ctx context.Context, root string) (snapshot.Snapshotter, fun
 func TestMetadata(t *testing.T) {
 	// Snapshot tests require mounting, still requires root
 	testutil.RequiresRoot(t)
-	testsuite.SnapshotterSuite(t, "Metadata", newSnapshotter)
+	testsuite.SnapshotterSuite(t, "Metadata", newTestSnapshotter)
 }