netdev - Re: [patch net-next v2 0/9] net: sched: introduce chain templates support with offloading to mlxsw

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Date:   Thu, 28 Jun 2018 18:08:22 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     David Ahern <dsahern@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jhs@...atatu.com,
        xiyou.wangcong@...il.com, jakub.kicinski@...ronome.com,
        simon.horman@...ronome.com, john.hurley@...ronome.com,
        mlxsw@...lanox.com, sridhar.samudrala@...el.com
Subject: Re: [patch net-next v2 0/9] net: sched: introduce chain templates
 support with offloading to mlxsw

Thu, Jun 28, 2018 at 05:50:08PM CEST, dsahern@...il.com wrote:
>On 6/28/18 9:37 AM, Jiri Pirko wrote:
>>>>>
>>>>> Why this restriction? It's a template, so why can't it be removed
>>>>> regardless of whether there are filters?
>>>>
>>>> That means you could start to insert filters that does not match the
>>>> original template. I wanted to avoid it. The chain is utilized in hw for
>>>> the original template, the filter insertion would have to be sanitized
>>>> in driver. With this restriction, drivers can depend on filters always
>>>> be fitting.
>>>>
>>>
>>> Then the hardware driver should have that restriction not the core tc code.
>> 
>> But why? The same restriction would be in all drivers. I believe it is
>> better to have in in tc in single place. Drivers can then depend on it.
>> Do you have a usecase where you need to remove template for non-empty
>> chain?
>> 
>
>If the hardware has the limitation then the driver should be rejecting a
>change.

The behaviour I defend is symmetrical with "template add". There is also
possible to add the template only if the chain is empty.