New function blk_req_append_bio

ll_back_merge_fn is currently exported to SCSI where is it used,
together with blk_rq_bio_prep, in exactly the same way these
functions are used in __blk_rq_map_user.

So move the common code into a new function (blk_rq_append_bio), and
don't export ll_back_merge_fn any longer.

Signed-off-by: Neil Brown <neilb@suse.de>

diff .prev/block/ll_rw_blk.c ./block/ll_rw_blk.c
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index a4b13b8..3021a5b 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -675,8 +675,8 @@
 /*
  * Temporary export, until SCSI gets fixed up.
  */
-extern int ll_back_merge_fn(struct request_queue *, struct request *,
-		struct bio *);
+extern int blk_rq_append_bio(struct request_queue *q, struct request *rq,
+			     struct bio *bio);
 
 /*
  * A queue has just exitted congestion.  Note this in the global counter of