[PATCH 1/4] Check that the target supports discard

[Mikulas Patocka <mpatocka@redhat.com>]

Check that the target supports discard

Because of a various race conditions, discard request may be submitted to
device mapper even if device mapper advertises that it doesn't support
discards. (for example, the device is linear, dm advertises discard support,
discard request is constructed, the table is reloaded with mirror, the discard
is submitted to the mirror target that doesn't support it).

To solve these problems we must check that the target supports discard
just before submitting discard request to it.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux-2.6.35-rc3-fast/drivers/md/dm.c
===================================================================
--- linux-2.6.35-rc3-fast.orig/drivers/md/dm.c	2010-07-02 16:10:25.000000000 +0200
+++ linux-2.6.35-rc3-fast/drivers/md/dm.c	2010-07-02 16:11:22.000000000 +0200
@@ -1223,6 +1223,9 @@ static int __clone_and_map_discard(struc
 	if (!dm_target_is_valid(ti))
 		return -EIO;
 
+	if (!(ti->type->features & DM_TARGET_SUPPORTS_DISCARDS))
+		return -EOPNOTSUPP;
+
 	max = max_io_len(ci->md, ci->sector, ti);
 
 	if (ci->sector_count > max)