[virtio-dev] Re: [PATCH] qemu: Introduce VIRTIO_NET_F_STANDBY feature bit to virtio_net

Michael S. Tsirkin
Fri, 22 Jun 2018 21:47:33 -0000

On Fri, Jun 22, 2018 at 12:43:26PM -0700, Siwei Liu
wrote:
> > The semantics are that the primary is always used if present in
> > preference to standby.
> OK. If this is the only semantics of what "standby" refers to in
> general, that is fine.
>
> I just don't want to limit the failover/standby semantics to the
> device model specifics, the "accelerated datapath" thing or
whatever.
> I really don't know where the requirements of the "accelerated
> datapath" came from,

It's a way to put it that matches what failover actually provides.

> as the originial problem is migrating vfio
> devices which is in match of QEMU's live migration model.

If you put it this way then it's natural to require that we have a
config with a working vfio device, and that we somehow add virtio for
duration of migration.

> Hyper-V has
> it's limitation to do 1-netdev should not impact how KVM/QEMU should
> be doing it.

That's a linux thing and pretty orthogonal to host/guest interface.

> > Jason said virtio net is sometimes preferable.
> > If that's the case don't make it a standby.
> >
> > More advanced use-cases do exist and e.g. Alexander Duyck
> > suggested using a switch-dev.
>
> The switchdev case would need a new feature bit, right?
>
> -Siwei

I think it would need to be a completely new device.

> > failover isn't it though.
> >
> > --
> > MST