code: func (pm *VolumePluginMgr) FindVolumePluginWithLimitsBySpec(spec *Spec) (VolumePluginWithAttachLimits, error) {
  	volumePlugin, err := pm.FindPluginBySpec(spec)
  	if err != nil {
  		return nil, fmt.Errorf("Could not find volume plugin for spec : %#v", spec)
  	}
  
  	if limitedPlugin, ok := volumePlugin.(VolumePluginWithAttachLimits); ok {
  		return limitedPlugin, nil
  	}
  	return nil, fmt.Errorf("no plugin with limits found")
  }
docs: // FindVolumePluginWithLimitsBySpec returns volume plugin that has a limit on how many
  // of them can be attached to a node