rd_walktree
int rd_walktree(struct radish_head *, int (*)(struct radish *, void *), void *);
return rd_walktree(h, rd2slist_walk, list);
rd_walktree(rd_new,
if (rd_walktree(_this->npppd->rd, npppd_ctl_who_walk_rd, _this) != 0)
rd_walktree(((npppd *)(_this->npppd))->rd,