netdev - Re: [PATCH bpf-next 09/10] [bpf]: make tun compatible w/ bpf_xdp_adjust

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Date:   Wed, 18 Apr 2018 10:16:25 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Nikita V. Shirokov" <tehnerd@...nerd.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, mst@...hat.com
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next 09/10] [bpf]: make tun compatible w/
 bpf_xdp_adjust_tail



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 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)
>
> Signed-off-by: Nikita V. Shirokov <tehnerd@...nerd.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 28583aa0c17d..0b488a958076 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1688,6 +1688,7 @@ 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);
> @@ -1708,7 +1709,7 @@ 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;
>   

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