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

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Date:   Fri, 13 Nov 2020 19:52:09 -0700
From:   David Ahern <dsahern@...il.com>
To:     Andrea Mayer <andrea.mayer@...roma2.it>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     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 11/13/20 7:29 PM, Andrea Mayer wrote:
> Hi Jakub,
> 
> On Fri, 13 Nov 2020 18:01:26 -0800
> Jakub Kicinski <kuba@...nel.org> wrote:
> 
>>> UAPI solution 2
>>>
>>> we turn "table" into an optional parameter and we add the "vrftable" optional
>>> parameter. DT4 can only be used with the "vrftable" (hence it is a required
>>> parameter for DT4).
>>> DT6 can be used with "vrftable" (new vrf mode) or with "table" (legacy mode)
>>> (hence it is an optional parameter for DT6).
>>>
>>> UAPI solution 2 examples:
>>>
>>> ip -6 route add 2001:db8::1/128 encap seg6local action End.DT4 vrftable 100 dev eth0
>>> ip -6 route add 2001:db8::1/128 encap seg6local action End.DT6 vrftable 100 dev eth0
>>> ip -6 route add 2001:db8::1/128 encap seg6local action End.DT6 table 100 dev eth0
>>>
>>> IMO solution 2 is nicer from UAPI POV because we always have only one 
>>> parameter, maybe solution 1 is slightly easier to implement, all in all 
>>> we prefer solution 2 but we can go for 1 if you prefer.
>>
>> Agreed, 2 looks better to me as well. But let's not conflate uABI with
>> iproute2's command line. I'm more concerned about the kernel ABI.
> 
> Sorry I was a little imprecise here. I reported only the user command perspective.
> From the kernel point of view in solution 2 the vrftable will be a new
> [SEG6_LOCAL_VRFTABLE] optional parameter.
> 
>> BTW you prefer to operate on tables (and therefore require
>> net.vrf.strict_mode=1) because that's closer to the spirit of the RFC,
>> correct? As I said from the implementation perspective passing any VRF
>> ifindex down from user space to the kernel should be fine?
> 
> Yes, I definitely prefer to operate on tables (and so on the table ID) due to
> the spirit of the RFC. We have discussed in depth this design choice with
> David Ahern when implementing the DT4 patch and we are confident that operating
> with VRF strict mode is a sound approach also for DT6. 
> 

I like the vrftable option. Straightforward extension from current table
argument.