pathbuf_maybe_copyin
error = pathbuf_maybe_copyin(path, where, &pb);
error = pathbuf_maybe_copyin(pathname, seg, &pb);
error = pathbuf_maybe_copyin(arg, seg, &pb);
error = pathbuf_maybe_copyin(from, seg, &fpb);
error = pathbuf_maybe_copyin(to, seg, &tpb);
error = pathbuf_maybe_copyin(path, seg, &pb);
int pathbuf_maybe_copyin(const char *userpath, enum uio_seg seg, struct pathbuf **ret);