netdev - Re: [PATCH bpf-next v3 07/11] bpf: make tun compatible w/ bpf_xdp_adjust

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Date:   Wed, 18 Apr 2018 19:16:11 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     "Nikita V. Shirokov" <tehnerd@...nerd.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 07/11] bpf: make tun compatible w/
 bpf_xdp_adjust_tail

On Tue, Apr 17, 2018 at 09:42:19PM -0700, 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 tun driver we need to adjust XDP_PASS handling by recalculating
> length of the packet if it was passed to the TCP/IP stack
> (in case if after xdp's prog run data_end pointer was adjusted)
> 
> Reviewed-by: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Nikita V. Shirokov <tehnerd@...nerd.com>

Acked-by: Michael S. Tsirkin <mst@...hat.com>

> ---
>  drivers/net/tun.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 1e58be152d5c..901351a6ed21 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1696,6 +1696,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
>  			return NULL;
>  		case XDP_PASS:
>  			delta = orig_data - xdp.data;
> +			len = xdp.data_end - xdp.data;
>  			break;
>  		default:
>  			bpf_warn_invalid_xdp_action(act);
> @@ -1716,7 +1717,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
>  	}
>  
>  	skb_reserve(skb, pad - delta);
> -	skb_put(skb, len + delta);
> +	skb_put(skb, len);
>  	get_page(alloc_frag->page);
>  	alloc_frag->offset += buflen;
>  
> -- 
> 2.15.1