netdev - Re: [PATCH iproute2] man: tc-u32: Fix page to match new firstfrag behavior

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Date:   Thu, 4 Nov 2021 17:06:45 +0100
From:   Phil Sutter <phil@....cc>
To:     Anssi Hannula <anssi.hannula@...wise.fi>
Cc:     netdev@...r.kernel.org, stephen@...workplumber.org,
        Hiroaki SHIMODA <shimoda.hiroaki@...il.com>
Subject: Re: [PATCH iproute2] man: tc-u32: Fix page to match new firstfrag
 behavior

On Thu, Nov 04, 2021 at 04:42:05PM +0200, Anssi Hannula wrote:
> Commit 690b11f4a6b8 ("tc: u32: Fix firstfrag filter.") applied in 2012
> changed the "ip firstfrag" selector to not match non-fragmented packets
> anymore.
> 
> However, the documentation added in f15a23966fff ("tc: add a man page
> for u32 filter") in 2015 includes an example that relies on the previous
> behavior (non-fragmented packet counted as first fragment).
> 
> Due to this, the example does not work correctly and does not actually
> classify regular SSH packets.
> 
> Modify the example to use a raw u16 selector on the fragment offset to
> make it work, and also make the firstfrag description more clear about
> the current behavior.
> 
> Fixes: f15a23966fff ("tc: add a man page for u32 filter")
> Signed-off-by: Anssi Hannula <anssi.hannula@...wise.fi>
> Cc: Phil Sutter <phil@....cc>
> Cc: Hiroaki SHIMODA <shimoda.hiroaki@...il.com>

Acked-by: Phil Sutter <phil@....cc>

> I suspect the original behavior was intentional, but the new one has
> been out for 9 years now so I guess it is too late to change again.

At least it seems nobody really depends on the old behaviour (or doesn't
update iproute2 then). :)

Thanks, Phil