On Tue, Mar 15, 2016 at 05:04:13PM -0400, Aaron Conole wrote:
> This patch checks the feature bit for the VIRTIO_NET_F_MTU feature. If it
> exists, read the advised MTU and use it.
>
> No proper error handling is provided for the case where a user changes the
> negotiated MTU. A future commit will add proper error handling. Instead, a
> warning is emitted if the guest changes the device MTU after previously
> being given advice.
I don't see this as an error. Device might at best give a hint,
user/network admin always knows best.
>
> Signed-off-by: Aaron Conole <acon...@bytheb.org>
> ---
> v2:
> * Whitespace cleanup in the last hunk
> * Code style change around the pr_warn
> * Additional test for mtu change before printing warning
>
> drivers/net/virtio_net.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 767ab11..429fe01 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -146,6 +146,7 @@ struct virtnet_info {
> virtio_net_ctrl_ack ctrl_status;
> u8 ctrl_promisc;
> u8 ctrl_allmulti;
> + bool negotiated_mtu;
> };
>
> struct padded_vnet_hdr {
> @@ -1390,8 +1391,11 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
>
> static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
> {
> + struct virtnet_info *vi = netdev_priv(dev);
> if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
> return -EINVAL;
> + if ((vi->negotiated_mtu) && (dev->mtu != new_mtu))
> + pr_warn("changing mtu while the advised mtu bit exists.");
I don't really see why are we warning here. Just drop this chunk,
as well as the flag in struct virtnet_info.
> dev->mtu = new_mtu;
> return 0;
> }
> @@ -1836,6 +1840,13 @@ static int virtnet_probe(struct virtio_device *vdev)
> if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
> vi->has_cvq = true;
>
> + if (virtio_has_feature(vdev, VIRTIO_NET_F_MTU)) {
> + vi->negotiated_mtu = true;
> + dev->mtu = virtio_cread16(vdev,
> + offsetof(struct virtio_net_config,
> + mtu));
> + }
> +
> if (vi->any_header_sg)
> dev->needed_headroom = vi->hdr_len;
>
> @@ -2019,6 +2030,7 @@ static unsigned int features[] = {
> VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ,
> VIRTIO_NET_F_CTRL_MAC_ADDR,
> VIRTIO_F_ANY_LAYOUT,
> + VIRTIO_NET_F_MTU,
> };
>
> static struct virtio_driver virtio_net_driver = {
> --
> 2.5.0
