Add the Checkpointed state

I don't like the current logic in ct.Destroy(). I think ct.Destroy
must destoy ct or return an error.

Signed-off-by: Andrey Vagin <avagin@openvz.org>

container.go

@@ -21,6 +21,9 @@ const (
 	// The container exists, but all its processes are paused.
 	Paused
 
+	// The container exists, but its state is saved on disk
+	Checkpointed
+
 	// The container does not exist.
 	Destroyed
 )

container_linux.go

@@ -223,12 +223,6 @@ func newPipe() (parent *os.File, child *os.File, err error) {
 func (c *linuxContainer) Destroy() error {
 	c.m.Lock()
 	defer c.m.Unlock()
-	// Since the state.json and CRIU image files are in the c.root
-	// directory, we should not remove it after checkpoint.  Also,
-	// when     CRIU exits after restore, we should not kill the processes.
-	if _, err := os.Stat(filepath.Join(c.root, "checkpoint")); err == nil {
-		return nil
-	}
 	status, err := c.currentStatus()
 	if err != nil {
 		return err
@@ -569,10 +563,14 @@ func (c *linuxContainer) updateState(process parentProcess) error {
 		return err
 	}
 	defer f.Close()
+	os.RemoveAll(filepath.Join(c.root, "checkpoint"))
 	return json.NewEncoder(f).Encode(state)
 }
 
 func (c *linuxContainer) currentStatus() (Status, error) {
+	if _, err := os.Stat(filepath.Join(c.root, "checkpoint")); err == nil {
+		return Checkpointed, nil
+	}
 	if c.initProcess == nil {
 		return Destroyed, nil
 	}

nsinit/exec.go

@@ -93,10 +93,17 @@ func execAction(context *cli.Context) {
 		}
 	}
 	if created {
-		if err := container.Destroy(); err != nil {
+		status, err := container.Status()
+		if err != nil {
 			tty.Close()
 			fatal(err)
 		}
+		if status != libcontainer.Checkpointed {
+			if err := container.Destroy(); err != nil {
+				tty.Close()
+				fatal(err)
+			}
+		}
 	}
 	tty.Close()
 	os.Exit(utils.ExitStatus(status.Sys().(syscall.WaitStatus)))

nsinit/restore.go

@@ -53,8 +53,11 @@ var restoreCommand = cli.Command{
 				fatal(err)
 			}
 		}
-		if err := container.Destroy(); err != nil {
-			fatal(err)
+		ctStatus, err := container.Status()
+		if ctStatus == libcontainer.Destroyed {
+			if err := container.Destroy(); err != nil {
+				fatal(err)
+			}
 		}
 		os.Exit(utils.ExitStatus(status.Sys().(syscall.WaitStatus)))
 	},