[PATCH] Add blk_start_queueing() helper

CFQ implements this on its own now, but it's really block layer
knowledge. Tells a device queue to start dispatching requests to
the driver, taking care to unplug if needed. Also fixes the issue
where as/cfq will invoke a stopped queue, which we really don't
want.

Signed-off-by: Jens Axboe <axboe@suse.de>

1 files changed, 20 insertions, 5 deletions

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index c6dfa889206c..346be9ae31f6 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -2267,6 +2267,25 @@ struct request *blk_get_request(request_queue_t *q, int rw, gfp_t gfp_mask)
 EXPORT_SYMBOL(blk_get_request);
 
 /**
+ * blk_start_queueing - initiate dispatch of requests to device
+ * @q:          request queue to kick into gear
+ *
+ * This is basically a helper to remove the need to know whether a queue
+ * is plugged or not if someone just wants to initiate dispatch of requests
+ * for this queue.
+ *
+ * The queue lock must be held with interrupts disabled.
+ */
+void blk_start_queueing(request_queue_t *q)
+{
+        if (!blk_queue_plugged(q))
+                q->request_fn(q);
+        else
+                __generic_unplug_device(q);
+}
+EXPORT_SYMBOL(blk_start_queueing);
+
+/**
  * blk_requeue_request - put a request back on queue
  * @q:          request queue where request should be inserted
  * @rq:         request to be inserted
@@ -2333,11 +2352,7 @@ void blk_insert_request(request_queue_t *q, struct request *rq,
 
         drive_stat_acct(rq, rq->nr_sectors, 1);
         __elv_add_request(q, rq, where, 0);
-
-        if (blk_queue_plugged(q))
-                __generic_unplug_device(q);
-        else
-                q->request_fn(q);
+        blk_start_queueing(q);
         spin_unlock_irqrestore(q->queue_lock, flags);
 }