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, 6 insertions, 1 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ec0357d8c4a5..f3f7879391a7 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -860,8 +860,13 @@ extern void blk_put_queue(struct request_queue *);
 struct blk_plug {
         unsigned long magic;
         struct list_head list;
+        struct list_head cb_list;
         unsigned int should_sort;
 };
+struct blk_plug_cb {
+        struct list_head list;
+        void (*callback)(struct blk_plug_cb *);
+};
 
 extern void blk_start_plug(struct blk_plug *);
 extern void blk_finish_plug(struct blk_plug *);
@@ -887,7 +892,7 @@ static inline bool blk_needs_flush_plug(struct task_struct *tsk)
 {
         struct blk_plug *plug = tsk->plug;
 
-        return plug && !list_empty(&plug->list);
+        return plug && (!list_empty(&plug->list) || !list_empty(&plug->cb_list));
 }
 
 /*