Re: [PATCH 2/3] NET: [SCHED] Qdisc changes and sch_rr added for multiqueue

[Patrick McHardy <kaber@trash.net>]

Waskiewicz Jr, Peter P wrote:
>> Nested netlink attributes, like most qdisc use, instead of 
>> struct tc_rr_qopt (or additionally). The way you've done it 
>> makes it hard to add further attributes later.
>>     
>
> I'm going to need to think about this more, since I'm not immediately
> getting what you're referring to.  I see the qdisc using tc_prio_qopt as
> a single member; do you have an example outside of the qdiscs I can look
> at and see what you're referring to?  Please bear with me: my netlink
> skills are still very green.
>   

Qdisc private parameters are within the TCA_OPTION attribute. The
data under that attribute can either be a structure (which you used)
or more netlink attributes specific to a single qdisc, which allows
to easily add new attributes.

For a simple qdisc example look at sch_red or grep for rta_parse_nested
and nla_parse_nested.

>   
>> BTw, couldn't you just merge sch_rr with prio? AFAICT you 
>> only need a new dequeue function, a new struct Qdisc_ops and 
>> a MODULE_ALIAS.
>>     
>
> Are you suggesting a module that can determine RR or PRIO at runtime?
> Because the two are so similar, I definitely thought about combining
> them, but because of the dequeue difference, you'd need a load-time
> switch to determine which mode to run the module in.  That would break
> ABI for sch_prio, which I was trying to avoid.

Yes, all you need to do is register two different struct Qdisc_ops and
provide an alias for autoloading.