block: implement blk_queue_bypass_start/end()

Rename and extend elv_queisce_start/end() to
blk_queue_bypass_start/end() which are exported and supports nesting
via @q->bypass_depth.  Also add blk_queue_bypass() to test bypass
state.

This will be further extended and used for blkio_group management.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 3 insertions, 22 deletions

diff --git a/block/elevator.c b/block/elevator.c
index f81c061dad1..0bdea0ed03a 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -553,25 +553,6 @@ void elv_drain_elevator(struct request_queue *q)
         }
 }
 
-void elv_quiesce_start(struct request_queue *q)
-{
-        if (!q->elevator)
-                return;
-
-        spin_lock_irq(q->queue_lock);
-        queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
-        spin_unlock_irq(q->queue_lock);
-
-        blk_drain_queue(q, false);
-}
-
-void elv_quiesce_end(struct request_queue *q)
-{
-        spin_lock_irq(q->queue_lock);
-        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
-        spin_unlock_irq(q->queue_lock);
-}
-
 void __elv_add_request(struct request_queue *q, struct request *rq, int where)
 {
         trace_block_rq_insert(q, rq);
@@ -903,7 +884,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
          * using INSERT_BACK.  All requests have SOFTBARRIER set and no
          * merge happens either.
          */
-        elv_quiesce_start(q);
+        blk_queue_bypass_start(q);
 
         /* unregister and clear all auxiliary data of the old elevator */
         if (registered)
@@ -933,7 +914,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 
         /* done, kill the old one and finish */
         elevator_exit(old);
-        elv_quiesce_end(q);
+        blk_queue_bypass_end(q);
 
         blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
 
@@ -945,7 +926,7 @@ fail_init:
         /* switch failed, restore and re-register old elevator */
         q->elevator = old;
         elv_register_queue(q);
-        elv_quiesce_end(q);
+        blk_queue_bypass_end(q);
 
         return err;
 }