md/raid5: add simple plugging infrastructure.

md/raid5 uses the plugging infrastructure provided by the block layer
and 'struct request_queue'.  However when we plug raid5 under dm there
is no request queue so we cannot use that.

So create a similar infrastructure that is much lighter weight and use
it for raid5.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 45 insertions, 0 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index f8775699e15..eec75f13070 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -386,6 +386,51 @@ void md_barrier_request(mddev_t *mddev, struct bio *bio)
 }
 EXPORT_SYMBOL(md_barrier_request);
 
+/* Support for plugging.
+ * This mirrors the plugging support in request_queue, but does not
+ * require having a whole queue
+ */
+static void plugger_work(struct work_struct *work)
+{
+	struct plug_handle *plug =
+		container_of(work, struct plug_handle, unplug_work);
+	plug->unplug_fn(plug);
+}
+static void plugger_timeout(unsigned long data)
+{
+	struct plug_handle *plug = (void *)data;
+	kblockd_schedule_work(NULL, &plug->unplug_work);
+}
+void plugger_init(struct plug_handle *plug,
+		  void (*unplug_fn)(struct plug_handle *))
+{
+	plug->unplug_flag = 0;
+	plug->unplug_fn = unplug_fn;
+	init_timer(&plug->unplug_timer);
+	plug->unplug_timer.function = plugger_timeout;
+	plug->unplug_timer.data = (unsigned long)plug;
+	INIT_WORK(&plug->unplug_work, plugger_work);
+}
+EXPORT_SYMBOL_GPL(plugger_init);
+
+void plugger_set_plug(struct plug_handle *plug)
+{
+	if (!test_and_set_bit(PLUGGED_FLAG, &plug->unplug_flag))
+		mod_timer(&plug->unplug_timer, jiffies + msecs_to_jiffies(3)+1);
+}
+EXPORT_SYMBOL_GPL(plugger_set_plug);
+
+int plugger_remove_plug(struct plug_handle *plug)
+{
+	if (test_and_clear_bit(PLUGGED_FLAG, &plug->unplug_flag)) {
+		del_timer(&plug->unplug_timer);
+		return 1;
+	} else
+		return 0;
+}
+EXPORT_SYMBOL_GPL(plugger_remove_plug);
+
+
 static inline mddev_t *mddev_get(mddev_t *mddev)
 {
 	atomic_inc(&mddev->active);