netdev - Re: [RESEND PATCH 2/2] TCP: pass accepted-TFO indication through getsockopt

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Message-ID: <20250416192705.16673-1-kuniyu@amazon.com>
Date: Wed, 16 Apr 2025 12:26:54 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <jgh@...m.org>
CC: <edumazet@...gle.com>, <ncardwell@...gle.com>, <netdev@...r.kernel.org>
Subject: Re: [RESEND PATCH 2/2] TCP: pass accepted-TFO indication through getsockopt

From: Jeremy Harris <jgh@...m.org>
Date: Wed, 16 Apr 2025 10:15:38 +0100
> Signed-off-by: Jeremy Harris <jgh@...m.org>
> ---
>  include/uapi/linux/tcp.h | 1 +
>  net/ipv4/tcp.c           | 2 ++
>  2 files changed, 3 insertions(+)
> 
> diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
> index dc8fdc80e16b..ae8c5a8af0e5 100644
> --- a/include/uapi/linux/tcp.h
> +++ b/include/uapi/linux/tcp.h
> @@ -184,6 +184,7 @@ enum tcp_fastopen_client_fail {
>  #define TCPI_OPT_ECN_SEEN	16 /* we received at least one packet with ECT */
>  #define TCPI_OPT_SYN_DATA	32 /* SYN-ACK acked data in SYN sent or rcvd */
>  #define TCPI_OPT_USEC_TS	64 /* usec timestamps */
> +#define TCPI_OPT_TFO_SEEN	128 /* we accepted a Fast Open option on SYN */

This is the last bit of tcpi_options.

We can add another field at the end of the struct if necessary in
the future, but from the cover letter and commit message, I didn't
get why this info is needed at per-socket granurality.

Also, This can be retrieved with BPF.


>  
>  /*
>   * Sender's congestion state indicating normal or abnormal situations
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index e0e96f8fd47c..b45eb7cb2909 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -4164,6 +4164,8 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
>  		info->tcpi_options |= TCPI_OPT_SYN_DATA;
>  	if (tp->tcp_usec_ts)
>  		info->tcpi_options |= TCPI_OPT_USEC_TS;
> +	if (tp->syn_fastopen_in)
> +		info->tcpi_options |= TCPI_OPT_TFO_SEEN;
>  
>  	info->tcpi_rto = jiffies_to_usecs(icsk->icsk_rto);
>  	info->tcpi_ato = jiffies_to_usecs(min_t(u32, icsk->icsk_ack.ato,
> -- 
> 2.49.0