Subject: Re: [PATCH net-next v2 1/3] virtio_net: propagate linkspeed/duplex settings from the hypervisor

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 3 Jan 2018 16:01:55 +0200

On Fri, Dec 22, 2017 at 04:54:01PM -0500, Jason Baron wrote:
> The ability to set speed and duplex for virtio_net in useful in various
> scenarios as described here:
> 
> 16032be virtio_net: add ethtool support for set and get of settings
> 
> However, it would be nice to be able to set this from the hypervisor,
> such that virtio_net doesn't require custom guest ethtool commands.
> 
> Introduce a new feature flag, VIRTIO_NET_F_SPEED_DUPLEX, which allows
> the hypervisor to export a linkspeed and duplex setting. The user can
> subsequently overwrite it later if desired via: 'ethtool -s'.
> 
> Signed-off-by: Jason Baron <[email-masked]>
> Cc: "Michael S. Tsirkin" <[email-masked]>
> Cc: Jason Wang <[email-masked]>
> ---
>  drivers/net/virtio_net.c        | 17 ++++++++++++++++-
>  include/uapi/linux/virtio_net.h |  5 +++++
>  2 files changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 511f833..4168d82 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2621,6 +2621,20 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	netif_set_real_num_rx_queues(dev, vi->curr_queue_pairs);
>  
>  	virtnet_init_settings(dev);
> +	if (virtio_has_feature(vdev, VIRTIO_NET_F_SPEED_DUPLEX)) {
> +		u32 speed;
> +		u8 duplex;
> +
> +		speed = virtio_cread32(vdev, offsetof(struct virtio_net_config,
> +				       speed));
> +		if (ethtool_validate_speed(speed))
> +			vi->speed = speed;
> +		duplex = virtio_cread8(vdev,
> +				       offsetof(struct virtio_net_config,
> +				       duplex));
> +		if (ethtool_validate_duplex(duplex))
> +			vi->duplex = duplex;
> +	}
>  
>  	err = register_netdev(dev);
>  	if (err) {

It would seem that speed/duplex can change at link up time.
Update it from virtnet_config_changed_work please.

> @@ -2746,7 +2760,8 @@ static struct virtio_device_id id_table[] = {
>  	VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN, \
>  	VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, \
>  	VIRTIO_NET_F_CTRL_MAC_ADDR, \
> -	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS
> +	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \
> +	VIRTIO_NET_F_SPEED_DUPLEX
>  
>  static unsigned int features[] = {
>  	VIRTNET_FEATURES,
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index fc353b5..0f1548e 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -57,6 +57,8 @@
>  					 * Steering */
>  #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
>  
> +#define VIRTIO_NET_F_SPEED_DUPLEX 63	/* Host set linkspeed and duplex */
> +

Host -> device, to match virtio spec terminology.

>  #ifndef VIRTIO_NET_NO_LEGACY
>  #define VIRTIO_NET_F_GSO	6	/* Host handles pkts w/ any GSO type */
>  #endif /* VIRTIO_NET_NO_LEGACY */
> @@ -76,6 +78,9 @@ struct virtio_net_config {
>  	__u16 max_virtqueue_pairs;
>  	/* Default maximum transmit unit advice */
>  	__u16 mtu;
> +	/* Host exported linkspeed and duplex */

I would rather drop this and document each field.

/*
speed, in units of 1Mb. All values 0 to INT_MAX are legal.
Any other value stands for unknown.
*/

> +	__u32 speed;

/*
0x00 - half duplex
0x01 - full duplex
Any other value stands for unknown.
*/

> +	__u8 duplex;

>  } __attribute__((packed));
>  
>  /*
> -- 
> 2.6.1