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: <1c79daaf-c092-4c49-a715-52aeb9688b48@redhat.com>
Date: Thu, 6 Nov 2025 12:26:28 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: chia-yu.chang@...ia-bell-labs.com, edumazet@...gle.com, parav@...dia.com,
 linux-doc@...r.kernel.org, corbet@....net, horms@...nel.org,
 dsahern@...nel.org, kuniyu@...gle.com, bpf@...r.kernel.org,
 netdev@...r.kernel.org, dave.taht@...il.com, jhs@...atatu.com,
 kuba@...nel.org, stephen@...workplumber.org, xiyou.wangcong@...il.com,
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 donald.hunter@...il.com, ast@...erby.net, liuhangbin@...il.com,
 shuah@...nel.org, linux-kselftest@...r.kernel.org, ij@...nel.org,
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 mirja.kuehlewind@...csson.com, cheshire@...le.com, rs.ietf@....at,
 Jason_Livingood@...cast.com, vidhi_goel@...le.com
Subject: Re: [PATCH v5 net-next 03/14] net: update commnets for
 SKB_GSO_TCP_ECN and SKB_GSO_TCP_ACCECN

On 11/6/25 12:06 PM, Paolo Abeni wrote:
> 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?

Uhm... I missed completely the point that SKB_GSO_TCP_ECN is TX path
only, i.e. GRO never produces aggregated SKB_GSO_TCP_ECN packets. Except
virtio_net uses it in the RX path ( virtio_net_hdr_to_skb ). Please
clarify the statement accordingly.

/P