code: func (i *ImageService) Cleanup() {
  	for os, ls := range i.layerStores {
  		if ls != nil {
  			if err := ls.Cleanup(); err != nil {
  				logrus.Errorf("Error during layer Store.Cleanup(): %v %s", err, os)
  			}
  		}
  	}
  }
docs: // Cleanup resources before the process is shutdown.
  // called from daemon.go Daemon.Shutdown()