block: ublk_drv: don't consider flush request in map/unmap io

There isn't data in request of REQ_OP_FLUSH always, so don't consider
it in both ublk_map_io() and ublk_unmap_io().
Reviewed-by: Ziyang Zhang <ZiyangZhang@linux.alibaba.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/ublk_drv.c

@@ -529,15 +529,13 @@ static int ublk_map_io(const struct ublk_queue *ubq, const struct request *req,
 		struct ublk_io *io)
 {
 	const unsigned int rq_bytes = blk_rq_bytes(req);
+
 	/*
 	 * no zero copy, we delay copy WRITE request data into ublksrv
 	 * context and the big benefit is that pinning pages in current
 	 * context is pretty fast, see ublk_pin_user_pages
 	 */
-	if (req_op(req) != REQ_OP_WRITE && req_op(req) != REQ_OP_FLUSH)
-		return rq_bytes;
-
-	if (ublk_rq_has_data(req)) {
+	if (ublk_rq_has_data(req) && req_op(req) == REQ_OP_WRITE) {
 		struct ublk_map_data data = {
 			.ubq	=	ubq,
 			.rq	=	req,
@@ -772,9 +770,7 @@ static inline void __ublk_rq_task_work(struct request *req)
 		return;
 	}
 
-	if (ublk_need_get_data(ubq) &&
-			(req_op(req) == REQ_OP_WRITE ||
-			req_op(req) == REQ_OP_FLUSH)) {
+	if (ublk_need_get_data(ubq) && (req_op(req) == REQ_OP_WRITE)) {
 		/*
 		 * We have not handled UBLK_IO_NEED_GET_DATA command yet,
 		 * so immepdately pass UBLK_IO_RES_NEED_GET_DATA to ublksrv