(Why did I manage to succesfully build n times, including a full distribution build, without tripping this before ?!?)
E.g.: golem> dtfs -r 'chr 15 25' dtfs /puffs golem> mount_puffs -o getargs dtfs /puffs version=26, flags=0x10, root cookie=0xbb90c0c0, root type=VCHR, root size=0, root rdev=0xf19