add ErrCgroupNotExist

For some rootless container, runc has no access to cgroup,
But the container is still running. So we should return the
`ErrNotRunning` and `ErrCgroupNotExist` error seperatlly.

Signed-off-by: lifubang <lifubang@acmcoder.com>

libcontainer/error.go

@@ -3,11 +3,12 @@ package libcontainer
 import "errors"
 
 var (
-	ErrExist      = errors.New("container with given ID already exists")
-	ErrInvalidID  = errors.New("invalid container ID format")
-	ErrNotExist   = errors.New("container does not exist")
-	ErrPaused     = errors.New("container paused")
-	ErrRunning    = errors.New("container still running")
-	ErrNotRunning = errors.New("container not running")
-	ErrNotPaused  = errors.New("container not paused")
+	ErrExist          = errors.New("container with given ID already exists")
+	ErrInvalidID      = errors.New("invalid container ID format")
+	ErrNotExist       = errors.New("container does not exist")
+	ErrPaused         = errors.New("container paused")
+	ErrRunning        = errors.New("container still running")
+	ErrNotRunning     = errors.New("container not running")
+	ErrNotPaused      = errors.New("container not paused")
+	ErrCgroupNotExist = errors.New("cgroup not exist")
 )

libcontainer/init_linux.go

@@ -699,7 +699,7 @@ func setupPersonality(config *configs.Config) error {
 // signalAllProcesses returns ErrNotRunning when the cgroup does not exist.
 func signalAllProcesses(m cgroups.Manager, s unix.Signal) error {
 	if !m.Exists() {
-		return ErrNotRunning
+		return ErrCgroupNotExist
 	}
 	// Use cgroup.kill, if available.
 	if s == unix.SIGKILL {