Update plugin load and snapshot service

Allow plugins to be mapped and returned by their ID.
Add skip plugin to allow plugins to decide whether they should
be loaded.

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

cmd/containerd/config_linux.go

@@ -15,7 +15,5 @@ func defaultConfig() *server.Config {
 			Level:   "info",
 			Address: "/run/containerd/debug.sock",
 		},
-		Snapshotter: "io.containerd.snapshotter.v1.overlayfs",
-		Differ:      "io.containerd.differ.v1.base-diff",
 	}
 }

cmd/containerd/config_unix.go

@@ -14,7 +14,5 @@ func defaultConfig() *server.Config {
 			Level:   "info",
 			Address: "/run/containerd/debug.sock",
 		},
-		Snapshotter: "io.containerd.snapshotter.v1.naive",
-		Differ:      "io.containerd.differ.v1.base-diff",
 	}
 }

cmd/containerd/config_windows.go

@@ -17,7 +17,5 @@ func defaultConfig() *server.Config {
 			Level:   "info",
 			Address: `\\.\pipe\containerd-debug`,
 		},
-		Snapshotter: "io.containerd.snapshotter.v1.windows",
-		Differ:      "io.containerd.differ.v1.base-diff",
 	}
 }

plugin/context.go

@@ -9,7 +9,7 @@ import (
 	"github.com/containerd/containerd/log"
 )
 
-func NewContext(ctx context.Context, plugins map[PluginType][]interface{}, root, id string) *InitContext {
+func NewContext(ctx context.Context, plugins map[PluginType]map[string]interface{}, root, id string) *InitContext {
 	return &InitContext{
 		plugins: plugins,
 		Root:    filepath.Join(root, id),
@@ -23,18 +23,17 @@ type InitContext struct {
 	Config  interface{}
 	Emitter *events.Emitter
 
-	plugins map[PluginType][]interface{}
+	plugins map[PluginType]map[string]interface{}
 }
 
 func (i *InitContext) Get(t PluginType) (interface{}, error) {
-	p := i.plugins[t]
+	for _, v := range i.plugins[t] {
-	if len(p) == 0 {
+		return v, nil
-		return nil, fmt.Errorf("no plugins registered for %s", t)
 	}
-	return p[0], nil
+	return nil, fmt.Errorf("no plugins registered for %s", t)
 }
 
-func (i *InitContext) GetAll(t PluginType) ([]interface{}, error) {
+func (i *InitContext) GetAll(t PluginType) (map[string]interface{}, error) {
 	p, ok := i.plugins[t]
 	if !ok {
 		return nil, fmt.Errorf("no plugins registered for %s", t)

plugin/plugin.go

@@ -1,18 +1,31 @@
 package plugin
 
 import (
-	"errors"
 	"fmt"
 	"sync"
 
+	"github.com/pkg/errors"
 	"google.golang.org/grpc"
 )
 
 var (
 	ErrNoPluginType = errors.New("plugin: no type")
 	ErrNoPluginID   = errors.New("plugin: no id")
+
+	// SkipPlugin is used when a plugin is not initialized and should not be loaded,
+	// this allows the plugin loader differentiate between a plugin which is configured
+	// not to load and one that fails to load.
+	SkipPlugin = errors.New("skip plugin")
 )
 
+// IsSkipPlugin returns true if the error is skipping the plugin
+func IsSkipPlugin(err error) bool {
+	if errors.Cause(err) == SkipPlugin {
+		return true
+	}
+	return false
+}
+
 type PluginType string
 
 const (

server/config.go

@@ -17,11 +17,6 @@ type Config struct {
 	Debug Debug `toml:"debug"`
 	// Metrics and monitoring settings
 	Metrics MetricsConfig `toml:"metrics"`
-	// Snapshotter specifies which snapshot driver to use
-	Snapshotter string `toml:"snapshotter"`
-	// Differ specifies which differ to use. Differ is tightly coupled with the snapshotter
-	// so not all combinations may work.
-	Differ string `toml:"differ"`
 	// Plugins provides plugin specific configuration for the initialization of a plugin
 	Plugins map[string]toml.Primitive `toml:"plugins"`
 	// Enable containerd as a subreaper

server/server.go

@@ -55,14 +55,10 @@ func New(ctx context.Context, config *Config) (*Server, error) {
 			rpc:     rpc,
 			emitter: events.NewEmitter(),
 		}
-		initialized = make(map[plugin.PluginType][]interface{})
+		initialized = make(map[plugin.PluginType]map[string]interface{})
 	)
 	for _, p := range plugins {
 		id := p.URI()
-		if !shouldLoadPlugin(p, config) {
-			log.G(ctx).WithField("type", p.Type).Infof("skip loading plugin %q...", id)
-			continue
-		}
 		log.G(ctx).WithField("type", p.Type).Infof("loading plugin %q...", id)
 
