netdev - Re: [PATCH 0/2 net-next] geneve: fix TOS inheriting

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Message-ID: <20220725165745.GC18808@pc-4.home>
Date:   Mon, 25 Jul 2022 18:57:45 +0200
From:   Guillaume Nault <gnault@...hat.com>
To:     Matthias May <matthias.may@...termo.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        yoshfuji@...ux-ipv6.org, dsahern@...nel.org, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, nicolas.dichtel@...nd.com,
        eyal.birger@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2 net-next] geneve: fix TOS inheriting

On Sun, Jul 24, 2022 at 02:37:39AM +0200, Matthias May wrote:
> Is there any reason why the flowlabel should be restricted to these
> 3 bits?

It's a bug, likely a copy/paste mistake.

> The patch simply removes the usage of this macro, but i don't
> know if there was a specific intention behind that.

RT_TOS() is an old macro used to interprete IPv4 TOS as described in
the obsolete RFC 1349. It's conceptually wrong to use it even in IPv4
code, although, given the current state of the code, most of the
existing calls have no consequence.

But using RT_TOS() in IPv6 code is always a bug: IPv6 never had a "TOS"
field to be interpreted the RFC 1349 way. There's no historical
compatibility to worry about.