netdev - 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 10:22:48 +0200
From:   Petr Machata <petrm@...dia.com>
To:     <Daniel.Machon@...rochip.com>
CC:     <petrm@...dia.com>, <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


<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.