[libvirt] [PATCH] util: netdevbridge: fall back to ioctl from sysfs

[Daniel P. Berrangé]

On Tue, Nov 20, 2018 at 01:03:09PM +0100, Christian Ehrhardt wrote:
> On Tue, Nov 20, 2018 at 12:58 PM Daniel P. Berrangé <berrange at redhat.com> wrote:
> >
> > On Tue, Nov 20, 2018 at 11:17:07AM +0100, Christian Ehrhardt wrote:
> > > There are certain cases e.g. containers where the sysfs path might
> > > exists, but might fail. Unfortunately the exact restrictions are only
> > > known to libvirt when trying to write to it so we need to try it.
> > >
> > > But in case it fails there is no need to fully abort, in those cases try
> > > to fall back to the older ioctl interface which can still work.
> > >
> > > That makes setting up a bridge in unprivileged LXD containers work.
> > >
> > > Fixes: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1802906
> > >
> > > Signed-off-by: Christian Ehrhardt <christian.ehrhardt at canonical.com>
> > > ---
> > >  src/util/virnetdevbridge.c | 48 +++++++++++++++++++++-----------------
> > >  1 file changed, 26 insertions(+), 22 deletions(-)
> > >
> > > diff --git a/src/util/virnetdevbridge.c b/src/util/virnetdevbridge.c
> > > index 071ebb7b35..cbba3c9652 100644
> > > --- a/src/util/virnetdevbridge.c
> > > +++ b/src/util/virnetdevbridge.c
> > > @@ -113,6 +113,8 @@ static int virNetDevBridgeCmd(const char *brname,
> > >   * or by  ioctl on older kernels. Perhaps we could just use
> > >   * ioctl for every kernel, but its not clear what the long
> > >   * term lifespan of the ioctl interface is...
> > > + * Fall back to ioctl if sysfs interface is not available or
> > > + * failing (e.g. due to container isolation).
> > >   */
> > >  static int virNetDevBridgeSet(const char *brname,
> > >                                const char *paramname,  /* sysfs param name */
> > > @@ -128,29 +130,31 @@ static int virNetDevBridgeSet(const char *brname,
> > >      if (virFileExists(path)) {
> > >          char valuestr[INT_BUFSIZE_BOUND(value)];
> > >          snprintf(valuestr, sizeof(valuestr), "%lu", value);
> > > -        if (virFileWriteStr(path, valuestr, 0) < 0) {
> > > -            virReportSystemError(errno,
> > > -                                 _("Unable to set bridge %s %s"), brname, paramname);
> > > -            return -1;
> > > -        }
> > > +        if (virFileWriteStr(path, valuestr, 0) >= 0)
> > > +            return 0;
> > > +        virReportSystemError(errno,
> > > +                             _("Unable to set bridge %s %s via sysfs"),
> > > +                             brname, paramname);
> >
> > The virReportSystemError line should be dropped, since we're not
> > returning an error - we're moving onto the second code path instead.
> 
> Yeah that sounds fine - would we want a VIR_WARN or VIR_INFO instead
> at this place.
> Any preferences?

I dont think it needs anything more than a VIR_DEBUG, since it is a normal
expected thing in the scenario you described.


Regards,
Daniel
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