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

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Message-ID: <0607b63a-7555-44e2-b040-949a34c07f12@exim.org>
Date: Wed, 23 Apr 2025 12:48:34 +0100
From: jgh@...m.org
To: Neal Cardwell <ncardwell@...gle.com>, Jeremy Harris <jgh@...m.org>
Cc: netdev@...r.kernel.org, edumazet@...gle.com
Subject: Re: [RESEND PATCH 2/2] TCP: pass accepted-TFO indication through
 getsockopt

Thanks for the review.  I'm preparing a v2, and a patch to "ss" in iproute2.

On 2025/04/22 4:50 PM, Neal Cardwell wrote:
>    TCP: pass accepted-TFO indication through getsockopt
> 
> Please use something more like:
> 
>    tcp: fastopen: pass TFO child indication through getsockopt

Will change for v2.

>> +#define TCPI_OPT_TFO_SEEN      128 /* we accepted a Fast Open option on SYN */
> 
> IMHO this bit name is slightly misleading, and does not match the comment.
> 
> Sometimes when a SYN is received with a TFO option the server will
> fail to create a child because the TFO cookie is incorrect. In such a
> case, a TFO option is "seen", but TFO is not *used* because the TFO
> cookie is incorrect; so this "TFO_SEEN" bit would be 0 even though a
> TFO option was "seen". IMHO that is confusing/misleading.
> 
> When this bit is set, we know not only that the "Received SYN includes
> Fast Open option" (comment from the previous patch), but we also know
> that the TFO cookie was correct and a child socket was created.
> 
> So I would suggest a more specific bit name, something like:
> 
> +#define TCPI_OPT_TFO_CHILD      128 /* child from a Fast Open option on SYN */
> 
> +       if (tp->syn_fastopen_child)
> +               info->tcpi_options |= TCPI_OPT_TFO_CHILD;

Done.

-- 
Cheers,
   Jeremy