Add exec support to client

This also fixes a deadlock in the shim's reaper where execs would lockup
and/or miss a quick exiting exec process's exit status.

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

container_test.go

@@ -3,9 +3,14 @@ package containerd
 import (
 	"bytes"
 	"context"
+	"syscall"
 	"testing"
 )
 
+func empty() IOCreation {
+	return BufferedIO(bytes.NewBuffer(nil), bytes.NewBuffer(nil), bytes.NewBuffer(nil))
+}
+
 func TestContainerList(t *testing.T) {
 	if testing.Short() {
 		t.Skip()
@@ -64,7 +69,6 @@ func TestNewContainer(t *testing.T) {
 func TestContainerStart(t *testing.T) {
 	if testing.Short() {
 		t.Skip()
-		return
 	}
 	client, err := New(address)
 	if err != nil {
@@ -133,7 +137,6 @@ func TestContainerStart(t *testing.T) {
 func TestContainerOutput(t *testing.T) {
 	if testing.Short() {
 		t.Skip()
-		return
 	}
 	client, err := New(address)
 	if err != nil {
@@ -201,3 +204,88 @@ func TestContainerOutput(t *testing.T) {
 		t.Errorf("expected output %q but received %q", expected, actual)
 	}
 }
+
+func TestContainerExec(t *testing.T) {
+	if testing.Short() {
+		t.Skip()
+	}
+	client, err := New(address)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer client.Close()
+
+	var (
+		ctx = context.Background()
+		id  = "ContainerExec"
+	)
+	image, err := client.GetImage(ctx, testImage)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	spec, err := GenerateSpec(WithImageConfig(ctx, image), WithProcessArgs("sleep", "100"))
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	container, err := client.NewContainer(ctx, id, spec, WithImage(image), WithNewRootFS(id, image))
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	defer container.Delete(ctx)
+
+	task, err := container.NewTask(ctx, empty())
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	defer task.Delete(ctx)
+
+	finished := make(chan struct{}, 1)
+	go func() {
+		if _, err := task.Wait(ctx); err != nil {
+			t.Error(err)
+		}
+		close(finished)
+	}()
+
+	// start an exec process without running the original container process info
+	processSpec := spec.Process
+	processSpec.Args = []string{
+		"sh", "-c",
+		"exit 6",
+	}
+
+	process, err := task.Exec(ctx, &processSpec, empty())
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	processStatusC := make(chan uint32, 1)
+	go func() {
+		status, err := process.Wait(ctx)
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		processStatusC <- status
+	}()
+
+	if err := process.Start(ctx); err != nil {
+		t.Error(err)
+		return
+	}
+
+	// wait for the exec to return
+	status := <-processStatusC
+
+	if status != 6 {
+		t.Errorf("expected exec exit code 6 but received %d", status)
+	}
+	if err := task.Kill(ctx, syscall.SIGKILL); err != nil {
+		t.Error(err)
+	}
+	<-finished
+}

linux/shim/service.go

@@ -101,19 +101,18 @@ func (s *Service) Exec(ctx context.Context, r *shimapi.ExecRequest) (*shimapi.Ex
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	s.execID++
-	reaper.Default.Lock()
+
 	process, err := newExecProcess(ctx, s.path, r, s.initProcess, s.execID)
 	if err != nil {
-		reaper.Default.Unlock()
 		return nil, err
 	}
 	pid := process.Pid()
-	s.processes[pid] = process
 	cmd := &reaper.Cmd{
 		ExitCh: make(chan int, 1),
 	}
-	reaper.Default.RegisterNL(pid, cmd)
+	reaper.Default.Register(pid, cmd)
-	reaper.Default.Unlock()
+	s.processes[pid] = process
+
 	s.events <- &task.Event{
 		Type: task.Event_EXEC_ADDED,
 		ID:   s.id,
@@ -290,6 +289,8 @@ func (s *Service) Checkpoint(ctx context.Context, r *shimapi.CheckpointRequest)
 func (s *Service) waitExit(p process, pid int, cmd *reaper.Cmd) {
 	status := <-cmd.ExitCh
 	p.Exited(status)
+
+	reaper.Default.Delete(pid)
 	s.events <- &task.Event{
 		Type:       task.Event_EXIT,
 		ID:         s.id,

