block: Consolidate command flag and queue limit checks for merges

 - blk_check_merge_flags() verifies that cmd_flags / bi_rw are
   compatible. This function is called for both req-req and req-bio
   merging.

 - blk_rq_get_max_sectors() and blk_queue_get_max_sectors() can be used
   to query the maximum sector count for a given request or queue. The
   calls will return the right value from the queue limits given the
   type of command (RW, discard, write same, etc.)

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 12 insertions, 18 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 86710ca408b8..642b862608a1 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -275,14 +275,8 @@ no_merge:
 int ll_back_merge_fn(struct request_queue *q, struct request *req,
                      struct bio *bio)
 {
-        unsigned short max_sectors;
-
-        if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC))
-                max_sectors = queue_max_hw_sectors(q);
-        else
-                max_sectors = queue_max_sectors(q);
-
-        if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
+        if (blk_rq_sectors(req) + bio_sectors(bio) >
+            blk_rq_get_max_sectors(req)) {
                 req->cmd_flags |= REQ_NOMERGE;
                 if (req == q->last_merge)
                         q->last_merge = NULL;
@@ -299,15 +293,8 @@ int ll_back_merge_fn(struct request_queue *q, struct request *req,
 int ll_front_merge_fn(struct request_queue *q, struct request *req,
                       struct bio *bio)
 {
-        unsigned short max_sectors;
-
-        if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC))
-                max_sectors = queue_max_hw_sectors(q);
-        else
-                max_sectors = queue_max_sectors(q);
-
-
-        if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
+        if (blk_rq_sectors(req) + bio_sectors(bio) >
+            blk_rq_get_max_sectors(req)) {
                 req->cmd_flags |= REQ_NOMERGE;
                 if (req == q->last_merge)
                         q->last_merge = NULL;
@@ -338,7 +325,8 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
         /*
          * Will it become too large?
          */
-        if ((blk_rq_sectors(req) + blk_rq_sectors(next)) > queue_max_sectors(q))
+        if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
+            blk_rq_get_max_sectors(req))
                 return 0;
 
         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
@@ -417,6 +405,9 @@ static int attempt_merge(struct request_queue *q, struct request *req,
         if (!rq_mergeable(req) || !rq_mergeable(next))
                 return 0;
 
+        if (!blk_check_merge_flags(req->cmd_flags, next->cmd_flags))
+                return 0;
+
         /*
          * not contiguous
          */
@@ -512,6 +503,9 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
         if (!rq_mergeable(rq) || !bio_mergeable(bio))
                 return false;
 
+        if (!blk_check_merge_flags(rq->cmd_flags, bio->bi_rw))
+                return false;
+
         /* different data direction or already started, don't merge */
         if (bio_data_dir(bio) != rq_data_dir(rq))
                 return false;