BLOCK_EXT_MAJOR
if (MAJOR(bdev->bd_dev) == BLOCK_EXT_MAJOR)
register_blkdev(BLOCK_EXT_MAJOR, "blkext");
disk->major = BLOCK_EXT_MAJOR;
if (disk->major == BLOCK_EXT_MAJOR)
devt = MKDEV(BLOCK_EXT_MAJOR, err);