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, 6 insertions, 3 deletions

diff --git a/fs/bio.c b/fs/bio.c
index 13e9567..f855e0e 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -1487,9 +1487,12 @@ struct bio_pair *bio_split(struct bio *bi, int first_sectors)
 
 	bp->bv1 = bi->bi_io_vec[0];
 	bp->bv2 = bi->bi_io_vec[0];
-	bp->bv2.bv_offset += first_sectors << 9;
-	bp->bv2.bv_len -= first_sectors << 9;
-	bp->bv1.bv_len = first_sectors << 9;
+
+	if (bio_is_rw(bi)) {
+		bp->bv2.bv_offset += first_sectors << 9;
+		bp->bv2.bv_len -= first_sectors << 9;
+		bp->bv1.bv_len = first_sectors << 9;
+	}
 
 	bp->bio1.bi_io_vec = &bp->bv1;
 	bp->bio2.bi_io_vec = &bp->bv2;