linux-kernel - Re: [PATCH bpf-next v4] virtio_net: add XDP meta data support

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Date:   Wed, 5 Feb 2020 00:33:52 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Yuya Kusakabe <yuya.kusakabe@...il.com>
Cc:     jasowang@...hat.com, ast@...nel.org, daniel@...earbox.net,
        davem@...emloft.net, hawk@...nel.org, john.fastabend@...il.com,
        kafai@...com, songliubraving@...com, yhs@...com, kuba@...nel.org,
        andriin@...com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v4] virtio_net: add XDP meta data support

On Tue, Feb 04, 2020 at 04:16:55PM +0900, Yuya Kusakabe wrote:
> @@ -852,8 +868,9 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  			 * adjustments. Note other cases do not build an
>  			 * skb and avoid using offset
>  			 */
> -			offset = xdp.data -
> -					page_address(xdp_page) - vi->hdr_len;
> +			metasize = xdp.data - xdp.data_meta;
> +			offset = xdp.data - page_address(xdp_page) -
> +				 vi->hdr_len - metasize;
>  
>  			/* recalculate len if xdp.data or xdp.data_end were
>  			 * adjusted

Tricky to get one's head around.
Can you pls update the comment above to document the new math?

-- 
MST