netdev - Re: [PATCH iproute2] vxlan: add support for flowlab inherit

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Message-ID: <e60e2cc1-02c0-452b-8bb1-b2fb741e7b43@bernat.ch>
Date: Fri, 26 Jan 2024 07:28:35 +0100
From: Vincent Bernat <vincent@...nat.ch>
To: David Ahern <dsahern@...il.com>, Ido Schimmel <idosch@...sch.org>,
 Alce Lafranque <alce@...ranque.net>
Cc: netdev@...r.kernel.org, stephen@...workplumber.org
Subject: Re: [PATCH iproute2] vxlan: add support for flowlab inherit

On 2024-01-25 16:50, David Ahern wrote:

>>>>>> My personal
>>>>>> preference would be to add a new keyword for the new attribute:
>>>>>>
>>>>>> # ip link set dev vx0 type vxlan flowlabel_policy inherit
>>>>>> # ip link set dev vx0 type vxlan flowlabel_policy fixed flowlabel 10
>>>>>>
>>>>>> But let's see what David thinks.
>>>>>>
>>>>>
>>>>> A new keyword for the new attribute seems like the most robust.
>>>>>
>>>>> That said, inherit is already used in several ip commands for dscp, ttl
>>>>> and flowlabel for example; I do not see a separate keyword - e.g.,
>>>>> ip6tunnel.c.
>>>>
>>>> The implementation for flowlabel was modeled along ttl. We did diverge
>>>> for kernel, we can diverge for iproute2 as well. However, I am unsure if
>>>> you say we should go for option A (new attribute) or option B (do like
>>>> for dscp/ttl).
>>>
>>> A divergent kernel API does not mean the command line for iproute2 needs
>>> to be divergent. Consistent syntax across ip commands is best from a
>>> user perspective. What are the downsides to making 'inherit' for
>>> flowlabel work for vxlan like it does for ip6tunnel, ip6tnl and gre6?
>>> Presumably inherit is relevant for geneve? (We really need to stop
>>> making these tweaks on a single protocol basis.)
>>
>> Currently, the patch implements "inherit" without a new keyword, like
>> this is done for the other protocols. I don't really see a downside,
>> except the kernel could one day implement a policy that may be difficult
>> to express this way (inherit-during-the-day-fixed-during-the-night).
> 
> Wouldn't other uses of inherit be subject to the same kind of problem?
> ie., my primary point is for consistency in behavior across commands.

Honestly, I have a hard time finding a real downside. The day we need to 
specify both a value and a policy, it will still be time to introduce a 
new keyword. For now, it seems better to be consistent with the other 
protocols and with the other keywords (ttl, for example) using the same 
approach.