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>

diff --git a/block/blk-core.c b/block/blk-core.c
index 78b7b0cb7216ec1c3a86545ad86ece5cd85a24da..77edf051233868c50f26c4130549888dd88b5ca0 100644 (file)
--- 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;
 

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ec0357d8c4a58679c96bc3e937b5de97e9a4063c..f3f7879391a7c380ac7daa40757245dafea021c5 100644 (file)
--- 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));
 }
 
 /*