On Thu, Jun 02, 2016 at 05:10:59PM -0400, Aaron Conole wrote:
> This commit adds the feature bit and associated mtu device entry for the
> virtio network device. When a virtio device comes up, it checks the
> feature bit for the VIRTIO_NET_F_MTU feature. If such feature bit is
> enabled, the driver will read the advised MTU and use it as the initial
> value.
>
> Signed-off-by: Aaron Conole <aconole@xxxxxxxxxx>
> ---
> v1->v2:
> * Fixed omitted hunk from virtio_net.h
> * Squashed to a single commit
> * Fixed commit message.
>
> drivers/net/virtio_net.c | 7 +++++++
> include/uapi/linux/virtio_net.h | 3 +++
> 2 files changed, 10 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index e0638e5..ef5ee01 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1896,6 +1896,12 @@ 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)) {
> + dev->mtu = virtio_cread16(vdev,
> + offsetof(struct virtio_net_config,
> + mtu));
> + }
> +
> if (vi->any_header_sg)
> dev->needed_headroom = vi->hdr_len;
>
One comment though: I think we should validate the mtu.
If it's invalid, clear VIRTIO_NET_F_MTU and ignore.
> @@ -2067,6 +2073,7 @@ 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 = {
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index ec32293..1ab4ea6 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -55,6 +55,7 @@
> #define VIRTIO_NET_F_MQ 22 /* Device supports Receive Flow
> * Steering */
> #define VIRTIO_NET_F_CTRL_MAC_ADDR 23 /* Set MAC address */
> +#define VIRTIO_NET_F_MTU 25 /* Initial MTU advice */
>
> #ifndef VIRTIO_NET_NO_LEGACY
> #define VIRTIO_NET_F_GSO 6 /* Host handles pkts w/ any GSO type */
> @@ -73,6 +74,8 @@ struct virtio_net_config {
> * Legal values are between 1 and 0x8000
> */
> __u16 max_virtqueue_pairs;
> + /* Default maximum transmit unit advice */
> + __u16 mtu;
> } __attribute__((packed));
>
> /*
> --
> 2.5.5
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