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

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Date:   Mon, 21 Sep 2020 10:09:13 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Andrew Lunn <andrew@...n.ch>
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 05:02:13AM +0200, Andrew Lunn wrote:
> 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.

See, I don't think that the check would be useful. By the time the new
kernel understands DEVLINK_ATTR_PORT_INDEX, the global and port regions
are already properly namespaced. So future drivers can have a port and
a global region of the same name. The problem is only with kernels that
don't understand DEVLINK_ATTR_PORT_INDEX. These only support global
regions. The concern is that future port regions for these specific 4
drivers might confuse them.

-Vladimir