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 <redacted>
Cc: Phil Sutter <phil@nwl.cc>
Cc: Hiroaki SHIMODA <redacted>

Acked-by: Phil Sutter <phil@nwl.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