code: func (pm *VolumePluginMgr) FindDeletablePluginByName(name string) (DeletableVolumePlugin, error) {
  	volumePlugin, err := pm.FindPluginByName(name)
  	if err != nil {
  		return nil, err
  	}
  	if deletableVolumePlugin, ok := volumePlugin.(DeletableVolumePlugin); ok {
  		return deletableVolumePlugin, nil
  	}
  	return nil, fmt.Errorf("no deletable volume plugin matched")
  }
docs: // FindDeletablePluginByName fetches a persistent volume plugin by name.  If
  // no plugin is found, returns error.