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 08:03:08 -0800
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     Jason Wang <jasowang@...hat.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 1/23/2018 2:33 AM, Jason Wang wrote:
>
>
> 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).

Actually, virtnet_vf_xmit() calls dev_queue_xmit() after updating 
skb->dev to vf netdev.
So the features get validated against VF features and the right tx queue 
is selected
before the real transmit.

Thanks
Sridhar