Re: [Qemu-devel] [PATCH] qemu: Introduce VIRTIO_NET_F_STANDBY feature bit to virtio_net

[Jason Wang]

On 2018年06月13日 08:20, Samudrala, Sridhar wrote:
> On 6/12/2018 4:54 AM, Michael S. Tsirkin wrote:
> > On Wed, Jun 06, 2018 at 10:29:03AM +0800, Jason Wang wrote:
> > > On 2018年06月05日 20:33, Michael S. Tsirkin wrote:
> > > > I don't think this is sufficient.
> > > >
> > > > If both primary and standby devices are present, a legacy guest 
> > > > without
> > > > support for the feature might see two devices with same mac and get
> > > > confused.
> > > >
> > > > I think that we should only make primary visible after guest acked the
> > > > backup feature bit.
> > > I think we want exactly the reverse? E.g fail the negotiation when 
> > > guest
> > > does not ack backup feature.
> > >
> > > Otherwise legacy guest won't even have the chance to see primary 
> > > device in
> > > the guest.
> > That's by design.
> >
> > > > And on reset or when backup is cleared in some other way, unplug the
> > > > primary.
> > > What if guest does not support hotplug?
> > It shouldn't ack the backup feature then and it's a good point.
> > We should both document this and check kernel config has
> > hotplug support. Sridhar could you take a look pls?
>
> Right now we select NET_FAILOVER when virtio-net is enabled, Should we 
> select
> PCI_HOTPLUG when NET_FAILOVER is enabled? 

Maybe I was wrong but it looks to me PCI_HOTPLUG is no sufficient since 
it depends on other to work e.g HOTPLUG_PCI_ACPI.

Thanks