code: func setupStage1Image(cfg RunConfig, cdir string, useOverlay bool) error {
  	s1 := common.Stage1ImagePath(cdir)
  	if useOverlay {
  		treeStoreID, err := ioutil.ReadFile(filepath.Join(cdir, common.Stage1TreeStoreIDFilename))
  		if err != nil {
  			return err
  		}
  
  		// pass an empty appName
  		if err := overlayRender(cfg, string(treeStoreID), cdir, s1, ""); err != nil {
  			return errwrap.Wrap(errors.New("error rendering overlay filesystem"), err)
  		}
  
  		// we will later read the status from the upper layer of the overlay fs
  		// force the status directory to be there by touching it
  		statusPath := filepath.Join(s1, "rootfs", "rkt", "status")
  		if err := os.Chtimes(statusPath, time.Now(), time.Now()); err != nil {
  			return errwrap.Wrap(errors.New("error touching status dir"), err)
  		}
  	}
  
  	return nil
  }
docs: // setupStage1Image mounts the overlay filesystem for stage1.
  // When useOverlay is false it is a noop