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Date:	Sun, 17 May 2015 17:59:56 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	Florian Westphal <fw@...len.de>,
	Mirja K├╝hlewind 
	<mirja.kuehlewind@....ee.ethz.ch>,
	Brian Trammell <trammell@....ee.ethz.ch>,
	Eric Dumazet <edumazet@...gle.com>,
	Dave That <dave.taht@...il.com>
Subject: Re: [PATCH net-next] tcp: add rfc3168, section 6.1.1.1. fallback

On Sun, 2015-05-17 at 22:11 +0200, Daniel Borkmann wrote:

>  
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 7386d32..b05d6df 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -350,6 +350,16 @@ static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
>  	}
>  }
>  
> +static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
> +{
> +	struct tcp_sock *tp = tcp_sk(sk);
> +
> +	if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback) {
> +		TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
> +		tp->ecn_flags = 0;
> +	}
> +}
> +

Hi Daniel

If first SYNACK ECE was delayed (our SYN rtx was spurious), maybe we can
still keep ECN enabled ?

So maybe do not clear tp->ecn_flags here, as it should be ultimately
cleared in tcp_ecn_rcv_synack().





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