Re: [PATCH] vhost-user: save features of multiqueues if chardev is closed

[Michael S. Tsirkin]

On Wed, Sep 23, 2020 at 11:44:41AM +0200, Adrian Moreno wrote:
> Thanks Haibin,
> 
> 
> On 9/22/20 5:27 AM, haibinzhang(张海斌) wrote:
> > Fore-commit(c6beefd674) only saves features of queue0,
> > this makes wrong features of other queues in multiqueues
> > situation.
> > For examples:
> >   qemu-system-aarch64 ... \
> >   -chardev socket,id=charnet0,path=/var/run/vhost_sock \
> >   -netdev vhost-user,chardev=charnet0,queues=2,id=hostnet0 \
> >   ...
> > There are two queues in nic assocated with one chardev.
> > When chardev is reconnected, it is necessary to save and
> > restore features of all queues.
> > 
> > Signed-of-by: Haibin Zhang <haibinzhang@tencent.com>
> > 
> 
> 
> Indeed, this fixes the issue of vhost-user reconnection on multiqueue that 
> I've
> also reproduced, thanks for posting it.
> 
> However, I'd like to ask some questions to the experts:
> - Why do we need a feature negotiation per queue-pair on vhost-user?
> - Maybe I'm missing something but, isn't the problem that vhost-user device is
> reusing vhost_net layer (which forces nqueues = 2)?
> - Won't we have the same issue with vdpa?

queued this for now. Jason, what are your thoughts on the questions?

> ---
> >  net/vhost-user.c | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> > 
> > diff --git a/net/vhost-user.c b/net/vhost-user.c
> > index 17532daaf3..ffbd94d944 100644
> > --- a/net/vhost-user.c
> > +++ b/net/vhost-user.c
> > @@ -226,7 +226,7 @@ static void chr_closed_bh(void *opaque)
> >      NetClientState *ncs[MAX_QUEUE_NUM];
> >      NetVhostUserState *s;
> >      Error *err = NULL;
> > -    int queues;
> > +    int queues, i;
> >  
> >      queues = qemu_find_net_clients_except(name, ncs,
> >                                            NET_CLIENT_DRIVER_NIC,
> > @@ -235,8 +235,12 @@ static void chr_closed_bh(void *opaque)
> >  
> >      s = DO_UPCAST(NetVhostUserState, nc, ncs[0]);
> >  
> > -    if (s->vhost_net) {
> > -        s->acked_features = vhost_net_get_acked_features(s->vhost_net);
> > +    for (i = queues -1; i >= 0; i--) {
> > +        s = DO_UPCAST(NetVhostUserState, nc, ncs[i]);
> > +
> > +        if (s->vhost_net) {
> > +            s->acked_features = vhost_net_get_acked_features(s->vhost_net);
> > +        }
> >      }
> >  
> >      qmp_set_link(name, false, &err);
> > 
> 
> Thanks
> -- 
> Adrián Moreno