block: reorganize queue draining

Reorganize queue draining related code in preparation of queue exit
changes.

* Factor out actual draining from elv_quiesce_start() to
  blk_drain_queue().

* Make elv_quiesce_start/end() responsible for their own locking.

* Replace open-coded ELVSWITCH clearing in elevator_switch() with
  elv_quiesce_end().

This patch doesn't cause any visible functional difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 1 insertions, 0 deletions

diff --git a/block/blk.h b/block/blk.h
index da247ba2aeaf..2b66dc21a493 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -15,6 +15,7 @@ void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
                         struct bio *bio);
 int blk_rq_append_bio(struct request_queue *q, struct request *rq,
                       struct bio *bio);
+void blk_drain_queue(struct request_queue *q);
 void blk_dequeue_request(struct request *rq);
 void __blk_queue_free_tags(struct request_queue *q);
 bool __blk_end_bidi_request(struct request *rq, int error,