code: func (d *Driver) setLayerChain(id string, chain []string) error {
  	content, err := json.Marshal(&chain)
  	if err != nil {
  		return fmt.Errorf("Failed to marshall layerchain json - %s", err)
  	}
  
  	jPath := filepath.Join(d.dir(id), "layerchain.json")
  	err = ioutil.WriteFile(jPath, content, 0600)
  	if err != nil {
  		return fmt.Errorf("Unable to write layerchain file - %s", err)
  	}
  
  	return nil
  }
docs: // setLayerChain stores the layer chain information in disk.