diff options
| author | Chaitanya Kulkarni <ckulkarnilinux@gmail.com> | 2025-12-02 19:58:09 -0800 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2025-12-04 07:19:26 -0700 |
| commit | 71075d25ca5cae732fb57da065fbf14aeb3bcfc7 (patch) | |
| tree | 67e1d4a379eeb83bda78213fbf3239f75eca2e67 | |
| parent | 3e2cb9ee76c27f57bfdb7b4753b909594d4fa31a (diff) | |
blk-mq: add blk_rq_nr_bvec() helper
Add a new helper function blk_rq_nr_bvec() that returns the number of
bvecs in a request. This count represents the number of iterations
rq_for_each_bvec() would perform on a request.
Drivers need to pre-allocate bvec arrays before iterating through
a request's bvecs. Currently, they manually count bvecs using
rq_for_each_bvec() in a loop, which is repetitive. The new helper
centralizes this logic.
This pattern exists in loop and zloop drivers, where multi-bio requests
require copying bvecs into a contiguous array before creating
an iov_iter for file operations.
Update loop and zloop drivers to use the new helper, eliminating
duplicate code.
This patch also provides a clear API to avoid any potential misuse of
blk_nr_phys_segments() for calculating the bvecs since, one bvec can
have more than one segments and use of blk_nr_phys_segments() can
lead to extra memory allocation :-
[ 6155.673749] nullb_bio: 128K bio as ONE bvec: sector=0, size=131072
[ 6155.673846] null_blk: #### null_handle_data_transfer:1375
[ 6155.673850] null_blk: nr_bvec=1 blk_rq_nr_phys_segments=2
[ 6155.674263] null_blk: #### null_handle_data_transfer:1375
[ 6155.674267] null_blk: nr_bvec=1 blk_rq_nr_phys_segments=1
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
| -rw-r--r-- | drivers/block/loop.c | 5 | ||||
| -rw-r--r-- | drivers/block/zloop.c | 5 | ||||
| -rw-r--r-- | include/linux/blk-mq.h | 18 |
3 files changed, 22 insertions, 6 deletions
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index ebe751f39742..272bc608e528 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -348,11 +348,10 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, struct file *file = lo->lo_backing_file; struct bio_vec tmp; unsigned int offset; - int nr_bvec = 0; + unsigned int nr_bvec; int ret; - rq_for_each_bvec(tmp, rq, rq_iter) - nr_bvec++; + nr_bvec = blk_rq_nr_bvec(rq); if (rq->bio != rq->biotail) { diff --git a/drivers/block/zloop.c b/drivers/block/zloop.c index 3f50321aa4a7..77bd6081b244 100644 --- a/drivers/block/zloop.c +++ b/drivers/block/zloop.c @@ -394,7 +394,7 @@ static void zloop_rw(struct zloop_cmd *cmd) struct bio_vec tmp; unsigned long flags; sector_t zone_end; - int nr_bvec = 0; + unsigned int nr_bvec; int ret; atomic_set(&cmd->ref, 2); @@ -487,8 +487,7 @@ static void zloop_rw(struct zloop_cmd *cmd) spin_unlock_irqrestore(&zone->wp_lock, flags); } - rq_for_each_bvec(tmp, rq, rq_iter) - nr_bvec++; + nr_bvec = blk_rq_nr_bvec(rq); if (rq->bio != rq->biotail) { struct bio_vec *bvec; diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index eb7254b3dddd..cae9e857aea4 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -1213,6 +1213,24 @@ static inline unsigned short blk_rq_nr_discard_segments(struct request *rq) return max_t(unsigned short, rq->nr_phys_segments, 1); } +/** + * blk_rq_nr_bvec - return number of bvecs in a request + * @rq: request to calculate bvecs for + * + * Returns the number of bvecs. + */ +static inline unsigned int blk_rq_nr_bvec(struct request *rq) +{ + struct req_iterator rq_iter; + struct bio_vec bv; + unsigned int nr_bvec = 0; + + rq_for_each_bvec(bv, rq, rq_iter) + nr_bvec++; + + return nr_bvec; +} + int __blk_rq_map_sg(struct request *rq, struct scatterlist *sglist, struct scatterlist **last_sg); static inline int blk_rq_map_sg(struct request *rq, struct scatterlist *sglist) |