[PATCH] md: fail IO request to md that require a barrier.

md does not yet support BIO_RW_BARRIER, so be honest about it and fail
(-EOPNOTSUPP) any such requests.

Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/md/multipath.c b/drivers/md/multipath.c
index 2d2ca7f..2863423 100644
--- a/drivers/md/multipath.c
+++ b/drivers/md/multipath.c
@@ -169,6 +169,11 @@
 	struct multipath_bh * mp_bh;
 	struct multipath_info *multipath;
 
+	if (unlikely(bio_barrier(bio))) {
+		bio_endio(bio, bio->bi_size, -EOPNOTSUPP);
+		return 0;
+	}
+
 	mp_bh = mempool_alloc(conf->pool, GFP_NOIO);
 
 	mp_bh->master_bio = bio;