From dad7758459bc6097115f5e783eda232f36b1ad99 Mon Sep 17 00:00:00 2001 From: Bart Van Assche Date: Thu, 1 Aug 2019 15:50:41 -0700 Subject: block: Document the bio splitting functions Since what the bio splitting functions do is nontrivial, document these functions. Reviewed-by: Johannes Thumshirn Cc: Christoph Hellwig Cc: Ming Lei Cc: Hannes Reinecke Signed-off-by: Bart Van Assche Signed-off-by: Jens Axboe --- block/blk-merge.c | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) (limited to 'block/blk-merge.c') diff --git a/block/blk-merge.c b/block/blk-merge.c index 8344d94f13e0..51ed971709c3 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -195,6 +195,25 @@ static bool bvec_split_segs(const struct request_queue *q, return !!len; } +/** + * blk_bio_segment_split - split a bio in two bios + * @q: [in] request queue pointer + * @bio: [in] bio to be split + * @bs: [in] bio set to allocate the clone from + * @segs: [out] number of segments in the bio with the first half of the sectors + * + * Clone @bio, update the bi_iter of the clone to represent the first sectors + * of @bio and update @bio->bi_iter to represent the remaining sectors. The + * following is guaranteed for the cloned bio: + * - That it has at most get_max_io_size(@q, @bio) sectors. + * - That it has at most queue_max_segments(@q) segments. + * + * Except for discard requests the cloned bio will point at the bi_io_vec of + * the original bio. It is the responsibility of the caller to ensure that the + * original bio is not freed before the cloned bio. The caller is also + * responsible for ensuring that @bs is only destroyed after processing of the + * split bio has finished. + */ static struct bio *blk_bio_segment_split(struct request_queue *q, struct bio *bio, struct bio_set *bs, @@ -251,6 +270,19 @@ split: return bio_split(bio, sectors, GFP_NOIO, bs); } +/** + * __blk_queue_split - split a bio and submit the second half + * @q: [in] request queue pointer + * @bio: [in, out] bio to be split + * @nr_segs: [out] number of segments in the first bio + * + * Split a bio into two bios, chain the two bios, submit the second half and + * store a pointer to the first half in *@bio. If the second bio is still too + * big it will be split by a recursive call to this function. Since this + * function may allocate a new bio from @q->bio_split, it is the responsibility + * of the caller to ensure that @q is only released after processing of the + * split bio has finished. + */ void __blk_queue_split(struct request_queue *q, struct bio **bio, unsigned int *nr_segs) { @@ -295,6 +327,17 @@ void __blk_queue_split(struct request_queue *q, struct bio **bio, } } +/** + * blk_queue_split - split a bio and submit the second half + * @q: [in] request queue pointer + * @bio: [in, out] bio to be split + * + * Split a bio into two bios, chains the two bios, submit the second half and + * store a pointer to the first half in *@bio. Since this function may allocate + * a new bio from @q->bio_split, it is the responsibility of the caller to + * ensure that @q is only released after processing of the split bio has + * finished. + */ void blk_queue_split(struct request_queue *q, struct bio **bio) { unsigned int nr_segs; -- cgit v1.2.3