/* this unplugs every device on the box, and it is only used when page is null  */
static void __unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
/* this unplugs every device on the box, and it is only used when page is null  */
static void __unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
{
	struct btrfs_device *device;
	struct btrfs_fs_info *info;
	info = (struct btrfs_fs_info *)bdi->unplug_io_data;
	list_for_each_entry(device, &info->fs_devices->devices, dev_list) {
		if (!device->bdev)
			continue;
		bdi = blk_get_backing_dev_info(device->bdev);
		if (bdi->unplug_io_fn)
			bdi->unplug_io_fn(bdi, page);
	}
}