Re: [PATCH bpf-next 10/10] [bpf]: make virtio compatible w/ bpf_xdp_adjust_tail

[Jason Wang <jasowang@redhat.com>]

On 2018年04月17日 14:51, Nikita V. Shirokov wrote:
> w/ bpf_xdp_adjust_tail helper xdp's data_end pointer could be changed as
> well (only "decrease" of pointer's location is going to be supported).
> changing of this pointer will change packet's size.
> for virtio driver we need to adjust XDP_PASS handling by recalculating
> length of the packet if it was passed to the TCP/IP stack
>
> Signed-off-by: Nikita V. Shirokov <tehnerd@tehnerd.com>
> ---
>   drivers/net/virtio_net.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 7b187ec7411e..115d85f7360a 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -604,6 +604,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
>   		case XDP_PASS:
>   			/* Recalculate length in case bpf program changed it */
>   			delta = orig_data - xdp.data;
> +			len = xdp.data_end - xdp.data;
>   			break;
>   		case XDP_TX:
>   			sent = __virtnet_xdp_xmit(vi, &xdp);
> @@ -637,7 +638,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
>   		goto err;
>   	}
>   	skb_reserve(skb, headroom - delta);
> -	skb_put(skb, len + delta);
> +	skb_put(skb, len);
>   	if (!delta) {
>   		buf += header_offset;
>   		memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
> @@ -752,6 +753,10 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>   			offset = xdp.data -
>   					page_address(xdp_page) - vi->hdr_len;
>   
> +			/* recalculate len if xdp.data or xdp.data_end were
> +			 * adjusted
> +			 */
> +			len = xdp.data_end - xdp.data;
>   			/* We can only create skb based on xdp_page. */
>   			if (unlikely(xdp_page != page)) {
>   				rcu_read_unlock();

Reviewed-by: Jason Wang <jasowang@redhat.com>