netdev - Re: ping -I eth1 ....

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Date:	Tue, 9 Nov 2010 20:33:37 +0100
From:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To:	unlisted-recipients:; (no To-header on input)
Cc:	Thomas Graf <tgraf@...radead.org>,
	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Subject: Re: ping -I eth1 ....

Joakim Tjernlund/Transmode wrote on 2010/11/06 10:42:46:
> Thomas Graf <tgr@...radead.org> wrote on 2010/11/05 21:31:50:
> >
> > On Fri, Nov 05, 2010 at 04:54:18PM +0100, Joakim Tjernlund wrote:
> > > Eric Dumazet <eric.dumazet@...il.com> wrote on 2010/11/05 16:06:54:
> > > >
> > > > > Hopefully most of that is legacy or just plain wrong? Unless
> > > > > someone can say why only test IFF_UP one should consider changing them.
> > > > >
> > > >
> > > > Most of the places are hot path.
> > > >
> > > > You dont want to replace one test by four tests.
> > > >
> > > > _This_ would be wrong :)
> > >
> > > Wrong is wrong, even if it is in the hot path :)
> > > Perhaps it is time define and internal IFF_OPERATIONAL flag
> > > which is the sum of IFF_UP, IFF_RUNNING etc.? Tht
> > > way you still get one test in the hot path and can abstract
> > > what defines an operational link.
> >
> > You definitely don't want to have your send() call fail simply because
> > the carrier was off for a few msec or the routing daemon has put a link
> > down temporarly. Also, the outgoing interface looked up at routing
> > decision is not necessarly the interface used for sending in the end.
> > The packet may get mangled and rerouted by netfilter or tc on the way.
>
> But do you handle the case when the link is non operational for a long time?
>
> >
> > Personally I'm even ok with the current behaviour of sendto() while the
> > socket is bound to an interface but if we choose to return an error
> > if the interface is down we might as well do so based on the operational
> > status.

> Perhaps there is a better way. This all started when pppd hung because
> of ping -I <ppp interface>, then someone pulled the cable for the on the link.
>
> This is a strace where we have two ping -I,
> ping -I p1-2-1-2-2 .. and ping -I p1-2-3-2-4 ..
> Notice how pppd hangs for a long time in PPPIOCDETACH
> As far as I can tell this is due to ping -I has claimed the ppp interfaces
> and doesn't noticed that the link is down. Ideally ping should receive
> a ENODEV as soon as pppd calls PPPIOCDETACH.
>
>    0.000908 write(0, "Connection terminated.\n", 23) = 23
>      0.000481 gettimeofday({1288952770, 566048}, NULL) = 0
>      0.001553 ioctl(7, PPPIOCDETACH
> Message from syslogd@...zil at Fri Nov  5 11:26:20 2010 ...
> Brazil kernel: unregister_netdevice: waiting for p1-2-1-2-2 to become free. Usage count = 3
> Message from syslogd@...zil at Fri Nov  5 11:26:20 2010 ...
> Brazil kernel: unregister_netdevice: waiting for p1-2-3-2-4 to become free. Usage count = 3
> Message from syslogd@...zil at Fri Nov  5 11:26:51 2010 ...
> Brazil last message repeated 3 times
> , 0xbfbc3398) = 0
>     66.559216 connect(9, {sa_family=AF_PPPOX, sa_data="\0\0\0\0\0\0\0\252\273\314\335\356hd"}, 30) = 0
>      0.000693 close(10)                 = 0
>      0.000449 close(7)                  = 0
>      0.009801 close(9)                  = 0

Any comment on this last strace? It is expected that ping -I should
hold pppd hostage?

 Jocke

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