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, 20 insertions, 0 deletions

diff --git a/drivers/md/md.h b/drivers/md/md.h
index c88b04745e85..5be0d6921b9d 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -29,6 +29,26 @@
 typedef struct mddev_s mddev_t;
 typedef struct mdk_rdev_s mdk_rdev_t;
 
+/* generic plugging support - like that provided with request_queue,
+ * but does not require a request_queue
+ */
+struct plug_handle {
+        void                    (*unplug_fn)(struct plug_handle *);
+        struct timer_list       unplug_timer;
+        struct work_struct      unplug_work;
+        unsigned long           unplug_flag;
+};
+#define PLUGGED_FLAG 1
+void plugger_init(struct plug_handle *plug,
+                  void (*unplug_fn)(struct plug_handle *));
+void plugger_set_plug(struct plug_handle *plug);
+int plugger_remove_plug(struct plug_handle *plug);
+static inline void plugger_flush(struct plug_handle *plug)
+{
+        del_timer_sync(&plug->unplug_timer);
+        cancel_work_sync(&plug->unplug_work);
+}
+
 /*
  * MD's 'extended' device
  */