Re: [Qemu-devel] [PATCH V2 3/3] virtio-net: announce self by guest

[Michael S. Tsirkin]

On Tue, Jun 10, 2014 at 11:50:33AM +0530, Amit Shah wrote:
> On (Tue) 20 May 2014 [14:01:44], Jason Wang wrote:
> > It's hard to track all mac addresses and their configurations (e.g
> > vlan or ipv6) in qemu. Without this information, it's impossible to
> > build proper garp packet after migration. The only possible solution
> > to this is let guest (who knows all configurations) to do this.
> > 
> > So, this patch introduces a new readonly config status bit of virtio-net,
> > VIRTIO_NET_S_ANNOUNCE which is used to notify guest to announce
> > presence of its link through config update interrupt.When guest has
> > done the announcement, it should ack the notification through
> > VIRTIO_NET_CTRL_ANNOUNCE_ACK cmd. This feature is negotiated by a new
> > feature bit VIRTIO_NET_F_ANNOUNCE (which has already been supported by
> > Linux guest).
> > 
> > During load, a counter of announcing rounds is set so that after the vm is
> > running it can trigger rounds of config interrupts to notify the guest to 
> > build
> > and send the correct garps.
> 
> Live migration is supposed to be transparent to guests.
> 
> Doing things this way makes the guest involved in live migration.
> It's not desirable.

I'm not sure there's a problem.
As long as guest doesn't use networking, it does not
need to be involved. If guest does want to use networking,
it needs to be involved, but then it's accessing the
device anyway.

> For networking, this may well be not possible.
> Are there any ways of doing this w/o involving the guest that have
> been considered?
> 
> 
>               Amit

Since we don't know guest addresses, this looks like the only way to me.

-- 
MST