netdev - Re: [PATCH net-next 2/6] net: sched: Add centralized RED flag checking

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Date:   Wed, 11 Mar 2020 00:53:29 +0100
From:   Petr Machata <petrm@...lanox.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Ido Schimmel <idosch@...sch.org>, netdev@...r.kernel.org,
        davem@...emloft.net, jiri@...lanox.com, jhs@...atatu.com,
        xiyou.wangcong@...il.com, mlxsw@...lanox.com,
        Ido Schimmel <idosch@...lanox.com>
Subject: Re: [PATCH net-next 2/6] net: sched: Add centralized RED flag checking


Jakub Kicinski <kuba@...nel.org> writes:

> On Tue, 10 Mar 2020 23:23:23 +0100 Petr Machata wrote:
>> Jakub Kicinski <kuba@...nel.org> writes:
>> 
>> > On Tue, 10 Mar 2020 10:48:24 +0100 Petr Machata wrote:  
>> >> > The only flags which are validated today are the gRED per-vq ones, which
>> >> > are a recent addition and were validated from day one.  
>> >>
>> >> Do you consider the validation as such to be a problem? Because that
>> >> would mean that the qdiscs that have not validated flags this way
>> >> basically cannot be extended ever ("a buggy userspace used to get a
>> >> quiet slicing of flags, and now they mean something").  
>> >
>> > I just remember leaving it as is when I was working on GRED, because
>> > of the potential breakage. The uAPI policy is what it is, then again
>> > we probably lose more by making the code of these ancient Qdiscs ugly
>> > than we win :(
>> >
>> > I don't feel like I can ack it with clear conscience tho.  
>> 
>> Just to make sure -- are you opposed to adding a new flag, or to
>> validation? 
>
> They are both uABI changes, so both.
>
>> At least the adaptative flag was added years after the
>> others in 2011. I wasn't paying much attention to kernel back then, but
>> I think the ABI rules are older than that.
>
> Yes, but some (e.g. TC subsystem) didn't really care much about those
> rules until more recently.
>
> The alternative to validation/adding flag in place is obviously to add 
> a new netlink attribute which would be validated from the start. Can you
> give it a try and see how ugly it gets?

Yeah, I'll give it a stab tomorrow.