BBRv3 for v6.15-rc1

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Oleksandr Natalenko

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Apr 7, 2025, 11:11:35 AMApr 7

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Hello.

While forward-porting BBRv3 for v6.15-rc1 I've bumped into the upstream commit 041fb11d518f5d that changed TCP_ECN_OK definition into TCP_ECN_MODE_RFC3168 and also introduced TCP_ECN_MODE_ACCECN.

My question is, given there's AccECN available now, should bbr_can_use_ecn() still check for TCP_ECN_OK aka TCP_ECN_MODE_RFC3168 only, or tcp_ecn_mode_any() should be used?

Currently, I've ended up doing this:

static bool bbr_can_use_ecn(const struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);

return tcp_ecn_mode_any(tp) &&
(tcp_sk(sk)->ecn_flags & TCP_ECN_LOW);
}