block: rename and export rq_init()

This rename rq_init() blk_rq_init() and export it. Any path that hands
the request to the block layer needs to call it to initialize the
request.

This is a preparation for large command support, which needs to
initialize the request in a proper way (that is, just doing a memset()
will not work).

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/blk-barrier.c b/block/blk-barrier.c
index 47127ba..66e5528 100644
--- a/block/blk-barrier.c
+++ b/block/blk-barrier.c
@@ -143,7 +143,7 @@
 		end_io = post_flush_end_io;
 	}
 
-	rq_init(q, rq);
+	blk_rq_init(q, rq);
 	rq->cmd_flags = REQ_HARDBARRIER;
 	rq->rq_disk = q->bar_rq.rq_disk;
 	rq->end_io = end_io;
@@ -165,7 +165,7 @@
 	blkdev_dequeue_request(rq);
 	q->orig_bar_rq = rq;
 	rq = &q->bar_rq;
-	rq_init(q, rq);
+	blk_rq_init(q, rq);
 	if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
 		rq->cmd_flags |= REQ_RW;
 	if (q->ordered & QUEUE_ORDERED_FUA)