block: Implement support for WRITE SAME

The WRITE SAME command supported on some SCSI devices allows the same
block to be efficiently replicated throughout a block range. Only a
single logical block is transferred from the host and the storage device
writes the same data to all blocks described by the I/O.

This patch implements support for WRITE SAME in the block layer. The
blkdev_issue_write_same() function can be used by filesystems and block
drivers to replicate a buffer across a block range. This can be used to
efficiently initialize software RAID devices, etc.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 9 insertions, 0 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 642b862608a1..936a110de0b9 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -419,6 +419,10 @@ static int attempt_merge(struct request_queue *q, struct request *req,
             || next->special)
                 return 0;
 
+        if (req->cmd_flags & REQ_WRITE_SAME &&
+            !blk_write_same_mergeable(req->bio, next->bio))
+                return 0;
+
         /*
          * If we are allowed to merge, then append bio list
          * from next to rq and release next. merge_requests_fn
@@ -518,6 +522,11 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
         if (bio_integrity(bio) != blk_integrity_rq(rq))
                 return false;
 
+        /* must be using the same buffer */
+        if (rq->cmd_flags & REQ_WRITE_SAME &&
+            !blk_write_same_mergeable(rq->bio, bio))
+                return false;
+
         return true;
 }