From 048c9374a749a27f16493cea033fa4a8ff492356 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.de>
Date: Mon, 18 Apr 2011 09:52:22 +0200
Subject: [PATCH] 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>
---
 block/blk-core.c       | 20 ++++++++++++++++++++
 include/linux/blkdev.h |  7 ++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

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;
 
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));
 }
 
 /*