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: Jens Axboe <axboe@fb.com>
diff --git a/block/blk-merge.c b/block/blk-merge.c
index b3bf0df..5453583 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -568,6 +568,8 @@
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 @@
!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;
}