func: static int bdrv_get_cluster_size(BlockDriverState *bs)
  
  {
  
      BlockDriverInfo bdi;
  
      int ret;
  
  
  
      ret = bdrv_get_info(bs, &bdi);
  
      if (ret < 0 || bdi.cluster_size == 0) {
  
          return bs->request_alignment;
  
      } else {
  
          return bdi.cluster_size;
  
      }
  
  }
  