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 16:34:50 -0700
From:   Jakub Kicinski <kuba@...nel.org>
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>,
        <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

On Mon, 3 Oct 2022 21:59:49 +0000 Daniel.Machon@...rochip.com wrote:
> If lldpad was idd able to emit the new pcp app entries, they would be

idd?

> emitted as invalid TLV's (assuming 255 or 24 selector value), because the
> selector would be either zero or seven, which is currently not used for
> any selector by the std. We then have time to patch lldpad to do whatever
> with the new attr. Wouldn't this be acceptable?

I'm not sure I can provide sensible advice given I don't really know
how the information flow looks in case of DCB.

First off - we're talking about netlink TLVs not LLDP / DCB wire message
TLVs?

What I was saying is that if lldpad dumps the information from the
kernel and gets confused by certain TLVs - we can add an opt-in
attribute to whatever Netlink request lldpad uses, and only add the new
attrs if that opt-in attribute is present. Normal GET or DUMP requests
can both take input attributes.

Old lldpad will not send this attribute to the kernel - the kernel will
not respond with confusing attrs. The new lldpad can be patched to send
the attribute and will get all the attrs (if it actually cares).