DATA_INDEX
return (DATA_INDEX(data_ring, blk_lpos->next) -
DATA_INDEX(data_ring, blk_lpos->begin));
return (DATA_INDEX(data_ring, blk_lpos->next) +
DATA_SIZE(data_ring) - DATA_INDEX(data_ring, blk_lpos->begin));
*data_size = DATA_INDEX(data_ring, blk_lpos->next);
return (void *)&data_ring->data[DATA_INDEX(data_ring, begin_lpos)];