netdev - Re: [PATCH net-next v2 1/7] net: devlink: Add unused port flavour

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Date:   Mon, 28 Sep 2020 22:05:08 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     Andrew Lunn <andrew@...n.ch>, David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH net-next v2 1/7] net: devlink: Add unused port flavour

On Mon, Sep 28, 2020 at 02:31:55PM -0700, Jakub Kicinski wrote:
> On Sat, 26 Sep 2020 23:06:26 +0200 Andrew Lunn wrote:
> > Not all ports of a switch need to be used, particularly in embedded
> > systems. Add a port flavour for ports which physically exist in the
> > switch, but are not connected to the front panel etc, and so are
> > unused.
>
> This is missing the explanation of why reporting such ports makes sense.

Because this is a core devlink patch, we're talking really generalistic
here. And since devlink regions are a debugging features, it makes sense
to tell a debugging story. Let's say there is a switch which had
configured all its ports to be part of the flooding replication lists,
but also configured other things incorrectly such that attempting to
flood a frame to a disabled port would leak a memory buffer. After
enough time, the system would lock up. So unused ports are not absent
from the system and they might even make a difference if the procedure
to disable a port is buggy (and there would be no debugging without
bugs, right?). I see no reason why we would hide them. Devlink ports are
not net devices, I thought that was the whole point, to have insight
into the hardware and not have to deal with an approximate abstraction.