Re: [Qemu-devel] [PATCH 3/3] net: virtio-net discards TX data after link down

[Jason Wang <jasowang@redhat.com>]

On 2016年11月07日 16:20, yuri.benditovich@daynix.com wrote:
> From: Yuri Benditovich <yuri.benditovich@daynix.com>
>
> https://bugzilla.redhat.com/show_bug.cgi?id=1295637
> Upon set_link monitor command or upon netdev deletion
> virtio-net sends link down indication to the guest
> and stops vhost if one is used.
> Guest driver can still submit data for TX until it
> recognizes link loss. If these packets not returned by
> the host, the Windows guest will never be able to finish
> disable/removal/shutdown.
> Now each packet sent by guest after NIC indicated link
> down will be completed immediately.
>
> Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>
> ---
>   hw/net/virtio-net.c | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 06bfe4b..6158de0 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -1200,6 +1200,16 @@ static ssize_t virtio_net_receive(NetClientState *nc, const uint8_t *buf, size_t
>       return size;
>   }
>   
> +static void virtio_net_drop_tx_queue_data(VirtIODevice *vdev, VirtQueue *vq)
> +{
> +    VirtQueueElement *elem;
> +    while ((elem = virtqueue_pop(vq, sizeof(VirtQueueElement)))) {
> +        virtqueue_push(vq, elem, 0);
> +        virtio_notify(vdev, vq);
> +        g_free(elem);
> +    }
> +}
> +
>   static int32_t virtio_net_flush_tx(VirtIONetQueue *q);
>   
>   static void virtio_net_tx_complete(NetClientState *nc, ssize_t len)
> @@ -1345,6 +1355,11 @@ static void virtio_net_handle_tx_bh(VirtIODevice *vdev, VirtQueue *vq)
>       VirtIONet *n = VIRTIO_NET(vdev);
>       VirtIONetQueue *q = &n->vqs[vq2q(virtio_get_queue_index(vq))];
>   
> +    if (unlikely((n->status & VIRTIO_NET_S_LINK_UP) == 0)) {
> +        virtio_net_drop_tx_queue_data(vdev, vq);
> +        return;
> +    }
> +
>       if (unlikely(q->tx_waiting)) {
>           return;
>       }

This doesn't work for tx timer, you may want to do the modification on 
virtio_net_flush_tx().

What's more, when link_down is true, qemu_send_packet_async() will 
return size of iov, can we do some check there?

Thanks