code: func getCgroupParentPath(mountpoint, root string) (string, error) {
  	// Use GetThisCgroupDir instead of GetInitCgroupDir, because the creating
  	// process could in container and shared pid namespace with host, and
  	// /proc/1/cgroup could point to whole other world of cgroups.
  	initPath, err := libcontainercgroups.GetOwnCgroup("devices")
  	if err != nil {
  		return "", err
  	}
  	// This is needed for nested containers, because in /proc/self/cgroup we
  	// see paths from host, which don't exist in container.
  	relDir, err := filepath.Rel(root, initPath)
  	if err != nil {
  		return "", err
  	}
  	return filepath.Join(mountpoint, relDir), nil
  }
docs: // getCgroupParentPath gets the parent filepath to this cgroup, for resolving relative cgroup paths.