following rn_dupedkey chains in rtsock.c

[David Young <dyoung%pobox.com@localhost>]

I'm trying to hide the radix-trie implementation of the forwarding
table so that it is easier to replace the implementation.  I've found
radix_nodes used strangely in the routing socket code.  I don't think
that this code in route_output() that walks an rn_dupedkey chain is
necessary, but I would like a second opinion:

        case RTM_GET:
        case RTM_CHANGE:
        case RTM_LOCK:  
                /* XXX This will mask info.rti_info[RTAX_DST] with
                 * info.rti_info[RTAX_NETMASK] before
                 * searching.  It did not used to do that.  --dyoung
                 */
                error = rtrequest1(RTM_GET, &info, &rt);
                if (error != 0)
                        senderr(error);
                if (rtm->rtm_type != RTM_GET) {/* XXX: too grotty */
                        struct radix_node *rn;

                        if (memcmp(info.rti_info[RTAX_DST], rt_getkey(rt),
                            info.rti_info[RTAX_DST]->sa_len) != 0)
                                senderr(ESRCH);
                        info.rti_info[RTAX_NETMASK] = intern_netmask(
                            info.rti_info[RTAX_NETMASK]);
                        for (rn = rt->rt_nodes; rn; rn = rn->rn_dupedkey)
                                if (info.rti_info[RTAX_NETMASK] ==
                                    (const struct sockaddr *)rn->rn_mask)
                                        break;
                        if (rn == NULL)
                                senderr(ETOOMANYREFS);
                        rt = (struct rtentry *)rn;
                }

It follows from the implementation of rn_lookup(), which
rtrequest1(RTM_GET) calls via rnh->rnh_lookup(), that

1 if the query mask, info.rti_info[RTAX_NETMASK], is not NULL, then the
  rtrequest1(RTM_GET) call returns either the one and only rtentry that
  has a matching mask, or no rtentry at all.  I.e., rtrequest1() returns
  an exact match.  It also follows that

2 if the query mask is NULL, then rtrequest1() returns either an rtentry
  whose mask is also NULL (an exact match), or an rtentry that cannot
  possibly be followed in the rn_dupedkey chain by an rtentry with NULL
  mask, because NULL masks are most specific (they indicate a host
  route), and rn_dupedkey chains are sorted from most to least specific.

In either case, there is no point following the rn_dupedkey chain.  We
can compare the rtentry's mask with the query mask and be done with it.
This code,

                        for (rn = rt->rt_nodes; rn; rn = rn->rn_dupedkey)
                                if (info.rti_info[RTAX_NETMASK] ==
                                    (const struct sockaddr *)rn->rn_mask)
                                        break;
                        if (rn == NULL)
                                senderr(ETOOMANYREFS);
                        rt = (struct rtentry *)rn;

becomes this code,

                        if (info.rti_info[RTAX_NETMASK] != rt_mask(rt))
                                senderr(ETOOMANYREFS);

Please tell me what I have missed. :-)

Dave

-- 
David Young             OJC Technologies
dyoung%ojctech.com@localhost      Urbana, IL * (217) 344-0444 x24