From mboxrd@z Thu Jan  1 00:00:00 1970
From: James Chapman <jchapman@katalix.com>
Subject: Re: [PATCH net-next 2/2] l2tp: add peer_offset parameter
Date: Tue, 2 Jan 2018 20:08:18 +0000
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Cc: "David S. Miller" <davem@davemloft.net>, netdev@vger.kernel.org,
        Hangbin Liu <liuhangbin@gmail.com>
To: Guillaume Nault <g.nault@alphalink.fr>,
        Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
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On 02/01/18 18:05, Guillaume Nault wrote:
>>> Lorenzo, is this being added to fix interoperability with another L2TPv3
>>> implementation? If so, can you share more details?
>>>
>> Hi James,
>>
>> I introduced peer_offset parameter to fix a specific setup where
>> tunnel endpoints
>> running L2TPv3 would use different values for tx offset (since in
>> iproute2 there is no
>> restriction on it), not to fix a given an interoperability issue.
>>
> Yes, but was it just to test iproute2's peer_offset option? Or is there
> a plan to use it for real?
>
>> I introduced this feature since:
>>   - offset has been added for long time to L2TPv3 implementation
>>     (commit f7faffa3ff8ef6ae712ef16312b8a2aa7a1c95fe and
>>     commit 309795f4bec2d69cd507a631f82065c2198a0825) and I wanted to
>> preserve UABI
>>   - have the same degree of freedom for offset parameter we have in
>> L2TPv2 and fix the issue
>>     described above
>>
> AFAIU, the current L2TPv2 implementation never sets the offset field
> and nobody ever realised.
>
>> Now what we can do I guess is:
>> - as suggested by Guillaume drop completely the offset support without removing
>>    netlink attribute in order to not break UABI
>> - fix offset support initializing properly padding bits
>>
> I'd go for the first one. I just wonder if that looks acceptable to
> David an James.

I think the first one too. Also update iproute2 to remove or hide the 
offset and peer_offset parameters.