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>

services/content/service.go

@@ -39,7 +39,6 @@ func init() {
 		Type: plugin.GRPCPlugin,
 		ID:   "content",
 		Requires: []plugin.Type{
-			plugin.ContentPlugin,
 			plugin.MetadataPlugin,
 		},
 		Init: NewService,
@@ -47,19 +46,13 @@ func init() {
 }
 
 func NewService(ic *plugin.InitContext) (interface{}, error) {
-	c, err := ic.Get(plugin.ContentPlugin)
-	if err != nil {
-		return nil, err
-	}
 	m, err := ic.Get(plugin.MetadataPlugin)
 	if err != nil {
 		return nil, err
 	}
 
-	cs := metadata.NewContentStore(m.(*metadata.DB), c.(content.Store))
-
 	return &Service{
-		store:     cs,
+		store:     m.(*metadata.DB).ContentStore(),
 		publisher: ic.Events,
 	}, nil
 }

services/snapshot/service.go

@@ -14,7 +14,6 @@ import (
 	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/snapshot"
 	protoempty "github.com/golang/protobuf/ptypes/empty"
-	"github.com/pkg/errors"
 	"golang.org/x/net/context"
 	"google.golang.org/grpc"
 )
@@ -24,7 +23,6 @@ func init() {
 		Type: plugin.GRPCPlugin,
 		ID:   "snapshots",
 		Requires: []plugin.Type{
-			plugin.SnapshotPlugin,
 			plugin.MetadataPlugin,
 		},
 		Init: newService,
@@ -34,31 +32,19 @@ func init() {
 var empty = &protoempty.Empty{}
 
 type service struct {
-	snapshotters map[string]snapshot.Snapshotter
-	publisher    events.Publisher
+	db        *metadata.DB
+	publisher events.Publisher
 }
 
 func newService(ic *plugin.InitContext) (interface{}, error) {
-	rawSnapshotters, err := ic.GetAll(plugin.SnapshotPlugin)
-	if err != nil {
-		return nil, err
-	}
 	md, err := ic.Get(plugin.MetadataPlugin)
 	if err != nil {
 		return nil, err
 	}
-	snapshotters := make(map[string]snapshot.Snapshotter)
-	for name, sn := range rawSnapshotters {
-		snapshotters[name] = metadata.NewSnapshotter(md.(*metadata.DB), name, sn.(snapshot.Snapshotter))
-	}
-
-	if len(snapshotters) == 0 {
-		return nil, errors.Errorf("failed to create snapshotter service: no snapshotters loaded")
-	}
 
 	return &service{
-		snapshotters: snapshotters,
-		publisher:    ic.Events,
+		db:        md.(*metadata.DB),
+		publisher: ic.Events,
 	}, nil
 }
 
@@ -67,8 +53,8 @@ func (s *service) getSnapshotter(name string) (snapshot.Snapshotter, error) {
 		return nil, errdefs.ToGRPCf(errdefs.ErrInvalidArgument, "snapshotter argument missing")
 	}
 
-	sn, ok := s.snapshotters[name]
-	if !ok {
+	sn := s.db.Snapshotter(name)
+	if sn == nil {
 		return nil, errdefs.ToGRPCf(errdefs.ErrInvalidArgument, "snapshotter not loaded: %s", name)
 	}
 	return sn, nil

services/tasks/service.go

@@ -44,7 +44,6 @@ func init() {
 		Requires: []plugin.Type{
 			plugin.RuntimePlugin,
 			plugin.MetadataPlugin,
-			plugin.ContentPlugin,
 		},
 		Init: New,
 	})
@@ -59,11 +58,7 @@ func New(ic *plugin.InitContext) (interface{}, error) {
 	if err != nil {
 		return nil, err
 	}
-	ct, err := ic.Get(plugin.ContentPlugin)
-	if err != nil {
-		return nil, err
-	}
-	cs := metadata.NewContentStore(m.(*metadata.DB), ct.(content.Store))
+	cs := m.(*metadata.DB).ContentStore()
 	runtimes := make(map[string]runtime.Runtime)
 	for _, rr := range rt {
 		r := rr.(runtime.Runtime)