osdblk: stop using q->prepare_flush_fn

use REQ_FLUSH flag instead.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

drivers/block/osdblk.c

@@ -323,7 +323,7 @@ static void osdblk_rq_fn(struct request_queue *q)
 		 * driver-specific, etc.
 		 */
 
-		do_flush = (rq->special == (void *) 0xdeadbeefUL);
+		do_flush = rq->cmd_flags & REQ_FLUSH;
 		do_write = (rq_data_dir(rq) == WRITE);
 
 		if (!do_flush) { /* osd_flush does not use a bio */
@@ -380,14 +380,6 @@ static void osdblk_rq_fn(struct request_queue *q)
 	}
 }
 
-static void osdblk_prepare_flush(struct request_queue *q, struct request *rq)
-{
-	/* add driver-specific marker, to indicate that this request
-	 * is a flush command
-	 */
-	rq->special = (void *) 0xdeadbeefUL;
-}
-
 static void osdblk_free_disk(struct osdblk_device *osdev)
 {
 	struct gendisk *disk = osdev->disk;
@@ -447,7 +439,7 @@ static int osdblk_init_disk(struct osdblk_device *osdev)
 	blk_queue_stack_limits(q, osd_request_queue(osdev->osd));
 
 	blk_queue_prep_rq(q, blk_queue_start_tag);
-	blk_queue_ordered(q, QUEUE_ORDERED_DRAIN_FLUSH, osdblk_prepare_flush);
+	blk_queue_ordered(q, QUEUE_ORDERED_DRAIN_FLUSH, NULL);
 
 	disk->queue = q;