Commit 5cb8850c authored by Kent Overstreet's avatar Kent Overstreet Committed by Jens Axboe
Browse files

block: Explicitly handle discard/write same segments 



Immutable biovecs changed the way biovecs are interpreted - drivers no
longer use bi_vcnt, they have to go by bi_iter.bi_size (to allow for
using part of an existing segment without modifying it).

This breaks with discards and write_same bios, since for those bi_size
has nothing to do with segments in the biovec. So for now, we need a
fairly gross hack - we fortunately know that there will never be more
than one segment for the entire request, so we can special case
discard/write_same.

Signed-off-by: default avatarKent Overstreet <kmo@daterainc.com>
Tested-by: default avatarHugh Dickins <hughd@google.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 08778795

block/blk-merge.c

+62 −29
Original line number Diff line number Diff line
@@ -21,6 +21,16 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q, 
	if (!bio)

		return 0;



	/*

	 * This should probably be returning 0, but blk_add_request_payload()

	 * (Christoph!!!!)

	 */

	if (bio->bi_rw & REQ_DISCARD)

		return 1;



	if (bio->bi_rw & REQ_WRITE_SAME)

		return 1;



	fbio = bio;

	cluster = blk_queue_cluster(q);

	seg_size = 0;
@@ -161,30 +171,60 @@ new_segment: 
	*bvprv = *bvec;

}



/*

 * map a request to scatterlist, return number of sg entries setup. Caller

 * must make sure sg can hold rq->nr_phys_segments entries

 */

int blk_rq_map_sg(struct request_queue *q, struct request *rq,

		  struct scatterlist *sglist)

static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,

			     struct scatterlist *sglist,

			     struct scatterlist **sg)

{

	struct bio_vec bvec, bvprv = { NULL };

	struct req_iterator iter;

	struct scatterlist *sg;

	struct bvec_iter iter;

	int nsegs, cluster;



	nsegs = 0;

	cluster = blk_queue_cluster(q);



	if (bio->bi_rw & REQ_DISCARD) {

		/*

	 * for each bio in rq

		 * This is a hack - drivers should be neither modifying the

		 * biovec, nor relying on bi_vcnt - but because of

		 * blk_add_request_payload(), a discard bio may or may not have

		 * a payload we need to set up here (thank you Christoph) and

		 * bi_vcnt is really the only way of telling if we need to.

		 */

	sg = NULL;

	rq_for_each_segment(bvec, rq, iter) {

		__blk_segment_map_sg(q, &bvec, sglist, &bvprv, &sg,



		if (bio->bi_vcnt)

			goto single_segment;



		return 0;

	}



	if (bio->bi_rw & REQ_WRITE_SAME) {

single_segment:

		*sg = sglist;

		bvec = bio_iovec(bio);

		sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);

		return 1;

	}



	for_each_bio(bio)

		bio_for_each_segment(bvec, bio, iter)

			__blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,

					     &nsegs, &cluster);

	} /* segments in rq */



	return nsegs;

}



/*

 * map a request to scatterlist, return number of sg entries setup. Caller

 * must make sure sg can hold rq->nr_phys_segments entries

 */

int blk_rq_map_sg(struct request_queue *q, struct request *rq,

		  struct scatterlist *sglist)

{

	struct scatterlist *sg = NULL;

	int nsegs = 0;



	if (rq->bio)

		nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);



	if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&

	    (blk_rq_bytes(rq) & q->dma_pad_mask)) {
@@ -230,20 +270,13 @@ EXPORT_SYMBOL(blk_rq_map_sg); 
int blk_bio_map_sg(struct request_queue *q, struct bio *bio,

		   struct scatterlist *sglist)

{

	struct bio_vec bvec, bvprv = { NULL };

	struct scatterlist *sg;

	int nsegs, cluster;

	struct bvec_iter iter;



	nsegs = 0;

	cluster = blk_queue_cluster(q);



	sg = NULL;

	bio_for_each_segment(bvec, bio, iter) {

		__blk_segment_map_sg(q, &bvec, sglist, &bvprv, &sg,

				     &nsegs, &cluster);

	} /* segments in bio */

	struct scatterlist *sg = NULL;

	int nsegs;

	struct bio *next = bio->bi_next;

	bio->bi_next = NULL;



	nsegs = __blk_bios_map_sg(q, bio, sglist, &sg);

	bio->bi_next = next;

	if (sg)

		sg_mark_end(sg);

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