Re: [Qemu-devel] [RFC 0/2] virtio-vhost-user: add virtio-vhost-user device

[Wei Wang]

On 02/02/2018 01:08 AM, Michael S. Tsirkin wrote:
> On Tue, Jan 30, 2018 at 08:09:19PM +0800, Wei Wang wrote:
> > Issues:
> > Suppose we have both the vhost and virtio-net set up, and vhost pmd <->
> > virtio-net pmd communication works well. Now, vhost pmd exits (virtio-net
> > pmd is still there). Some time later, we re-run vhost pmd, the vhost pmd
> > doesn't know the virtqueue addresses of the virtio-net pmd, unless the
> > virtio-net pmd reloads to start the 2nd phase of the vhost-user protocol. So
> > the second run of the vhost pmd won't work.
> >
> > Any thoughts?
> >
> > Best,
> > Wei
> So vhost in qemu must resend all configuration on reconnect.
> Does this address the issues?

Yes, but the issues are
1) there is no reconnecting when a pmd exits (the socket connection 
seems still on at the device layer);
2) If we find a way to break the QEMU layer socket connection when pmd 
exits and get it reconnect, virtio-net device still won't send all the 
configure when reconnecting, because socket connecting only triggers 
phase 1 of vhost-user negotiation (i.e. vhost_user_init). Phase 2 is 
triggered after the driver loads (i.e. vhost_net_start). If the 
virtio-net pmd doesn't reload, there are no phase 2 messages (like 
virtqueue addresses which are allocated by the pmd). I think we need to 
think more about this before moving forward.

Best,
Wei