Re: [Qemu-devel] [PATCH] vhost-user: sync backend features

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jul 29, 2015 at 08:11:58PM +0300, Marcel Apfelbaum wrote:
> Complete vhost-user negotiation by syncing the features
> supported by the backend.
> 
> Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
> ---
>  To be used on top of:
>  [PATCH 0/4] vhost-user: protocol updates
>  https://lists.gnu.org/archive/html/qemu-devel/2015-07/msg03842.html 
> 
>  Currently the vhost-user supported features are not evaluated.
>  The way I see it, and please correct me, the best way to do
>  this is to:
>   1. get the backend features on vhost init
>   2. Instead of simply copying them during features ack,
>      check that that all backend features are supported by current QEMU
>   3. All other code should remain the same.
> 
>   Thanks,
>   Marcel
> 
>  hw/net/vhost_net.c     | 3 ++-
>  hw/virtio/vhost-user.c | 4 ++--
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> index c864237..1ea5866 100644
> --- a/hw/net/vhost_net.c
> +++ b/hw/net/vhost_net.c
> @@ -118,7 +118,8 @@ uint64_t vhost_net_get_features(struct vhost_net *net, uint64_t features)
>  
>  void vhost_net_ack_features(struct vhost_net *net, uint64_t features)
>  {
> -    net->dev.acked_features = net->dev.backend_features;
> +    vhost_ack_features(&net->dev, vhost_net_get_feature_bits(net),
> +                       net->dev.backend_features);
>      vhost_ack_features(&net->dev, vhost_net_get_feature_bits(net), features);

So you ack it twice?

>  }
>  
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index c4428a1..077457b 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -358,9 +358,9 @@ static int vhost_user_init(struct vhost_dev *dev, void *opaque)
>          return err;
>      }
>  
> -    if (__virtio_has_feature(msg.u64, VHOST_USER_F_PROTOCOL_FEATURES)) {
> -        dev->backend_features |= 1ULL << VHOST_USER_F_PROTOCOL_FEATURES;
> +    dev->backend_features = msg.u64;
>  
> +    if (__virtio_has_feature(msg.u64, VHOST_USER_F_PROTOCOL_FEATURES)) {
>          msg.request = VHOST_USER_GET_PROTOCOL_FEATURES;
>          msg.flags = VHOST_USER_VERSION;
>          msg.size = 0;
> -- 
> 2.1.0