[PATCH] ifplugd: Allow ENODEV when upping interface for -M

[Jate Sujjavanich]

I am able to reproduce the issue on my system consistently. I'm using
modprobe to remove the driver for g_ether on my ARM system. Using strace
reduces the frequency of the bug, but it still occurs.

Here's the output from strace:

14:50:53.886676 ioctl(3, SIOCGIFFLAGS, {ifr_name="usb0",
ifr_flags=IFF_BROADCAS
T|IFF_MULTICAST}) = 0
14:50:53.887140 write(2, "ifplugd(usb0): upping interface\n",
32ifplugd(usb0):
upping interface
) = 32
14:50:53.887584 gettimeofday({1471546253, 887734}, NULL) = 0
14:50:53.888011 send(5, "<27>Aug 18 14:50:53 ifplugd(usb0"..., 52,
MSG_NOSIGNAL
) = 52
14:50:53.888431 ioctl(3, SIOCSIFFLAGS, {ifr_name="usb0", ???}) = -1 ENODEV
(No
such device)
14:50:53.895989 write(2, "ifplugd(usb0): setting interface"...,
62ifplugd(usb0)
: setting interface flags failed: No such device
) = 62


On Tue, Aug 16, 2016 at 7:52 PM, Denys Vlasenko <vda.linux at googlemail.com>
wrote:

> On Thu, Aug 11, 2016 at 5:21 PM, Jate Sujjavanich <jatedev at gmail.com>
> wrote:
> > The following changes since commit 150dc7a2b483b8338a3e185c478b4b
> 23ee884e71:
> >
> >   ntpd: respond only to client and symmetric active packets (2016-08-01
> > 20:25:06 +0200)
> >
> > are available in the git repository at:
> >
> >   https://github.com/jatedev/busybox work-ifplugd-device-detect
> >
> > for you to fetch changes up to a5d29d0cc0ff79214465a66fc8cd49757bf72064:
> >
> >   ifplugd: Allow ENODEV when upping interface for -M (2016-08-11 11:09:21
> > -0400)
> >
> > ----------------------------------------------------------------
> > Jate Sujjavanich (1):
> >       ifplugd: Allow ENODEV when upping interface for -M
> >
> >  networking/ifplugd.c |    6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/networking/ifplugd.c b/networking/ifplugd.c
> > index 28c49e2..67251ae 100644
> > --- a/networking/ifplugd.c
> > +++ b/networking/ifplugd.c
> > @@ -359,7 +359,11 @@ static void up_iface(void)
> >                 /* Let user know we mess up with interface */
> >                 bb_error_msg("upping interface");
> >                 if (network_ioctl(SIOCSIFFLAGS, &ifrequest, "setting
> > interface flags") < 0)
> > -                       xfunc_die();
> > +                       if (errno == ENODEV) {
> > +                               G.iface_exists = 0;
> > +                               return;
> > +                       } else
> > +                               xfunc_die();
> >         }
>
> This makes sense. But...
>
>         set_ifreq_to_ifname(&ifrequest);
>         if (network_ioctl(SIOCGIFFLAGS, &ifrequest, "getting interface
> flags") < 0) {
>                 G.iface_exists = 0;
>                 return;
>         }
>
>         if (!(ifrequest.ifr_flags & IFF_UP)) {
>                 ifrequest.ifr_flags |= IFF_UP;
>                 /* Let user know we mess up with interface */
>                 bb_error_msg("upping interface");
>                 if (network_ioctl(SIOCSIFFLAGS, &ifrequest, "setting
> interface flags") < 0) {
>
>
>
> I just wonder, how on Earth SIOCGIFFLAGS just above did _not_ fail?
> The iface deletion race? Very tight, almost impossible to hit...
>
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