netdev - Re: [PATCH net-next v4 1/2] net sched actions: dump more than TCA_ACT_MAX

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Date:   Sat, 22 Apr 2017 07:30:46 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     David Miller <davem@...emloft.net>
Cc:     eric.dumazet@...il.com, jiri@...nulli.us, netdev@...r.kernel.org,
        xiyou.wangcong@...il.com
Subject: Re: [PATCH net-next v4 1/2] net sched actions: dump more than
 TCA_ACT_MAX_PRIO actions per batch

On 17-04-21 02:11 PM, Jamal Hadi Salim wrote:

> Please bear with me. I want to make sure to get this right.
>
> Lets say I updated the kernel today to reject transactions with
> bits it didnt understand. Lets call this "old kernel". A tc that
> understands/sets these bits and nothing else. Call it "old tc".
> 3 months later:
> I add one more bit setting to introduce a new feature in a new
> kernel version. Lets call this new "kernel". I update to
> understand new bits. Call it "new tc".
>
> The possibilities:
> a) old tc + old kernel combo. No problem
> b) new tc + new kernel combo. No problem.
> c) old tc + new kernel combo. No problem.
> d) new tc + old kernel. Rejection.
>
> For #d if i have a smart tc it would retry with a new combination
> which restores its behavior to old tc level. Of course this means
> apps would have to be rewritten going forward to understand these
> mechanics.
> Alternative is to request for capabilities first then doing a
> lowest common denominator request.
> But even that is a lot more code and crossing user/kernel twice.
>
> There is a simpler approach that would work going forward.
> How about letting the user choose their fate? Set something maybe
> in the netlink header to tell the kernel "if you dont understand
> something I am asking for - please ignore it and do what you can".
> This would maintain current behavior but would force the user to
> explicitly state so.
>


Tested patch that demonstrates this idea is attached.

cheers,
jamal


View attachment "patch-act-check-flags" of type "text/plain" (5986 bytes)