linux-kernel - Re: [PATCH v2 2/3] virtio_net: Add missing virtio header in skb for XDP

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Date: Wed, 24 Jan 2024 19:04:02 +0800
From: Heng Qi <hengqi@...ux.alibaba.com>
To: Liang Chen <liangchen.linux@...il.com>
Cc: virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
 "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH v2 2/3] virtio_net: Add missing virtio header in skb for
 XDP_PASS



在 2024/1/24 下午4:57, Liang Chen 写道:
> For the XDP_PASS scenario of the XDP path, the skb constructed with
> xdp_buff does not include the virtio header. Adding the virtio header
> information back when creating the skb.
>
> Signed-off-by: Liang Chen <liangchen.linux@...il.com>
> ---
>   drivers/net/virtio_net.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index b56828804e5f..2de46eb4c661 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1270,6 +1270,9 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>   	if (unlikely(!skb))
>   		goto err;
>   
> +	/* Store the original virtio header for subsequent use by the driver. */
> +	memcpy(skb_vnet_common_hdr(skb), &virtnet_xdp.hdr, vi->hdr_len);

If xdp push or xdp pull modifies xdp_buff, will the original header 
still apply to the modified data?

Thanks,
Heng

> +
>   	if (metasize)
>   		skb_metadata_set(skb, metasize);
>   
> @@ -1635,6 +1638,9 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>   		head_skb = build_skb_from_xdp_buff(dev, vi, xdp, xdp_frags_truesz);
>   		if (unlikely(!head_skb))
>   			break;
> +		/* Store the original virtio header for subsequent use by the driver. */
> +		memcpy(skb_vnet_common_hdr(head_skb), &virtnet_xdp.hdr, vi->hdr_len);
> +
>   		return head_skb;
>   
>   	case XDP_TX: