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Date:   Mon, 3 Oct 2022 16:34:50 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     <Daniel.Machon@microchip.com>
Cc:     <petrm@nvidia.com>, <netdev@vger.kernel.org>,
        <davem@davemloft.net>, <maxime.chevallier@bootlin.com>,
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        <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
Message-ID: <20221003163450.7e6cbf3a@kernel.org>
In-Reply-To: <YztdsF6b6SM9E5rw@DEN-LT-70577>
References: <20220929185207.2183473-1-daniel.machon@microchip.com>
        <20220929185207.2183473-2-daniel.machon@microchip.com>
        <87leq1uiyc.fsf@nvidia.com>
        <20220930175452.1937dadd@kernel.org>
        <87pmf9xrrd.fsf@nvidia.com>
        <20221003092522.6aaa6d55@kernel.org>
        <YztdsF6b6SM9E5rw@DEN-LT-70577>
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On Mon, 3 Oct 2022 21:59:49 +0000 Daniel.Machon@microchip.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).