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

[Marcel Apfelbaum]

On 07/29/2015 08:20 PM, Michael S. Tsirkin wrote:
> 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 <address@hidden>
> > ---
> >   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?
Not really, first call to vhost_ack_features acks the net->dev.backend_features,
the second one acks the guest features.

The first call replaces the previous assignment that assumes that all backend 
features are
supported by QEMU.

Thanks,
Marcel


> >   }
> >
> > 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