code: func (i *ImageService) LayerStoreStatus() map[string][][2]string {
  	result := make(map[string][][2]string)
  	for os, store := range i.layerStores {
  		result[os] = store.DriverStatus()
  	}
  	return result
  }
docs: // LayerStoreStatus returns the status for each layer store
  // called from info.go