defer closeDir(dir)
var args C.struct_btrfs_ioctl_qgroup_limit_args
args.lim.max_referenced = C.__u64(size)
args.lim.max_rfer = C.__u64(size)
args.lim.flags = C.BTRFS_QGROUP_LIMIT_MAX_RFER
_, _, errno := unix.Syscall(unix.SYS_IOCTL, getDirFd(dir), C.BTRFS_IOC_QGROUP_LIMIT,
uintptr(unsafe.Pointer(&args)))