btrfs: Cleanup the btrfs_workqueue related function type

The new btrfs_workqueue still use open-coded function defition,
this patch will change them into btrfs_func_t type which is much the
same as kernel workqueue.
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

fs/btrfs/async-thread.c

@@ -255,9 +255,9 @@ static void normal_work_helper(struct work_struct *arg)
 }
 
 void btrfs_init_work(struct btrfs_work *work,
-		     void (*func)(struct btrfs_work *),
-		     void (*ordered_func)(struct btrfs_work *),
-		     void (*ordered_free)(struct btrfs_work *))
+		     btrfs_func_t func,
+		     btrfs_func_t ordered_func,
+		     btrfs_func_t ordered_free)
 {
 	work->func = func;
 	work->ordered_func = ordered_func;

fs/btrfs/async-thread.h

@@ -23,11 +23,13 @@
 struct btrfs_workqueue;
 /* Internal use only */
 struct __btrfs_workqueue;
+struct btrfs_work;
+typedef void (*btrfs_func_t)(struct btrfs_work *arg);
 
 struct btrfs_work {
-	void (*func)(struct btrfs_work *arg);
-	void (*ordered_func)(struct btrfs_work *arg);
-	void (*ordered_free)(struct btrfs_work *arg);
+	btrfs_func_t func;
+	btrfs_func_t ordered_func;
+	btrfs_func_t ordered_free;
 
 	/* Don't touch things below */
 	struct work_struct normal_work;
@@ -41,9 +43,9 @@ struct btrfs_workqueue *btrfs_alloc_workqueue(char *name,
 					      int max_active,
 					      int thresh);
 void btrfs_init_work(struct btrfs_work *work,
-		     void (*func)(struct btrfs_work *),
-		     void (*ordered_func)(struct btrfs_work *),
-		     void (*ordered_free)(struct btrfs_work *));
+		     btrfs_func_t func,
+		     btrfs_func_t ordered_func,
+		     btrfs_func_t ordered_free);
 void btrfs_queue_work(struct btrfs_workqueue *wq,
 		      struct btrfs_work *work);
 void btrfs_destroy_workqueue(struct btrfs_workqueue *wq);