block: enumify ELEVATOR_*_MERGE

Switch these constants to an enum, and make let the compiler ensure that
all callers of blk_try_merge and elv_merge handle all potential values.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 17 insertions, 18 deletions

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index ee455e7..72d0d83 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -238,30 +238,29 @@ bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
 			    struct request **merged_request)
 {
 	struct request *rq;
-	int ret;
 
-	ret = elv_merge(q, &rq, bio);
-	if (ret == ELEVATOR_BACK_MERGE) {
+	switch (elv_merge(q, &rq, bio)) {
+	case ELEVATOR_BACK_MERGE:
 		if (!blk_mq_sched_allow_merge(q, rq, bio))
 			return false;
-		if (bio_attempt_back_merge(q, rq, bio)) {
-			*merged_request = attempt_back_merge(q, rq);
-			if (!*merged_request)
-				elv_merged_request(q, rq, ret);
-			return true;
-		}
-	} else if (ret == ELEVATOR_FRONT_MERGE) {
+		if (!bio_attempt_back_merge(q, rq, bio))
+			return false;
+		*merged_request = attempt_back_merge(q, rq);
+		if (!*merged_request)
+			elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
+		return true;
+	case ELEVATOR_FRONT_MERGE:
 		if (!blk_mq_sched_allow_merge(q, rq, bio))
 			return false;
-		if (bio_attempt_front_merge(q, rq, bio)) {
-			*merged_request = attempt_front_merge(q, rq);
-			if (!*merged_request)
-				elv_merged_request(q, rq, ret);
-			return true;
-		}
+		if (!bio_attempt_front_merge(q, rq, bio))
+			return false;
+		*merged_request = attempt_front_merge(q, rq);
+		if (!*merged_request)
+			elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
+		return true;
+	default:
+		return false;
 	}
-
-	return false;
 }
 EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);