netdev - Re: [PATCH linux-next] Documentation: fix outdated interpretation of ip_no_pmtu

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Date:   Wed, 29 Dec 2021 12:15:36 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     cgel.zte@...il.com
Cc:     davem@...emloft.net, corbet@....net, netdev@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        xu xin <xu.xin16@....com.cn>, Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH linux-next] Documentation: fix outdated interpretation
 of ip_no_pmtu_disc

On Wed, 29 Dec 2021 03:12:45 +0000 cgel.zte@...il.com wrote:
> From: xu xin <xu.xin16@....com.cn>
> 
> The updating way of pmtu has changed, but documentation is still in the
> old way. See commit-id 28d35bcdd3925e7293408cdb8aa5f2aac5f0d6e3. So This

not a correct way to quote a commit, please use: %h (\"%s\")
as the format.

> patch fix interpretation of ip_no_pmtu_disc.
> 
> Besides, min_pmtu seems not to be discoverd, but set.
> 
> Reported-by: Zeal Robot <zealci@....com.cn>

How does the bot discover this sort of problem?

> Signed-off-by: xu xin <xu.xin16@....com.cn>
> ---
>  Documentation/networking/ip-sysctl.rst | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
> index c04431144f7a..dd5e53318805 100644
> --- a/Documentation/networking/ip-sysctl.rst
> +++ b/Documentation/networking/ip-sysctl.rst
> @@ -25,9 +25,11 @@ ip_default_ttl - INTEGER
>  ip_no_pmtu_disc - INTEGER
>  	Disable Path MTU Discovery. If enabled in mode 1 and a
>  	fragmentation-required ICMP is received, the PMTU to this
> -	destination will be set to min_pmtu (see below). You will need
> -	to raise min_pmtu to the smallest interface MTU on your system
> -	manually if you want to avoid locally generated fragments.
> +	destination will be set to the smallest of the old MTU
> +        and ip_rt_min_pmtu (see __ip_rt_update_pmtu() in

I don't see how this is a meaningful distinction to someone reading
this documentation, more of a corner case.

> +        net/ipv4/route.c). You will need to raise min_pmtu to the
> +        smallest interface MTU on your system manually if you want to
> +        avoid locally generated fragments.

Use tabs instead of spaces.
 
>  	In mode 2 incoming Path MTU Discovery messages will be
>  	discarded. Outgoing frames are handled the same as in mode 1,
> @@ -49,7 +51,7 @@ ip_no_pmtu_disc - INTEGER
>  	Default: FALSE
>  
>  min_pmtu - INTEGER
> -	default 552 - minimum discovered Path MTU
> +	default 552 - minimum set Path MTU

Also not must of an improvement IMHO.

>  ip_forward_use_pmtu - BOOLEAN
>  	By default we don't trust protocol path MTUs while forwarding