Add shim skeleton code

This allows runtime authors to quickly bootstrap new shim
implementations.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

runtime/v2/example/README.md

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+# Example Shim
+
+This directory provides skeleton code as the starting point for creating a Runtime v2 shim.
+This allows runtime authors to quickly bootstrap new shim implementations.
+
+For full documentation on building a shim for containerd, see the [Shim Documentation](../README.md) file.

runtime/v2/example/cmd/main.go

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+// +build linux
+
+/*
+   Copyright 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 main
+
+import (
+	"github.com/containerd/containerd/runtime/v2/example"
+	"github.com/containerd/containerd/runtime/v2/shim"
+)
+
+func main() {
+	// init and execute the shim
+	shim.Run("io.containerd.example.v1", example.New)
+}

runtime/v2/example/example.go

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+// +build linux
+
+/*
+   Copyright 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 example
+
+import (
+	"context"
+	"os"
+
+	"github.com/containerd/containerd/errdefs"
+	"github.com/containerd/containerd/events"
+	"github.com/containerd/containerd/runtime/v2/shim"
+	taskAPI "github.com/containerd/containerd/runtime/v2/task"
+	ptypes "github.com/gogo/protobuf/types"
+)
+
+var (
+	// check to make sure the *service implements the GRPC API
+	_ = (taskAPI.TaskService)(&service{})
+	// common response type
+	empty = &ptypes.Empty{}
+)
+
+// New returns a new shim service
+func New(ctx context.Context, id string, publisher events.Publisher) (shim.Shim, error) {
+	return &service{}, nil
+}
+
+type service struct {
+}
+
+// StartShim is a binary call that executes a new shim returning the address
+func (s *service) StartShim(ctx context.Context, id, containerdBinary, containerdAddress string) (string, error) {
+	return "", nil
+}
+
+// Cleanup is a binary call that cleans up any resources used by the shim when the service crashes
+func (s *service) Cleanup(ctx context.Context) (*taskAPI.DeleteResponse, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Create a new container
+func (s *service) Create(ctx context.Context, r *taskAPI.CreateTaskRequest) (_ *taskAPI.CreateTaskResponse, err error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Start the primary user process inside the container
+func (s *service) Start(ctx context.Context, r *taskAPI.StartRequest) (*taskAPI.StartResponse, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Delete a process or container
+func (s *service) Delete(ctx context.Context, r *taskAPI.DeleteRequest) (*taskAPI.DeleteResponse, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Exec an additional process inside the container
+func (s *service) Exec(ctx context.Context, r *taskAPI.ExecProcessRequest) (*ptypes.Empty, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// ResizePty of a process
+func (s *service) ResizePty(ctx context.Context, r *taskAPI.ResizePtyRequest) (*ptypes.Empty, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// State returns runtime state of a process
+func (s *service) State(ctx context.Context, r *taskAPI.StateRequest) (*taskAPI.StateResponse, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Pause the container
+func (s *service) Pause(ctx context.Context, r *taskAPI.PauseRequest) (*ptypes.Empty, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Resume the container
+func (s *service) Resume(ctx context.Context, r *taskAPI.ResumeRequest) (*ptypes.Empty, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Kill a process
+func (s *service) Kill(ctx context.Context, r *taskAPI.KillRequest) (*ptypes.Empty, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Pids returns all pids inside the container
+func (s *service) Pids(ctx context.Context, r *taskAPI.PidsRequest) (*taskAPI.PidsResponse, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// CloseIO of a process
+func (s *service) CloseIO(ctx context.Context, r *taskAPI.CloseIORequest) (*ptypes.Empty, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Checkpoint the container
+func (s *service) Checkpoint(ctx context.Context, r *taskAPI.CheckpointTaskRequest) (*ptypes.Empty, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Connect returns shim information of the underlying service
+func (s *service) Connect(ctx context.Context, r *taskAPI.ConnectRequest) (*taskAPI.ConnectResponse, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Shutdown is called after the underlying resources of the shim are cleaned up and the service can be stopped
+func (s *service) Shutdown(ctx context.Context, r *taskAPI.ShutdownRequest) (*ptypes.Empty, error) {
+	os.Exit(0)
+	return empty, nil
+}
+
+// Stats returns container level system stats for a container and its processes
+func (s *service) Stats(ctx context.Context, r *taskAPI.StatsRequest) (*taskAPI.StatsResponse, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Update the live container
+func (s *service) Update(ctx context.Context, r *taskAPI.UpdateTaskRequest) (*ptypes.Empty, error) {
+	return nil, errdefs.ErrNotImplemented
+}
+
+// Wait for a process to exit
+func (s *service) Wait(ctx context.Context, r *taskAPI.WaitRequest) (*taskAPI.WaitResponse, error) {
+	return nil, errdefs.ErrNotImplemented
+}