netdev - Re: [PATCH net-next 0/5] net/sched: Retire some tc qdiscs and classifiers

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Date:   Wed, 15 Feb 2023 10:42:36 -0300
From:   Pedro Tammela <pctammela@...atatu.com>
To:     Jiri Pirko <jiri@...nulli.us>, Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        xiyou.wangcong@...il.com, davem@...emloft.net, edumazet@...gle.com,
        pabeni@...hat.com, stephen@...workplumber.org, dsahern@...il.com
Subject: Re: [PATCH net-next 0/5] net/sched: Retire some tc qdiscs and
 classifiers

On 15/02/2023 04:50, Jiri Pirko wrote:
> Wed, Feb 15, 2023 at 12:05:23AM CET, jhs@...atatu.com wrote:
>> On Tue, Feb 14, 2023 at 4:41 PM Jakub Kicinski <kuba@...nel.org> wrote:
>>>
>>> On Tue, 14 Feb 2023 13:40:13 -0800 Jakub Kicinski wrote:
>>>>> I think we have to let the UAPI there to rot in order not to break
>>>>> compilation of apps that use those (no relation to iproute2).
>>>>
>>>> Yeah, I was hoping there's no other users but this is the first match
>>>> on GitHub:
>>>>
>>>> https://github.com/t2mune/nield/blob/0c0848d1d1e6c006185465ee96aeb5a13a1589e6/src/tcmsg_qdisc_dsmark.c
>>>>
>>>> :(
>>>
>>> I mean that in the context of deleting the uAPI, not the support,
>>> to be clear.
>>
>> Looking at that code - the user is keeping their own copy of the uapi
>> and listening to generated events from the kernel.
>> With new kernels those events will never come, so they wont be able to
>> print them. IOW, there's no dependency on the uapi being in the kernel
>> - but maybe worth keeping.
>> Note, even if they were to send queries - they will just get a failure back.
> 
> Guys. I don't think that matters. There might be some non-public code
> using this headers and we don't want to break them either. I believe we
> have to stick with it. But perhaps we can include some note there.
> 

I don't know the compilation requirements for uapi, but it could 
leverage the deprecated attribute, when available as a compiler 
extension (it's queued for C23 as well[0]).

E.g. https://godbolt.org/z/d535jh9j8

Essentially anytime someone uses one of the Netlink attributes they will 
get a harmless warning like:
<source>:22:18: warning: 'TCA_TCINDEX_CLASSID' is deprecated 
[-Wdeprecated-declarations]

[0] https://en.cppreference.com/w/c/language/attributes/deprecated