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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: Kent Overstreet <kmo@daterainc.com>
Tested-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Kent Overstreet 2014-02-07 13:53:46 -07:00 committed by Jens Axboe
parent 087787959c
commit 5cb8850c9c
1 changed files with 62 additions and 29 deletions
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91
block/blk-merge.c
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@ -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;
@ -161,6 +171,48 @@ new_segment:
*bvprv = *bvec;
}
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 bvec_iter iter;
int nsegs, cluster;
nsegs = 0;
cluster = blk_queue_cluster(q);
if (bio->bi_rw & REQ_DISCARD) {
/*
* 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.
*/
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);
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
@ -168,23 +220,11 @@ new_segment:
int blk_rq_map_sg(struct request_queue *q, struct request *rq,
struct scatterlist *sglist)
{
struct bio_vec bvec, bvprv = { NULL };
struct req_iterator iter;
struct scatterlist *sg;
int nsegs, cluster;
nsegs = 0;
cluster = blk_queue_cluster(q);
/*
* for each bio in rq
*/
sg = NULL;
rq_for_each_segment(bvec, rq, iter) {
__blk_segment_map_sg(q, &bvec, sglist, &bvprv, &sg,
&nsegs, &cluster);
} /* segments in rq */
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);