netdev - Re: [net-next,v2,4/5] seg6: add support for the SRv6 End.DT4 behavior

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Message-ID: <20201113155437.7d82550b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 13 Nov 2020 15:54:37 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Andrea Mayer <andrea.mayer@...roma2.it>
Cc:     David Ahern <dsahern@...il.com>,
        Stefano Salsano <stefano.salsano@...roma2.it>,
        "David S. Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...nel.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Shuah Khan <shuah@...nel.org>,
        Shrijeet Mukherjee <shrijeet@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Paolo Lungaroni <paolo.lungaroni@...t.it>,
        Ahmed Abdelsalam <ahabdels.dev@...il.com>
Subject: Re: [net-next,v2,4/5] seg6: add support for the SRv6 End.DT4
 behavior

On Sat, 14 Nov 2020 00:00:24 +0100 Andrea Mayer wrote:
> On Fri, 13 Nov 2020 13:40:10 -0800
> Jakub Kicinski <kuba@...nel.org> wrote:
> 
> > On Fri, 13 Nov 2020 11:40:36 -0800 Jakub Kicinski wrote:  
> > > > agreed. The v6 variant has existed for a while. The v4 version is
> > > > independent.    
> > > 
> > > Okay, I'm not sure what's the right call so I asked DaveM.  
> > 
> > DaveM raised a concern that unless we implement v6 now we can't be sure
> > the interface we create for v4 is going to fit there.
> > 
> > So Andrea unless it's a major hurdle, could you take a stab at the v6
> > version with VRFs as part of this series?  
> 
> I can tackle the v6 version but how do we face the compatibility issue raised
> by Stefano in his message?
> 
> if it is ok to implement a uAPI that breaks the existing scripts, it is relatively
> easy to replicate the VRF-based approach also in v6.

We need to keep existing End.DT6 as is, and add a separate
implementation.

The way to distinguish between the two could be either by passing via
netlink a flag attribute (which would request use of VRF in both
cases); using a different attribute than SEG6_LOCAL_TABLE for the
table id (or perhaps passing VRF's ifindex instead), e.g.
SEG6_LOCAL_TABLE_VRF; or adding a new command
(SEG6_LOCAL_ACTION_END_DT6_VRF) which would behave like End.DT4.