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Commit 66cb45aa authored by Jens Axboe's avatar Jens Axboe
Browse files

block: add support for limiting gaps in SG lists 



Another restriction inherited for NVMe - those devices don't support
SG lists that have "gaps" in them. Gaps refers to cases where the
previous SG entry doesn't end on a page boundary. For NVMe, all SG
entries must start at offset 0 (except the first) and end on a page
boundary (except the last).

Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 3a4b0eda

block/bio.c

+8 −0
Original line number Diff line number Diff line
@@ -746,6 +746,14 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page 


			goto done;

		}



		/*

		 * If the queue doesn't support SG gaps and adding this

		 * offset would create a gap, disallow it.

		 */

		if (q->queue_flags & (1 << QUEUE_FLAG_SG_GAPS) &&

		    bvec_gap_to_prev(prev, offset))

			return 0;

	}



	if (bio->bi_vcnt >= bio->bi_max_vecs)

block/blk-merge.c

+10 −0
Original line number Diff line number Diff line
@@ -568,6 +568,8 @@ int blk_attempt_req_merge(struct request_queue *q, struct request *rq, 


bool blk_rq_merge_ok(struct request *rq, struct bio *bio)

{

	struct request_queue *q = rq->q;



	if (!rq_mergeable(rq) || !bio_mergeable(bio))

		return false;
@@ -591,6 +593,14 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio) 
	    !blk_write_same_mergeable(rq->bio, bio))

		return false;



	if (q->queue_flags & (1 << QUEUE_FLAG_SG_GAPS)) {

		struct bio_vec *bprev;



		bprev = &rq->biotail->bi_io_vec[bio->bi_vcnt - 1];

		if (bvec_gap_to_prev(bprev, bio->bi_io_vec[0].bv_offset))

			return false;

	}



	return true;

}

include/linux/bio.h

+9 −0
Original line number Diff line number Diff line
@@ -186,6 +186,15 @@ static inline void *bio_data(struct bio *bio) 
#define BIOVEC_SEG_BOUNDARY(q, b1, b2) \

	__BIO_SEG_BOUNDARY(bvec_to_phys((b1)), bvec_to_phys((b2)) + (b2)->bv_len, queue_segment_boundary((q)))



/*

 * Check if adding a bio_vec after bprv with offset would create a gap in

 * the SG list. Most drivers don't care about this, but some do.

 */

static inline bool bvec_gap_to_prev(struct bio_vec *bprv, unsigned int offset)

{

	return offset || ((bprv->bv_offset + bprv->bv_len) & (PAGE_SIZE - 1));

}



#define bio_io_error(bio) bio_endio((bio), -EIO)



/*

include/linux/blkdev.h

+1 −0
Original line number Diff line number Diff line
@@ -512,6 +512,7 @@ struct request_queue { 
#define QUEUE_FLAG_DEAD        19	/* queue tear-down finished */

#define QUEUE_FLAG_INIT_DONE   20	/* queue is initialized */

#define QUEUE_FLAG_NO_SG_MERGE 21	/* don't attempt to merge SG segments*/

#define QUEUE_FLAG_SG_GAPS     22	/* queue doesn't support SG gaps */



#define QUEUE_FLAG_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\

				 (1 << QUEUE_FLAG_STACKABLE)	|	\