netdev - Re: [net-next PATCH 3/4] net: sched: cls_u32 add bit to specify software only rules

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Date:	Thu, 25 Feb 2016 08:19:49 -0500
From:	Jamal Hadi Salim <jhs@...atatu.com>
To:	John Fastabend <john.fastabend@...il.com>,
	Jiri Benc <jbenc@...hat.com>
Cc:	Jiri Pirko <jiri@...nulli.us>, "Amir Vadai\"" <amir@...ai.me>,
	daniel@...earbox.net, netdev@...r.kernel.org,
	alexei.starovoitov@...il.com, davem@...emloft.net
Subject: Re: [net-next PATCH 3/4] net: sched: cls_u32 add bit to specify
 software only rules

On 16-02-24 11:09 PM, John Fastabend wrote:
> On 16-02-24 01:29 AM, Jiri Benc wrote:
>> On Wed, 24 Feb 2016 00:55:55 -0800, John Fastabend wrote:
>>> The flags however likely stays with with TCA_U32_FLAGS until there is
>>> some better way to group common attributes in 'tc' framework.
>>
>> That's pretty bad, as this is uAPI and will need to be supported
>> forever. And having a different attribute in every filter won't ease
>> things for user space tools. I'd say we need the "better way" to be
>> added before this patchset.
>>
>>   Jiri
>>
>
> The 'tc' semantics seem to support this "pretty bad" API design
> with many of the fields already duplicated.

Mostly this is a netlink-ism. Netlink has the same problem with
command name spaces. The problem is mixing verbs and nouns together.
I like the switchdev approach where you have very few verbs
(SET, GET etc) and the content of the object or path describes
the nouns. This is why initially i thought it was better to have
this offload passing by switchdev. Could we leverage some of that?

> I suppose we could
> put the flags at the same level as the TCA_* attributes but this
> also doesn't seem right to me as it isn't actually handled until
> we get into the TCA_#CLASSIFIER#_* set of attributes.
>

Could we not steal a couple of bits off netlink flags? Then it applies
to all subssystems.

cheers,
jamal