topo_mod_walk_init
if ((wp = topo_mod_walk_init(mod, node, hc_walker, (void *)hwp, &err))
extern topo_walk_t *topo_mod_walk_init(topo_mod_t *, tnode_t *,
twp = topo_mod_walk_init(mod, parent, strand_walker, swdp, &err);