netdev - Re: [RFC PATCH net-next 0/3] TC: Introduce qevents

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Date:   Mon, 1 Jun 2020 13:01:46 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Petr Machata <petrm@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...lanox.com>,
        Ido Schimmel <idosch@...lanox.com>
Subject: Re: [RFC PATCH net-next 0/3] TC: Introduce qevents

On Sat, May 30, 2020 at 1:55 AM Petr Machata <petrm@...lanox.com> wrote:
>
>
> Cong Wang <xiyou.wangcong@...il.com> writes:
>
> > On Thu, May 28, 2020 at 2:48 AM Petr Machata <petrm@...lanox.com> wrote:
> >> So you propose to have further division within the block? To have sort
> >> of namespaces within blocks or chains, where depending on the context,
> >> only filters in the corresponding namespace are executed?
> >
> > What I suggest is to let filters (or chain or block) decide where
> > they belong to, because I think that fit naturally.
>
> So filters would have this attribute that marks them for execution in
> the qevent context?

If you view it as position rather than qevent, sure, we already need to
specify the "context" for tc filter creations anyway, "dev... parent ..." is
is context to locate the filter placeholders. This is why it makes sense
to add one more piece, say "position", that is "dev... parent... position...".

It is you who calls it qevent which of course looks like only belong to
qdisc's.

>
> Ultimately the qdisc decides what qevents to expose. Qevents are closely
> tied to the inner workings of a qdisc algorithm, they can't be probed as
> modules the way qdiscs, filters and actions can. If a user wishes to
> make use of them, they will have to let qdiscs "dictate" where to put
> the filters one way or another.

For a specific event like early drop, sure. But if we think it generally,
"enqueue" has the same problem, there are a few qdisc's don't even
support filtering (noop). We can just return ENOSUPP anyway.