block: separate out blk_rq_merge_ok() and blk_try_merge() from elevator functions

blk_rq_merge_ok() is the elevator-neutral part of merge eligibility
test.  blk_try_merge() determines merge direction and expects the
caller to have tested elv_rq_merge_ok() previously.

elv_rq_merge_ok() now wraps blk_rq_merge_ok() and then calls
elv_iosched_allow_merge().  elv_try_merge() is removed and the two
callers are updated to call elv_rq_merge_ok() explicitly followed by
blk_try_merge().  While at it, make rq_merge_ok() functions return
bool.

This is to prepare for plug merge update and doesn't introduce any
behavior change.

This is based on Jens' patch to skip elevator_allow_merge_fn() from
plug merge.

Signed-off-by: Tejun Heo <tj@kernel.org>
LKML-Reference: <4F16F3CA.90904@kernel.dk>
Original-patch-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 37 insertions, 0 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
index cfcc37cb222..160035f5488 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -471,3 +471,40 @@ int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 {
         return attempt_merge(q, rq, next);
 }
+
+bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
+{
+        if (!rq_mergeable(rq))
+                return false;
+
+        /* don't merge file system requests and discard requests */
+        if ((bio->bi_rw & REQ_DISCARD) != (rq->bio->bi_rw & REQ_DISCARD))
+                return false;
+
+        /* don't merge discard requests and secure discard requests */
+        if ((bio->bi_rw & REQ_SECURE) != (rq->bio->bi_rw & REQ_SECURE))
+                return false;
+
+        /* different data direction or already started, don't merge */
+        if (bio_data_dir(bio) != rq_data_dir(rq))
+                return false;
+
+        /* must be same device and not a special request */
+        if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
+                return false;
+
+        /* only merge integrity protected bio into ditto rq */
+        if (bio_integrity(bio) != blk_integrity_rq(rq))
+                return false;
+
+        return true;
+}
+
+int blk_try_merge(struct request *rq, struct bio *bio)
+{
+        if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_sector)
+                return ELEVATOR_BACK_MERGE;
+        else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_sector)
+                return ELEVATOR_FRONT_MERGE;
+        return ELEVATOR_NO_MERGE;
+}