[libvirt] [PATCH] Wait for udev events to be handled after removing veth

[Daniel P. Berrange]

On Thu, Nov 26, 2015 at 04:01:31PM +0100, Michal Privoznik wrote:
> On 26.11.2015 09:15, Cédric Bosdonnat wrote:
> > As per http://www.redhat.com/archives/libvir-list/2013-July/msg01279.html,
> > wait for udev events to be handled after removing a virtual NIC.
> > Any udev rule associated to NIC destroy could happen to run with a new
> > device with the same name that is being created.
> > ---
> >  src/util/virnetdevveth.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/src/util/virnetdevveth.c b/src/util/virnetdevveth.c
> > index 6905168..c8a38fb 100644
> > --- a/src/util/virnetdevveth.c
> > +++ b/src/util/virnetdevveth.c
> > @@ -225,5 +225,8 @@ int virNetDevVethDelete(const char *veth)
> >      ret = 0;
> >   cleanup:
> >      virCommandFree(cmd);
> > +    /* Make sure the device is properly down: creating a new one
> > +     * with the same name could lead to troubles */
> > +    virFileWaitForDevices();
> >      return ret;
> >  }
> > 
> 
> 
> I'm not fully convinced this is right approach. I mean, we do create
> plenty of devices here and there and tear them down. How come this is
> the only place causing trouble?
> Then, this function you are patching is called in a loop in couple of
> places. Wouldn't it be better to wait for udev after the loop and not in it?

Yeah, calling udev settle in a loop is not going to be very attractive
from a performance POV. I'd really rather the udev rules were fixed to
skip the veth devices

Regards,
Daniel
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