block: Clean up special command handling logic

Remove special-casing of non-rw fs style requests (discard). The nomerge
flags are consolidated in blk_types.h, and rq_mergeable() and
bio_mergeable() have been modified to use them.

bio_is_rw() is used in place of bio_has_data() a few places. This is
done to to distinguish true reads and writes from other fs type requests
that carry a payload (e.g. write same).

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>
diff --git a/block/blk-core.c b/block/blk-core.c
index 2d739ca..5cc2929 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1657,8 +1657,8 @@
 		goto end_io;
 	}
 
-	if (unlikely(!(bio->bi_rw & REQ_DISCARD) &&
-		     nr_sectors > queue_max_hw_sectors(q))) {
+	if (likely(bio_is_rw(bio) &&
+		   nr_sectors > queue_max_hw_sectors(q))) {
 		printk(KERN_ERR "bio too big device %s (%u > %u)\n",
 		       bdevname(bio->bi_bdev, b),
 		       bio_sectors(bio),
@@ -1699,8 +1699,7 @@
 
 	if ((bio->bi_rw & REQ_DISCARD) &&
 	    (!blk_queue_discard(q) ||
-	     ((bio->bi_rw & REQ_SECURE) &&
-	      !blk_queue_secdiscard(q)))) {
+	     ((bio->bi_rw & REQ_SECURE) && !blk_queue_secdiscard(q)))) {
 		err = -EOPNOTSUPP;
 		goto end_io;
 	}
@@ -1818,7 +1817,7 @@
 	 * If it's a regular read/write or a barrier with data attached,
 	 * go through the normal accounting stuff before submission.
 	 */
-	if (bio_has_data(bio) && !(rw & REQ_DISCARD)) {
+	if (bio_has_data(bio)) {
 		if (rw & WRITE) {
 			count_vm_events(PGPGOUT, count);
 		} else {
@@ -1864,7 +1863,7 @@
  */
 int blk_rq_check_limits(struct request_queue *q, struct request *rq)
 {
-	if (rq->cmd_flags & REQ_DISCARD)
+	if (!rq_mergeable(rq))
 		return 0;
 
 	if (blk_rq_sectors(rq) > queue_max_sectors(q) ||
@@ -2338,7 +2337,7 @@
 	req->buffer = bio_data(req->bio);
 
 	/* update sector only for requests with clear definition of sector */
-	if (req->cmd_type == REQ_TYPE_FS || (req->cmd_flags & REQ_DISCARD))
+	if (req->cmd_type == REQ_TYPE_FS)
 		req->__sector += total_bytes >> 9;
 
 	/* mixed attributes always follow the first bio */