Am 13.01.2015 um 23:54 schrieb Jens Axboe: >>> blk_rq_map_sg returns the number of entries actually mapped, which >>> might be smaller than the number passed in due to merging. >> >> Yep, but the ubi_sql has a fixed number of scatterlist entries, >> UBI_MAX_SG_COUNT. >> And I limit it also to that using: blk_queue_max_segments(dev->rq, >> UBI_MAX_SG_COUNT); >> >> Is there another reason why I should use the return value of blk_rq_map_sg()? >> Please also note that the UBI block driver is read-only. > > It can return less than what you asked for, if segments are coalesced. > Read/write, doesn't matter. You should always use the returned value as > the indication of how many segments to access in pdu->usgl.sg for data > transfer.
Sorry, I don't fully understand. Currently the driver does: to_read = blk_rq_bytes(req); Then it fills pdu->usgl.sg up to to_read bytes and calls blk_mq_end_request(). If I understand you correctly it can happen that blk_rq_bytes() returns more bytes than blk_rq_map_sg() allocated, right? Thanks, //richard -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