process.go

@@ -0,0 +1,87 @@
+package containerd
+
+import (
+	"context"
+	"encoding/json"
+	"syscall"
+
+	"github.com/containerd/containerd/api/services/execution"
+	taskapi "github.com/containerd/containerd/api/types/task"
+	protobuf "github.com/gogo/protobuf/types"
+	specs "github.com/opencontainers/runtime-spec/specs-go"
+)
+
+type process struct {
+	task *task
+
+	// this is a hack to make a blocking Wait work
+	// exec does not have a create/start split so if a quick exiting process like `exit 1`
+	// run, the wait does not have enough time to get the pid catch the event.  So we need
+	// to lock this on process struct create and only unlock it after the pid is set
+	// this allow the wait to be called before calling process start and not race with the exit event
+	pidSync chan struct{}
+
+	io   *IO
+	pid  uint32
+	spec *specs.Process
+}
+
+func (p *process) Pid() uint32 {
+	return p.pid
+}
+
+func (p *process) Start(ctx context.Context) error {
+	data, err := json.Marshal(p.spec)
+	if err != nil {
+		return err
+	}
+	request := &execution.ExecRequest{
+		ContainerID: p.task.containerID,
+		Terminal:    p.io.Terminal,
+		Stdin:       p.io.Stdin,
+		Stdout:      p.io.Stdout,
+		Stderr:      p.io.Stderr,
+		Spec: &protobuf.Any{
+			TypeUrl: specs.Version,
+			Value:   data,
+		},
+	}
+	response, err := p.task.client.TaskService().Exec(ctx, request)
+	if err != nil {
+		return err
+	}
+	p.pid = response.Pid
+	close(p.pidSync)
+	return nil
+}
+
+func (p *process) Kill(ctx context.Context, s syscall.Signal) error {
+	_, err := p.task.client.TaskService().Kill(ctx, &execution.KillRequest{
+		Signal:      uint32(s),
+		ContainerID: p.task.containerID,
+		PidOrAll: &execution.KillRequest_Pid{
+			Pid: p.pid,
+		},
+	})
+	return err
+}
+
+func (p *process) Wait(ctx context.Context) (uint32, error) {
+	events, err := p.task.client.TaskService().Events(ctx, &execution.EventsRequest{})
+	if err != nil {
+		return UnknownExitStatus, err
+	}
+	<-p.pidSync
+	for {
+		e, err := events.Recv()
+		if err != nil {
+			return UnknownExitStatus, err
+		}
+		if e.Type != taskapi.Event_EXIT {
+			continue
+		}
+		if e.ID == p.task.containerID && e.Pid == p.pid {
+			return e.ExitStatus, nil
+		}
+	}
+}

reaper/reaper.go

@@ -19,30 +19,32 @@ func Reap() error {
 	for _, e := range exits {
 		Default.Lock()
 		c, ok := Default.cmds[e.Pid]
-		Default.Unlock()
 		if !ok {
+			Default.unknown[e.Pid] = e.Status
+			Default.Unlock()
 			continue
 		}
+		Default.Unlock()
 		if c.c != nil {
 			// after we get an exit, call wait on the go process to make sure all
 			// pipes are closed and finalizers are run on the process
 			c.c.Wait()
 		}
 		c.ExitCh <- e.Status
-		Default.Lock()
-		delete(Default.cmds, e.Pid)
-		Default.Unlock()
 	}
 	return err
 }
 
 var Default = &Monitor{
 	cmds:    make(map[int]*Cmd),
+	unknown: make(map[int]int),
 }
 
 type Monitor struct {
 	sync.Mutex
+
 	cmds    map[int]*Cmd
+	unknown map[int]int
 }
 
 func (m *Monitor) Output(c *exec.Cmd) ([]byte, error) {
@@ -93,6 +95,13 @@ func (m *Monitor) Wait(c *exec.Cmd) (int, error) {
 
 func (m *Monitor) Register(pid int, c *Cmd) {
 	m.Lock()
+	if status, ok := m.unknown[pid]; ok {
+		delete(m.unknown, pid)
+		m.cmds[pid] = c
+		m.Unlock()
+		c.ExitCh <- status
+		return
+	}
 	m.cmds[pid] = c
 	m.Unlock()
 }
@@ -117,6 +126,19 @@ func (m *Monitor) WaitPid(pid int) (int, error) {
 	return ec, nil
 }
 
+// Command returns the registered pid for the command created
+func (m *Monitor) Command(pid int) *Cmd {
+	m.Lock()
+	defer m.Unlock()
+	return m.cmds[pid]
+}
+
+func (m *Monitor) Delete(pid int) {
+	m.Lock()
+	delete(m.cmds, pid)
+	m.Unlock()
+}
+
 type Cmd struct {
 	c      *exec.Cmd
 	ExitCh chan int

task.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/containerd/containerd/api/services/execution"
 	taskapi "github.com/containerd/containerd/api/types/task"
+	specs "github.com/opencontainers/runtime-spec/specs-go"
 )
 
 const UnknownExitStatus = 255
@@ -21,14 +22,22 @@ const (
 )
 
 type Task interface {
+	Pid() uint32
 	Delete(context.Context) (uint32, error)
 	Kill(context.Context, syscall.Signal) error
 	Pause(context.Context) error
 	Resume(context.Context) error
-	Pid() uint32
 	Start(context.Context) error
 	Status(context.Context) (TaskStatus, error)
 	Wait(context.Context) (uint32, error)
+	Exec(context.Context, *specs.Process, IOCreation) (Process, error)
+}
+
+type Process interface {
+	Pid() uint32
+	Start(context.Context) error
+	Kill(context.Context, syscall.Signal) error
+	Wait(context.Context) (uint32, error)
 }
 
 var _ = (Task)(&task{})
@@ -121,3 +130,16 @@ func (t *task) Delete(ctx context.Context) (uint32, error) {
 	}
 	return r.ExitStatus, cerr
 }
+
+func (t *task) Exec(ctx context.Context, spec *specs.Process, ioCreate IOCreation) (Process, error) {
+	i, err := ioCreate()
+	if err != nil {
+		return nil, err
+	}
+	return &process{
+		task:    t,
+		io:      i,
+		spec:    spec,
+		pidSync: make(chan struct{}),
+	}, nil
+}