MNT_UPDATEMASK
data->mnt_flag = mp->mnt_flag & MNT_UPDATEMASK;
(MNT_UPDATEMASK | MNT_ROOTFS | MNT_RDONLY | MNT_FORCE));
mp->mnt_flag &= ~MNT_UPDATEMASK;
MNT_SNAPSHOT | MNT_ROOTFS | MNT_UPDATEMASK | MNT_RDONLY);