block/mq-deadline: Introduce dd_start_request()

Prepare for adding a second caller of this function. No functionality
has been changed.

Cc: Damien Le Moal <[e-mail]>
Cc: Yu Kuai <[e-mail]>
Cc: chengkaitao <[e-mail]>
Signed-off-by: Bart Van Assche <[e-mail]>
Reviewed-by: Damien Le Moal <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

block/mq-deadline.c

···
 	return time_after(start_time, latest_start);
 }
 
+static struct request *dd_start_request(struct deadline_data *dd,
+					enum dd_data_dir data_dir,
+					struct request *rq)
+{
+	u8 ioprio_class = dd_rq_ioclass(rq);
+	enum dd_prio prio = ioprio_class_to_prio[ioprio_class];
+
+	dd->per_prio[prio].latest_pos[data_dir] = blk_rq_pos(rq);
+	dd->per_prio[prio].stats.dispatched++;
+	rq->rq_flags |= RQF_STARTED;
+	return rq;
+}
+
 /*
  * deadline_dispatch_requests selects the best request according to
  * read/write expire, fifo_batch, etc and with a start time <= @latest_start.
···
 {
 	struct request *rq, *next_rq;
 	enum dd_data_dir data_dir;
-	enum dd_prio prio;
-	u8 ioprio_class;
 
 	lockdep_assert_held(&dd->lock);
 
···
 	dd->batching++;
 	deadline_move_request(dd, per_prio, rq);
 done:
-	ioprio_class = dd_rq_ioclass(rq);
-	prio = ioprio_class_to_prio[ioprio_class];
-	dd->per_prio[prio].latest_pos[data_dir] = blk_rq_pos(rq);
-	dd->per_prio[prio].stats.dispatched++;
-	rq->rq_flags |= RQF_STARTED;
-	return rq;
+	return dd_start_request(dd, data_dir, rq);
 }
 
 /*