block: fix failfast merge testing in elv_rq_merge_ok()

Commit ab0fd1debe730ec9998678a0c53caefbd121ed10 tries to prevent merge
of requests with different failfast settings.  In elv_rq_merge_ok(),
it compares new bio's failfast flags against the merge target
request's.  However, the flag testing accessors for bio and blk don't
return boolean but the tested bit value directly and FAILFAST on bio
and blk don't match, so directly comparing them with == results in
false negative unnecessary preventing merge of readahead requests.

This patch convert the results to boolean by negating them before
comparison.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Boaz Harrosh <bharrosh@panasas.com>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Jeff Garzik <jeff@garzik.org>

diff --git a/block/elevator.c b/block/elevator.c
index 6f2375339a996a794c17c96d0f32aa724fd1fae2..2d511f9105e16abcf93cad6ac849ad9996661a32 100644 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -101,11 +101,16 @@ int elv_rq_merge_ok(struct request *rq, struct bio *bio)
                return 0;
 
        /*
-        * Don't merge if failfast settings don't match
+        * Don't merge if failfast settings don't match.
+        *
+        * FIXME: The negation in front of each condition is necessary
+        * because bio and request flags use different bit positions
+        * and the accessors return those bits directly.  This
+        * ugliness will soon go away.
         */
-       if (bio_failfast_dev(bio)       != blk_failfast_dev(rq)         ||
-           bio_failfast_transport(bio) != blk_failfast_transport(rq)   ||
-           bio_failfast_driver(bio)    != blk_failfast_driver(rq))
+       if (!bio_failfast_dev(bio)       != !blk_failfast_dev(rq)       ||
+           !bio_failfast_transport(bio) != !blk_failfast_transport(rq) ||
+           !bio_failfast_driver(bio)    != !blk_failfast_driver(rq))
                return 0;
 
        if (!elv_iosched_allow_merge(rq, bio))