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

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Message-ID: <20180102180557.GB1402@alphalink.fr>
Date:   Tue, 2 Jan 2018 19:05:57 +0100
From:   Guillaume Nault <g.nault@...halink.fr>
To:     Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Cc:     James Chapman <jchapman@...alix.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Hangbin Liu <liuhangbin@...il.com>
Subject: Re: [PATCH net-next 2/2] l2tp: add peer_offset parameter

> > 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.