netdev - Re: [PATCH v6 net-next 03/14] net: update commnets for SKB_GSO_TCP_ECN and SKB_GSO_TCP

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Message-ID: <d87782d4-567d-4753-8435-fd52cd5b88da@redhat.com>
Date: Tue, 18 Nov 2025 13:02:20 +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,
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Subject: Re: [PATCH v6 net-next 03/14] net: update commnets for
 SKB_GSO_TCP_ECN and SKB_GSO_TCP_ACCECN

Note: typo in the subj

On 11/14/25 8:13 AM, chia-yu.chang@...ia-bell-labs.com wrote:
> From: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> 
> No functional changes.

Some real commit message is needed.

> 
> 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>
> 
> ---
> v6:
> - Update comments.
> ---
>  include/linux/skbuff.h | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index ff90281ddf90..e09455cee8e3 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -671,7 +671,13 @@ 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 is not
> +	 * used on Rx except for virtio_net. However, 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. Therefore, this cannot be used on Rx.

Stating both that is used by virtio_net and can not be used in the RX
path is a bit confusing. Random Contributor may be tempted from removing
ECN support from virtio_net

Please state explicitly:
- why it makes sense to use this in virtio_net
- this must not be used in the RX path _outside_ the virtio net driver

something alike:

/* For Tx, this indicates the first TCP segment has CWR set, and any
 * subsequent segment in the same skb has CWR cleared. However, 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. Therefore, this cannot be used on
 * Rx outside the virtio_net driver. Such exception exist due to
 * <reason>
 */

/P