Re: [PATCH 14/16] virtio-net: support queue_enable for vhost-user

[Jason Wang]

On Tue, Jul 26, 2022 at 2:54 PM Kangjie Xu <kangjie.xu@linux.alibaba.com> wrote:
>
>
> 在 2022/7/26 12:25, Jason Wang 写道:
> >
> > 在 2022/7/18 19:17, Kangjie Xu 写道:
> >> Support queue enable in vhost-user scenario. It will be called when
> >> a vq reset operation is performed and the vq will be restared.
> >>
> >> It should be noted that we can restart the vq when the vhost has
> >> already started. When launching a new vhost-user device, the vhost
> >> is not started and all vqs are not initalized until
> >> VIRTIO_PCI_COMMON_STATUS is written. Thus, we should use vhost_started
> >> to differentiate the two cases: vq reset and device start.
> >>
> >> Signed-off-by: Kangjie Xu <kangjie.xu@linux.alibaba.com>
> >> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> >> ---
> >>   hw/net/virtio-net.c | 20 ++++++++++++++++++++
> >>   1 file changed, 20 insertions(+)
> >>
> >> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> >> index 8396e21a67..2c26e2ef73 100644
> >> --- a/hw/net/virtio-net.c
> >> +++ b/hw/net/virtio-net.c
> >> @@ -544,6 +544,25 @@ static void virtio_net_queue_reset(VirtIODevice
> >> *vdev, uint32_t queue_index)
> >>       assert(!virtio_net_get_subqueue(nc)->async_tx.elem);
> >>   }
> >>   +static void virtio_net_queue_enable(VirtIODevice *vdev, uint32_t
> >> queue_index)
> >> +{
> >> +    VirtIONet *n = VIRTIO_NET(vdev);
> >> +    NetClientState *nc = qemu_get_subqueue(n->nic, vq2q(queue_index));
> >> +    int r;
> >> +
> >> +    if (!nc->peer || !vdev->vhost_started) {
> >> +        return;
> >> +    }
> >> +
> >> +    if (nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_USER) {
> >> +        r = vhost_virtqueue_restart(vdev, nc, queue_index);
> >> +        if (r < 0) {
> >> +            error_report("unable to restart vhost net virtqueue: %d, "
> >> +                            "when resetting the queue", queue_index);
> >> +        }
> >> +    }
> >> +}
> >
> >
> > So we don't check queue_enable in vhost_dev_start(), does this mean
> > the queue_enable is actually meaningless (since the virtqueue is
> > already started there)?
> >
> > And another issue is
> >
> > peet_attach/peer_detach() "abuse" vhost_set_vring_enable(). This
> > probably means we need to invent new type of request instead of
> > re-using VHOST_USER_SET_VRING_ENABLE.
> >
> > Thanks
> >
> >
> 1. Yes, we don't need queue_enable in vhost_dev_start(), queue_enable is
> only useful when restarting the queue. I name it as queue_enable()
> simply because it is called when VIRTIO_PCI_COMMON_Q_ENABLE is written.
> Would it look better if we rename it as "queue_reenable"?

I think the right approach is probably:

1) when VERSION_1 is negotiated, only start the virtqueue when queue_enable is 1
2) when VERSION_1 is not negotiated, start virtqueue when DRIVER_OK
(vhost_dev_start())

?

>
> 2. I think inventing a new type of vhost-protocol message can be a good
> choice. However, I don't know much about the vhost protocol. If we want
> to add a new message in vhost protocol, except the documentation and the
> code in qemu, Do we need to submit patches to other projects, e.g. some
> projects like virtio-spec?

Probably not since vhost-user doesn't belong to the spec currently.
The doc in qemu should be sufficient.

Thanks

>
> Thanks
>
> >> +
> >>   static void virtio_net_reset(VirtIODevice *vdev)
> >>   {
> >>       VirtIONet *n = VIRTIO_NET(vdev);
> >> @@ -3781,6 +3800,7 @@ static void virtio_net_class_init(ObjectClass
> >> *klass, void *data)
> >>       vdc->bad_features = virtio_net_bad_features;
> >>       vdc->reset = virtio_net_reset;
> >>       vdc->queue_reset = virtio_net_queue_reset;
> >> +    vdc->queue_enable = virtio_net_queue_enable;
> >>       vdc->set_status = virtio_net_set_status;
> >>       vdc->guest_notifier_mask = virtio_net_guest_notifier_mask;
> >>       vdc->guest_notifier_pending = virtio_net_guest_notifier_pending;
>