netdev - Re: [RFC PATCH net-next v2 2/2] virtio_net: Extend virtio to use VF datapath when available

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Date:   Tue, 23 Jan 2018 18:33:59 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Sridhar Samudrala <sridhar.samudrala@...el.com>, mst@...hat.com,
        stephen@...workplumber.org, davem@...emloft.net,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org, jesse.brandeburg@...el.com,
        alexander.h.duyck@...el.com, kubakici@...pl
Subject: Re: [RFC PATCH net-next v2 2/2] virtio_net: Extend virtio to use VF
 datapath when available



On 2018年01月12日 13:58, Sridhar Samudrala wrote:
>   static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>   {
>   	struct virtnet_info *vi = netdev_priv(dev);
>   	int qnum = skb_get_queue_mapping(skb);
>   	struct send_queue *sq = &vi->sq[qnum];
> +	struct net_device *vf_netdev;
>   	int err;
>   	struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
>   	bool kick = !skb->xmit_more;
>   	bool use_napi = sq->napi.weight;
>   
> +	/* If VF is present and up then redirect packets
> +	 * called with rcu_read_lock_bh
> +	 */
> +	vf_netdev = rcu_dereference_bh(vi->vf_netdev);
> +	if (vf_netdev && netif_running(vf_netdev) &&
> +	    !netpoll_tx_running(dev) &&
> +	    is_unicast_ether_addr(eth_hdr(skb)->h_dest))
> +		return virtnet_vf_xmit(dev, vf_netdev, skb);
> +

A question here.

If I read the code correctly, all features were validated against virtio 
instead VF before transmitting. This assumes VF's feature is a superset 
of virtio, does this really work? Do we need to sanitize the feature 
before joining? (e.g at last NETIF_R_GSO_ROBUST needs to be removed).

Thanks