netdev - Re: [PATCH iproute2-next] tc: pie: change maximum integer value of tc_pie

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Date:   Mon, 9 Mar 2020 10:48:50 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Ahern <dsahern@...il.com>,
        Leslie Monis <lesliemonis@...il.com>,
        Linux NetDev <netdev@...r.kernel.org>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        "Mohit P . Tahiliani" <tahiliani@...k.edu.in>,
        Gautam Ramakrishnan <gautamramk@...il.com>
Subject: Re: [PATCH iproute2-next] tc: pie: change maximum integer value of
 tc_pie_xstats->prob



On 3/8/20 7:49 PM, David Ahern wrote:
> On 3/5/20 9:25 AM, Leslie Monis wrote:
>> Kernel commit 105e808c1da2 ("pie: remove pie_vars->accu_prob_overflows"),
>> changes the maximum value of tc_pie_xstats->prob from (2^64 - 1) to
>> (2^56 - 1).
>>
>> Signed-off-by: Mohit P. Tahiliani <tahiliani@...k.edu.in>
>> Signed-off-by: Gautam Ramakrishnan <gautamramk@...il.com>
>> Signed-off-by: Leslie Monis <lesliemonis@...il.com>
>> ---
>>  tc/q_pie.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
> 
> applied to iproute2-next. Thanks
> 
> 

This means that iproute2 is incompatible with old kernels.

commit 105e808c1da2 ("pie: remove pie_vars->accu_prob_overflows") was wrong,
it should not have changed user ABI.

The rule is : iproute2 v-X should work with linux-<whatever-version>

Since pie MAX_PROB was implicitly in the user ABI, it can not be changed,
at least from user point of view.