-----Original Message----- From: Paolo Abeni pabeni@redhat.com Sent: Tuesday, November 18, 2025 1:02 PM To: Chia-Yu Chang (Nokia) chia-yu.chang@nokia-bell-labs.com; edumazet@google.com; parav@nvidia.com; linux-doc@vger.kernel.org; corbet@lwn.net; horms@kernel.org; dsahern@kernel.org; kuniyu@google.com; bpf@vger.kernel.org; netdev@vger.kernel.org; dave.taht@gmail.com; jhs@mojatatu.com; kuba@kernel.org; stephen@networkplumber.org; xiyou.wangcong@gmail.com; jiri@resnulli.us; davem@davemloft.net; andrew+netdev@lunn.ch; donald.hunter@gmail.com; ast@fiberby.net; liuhangbin@gmail.com; shuah@kernel.org; linux-kselftest@vger.kernel.org; ij@kernel.org; ncardwell@google.com; Koen De Schepper (Nokia) koen.de_schepper@nokia-bell-labs.com; g.white@cablelabs.com; ingemar.s.johansson@ericsson.com; mirja.kuehlewind@ericsson.com; cheshire cheshire@apple.com; rs.ietf@gmx.at; Jason_Livingood@comcast.com; Vidhi Goel vidhi_goel@apple.com Subject: Re: [PATCH v6 net-next 03/14] net: update commnets for SKB_GSO_TCP_ECN and SKB_GSO_TCP_ACCECN
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Note: typo in the subj
On 11/14/25 8:13 AM, chia-yu.chang@nokia-bell-labs.com wrote:
From: Chia-Yu Chang chia-yu.chang@nokia-bell-labs.com
No functional changes.
Some real commit message is needed.
Co-developed-by: Ilpo Järvinen ij@kernel.org Signed-off-by: Ilpo Järvinen ij@kernel.org Signed-off-by: Chia-Yu Chang chia-yu.chang@nokia-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
Hi Paolo and Ilpo,
I was thinking to totally remove ECN from Rx path, and add the comments only in AccECN, like below: Because we could use SKB_GSO_TCP_ACCECN in Rx to explicitly tell latter GSO Tx in a forwarding case that do NOT clean CWR flag. What do you think?
/* 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 * ACE signal of AccECN segments. Therefore, this cannot be used on Rx. */ SKB_GSO_TCP_ECN = 1 << 2, [...] /* 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,
Chia-Yu