Add containerd plugin mode.

Signed-off-by: Lantao Liu <lantaol@google.com>

cri.go

@@ -0,0 +1,70 @@
+/*
+Copyright 2018 The Containerd Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cri
+
+import (
+	"github.com/containerd/containerd/plugin"
+	"github.com/golang/glog"
+
+	"github.com/containerd/cri-containerd/cmd/cri-containerd/options"
+	"github.com/containerd/cri-containerd/pkg/server"
+)
+
+// Register CRI service plugin
+func init() {
+	plugin.Register(&plugin.Registration{
+		// In fact, cri is not strictly a GRPC plugin now.
+		Type: plugin.GRPCPlugin,
+		ID:   "cri",
+		Requires: []plugin.Type{
+			plugin.RuntimePlugin,
+			plugin.SnapshotPlugin,
+			plugin.TaskMonitorPlugin,
+			plugin.DiffPlugin,
+			plugin.MetadataPlugin,
+			plugin.ContentPlugin,
+			plugin.GCPlugin,
+		},
+		InitFn: initCRIService,
+	})
+}
+
+func initCRIService(_ *plugin.InitContext) (interface{}, error) {
+	// TODO(random-liu): Support Config through Registration.Config.
+	// TODO(random-liu): Validate the configuration.
+	// TODO(random-liu): Leverage other fields in InitContext, such as Root.
+	// TODO(random-liu): Register GRPC service onto containerd GRPC server.
+	// TODO(random-liu): Separate cri plugin config from cri-containerd server config,
+	// because many options only make sense to cri-containerd server.
+	// TODO(random-liu): Change all glog to logrus.
+	// TODO(random-liu): Handle graceful stop.
+	c := options.DefaultConfig()
+	glog.V(0).Infof("Start cri plugin with config %+v", c)
+	// Use a goroutine to start cri service. The reason is that currently
+	// cri service requires containerd to be running.
+	// TODO(random-liu): Resolve the circular dependency.
+	go func() {
+		s, err := server.NewCRIContainerdService(c)
+		if err != nil {
+			glog.Exitf("Failed to create CRI service: %v", err)
+		}
+		if err := s.Run(); err != nil {
+			glog.Exitf("Failed to run CRI grpc server: %v", err)
+		}
+	}()
+	return nil, nil
+}