netdev - Re: [PATCH v1 net-next 1/3] net: update commnets for SKB_GSO_TCP_ECN and SKB_GSO_TCP

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Message-ID: <20260201040043-mutt-send-email-mst@kernel.org>
Date: Sun, 1 Feb 2026 04:01:16 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: chia-yu.chang@...ia-bell-labs.com
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Subject: Re: [PATCH v1 net-next 1/3] net: update commnets for SKB_GSO_TCP_ECN
 and SKB_GSO_TCP_ACCECN

On Sat, Jan 31, 2026 at 11:55:08PM +0100, 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>

Subject: comments?

> ---
>  include/linux/skbuff.h | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index e6bfe5d0c525..30a8dc4233ba 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. However, because
> +	 * the connection to which the segment belongs is not tracked to use
> +	 * RFC3168 or AccECN (RFC9768), and using RFC3168 ECN offload may clear
> +	 * ACE signal (CWR is one of it). Therefore, this cannot be used on Rx.
> +	 * Instead, SKB_GSO_TCP_ACCECN shall be used to avoid CWR corruption.
> +	 */
>  	SKB_GSO_TCP_ECN = 1 << 2,
>  
>  	__SKB_GSO_TCP_FIXEDID = 1 << 3,
> @@ -706,6 +712,14 @@ enum {
>  
>  	SKB_GSO_FRAGLIST = 1 << 18,
>  
> +	/* For TX, this indicates the TCP segment uses the CWR flag as part of
> +	 * ACE signal, and the CWR flag is not modified in the skb. For RX, any
> +	 * CWR flagged segment must use SKB_GSO_TCP_ACCECN to ensure CWR flag
> +	 * is not cleared by any RFC3168 ECN offload, and thus keeping ACE
> +	 * signal of AccECN segments. This is particularly used for Rx of
> +	 * virtio_net driver in order to tell latter GSO Tx in a forwarding
> +	 * scenario that it is NOT ok to clean CWR flag from the 2nd segment.
> +	 */
>  	SKB_GSO_TCP_ACCECN = 1 << 19,
>  
>  	/* These indirectly map onto the same netdev feature.
> -- 
> 2.34.1