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Subject: Re: [PATCH 1/2] Revert "xfrm: interface with if_id 0 should return
 error"
To:     Steffen Klassert <steffen.klassert@secunet.com>
Cc:     Paul Chaignon <paul@cilium.io>,
        Eyal Birger <eyal.birger@gmail.com>, netdev@vger.kernel.org
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 <20220301150930.GA56710@Mem>
 <dcc83e93-4a28-896c-b3d3-8d675bb705eb@linux.microsoft.com>
 <20220301161001.GV1223722@gauss3.secunet.de>
From:   Kai Lueke <kailueke@linux.microsoft.com>
Message-ID: <f2dc1c09-6e3a-0563-491b-1b8de7a8f5ef@linux.microsoft.com>
Date:   Tue, 1 Mar 2022 17:44:44 +0100
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Hi,
> In general I agree that the userspace ABI has to be stable, but
> this never worked. We changed the behaviour from silently broken to
> notify userspace about a misconfiguration.
>
> It is the question what is more annoying for the users. A bug that
> we can never fix, or changing a broken behaviour to something that
> tells you at least why it is not working.
>
> In such a case we should gauge what's the better solution. Here
> I tend to keep it as it is.

alternatives are: docs to ensure the API is used the right way, maybe a
dmesg log entry if wrong usage is detected, and filing bugs where the
API is used wrong.

The chosen way led to having this change being introduced as part of an
LTS kernel bugfix update, breaking user's clusters:
https://github.com/flatcar-linux/Flatcar/issues/626

Please rethink how you want to handle this, also for not making a
precedent here so that this repeats.

Regards,
Kai (Flatcar Container Linux team)