On Thu, Nov 03, 2022 at 10:27:53PM +0000, Klemens Nanni wrote:
> RFC 2132 "DHCP Options and BOOTP Vendor Extensions"
> 3.8. Domain Name Server Option says:
>
> The domain name server option specifies a list of Domain Name System
> (STD 13, RFC 1035 [8]) name servers available to the client. Servers
> SHOULD be listed in order of preference.
>
> I'm on a wifi with three name servers in its DHCP OFFER, which tcpdump',
> `route monitor' and and `dhcpleasctl -l athn0' show in the same order.
>
> But in my case, resolvd writes them in reverse order, making our
> resolver query the least preferred one first as per resolv.conf(5):
>
> Up to ASR_MAXNS (currently 5) name servers may be listed, one
> per line. If there are multiple servers, the resolver
> library queries them in the order listed.
>
> I have yet into a specific problem due to this, but this behaviour did
> surprise me.
>
> Looking at resolvd(8), this is because it sorts the list of name servers
> by prio (makes sense) as well as IP (why?).
>
> If I sort them only by prio and switch to mergesort(3) to have a stable
> function, the resulting order in resolv.conf is exactly what I see in
> the DHCP OFFER, as expected.
New diff zapping duplicate IPs in a only prio-sorted list,
`route nameserver lo0 2.2.2.2 1.1.1.1 1.1.1.1' now yields
nameserver 127.0.0.1 # resolvd: unwind
#nameserver 2.2.2.2 # resolvd: lo0
#nameserver 1.1.1.1 # resolvd: lo0
#nameserver 8.8.4.4 # resolvd: athn0
#nameserver 8.8.8.8 # resolvd: athn0
lookup file bind
instead of
nameserver 127.0.0.1 # resolvd: unwind
#nameserver 1.1.1.1 # resolvd: lo0
#nameserver 2.2.2.2 # resolvd: lo0
#nameserver 8.8.4.4 # resolvd: athn0
#nameserver 8.8.8.8 # resolvd: athn0
lookup file bind
Did I miss anything
Index: resolvd.c
===================================================================
RCS file: /cvs/src/sbin/resolvd/resolvd.c,v
retrieving revision 1.28
diff -u -p -r1.28 resolvd.c
--- resolvd.c 2 Sep 2022 09:39:55 -0000 1.28
+++ resolvd.c 5 Nov 2022 11:10:08 -0000
@@ -503,17 +503,22 @@ handle_route_message(struct rt_msghdr *r
return;
}
- /* Sort proposals, based upon priority and IP */
- qsort(learning, ASR_MAXNS, sizeof(learning[0]), cmp);
+ /* Sort proposals, based upon priority */
+ if (mergesort(learning, ASR_MAXNS, sizeof(learning[0]), cmp) == -1)
+ lerr(1, "mergesort");
- /* Eliminate duplicates */
+ /* Eliminate duplicate IPs per interface */
for (i = 0; i < ASR_MAXNS - 1; i++) {
+ int j;
+
if (learning[i].prio == 0)
continue;
- if (learning[i].if_index == learning[i+1].if_index &&
- strcmp(learning[i].ip, learning[i+1].ip) == 0) {
- zeroslot(&learning[i + 1]);
- i--; /* backup and re-check */
+
+ for (j = i + 1; j < ASR_MAXNS; j++) {
+ if (learning[i].if_index == learning[j].if_index &&
+ strcmp(learning[i].ip, learning[j].ip) == 0) {
+ zeroslot(&learning[j]);
+ }
}
}
@@ -694,10 +699,7 @@ cmp(const void *a, const void *b)
{
const struct rdns_proposal *rpa = a, *rpb = b;
- if (rpa->prio == rpb->prio)
- return strcmp(rpa->ip, rpb->ip);
- else
- return rpa->prio < rpb->prio ? -1 : 1;
+ return (rpa->prio < rpb->prio) ? -1 : (rpa->prio > rpb->prio);
}
#ifndef SMALL
