netdev - Re: [PATCH net-next RFC v1 1/4] net: devlink: Add support for port regions

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Message-ID: <20200921030213.GC3702050@lunn.ch>
Date:   Mon, 21 Sep 2020 05:02:13 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev <netdev@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jakub Kicinski <kuba@...nel.org>, Jiri Pirko <jiri@...dia.com>,
        Chris Healy <cphealy@...il.com>
Subject: Re: [PATCH net-next RFC v1 1/4] net: devlink: Add support for port
 regions

On Mon, Sep 21, 2020 at 12:23:18AM +0000, Vladimir Oltean wrote:
> On Mon, Sep 21, 2020 at 02:45:39AM +0300, Vladimir Oltean wrote:
> > This looks like a simple enough solution, but am I right that old
> > kernels, which ignore this new DEVLINK_ATTR_PORT_INDEX netlink
> > attribute, will consequently interpret any devlink command for a port as
> > being for a global region? Sure, in the end, that kernel will probably
> > fail anyway, due to the region name mismatch. And at the moment there
> > isn't any driver that registers a global and a port region with the same
> > name. But when that will happen, the user space tools of the future will
> > trigger incorrect behavior into the kernel of today, instead of it
> > reporting an unsupported operation as it should. Or am I
> > misunderstanding?
> 
> Thinking about this more, I believe that the only conditions that need
> to be avoided are:
> - mlx4 should never create a port region called "cr-space" or "fw-health"
> - ice should never create a port region called "nvm-flash" or
>   "device-caps"
> - netdevsim should never create a port region called "dummy"
> - mv88e6xxx should never create a port region called "global1",
>   "global2" or "atu"
> 
> Because these are the only region names supported by kernels that don't
> parse DEVLINK_ATTR_PORT_INDEX, I think we don't need to complicate the
> solution, and go with DEVLINK_ATTR_PORT_INDEX.

It would be easy to check when adding a per port region if a global
region of the same name already exists. Checking when adding a global
region to see if there is a port region with the same name is a bit
more work, but doable.

     Andrew