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

[Christian Ehrhardt]

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?

> > +    }
> > +
> > +    unsigned long paramid;
> > +    if (STREQ(paramname, "stp_state")) {
> > +        paramid = BRCTL_SET_BRIDGE_STP_STATE;
> > +    } else if (STREQ(paramname, "forward_delay")) {
> > +        paramid = BRCTL_SET_BRIDGE_FORWARD_DELAY;
> >      } else {
> > -        unsigned long paramid;
> > -        if (STREQ(paramname, "stp_state")) {
> > -            paramid = BRCTL_SET_BRIDGE_STP_STATE;
> > -        } else if (STREQ(paramname, "forward_delay")) {
> > -            paramid = BRCTL_SET_BRIDGE_FORWARD_DELAY;
> > -        } else {
> > -            virReportSystemError(EINVAL,
> > -                                 _("Unable to set bridge %s %s"), brname, paramname);
> > -            return -1;
> > -        }
> > -        unsigned long args[] = { paramid, value, 0, 0 };
> > -        ifr->ifr_data = (char*)&args;
> > -        if (ioctl(fd, SIOCDEVPRIVATE, ifr) < 0) {
> > -            virReportSystemError(errno,
> > -                                 _("Unable to set bridge %s %s"), brname, paramname);
> > -            return -1;
> > -        }
> > +        virReportSystemError(EINVAL,
> > +                             _("Unable to set bridge %s %s via ioctl"),
> > +                             brname, paramname);
> > +        return -1;
> > +    }
> > +    unsigned long args[] = { paramid, value, 0, 0 };
> > +    ifr->ifr_data = (char*)&args;
> > +    if (ioctl(fd, SIOCDEVPRIVATE, ifr) < 0) {
> > +        virReportSystemError(errno,
> > +                             _("Failed to set bridge %s %s via ioctl"),
> > +                             brname, paramname);
> > +        return -1;
> >      }
> >
> >      return 0;
>
> Regards,
> Daniel
> --
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-- 
Christian Ehrhardt
Software Engineer, Ubuntu Server
Canonical Ltd