linux-kernel - Re: [PATCH v2 net-next 02/12] tsnep: deny tc-taprio changes to per-tc max SDU

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Date:   Tue, 27 Sep 2022 00:50:49 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        Rui Sousa <rui.sousa@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        UNGLinuxDriver@...rochip.com,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Michael Walle <michael@...le.cc>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Maxim Kochetkov <fido_max@...ox.ru>,
        Colin Foster <colin.foster@...advantage.com>,
        Richie Pearn <richard.pearn@....com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Gerhard Engleder <gerhard@...leder-embedded.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net-next 02/12] tsnep: deny tc-taprio changes to
 per-tc max SDU

On Mon, Sep 26, 2022 at 01:40:25PM -0700, Jakub Kicinski wrote:
> On Fri, 23 Sep 2022 19:33:00 +0300 Vladimir Oltean wrote:
> > Since the driver does not act upon the max_sdu argument, deny any other
> > values except the default all-zeroes, which means that all traffic
> > classes should use the same MTU as the port itself.
> 
> Don't all the driver patches make you wanna turn this into an opt-in?

Presumably you're thinking of a way through which the caller of
ndo_setup_tc(TC_SETUP_QDISC_TAPRIO, struct tc_taprio_qopt_offload *)
knows whether the driver took the new max_sdu field into consideration,
and not just accepted it blindly?

I'm not exactly up to date with all the techniques which can achieve
that without changes in drivers, and I haven't noticed other qdisc
offloads doing it either... but this would be a great trick to learn for
sure. Do you have any idea?

> What are the chances we'll catch all drivers missing the validation 
> in review?

Not that slim I think, they are all identifiable if you search for
TC_SETUP_QDISC_TAPRIO.