Paul Durrant writes ("RE: [PATCH v2 4/4] tools/hotplug: modify set_mtu() to
inform the frontend via xenstore"):
> > -----Original Message-----
> > From: Ian Jackson <ian.jack...@citrix.com>
...
> > Actually.
> >
> > This shouldn't be in the frontend at all, should it ? In general the
> > backend writes to the backend and the frontend to the frontend.
> >
> > So maybe I need to take back my R-b of
> > [PATCH v2 3/4] public/io/netif: specify MTU override node
> >
> > Sorry for the confusion. I seem rather undercaffienated today.
>
> Too late. The xenstore node has been used by Windows frontends for the best
> part of a decade so we can't practically change the
> path. Another way would be to also modify netback to simply echo the value
> from backend into frontend, but that seems rather
> pointless.
Hmm. How does this interact with driver domains ? I think a driver
domain might not have write access to this node.
Is there a value we can store in it that won't break these Windows
frontends, that libxl in the toolstack domain could write, before the
hotplug script runs in the driver domain ?
> Interestingly libxl does define an 'mtu' field for libxl_device_nic, which it
> sets to 1492 in libxl__device_nic_setdefault() but
> never writes it into xenstore. There is even a comment:
>
> /* nic->mtu = */
>
> in libxl__nic_from_xenstore() which implies it should have been there, but
> isn't.
> I still think picking up the MTU from the bridge is the better way though.
I agree that the default should come from the bridge. Ideally there
would be a way to override it in the config.
Thanks,
Ian.
