linux-kernel - Re: [PATCH net-next v2 1/6] net: dcb: add new pcp selector to app object

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Date:   Mon, 3 Oct 2022 09:33:41 +0000
From:   <Daniel.Machon@...rochip.com>
To:     <petrm@...dia.com>
CC:     <netdev@...r.kernel.org>, <davem@...emloft.net>,
        <maxime.chevallier@...tlin.com>, <thomas.petazzoni@...tlin.com>,
        <edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <Lars.Povlsen@...rochip.com>, <Steen.Hegelund@...rochip.com>,
        <UNGLinuxDriver@...rochip.com>, <joe@...ches.com>,
        <linux@...linux.org.uk>, <Horatiu.Vultur@...rochip.com>,
        <Julia.Lawall@...ia.fr>, <vladimir.oltean@....com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH net-next v2 1/6] net: dcb: add new pcp selector to app
 object

Den Mon, Oct 03, 2022 at 10:22:48AM +0200 skrev Petr Machata:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> <Daniel.Machon@...rochip.com> writes:
> 
> > Right, I see your point. But. First thought; this starts to look a little
> > hackish.
> 
> So it is. That's what poking backward compatible holes in an existing
> API gets you. Look at modern C++ syntax for an extreme example :)
> 
> But read Jakub's email. It looks like we don't actually need to worry
> about this.
> 
> > Looking through the 802.1Q-2018 std again, sel bits 0, 6 and 7 are
> > reserved (implicit for future standard implementation?). Do we know of
> > any cases, where a new standard version would introduce new values beyond
> > what was reserved in the first place for future use? I dont know myself.
> >
> > I am just trying to raise a question of whether using the std APP attr
> > with a new high (255) selector, really could be preferred over this new
> > non-std APP attr with new packed payload.
> 
> Yeah. We'll need to patch lldpad anyway. We can basically choose which
> way we patch it. And BTW, using the too-short attribute payload of
> course breaks it _as well_, because they don't do any payload size
> validation.

Right, unless we reconstruct std app entry payload from the "too-short"
attribute payload, before adding it the the app list or passing it to the 
driver.

Anyway. Considering Jakub's mail. I think this patch version with a non-std
attribute to do non-std app table contributions separates non-std from std
stuff nicely and is preffered over just adding the new selector. So if we can 
agree on this, I will prepare a new v. with the other changes suggested.

Wrt. lldpad we can then patch it to react on attrs or selectors > 7.