netdev - Does "TCP Fast Open": not work on 6.14.7?

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Message-ID: <985e79fa5c4ea841cb361458cdcf0114050bfb62.camel@yandex.ru>
Date: Mon, 26 May 2025 12:02:02 +0300
From: Konstantin Kharlamov <Hi-Angel@...dex.ru>
To: netdev@...r.kernel.org
Subject: Does "TCP Fast Open": not work on 6.14.7?

Hello, I may be missing something, but something seems off.

`/proc/net/netstat` contains TCP Fast Open counters. They are
undocumented, but `networking/snmp_counter.rst` says for
`TcpExtTCPFastOpenPassive` it's amount of times fast open connection
was made, which I presume pertains to `TCPFastOpenPassive` as well.

So, I

1. Have set `net.ipv4.tcp_fastopen = 3` (enables it for both incoming
and outgoing connections).
2. Launch "server" `nc -vkl 8080`
3. Connect to it with `nc -v localhost 8080`
4. Check "fast open" counters via `cat /proc/net/netstat | column -t |
less -Si`

Expected: at least some of the counters increased.
Actual: every "fast open" counter is 0 (zero).

That is on Archlinux, kernel 6.14.7. WDYDW?

P.S. pls keep me in CC, i'm not subscribed.
P.P.S. slightly offtopic, but am I correct to understand one-liners
like `cat … | column …` are the only way to read these counters? I've
searched far and wide, and from what I understand none of networking
utilities (at least not ss, netstat, ntstat) show them.