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, 14 insertions, 18 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index e9957df05700..dd9722df4afe 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -763,7 +763,7 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
         int checked = 8;
 
         list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
-                int el_ret;
+                bool merged = false;
 
                 if (!checked--)
                         break;
@@ -771,26 +771,22 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
                 if (!blk_rq_merge_ok(rq, bio))
                         continue;
 
-                el_ret = blk_try_merge(rq, bio);
-                if (el_ret == ELEVATOR_NO_MERGE)
-                        continue;
-
-                if (!blk_mq_sched_allow_merge(q, rq, bio))
+                switch (blk_try_merge(rq, bio)) {
+                case ELEVATOR_BACK_MERGE:
+                        if (blk_mq_sched_allow_merge(q, rq, bio))
+                                merged = bio_attempt_back_merge(q, rq, bio);
                         break;
-
-                if (el_ret == ELEVATOR_BACK_MERGE) {
-                        if (bio_attempt_back_merge(q, rq, bio)) {
-                                ctx->rq_merged++;
-                                return true;
-                        }
-                        break;
-                } else if (el_ret == ELEVATOR_FRONT_MERGE) {
-                        if (bio_attempt_front_merge(q, rq, bio)) {
-                                ctx->rq_merged++;
-                                return true;
-                        }
+                case ELEVATOR_FRONT_MERGE:
+                        if (blk_mq_sched_allow_merge(q, rq, bio))
+                                merged = bio_attempt_front_merge(q, rq, bio);
                         break;
+                default:
+                        continue;
                 }
+
+                if (merged)
+                        ctx->rq_merged++;
+                return merged;
         }
 
         return false;