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block: Document the bio splitting functions 

Since what the bio splitting functions do is nontrivial, document these
functions.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Bart Van Assche 2019-08-01 15:50:41 -07:00 committed by Jens Axboe
parent af2c68fe94
commit dad7758459
2 changed files with 45 additions and 2 deletions
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4
block/bio.c
View File

@ -1842,8 +1842,8 @@ EXPORT_SYMBOL(bio_endio);
* @bio, and updates @bio to represent the remaining sectors.
*
* Unless this is a discard request the newly allocated bio will point
* to @bio's bi_io_vec; it is the caller's responsibility to ensure that
* @bio is not freed before the split.
* to @bio's bi_io_vec. It is the caller's responsibility to ensure that
* neither @bio nor @bs are freed before the split bio.
*/
struct bio *bio_split(struct bio *bio, int sectors,
gfp_t gfp, struct bio_set *bs)

43
block/blk-merge.c
View File

@ -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 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
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;