netdev - Qdisc->u32_node - licence to kill

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Message-ID: <20170807164100.GK2085@nanopsycho.orion>
Date:   Mon, 7 Aug 2017 18:41:00 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     jhs@...atatu.com, xiyou.wangcong@...il.com, davem@...emloft.net
Cc:     netdev@...r.kernel.org, mlxsw@...lanox.com
Subject: Qdisc->u32_node - licence to kill

Hi Jamal/Cong/David/all.

Digging in the u32 code deeper now. I need to get rid of tp->q for shared
blocks, but I found out about this:

struct Qdisc {
	......
        void                    *u32_node;
	......
};

Yeah, ugly. u32 uses it to store some shared data, tp_c. It actually
stores a linked list of all hashtables added to one qdiscs.

So basically what you have is, you have 1 root ht per prio/pref. Then
you can have multiple hts, linked from any other ht, does not matter in
which prio/pref they are.

Do I understand that correctly that prio/pref only has meaning if
linking does not take place, because if there is linking, the prio/pref
of inserted rule is simply ignored?

That is the most confusing thing I saw in net/sched/ so far. 
Is this a bug? Sounds like one.

Did someone introduce *u32_node (formerly static struct tc_u_common
*u32_list;) just to allow this weirdness?

Can I just remove this shared tp_c and make the linking to other
hashtables only possible within the same prio/pref? That would make
sense to me.

Thanks.

Jiri