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

[Adrian Moreno <amorenoz@redhat.com>]

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?

---
>  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