netdev - Re: [PATCH net-next 2/2] l2tp: add peer

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Date:   Tue, 2 Jan 2018 20:59:44 +0000
From:   James Chapman <jchapman@...alix.com>
To:     Guillaume Nault <g.nault@...halink.fr>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Hangbin Liu <liuhangbin@...il.com>
Subject: Re: [PATCH net-next 2/2] l2tp: add peer_offset parameter

On 02/01/18 20:08, James Chapman wrote:
> 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.
>
>
I just realised the peer_offset attribute changes are already applied in 
net-next. (I missed these when they were submitted just before 
Christmas.) Should these commits be reverted? We probably don't want 
v4.15 to get an additional l2tp peer_offset attribute if we are going to 
remove it and the rest of the code supporting configurable offset 
attributes in the next release.

81487bf Merge branch 'l2tp-next'
f15bc54 l2tp: add peer_offset parameter
820da53 l2tp: fix missing print session offset info