RE: [PATCH v9 net-next 04/15] tcp: ECT_1_NEGOTIATION and NEEDS_ACCECN identifiers

-----Original Message-----
From: Eric Dumazet <edumazet@google.com> 
Sent: Tuesday, January 20, 2026 10:54 AM
To: Chia-Yu Chang (Nokia) <redacted>
Cc: pabeni@redhat.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) <redacted>; g.white@cablelabs.com; ingemar.s.johansson@ericsson.com; mirja.kuehlewind@ericsson.com; cheshire <redacted>; rs.ietf@gmx.at; Jason_Livingood@comcast.com; Vidhi Goel <redacted>; Olivier Tilmans (Nokia) <redacted>
Subject: Re: [PATCH v9 net-next 04/15] tcp: ECT_1_NEGOTIATION and NEEDS_ACCECN identifiers


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On Mon, Jan 19, 2026 at 7:59 PM [off-list ref] wrote:

quoted

From: Chia-Yu Chang <redacted>

Two CA module flags are added in this patch related to AccECN negotiation.
First, a new CA module flag (TCP_CONG_NEEDS_ACCECN) defines that the 
CA expects to negotiate AccECN functionality using the ECE, CWR and AE 
flags in the TCP header.

Second, during ECN negotiation, ECT(0) in the IP header is used. This 
patch enables CA to control whether ECT(0) or ECT(1) should be used on 
a per-segment basis. A new flag (TCP_CONG_ECT_1_NEGOTIATION) defines 
the expected ECT value in the IP header by the CA when not-yet initialized for the connection.

The detailed AccECN negotiaotn during the 3WHS can be found in the AccECN spec:
  https://tools.ietf.org/id/draft-ietf-tcpm-accurate-ecn-28.txt

While for some reason linux uses icsk_ca_ops, I think the terminology is about "CC : Congestion Control"

Not sure what CA means...

Reviewed-by: Eric Dumazet <edumazet@google.com>

Thanks for feedback, I will change into CC in the next version.

Chia-Yu