On 9/18/25 6:21 PM, [email protected] wrote:
> From: Chia-Yu Chang <[email protected]>
>
> Two CA module flags are added in this patch. 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.
> 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
>
> Second, when ECN is negociated for a TCP flow, it defaults to use
> ECT(0) in the IP header. L4S service, however, needs to se ECT(1).
> 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_WANTS_ECT_1)
I find this description confusing/contradictory with the implementation
where TCP_CONG_WANTS_ECT_1 is actually a mask.
> @@ -1322,6 +1328,18 @@ static inline bool tcp_ca_needs_ecn(const struct sock
> *sk)
> return icsk->icsk_ca_ops->flags & TCP_CONG_NEEDS_ECN;
> }
>
> +static inline bool tcp_ca_needs_accecn(const struct sock *sk)
> +{
> + const struct inet_connection_sock *icsk = inet_csk(sk);
> +
> + return icsk->icsk_ca_ops->flags & TCP_CONG_NEEDS_ACCECN;
> +}
> +
> +static inline bool tcp_ca_wants_ect_1(const struct sock *sk)
> +{
> + return inet_csk(sk)->icsk_ca_ops->flags & TCP_CONG_WANTS_ECT_1;
Should the above tests be:
(inet_csk(sk)->icsk_ca_ops->flags & TCP_CONG_WANTS_ECT_1) ==
TCP_CONG_WANTS_ECT_1
?
Otherwise existing CC with TCP_CONG_NEEDS_ECN will unexpectedly switch
to ECT_1 usage.
[...]
> diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
> index df758adbb445..f9efbcf1d856 100644
> --- a/net/ipv4/tcp_cong.c
> +++ b/net/ipv4/tcp_cong.c
> @@ -227,7 +227,7 @@ void tcp_assign_congestion_control(struct sock *sk)
>
> memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
> if (ca->flags & TCP_CONG_NEEDS_ECN)
> - INET_ECN_xmit(sk);
> + __INET_ECN_xmit(sk, tcp_ca_wants_ect_1(sk));
Possibly a new helper for the above statement could be useful
/P
