netdev - Re: [PATCH iproute2 v3 2/2] tc: pedit: add decrement operation

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Date:   Thu, 24 Jun 2021 16:24:17 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     David Ahern <dsahern@...il.com>,
        Asbjørn Sloth Tønnesen <asbjorn@...jorn.st>,
        netdev@...r.kernel.org, Cong Wang <xiyou.wangcong@...il.com>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH iproute2 v3 2/2] tc: pedit: add decrement operation

Hi Asbjørn,


On 2021-06-22 11:39 a.m., David Ahern wrote:
> [ looks fine to me; adding tc folks to make sure they see it ]
> 
> On 6/18/21 10:06 AM, Asbjørn Sloth Tønnesen wrote:
>> Implement a decrement operation for ttl and hoplimit.
>>
>> Since this is just syntactic sugar, it goes that:
>>
>>    tc filter add ... action pedit ex munge ip ttl dec ...
>>    tc filter add ... action pedit ex munge ip6 hoplimit dec ...
>>
>> is just a more readable version of this:
>>
>>    tc filter add ... action pedit ex munge ip ttl add 0xff ...
>>    tc filter add ... action pedit ex munge ip6 hoplimit add 0xff ...
>>

So you "add" essentially one's complement of the value you are trying to
decrement with?

>> This feature was suggested by some pseudo tc examples in Mellanox's
>> documentation[1], but wasn't present in neither their mlnx-iproute2
>> nor iproute2.
>>
>> Tested with skip_sw on Mellanox ConnectX-6 Dx.
>>
>> [1] https://docs.mellanox.com/pages/viewpage.action?pageId=47033989


I didnt see an example which showed using "dec" but what you described
above makes sense. And the changes below look sane. So:

Acked-by: Jamal Hadi Salim <jhs@...atatu.com>

cheers,
jamal