libcontainer: support creating cgroups v2 path

when creating a cgroups v2 path, propagate down all the enabled
controllers.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

Author: giuseppe

libcontainer/cgroups/systemd/apply_systemd.go

@@ -346,13 +346,64 @@ func (m *Manager) GetPaths() map[string]string {
 	return paths
 }
 
+func createCgroupsv2Path(path string) (Err error) {
+	content, err := ioutil.ReadFile("/sys/fs/cgroup/cgroup.controllers")
+	if err != nil {
+		return err
+	}
+	if !filepath.HasPrefix(path, "/sys/fs/cgroup") {
+		return fmt.Errorf("invalid cgroup path %s", path)
+	}
+
+	res := ""
+	for i, c := range strings.Split(strings.TrimSpace(string(content)), " ") {
+		if i == 0 {
+			res = fmt.Sprintf("+%s", c)
+		} else {
+			res = res + fmt.Sprintf(" +%s", c)
+		}
+	}
+	resByte := []byte(res)
+
+	current := "/sys/fs"
+	elements := strings.Split(path, "/")
+	for i, e := range elements[3:] {
+		current = filepath.Join(current, e)
+		if i > 0 {
+			if err := os.Mkdir(current, 0755); err != nil {
+				if !os.IsExist(err) {
+					return err
+				}
+			} else {
+				// If the directory was created, be sure it is not left around on errors.
+				defer func() {
+					if Err != nil {
+						os.Remove(current)
+					}
+				}()
+			}
+		}
+		if err := ioutil.WriteFile(filepath.Join(current, "cgroup.subtree_control"), resByte, 0755); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 func join(c *configs.Cgroup, subsystem string, pid int) (string, error) {
 	path, err := getSubsystemPath(c, subsystem)
 	if err != nil {
 		return "", err
 	}
-	if err := os.MkdirAll(path, 0755); err != nil {
-		return "", err
+
+	if cgroups.IsCgroup2UnifiedMode() {
+		if err := createCgroupsv2Path(path); err != nil {
+			return "", err
+		}
+	} else {
+		if err := os.MkdirAll(path, 0755); err != nil {
+			return "", err
+		}
 	}
 	if err := cgroups.WriteCgroupProc(path, pid); err != nil {
 		return "", err
@@ -361,6 +412,15 @@ func join(c *configs.Cgroup, subsystem string, pid int) (string, error) {
 }
 
 func joinCgroups(c *configs.Cgroup, pid int) error {
+	if cgroups.IsCgroup2UnifiedMode() {
+		path, err := getSubsystemPath(c, "memory")
+		if err != nil {
+			return err
+		}
+		if err := createCgroupsv2Path(path); err != nil {
+			return err
+		}
+	}
 	for _, sys := range subsystems {
 		name := sys.Name()
 		switch name {