Date: Thu, 20 Jun 1996 20:03:32 +0200 (MET DST) From: grog@lemis.de (Greg Lehey) To: hackers@freebsd.org (FreeBSD Hackers) Subject: IP question: who should return ENOBUFS? Message-ID: <199606201803.UAA19421@allegro.lemis.de>
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I've just spent a fair amount of time trying to figure out why our
ISDN software jams up if it can't establish a connection. The
symptoms are that if you can't establish a connection before a certain
number of packets have been sent, the whole interface just returns:
=== root@freebie (/dev/ttyp0) /sys/netinet 11 -> ping 192.109.197.38
PING 192.109.197.38 (192.109.197.38): 56 data bytes
ping: sendto: No buffer space available
ping: wrote 192.109.197.38 64 chars, ret=-1
ping: sendto: No buffer space available
I found this strange, since in the interface code (b_isdnipi.c, line
474) we have the code:
if (IF_QFULL(&ifp->if_snd))
{
if (ifp->if_flags & IFF_RUNNING)
isdn_output(sc->sc_appl);
IF_DROP(&ifp->if_snd);
m_freem(m);
splx(x);
ifp->if_oerrors++;
return (ENOBUFS);
}
This will drop the first packet *and* not enqueue the last if the
queue is full. So I set a breakpoint on the IF_DROP, and hey! nothing
happened. After a bit more investigation, I found this code in
ip_output.c:
/*
* Verify that we have any chance at all of being able to queue
* the packet or packet fragments
*/
if ((ifp->if_snd.ifq_len + ip->ip_len / ifp->if_mtu + 1) >=
ifp->if_snd.ifq_maxlen) {
error = ENOBUFS;
goto bad;
}
I think this is bogus. It's not present in the BSD/OS version, so I
assume it was added in FreeBSD. The problem is, it gives you no
possibility of recovery: the queue is full and stays that way. Can
anybody give me an idea of why it's there, when the interface is
perfectly capable of looking after itself?
Greg
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