Re: [virtio-dev] [PATCH] content: Introduce VIRTIO_NET_F_STANDBY feature

[Cornelia Huck <cohuck@redhat.com>]

On Sun, 22 Jul 2018 18:37:42 +0300
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Fri, Jul 20, 2018 at 09:44:50AM +0200, Cornelia Huck wrote:
> > On Thu, 19 Jul 2018 14:29:40 -0700
> > Sridhar Samudrala <sridhar.samudrala@intel.com> wrote:
> >   
> > > VIRTIO_NET_F_STANDBY feature enables hypervisor to indicate virtio_net
> > > driver to act as a standby for another device with the same MAC address.
> > > 
> > > Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com
> > > ---
> > >  content.tex | 10 ++++++++++
> > >  1 file changed, 10 insertions(+)

> > > @@ -2636,6 +2639,13 @@ If the driver negotiates VIRTIO_NET_F_MTU, it MUST NOT transmit packets of
> > >  size exceeding the value of \field{mtu} (plus low level ethernet header length)
> > >  with \field{gso_type} NONE or ECN.
> > >  
> > > +A driver SHOULD negotiate VIRTIO_NET_F_STANDBY feature if the device offers it.  
> > 
> > I'm not sure that this is the right section of the spec. Maybe we need
> > a new normative driver section for "cross-device features" (better
> > names wanted :), and the same for devices?  
> 
> You mean if we ever extend this to non-network devices?
> This is a network specific feature bit so what makes
> it a cross-device feature?

No, the network device location is alright. But it is in a section that
deals with how the config space etc. is handled, and I'm not sure
whether it fits well with the other statements in there. Not a major
gripe, though.

> 
> > > +
> > > +If the driver negotiates VIRTIO_NET_F_STANDBY, it should act as a standby  
> > for  
> > > +another device with the same MAC address when available. The hypervisor can
> > > +hot-plug a primary device with same MAC address if the feature is successfully
> > > +negotiated with the driver.  
> > 
> > I don't think you should add implementation details like hotplugging
> > into the spec.
> > 
> > What about:
> > 
> > "If the driver negotiates VIRTIO_NET_F_STANDBY, the device MAY act as a
> > standby device for another device with the same MAC address, the
> > 'failover device'.  
> 
> I find the name "failover device" confusing. Linux came up with
> names primary and standby.

"...the device MAY act as a standby device for a primary device with
the same MAC address."

?