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

On Tue, Nov 20, 2018 at 12:58 PM Daniel P. Berrangé <berrange(a)redhat.com&gt; 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(a)canonical.com&gt; > > --- > > 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?