iodev_walk
(void) iodev_walk(d1->is_children, NULL, cb, data);
(void) iodev_walk(NULL, d2->is_children, cb, data);
changed |= iodev_walk(d1->is_children,
(void) iodev_walk(d1->is_children, NULL, cb, data);
(void) iodev_walk(NULL, d2->is_children, cb, data);
changed = iodev_walk(old ? old->s_iodevs : NULL,