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>
diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/testing/sysfs-block
index c1eb41c..279da08 100644
--- a/Documentation/ABI/testing/sysfs-block
+++ b/Documentation/ABI/testing/sysfs-block
@@ -206,3 +206,17 @@
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.
+