code: func EnsureUserAddressDir() error {
  	xdgRuntimeDir := os.Getenv("XDG_RUNTIME_DIR")
  	if xdgRuntimeDir != "" {
  		dirs := strings.Split(xdgRuntimeDir, ":")
  		dir := filepath.Join(dirs[0], "buildkit")
  		if err := os.MkdirAll(dir, 0700); err != nil {
  			return err
  		}
  		return os.Chmod(dir, 0700|os.ModeSticky)
  	}
  	return nil
  }
docs: // EnsureUserAddressDir sets sticky bit on XDG_RUNTIME_DIR if XDG_RUNTIME_DIR is set.
  // See https://github.com/opencontainers/runc/issues/1694