 		initContext := plugin.NewContext(
@@ -83,10 +79,21 @@ func New(ctx context.Context, config *Config) (*Server, error) {
 		}
 		instance, err := p.Init(initContext)
 		if err != nil {
-			log.G(ctx).WithError(err).Warnf("failed to load plugin %s", id)
+			if plugin.IsSkipPlugin(err) {
+				log.G(ctx).WithField("type", p.Type).Infof("skip loading plugin %q...", id)
+			} else {
+				log.G(ctx).WithError(err).Warnf("failed to load plugin %s", id)
+			}
 			continue
 		}
-		initialized[p.Type] = append(initialized[p.Type], instance)
+
+		if types, ok := initialized[p.Type]; ok {
+			types[p.ID] = instance
+		} else {
+			initialized[p.Type] = map[string]interface{}{
+				p.ID: instance,
+			}
+		}
 		// check for grpc services that should be registered with the server
 		if service, ok := instance.(plugin.Service); ok {
 			services = append(services, service)
@@ -170,17 +177,6 @@ func loadPlugins(config *Config) ([]*plugin.Registration, error) {
 	return plugin.Graph(), nil
 }
 
-func shouldLoadPlugin(p *plugin.Registration, config *Config) bool {
-	switch p.Type {
-	case plugin.SnapshotPlugin:
-		return p.URI() == config.Snapshotter
-	case plugin.DiffPlugin:
-		return p.URI() == config.Differ
-	default:
-		return true
-	}
-}
-
 func interceptor(
 	ctx context.Context,
 	req interface{},

services/snapshot/default_linux.go

@@ -0,0 +1,5 @@
+package snapshot
+
+const (
+	defaultSnapshotter = "overlayfs"
+)

services/snapshot/default_unix.go

@@ -0,0 +1,7 @@
+// +build darwin freebsd
+
+package snapshot
+
+const (
+	defaultSnapshotter = "naive"
+)

services/snapshot/default_windows.go

@@ -0,0 +1,5 @@
+package snapshot
+
+const (
+	defaultSnapshotter = "windows"
+)

services/snapshot/service.go

@@ -3,36 +3,40 @@ package snapshot
 import (
 	gocontext "context"
 
+	"github.com/boltdb/bolt"
 	eventsapi "github.com/containerd/containerd/api/services/events/v1"
 	snapshotapi "github.com/containerd/containerd/api/services/snapshot/v1"
 	"github.com/containerd/containerd/api/types"
 	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/events"
 	"github.com/containerd/containerd/log"
+	"github.com/containerd/containerd/metadata"
 	"github.com/containerd/containerd/mount"
 	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/snapshot"
-	"github.com/containerd/containerd/snapshot/namespaced"
 	protoempty "github.com/golang/protobuf/ptypes/empty"
+	"github.com/pkg/errors"
 	"golang.org/x/net/context"
 	"google.golang.org/grpc"
 )
 
+type config struct {
+	// Default is the default snapshotter to use for the service
+	Default string `toml:"default,omitempty"`
+}
+
 func init() {
 	plugin.Register(&plugin.Registration{
 		Type: plugin.GRPCPlugin,
 		ID:   "snapshots",
 		Requires: []plugin.PluginType{
 			plugin.SnapshotPlugin,
+			plugin.MetadataPlugin,
 		},
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
+		Config: &config{
-			e := events.GetPoster(ic.Context)
+			Default: defaultSnapshotter,
-			s, err := ic.Get(plugin.SnapshotPlugin)
-			if err != nil {
-				return nil, err
-			}
-			return newService(s.(snapshot.Snapshotter), e)
 		},
+		Init: newService,
 	})
 }
 
@@ -43,9 +47,26 @@ type service struct {
 	emitter     events.Poster
 }
 
-func newService(snapshotter snapshot.Snapshotter, evts events.Poster) (*service, error) {
+func newService(ic *plugin.InitContext) (interface{}, error) {
+	evts := events.GetPoster(ic.Context)
+	snapshotters, err := ic.GetAll(plugin.SnapshotPlugin)
+	if err != nil {
+		return nil, err
+	}
+	cfg := ic.Config.(*config)
+
+	sn, ok := snapshotters[cfg.Default]
+	if !ok {
+		return nil, errors.Errorf("default snapshotter not loaded: %s", cfg.Default)
+	}
+
+	md, err := ic.Get(plugin.MetadataPlugin)
+	if err != nil {
+		return nil, err
+	}
+
 	return &service{
-		snapshotter: namespaced.NewSnapshotter(snapshotter),
+		snapshotter: metadata.NewSnapshotter(md.(*bolt.DB), cfg.Default, sn.(snapshot.Snapshotter)),
 		emitter:     evts,
 	}, nil
 }