block: add callback function for unplug notification

MD would like to know when a queue is unplugged, so it can flush
it's bitmap writes. Add such a callback.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 0c0ea10e61ea..76850fc9cf23 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2672,6 +2672,9 @@ static void queue_unplugged(struct request_queue *q, unsigned int depth)
 {
         trace_block_unplug_io(q, depth);
         __blk_run_queue(q, false);
+
+        if (q->unplugged_fn)
+                q->unplugged_fn(q);
 }
 
 static void flush_plug_list(struct blk_plug *plug)