block: Enhance new plugging support to support general callbacks

md/raid requires an unplug callback, but as it does not uses
requests the current code cannot provide one.

So allow arbitrary callbacks to be attached to the blk_plug.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 78b7b0cb7216..77edf0512338 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2638,6 +2638,7 @@ void blk_start_plug(struct blk_plug *plug)
 
         plug->magic = PLUG_MAGIC;
         INIT_LIST_HEAD(&plug->list);
+        INIT_LIST_HEAD(&plug->cb_list);
         plug->should_sort = 0;
 
         /*
@@ -2678,6 +2679,24 @@ static void queue_unplugged(struct request_queue *q, unsigned int depth,
                 q->unplugged_fn(q);
 }
 
+static void flush_plug_callbacks(struct blk_plug *plug)
+{
+        LIST_HEAD(callbacks);
+
+        if (list_empty(&plug->cb_list))
+                return;
+
+        list_splice_init(&plug->cb_list, &callbacks);
+
+        while (!list_empty(&callbacks)) {
+                struct blk_plug_cb *cb = list_first_entry(&callbacks,
+                                                          struct blk_plug_cb,
+                                                          list);
+                list_del(&cb->list);
+                cb->callback(cb);
+        }
+}
+
 void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 {
         struct request_queue *q;
@@ -2688,6 +2707,7 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 
         BUG_ON(plug->magic != PLUG_MAGIC);
 
+        flush_plug_callbacks(plug);
         if (list_empty(&plug->list))
                 return;