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, 14 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/testing/sysfs-block
index c1eb41cb9876..279da08f7541 100644
--- a/Documentation/ABI/testing/sysfs-block
+++ b/Documentation/ABI/testing/sysfs-block
@@ -206,3 +206,17 @@ Description:
                 when a discarded area is read the discard_zeroes_data
                 parameter will be set to one. Otherwise it will be 0 and
                 the result of reading a discarded area is undefined.
+
+What:           /sys/block/<disk>/queue/write_same_max_bytes
+Date:           January 2012
+Contact:        Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+                Some devices support a write same operation in which a
+                single data block can be written to a range of several
+                contiguous blocks on storage. This can be used to wipe
+                areas on disk or to initialize drives in a RAID
+                configuration. write_same_max_bytes indicates how many
+                bytes can be written in a single write same command. If
+                write_same_max_bytes is 0, write same is not supported
+                by the device.
+