On 11/14/25 8:13 AM, chia-yu.chang@nokia-bell-labs.com wrote:

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

Co-developed-by: Olivier Tilmans <redacted>
Signed-off-by: Olivier Tilmans <redacted>
Signed-off-by: Ilpo Järvinen <ij@kernel.org>
Signed-off-by: Chia-Yu Chang <redacted>

Acked-by: Paolo Abeni <pabeni@redhat.com>