dm: disable WRITE SAME

WRITE SAME bios are not yet handled correctly by device-mapper so
disable their use on device-mapper devices by setting
max_write_same_sectors to zero.

As an example, a ciphertext device is incompatible because the data
gets changed according to the location at which it written and so the
dm crypt target cannot support it.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
Cc: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-table.c

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 100368e..fa29557 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1445,6 +1445,8 @@
 	else
 		queue_flag_clear_unlocked(QUEUE_FLAG_NONROT, q);
 
+	q->limits.max_write_same_sectors = 0;
+
 	dm_table_set_integrity(t);
 
 	/*