Re: [Qemu-devel] [RFC v3 3/3] virtio-net: Add MTU feature support

[Jason Wang <jasowang@redhat.com>]

On 2016年11月30日 18:10, Maxime Coquelin wrote:
> This patch allows advising guest with host MTU's by setting
> host_mtu parameter.
>
> If VIRTIO_NET_F_MTU has been successfully negotiated, MTU
> value is passed to the backend.
>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Aaron Conole <aconole@redhat.com
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>   hw/net/virtio-net.c            | 13 +++++++++++++
>   include/hw/virtio/virtio-net.h |  1 +
>   2 files changed, 14 insertions(+)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 5009533..5225e9b 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -55,6 +55,8 @@ static VirtIOFeature feature_sizes[] = {
>        .end = endof(struct virtio_net_config, status)},
>       {.flags = 1 << VIRTIO_NET_F_MQ,
>        .end = endof(struct virtio_net_config, max_virtqueue_pairs)},
> +    {.flags = 1 << VIRTIO_NET_F_MTU,
> +     .end = endof(struct virtio_net_config, mtu)},
>       {}
>   };
>   
> @@ -81,6 +83,7 @@ static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config)
>   
>       virtio_stw_p(vdev, &netcfg.status, n->status);
>       virtio_stw_p(vdev, &netcfg.max_virtqueue_pairs, n->max_queues);
> +    virtio_stw_p(vdev, &netcfg.mtu, n->net_conf.mtu);
>       memcpy(netcfg.mac, n->mac, ETH_ALEN);
>       memcpy(config, &netcfg, n->config_size);
>   }
> @@ -152,6 +155,10 @@ static void virtio_net_vhost_status(VirtIONet *n, uint8_t status)
>               qemu_net_queue_purge(qnc->incoming_queue, qnc->peer);
>           }
>   
> +        if (virtio_has_feature(vdev->guest_features, VIRTIO_NET_F_MTU)) {
> +            vhost_net_set_mtu(get_vhost_net(nc->peer), n->net_conf.mtu);
> +        }

We'd better not ignore errors here and that's why we need management 
tool (who can make sure the mtu is set correctly before launching qemu).

> +
>           n->vhost_started = 1;
>           r = vhost_net_start(vdev, n->nic->ncs, queues);
>           if (r < 0) {
> @@ -1695,6 +1702,7 @@ static void virtio_net_set_config_size(VirtIONet *n, uint64_t host_features)
>   {
>       int i, config_size = 0;
>       virtio_add_feature(&host_features, VIRTIO_NET_F_MAC);
> +
>       for (i = 0; feature_sizes[i].flags != 0; i++) {
>           if (host_features & feature_sizes[i].flags) {
>               config_size = MAX(feature_sizes[i].end, config_size);
> @@ -1724,6 +1732,10 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
>       NetClientState *nc;
>       int i;
>   
> +    if (n->net_conf.mtu) {
> +        n->host_features |= (0x1 << VIRTIO_NET_F_MTU);
> +    }
> +
>       virtio_net_set_config_size(n, n->host_features);
>       virtio_init(vdev, "virtio-net", VIRTIO_ID_NET, n->config_size);
>   
> @@ -1922,6 +1934,7 @@ static Property virtio_net_properties[] = {
>       DEFINE_PROP_STRING("tx", VirtIONet, net_conf.tx),
>       DEFINE_PROP_UINT16("rx_queue_size", VirtIONet, net_conf.rx_queue_size,
>                          VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE),
> +    DEFINE_PROP_UINT16("host_mtu", VirtIONet, net_conf.mtu, 0),
>       DEFINE_PROP_END_OF_LIST(),
>   };
>   
> diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> index 0ced975..8ea56a8 100644
> --- a/include/hw/virtio/virtio-net.h
> +++ b/include/hw/virtio/virtio-net.h
> @@ -36,6 +36,7 @@ typedef struct virtio_net_conf
>       int32_t txburst;
>       char *tx;
>       uint16_t rx_queue_size;
> +    uint16_t mtu;
>   } virtio_net_conf;
>   
>   /* Maximum packet size we can receive from tap device: header + 64k */