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

From: <Daniel.Machon@microchip.com>
To: <petrm@nvidia.com>
Cc: <netdev@vger.kernel.org>, <davem@davemloft.net>,
	<maxime.chevallier@bootlin.com>, <thomas.petazzoni@bootlin.com>,
	<edumazet@google.com>, <kuba@kernel.org>, <pabeni@redhat.com>,
	<Lars.Povlsen@microchip.com>, <Steen.Hegelund@microchip.com>,
	<UNGLinuxDriver@microchip.com>, <joe@perches.com>,
	<linux@armlinux.org.uk>, <Horatiu.Vultur@microchip.com>,
	<Julia.Lawall@inria.fr>, <vladimir.oltean@nxp.com>,
	<linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH net-next v2 1/6] net: dcb: add new pcp selector to app object
Date: Mon, 3 Oct 2022 09:33:41 +0000	[thread overview]
Message-ID: <YzquziZD+T145jo0@DEN-LT-70577> (raw)
In-Reply-To: <87czb9xpsi.fsf@nvidia.com>

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@microchip.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.
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