netdev - Re: [PATCH v5 net-next 03/14] net: update commnets for SKB_GSO_TCP_ECN and SKB_GSO_TCP

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Message-ID: <f98d3cab-7668-4cf0-87bf-cd96ca5f7a5b@redhat.com>
Date: Thu, 6 Nov 2025 12:06:06 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: chia-yu.chang@...ia-bell-labs.com, edumazet@...gle.com, parav@...dia.com,
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Subject: Re: [PATCH v5 net-next 03/14] net: update commnets for
 SKB_GSO_TCP_ECN and SKB_GSO_TCP_ACCECN

On 10/30/25 3:34 PM, chia-yu.chang@...ia-bell-labs.com wrote:
> From: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> 
> No functional changes.
> 
> Co-developed-by: Ilpo Järvinen <ij@...nel.org>
> Signed-off-by: Ilpo Järvinen <ij@...nel.org>
> Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> ---
>  include/linux/skbuff.h | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index a7cc3d1f4fd1..74d6a209e203 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -671,7 +671,12 @@ enum {
>  	/* This indicates the skb is from an untrusted source. */
>  	SKB_GSO_DODGY = 1 << 1,
>  
> -	/* This indicates the tcp segment has CWR set. */
> +	/* For Tx, this indicates the first TCP segment has CWR set, and any
> +	 * subsequent segment in the same skb has CWR cleared. This cannot be
> +	 * used on Rx, because the connection to which the segment belongs is
> +	 * not tracked to use RFC3168 or Accurate ECN, and using RFC3168 ECN
> +	 * offload may corrupt AccECN signal of AccECN segments.
> +	 */

The intended difference between RX and TX sounds bad to me; I think it
conflicts with the basic GRO design goal of making aggregated and
re-segmented traffic indistinguishable from the original stream. Also
what about forwarded packet?

/P