Get PIDs from cgroups recursively

libcontainer/cgroups/fs/apply_raw.go

@@ -213,7 +213,7 @@ func (m *Manager) GetPids() ([]int, error) {
 		return nil, err
 	}
 
-	return cgroups.ReadProcsFile(dir)
+	return cgroups.GetPids(dir)
 }
 
 func getCgroupData(c *configs.Cgroup, pid int) (*data, error) {

libcontainer/cgroups/systemd/apply_systemd.go

@@ -411,12 +411,11 @@ func (m *Manager) Freeze(state configs.FreezerState) error {
 }
 
 func (m *Manager) GetPids() ([]int, error) {
-	path, err := getSubsystemPath(m.Cgroups, "cpu")
+	path, err := getSubsystemPath(m.Cgroups, "devices")
 	if err != nil {
 		return nil, err
 	}
-
-	return cgroups.ReadProcsFile(path)
+	return cgroups.GetPids(path)
 }
 
 func (m *Manager) GetStats() (*cgroups.Stats, error) {

libcontainer/cgroups/utils.go

@@ -193,7 +193,7 @@ func GetInitCgroupDir(subsystem string) (string, error) {
 	return getControllerPath(subsystem, cgroups)
 }
 
-func ReadProcsFile(dir string) ([]int, error) {
+func readProcsFile(dir string) ([]int, error) {
 	f, err := os.Open(filepath.Join(dir, "cgroup.procs"))
 	if err != nil {
 		return nil, err
@@ -322,3 +322,29 @@ func GetHugePageSize() ([]string, error) {
 
 	return pageSizes, nil
 }
+
+// GetPids returns all pids, that were added to cgroup at path and to all its
+// subcgroups.
+func GetPids(path string) ([]int, error) {
+	var pids []int
+	// collect pids from all sub-cgroups
+	err := filepath.Walk(path, func(p string, info os.FileInfo, iErr error) error {
+		if info.IsDir() {
+			return nil
+		}
+
+		dir, file := filepath.Split(p)
+		if file == "cgroup.procs" {
+			if iErr != nil {
+				return iErr
+			}
+			cPids, err := readProcsFile(dir)
+			if err != nil {
+				return err
+			}
+			pids = append(pids, cPids...)
+		}
+		return nil
+	})
+	return pids, err
+}