Re: [RFC PATCH v9 20/23] vdpa: Buffer CVQ support on shadow virtqueue

[Eugenio Perez Martin]

> > > +static void vhost_vdpa_net_handle_ctrl_used(VhostShadowVirtqueue *svq,
> > > +                                            void *vq_elem_opaque,
> > > +                                            uint32_t dev_written)
> > > +{
> > > +    g_autoptr(CVQElement) cvq_elem = vq_elem_opaque;
> > > +    virtio_net_ctrl_ack status = VIRTIO_NET_ERR;
> > > +    const struct iovec out = {
> > > +        .iov_base = cvq_elem->out_data,
> > > +        .iov_len = cvq_elem->out_len,
> > > +    };
> > > +    const DMAMap status_map_needle = {
> > > +        .translated_addr = (hwaddr)(uintptr_t)cvq_elem->in_buf,
> > > +        .size = sizeof(status),
> > > +    };
> > > +    const DMAMap *in_map;
> > > +    const struct iovec in = {
> > > +        .iov_base = &status,
> > > +        .iov_len = sizeof(status),
> > > +    };
> > > +    g_autofree VirtQueueElement *guest_elem = NULL;
> > > +
> > > +    if (unlikely(dev_written < sizeof(status))) {
> > > +        error_report("Insufficient written data (%llu)",
> > > +                     (long long unsigned)dev_written);
> > > +        goto out;
> > > +    }
> > > +
> > > +    in_map = vhost_iova_tree_find_iova(svq->iova_tree, 
> > > &status_map_needle);
> > > +    if (unlikely(!in_map)) {
> > > +        error_report("Cannot locate out mapping");
> > > +        goto out;
> > > +    }
> > > +
> > > +    switch (cvq_elem->ctrl.class) {
> > > +    case VIRTIO_NET_CTRL_MAC_ADDR_SET:
> > > +        break;
> > > +    default:
> > > +        error_report("Unexpected ctrl class %u", cvq_elem->ctrl.class);
> > > +        goto out;
> > > +    };
> > > +
> > > +    memcpy(&status, cvq_elem->in_buf, sizeof(status));
> > > +    if (status != VIRTIO_NET_OK) {
> > > +        goto out;
> > > +    }
> > > +
> > > +    status = VIRTIO_NET_ERR;
> > > +    virtio_net_handle_ctrl_iov(svq->vdev, &in, 1, &out, 1);
> >
> >
> > I wonder if this is the best choice. It looks to me it might be better
> > to extend the virtio_net_handle_ctrl_iov() logic:
> >
> > virtio_net_handle_ctrl_iov() {
> >      if (svq enabled) {
> >           host_elem = iov_copy(guest_elem);
> >           vhost_svq_add(host_elem);
> >           vhost_svq_poll(host_elem);
> >      }
> >      // usersapce ctrl vq logic
> > }
> >
> >
> > This can help to avoid coupling too much logic in cvq (like the
> > avail,used and detach ops).
> >
>
> Let me try that way and I'll come back to you.
>

The problem with that approach is that virtio_net_handle_ctrl_iov is
called from the SVQ used handler. How could we call it otherwise? I
find it pretty hard to do unless we return SVQ to the model where we
used VirtQueue.handle_output, discarded long ago.

I'm about to send a new version, but I still need to call
virtio_net_handle_ctrl_iov from the avail handler. The handlers used
and discard are removed at least.

Thanks!