[Cake] [lede-project/source] Add support for cake qdisc (#72)

[moeller0]

Hi Jonathan,

> On Jun 1, 2016, at 15:51 , Jonathan Morton <chromatix99 at gmail.com> wrote:
> 
> 
>> On 1 Jun, 2016, at 15:25, Benjamin Cronce <bcronce at gmail.com> wrote:
>> 
>> 1) Ideally, regardless of platform, should an AQM or scheduler have the responsibility of changing anything other than ECN?
> 
> This was in part my original objection to having the squash/wash feature in Cake.
> 
> The other part is that if we are going to rewrite the rest of the TOS byte (not just the ECN bits), then we should do it properly, which requires a rather substantial extension to the configuration API, even if we only try to cover the most obvious use-cases.

	To play devils advocate here, re-mapping to zero might be a special case, but probably the single most important special case, so lack of generality is not the strongest argument against it (as long as the goal is “good enough”). But I already conceded, it is contentious so needs to go, cake is your “baby” so you have the honor to make such calls…

> 
> This would then be a “semi proprietary” DSCP configurator, acting independently of Cake’s core AQM and shaping functions, which would have to be duplicated in other AQMs which had similar aims to Cake.  That’s not a good thing, and feeds back into the first point.

	Not necessarily, one could also argue that the first implementation is free to just “do it” and only after it proofed itself useful one needs to think about generalizing it.

> 
> Hence the correct solution is to put DSCP rewriting elsewhere, making it reusable.
> 
> In Linux, doing ingress DSCP rewriting before it hits the ingress qdisc presently requires the rewriter itself to be a qdisc, but this can have Cake as a child qdisc.  For the simple “clearing” case iptables can be used instead, as long as Cake is configured to ignore the inbound DSCP using the “besteffort” flag.

	I seem to recall that iptables/nftables folks want to be able to “connect” to the ingress ssytem, so maybe that solves the whole issue (short of making the common thing (re-map to zero) simple)

All that said, the decision is made and cake is on its path to upstream somehow, whoooot.

Best Regards
        Sebastian

> 
> - Jonathan Morton
>