netdev - Re: [RFC PATCH net] net: dsa: tear down devlink port regions when tearing down the devlink port on error

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Message-ID: <20210907084431.563ee411@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 7 Sep 2021 08:44:31 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Vladimir Oltean <vladimir.oltean@....com>,
        netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [RFC PATCH net] net: dsa: tear down devlink port regions when
 tearing down the devlink port on error

On Sun, 5 Sep 2021 14:07:35 +0300 Vladimir Oltean wrote:
> Again, fallback but not during devlink port register. The devlink port
> was registered just fine, but our plans changed midway. If you want to
> create a net device with an associated devlink port, first you need to
> create the devlink port and then the net device, then you need to link
> the two using devlink_port_type_eth_set, at least according to my
> understanding.
> 
> So the failure is during the creation of the **net device**, we now have a
> devlink port which was originally intended to be of the Ethernet type
> and have a physical flavour, but it will not be backed by any net device,
> because the creation of that just failed. So the question is simply what
> to do with that devlink port.

Is the failure you're referring to discovered inside the
register_netdevice() call?

> The only thing I said about the devlink API in the commit description is
> that it would have been nice to just flip the type and flavour of a
> devlink port, post registration. That would avoid a lot of complications
> in DSA. But that is obviously not possible, and my patch does not even
> attempt to do it. What DSA does today, and will still do after the patch
> we are discussing on, is to unregister that initial devlink port, and
> create another one with the unused flavour, and register that one.
> 
> The reason why we even bother to re-register a devlink port a second
> time for a port that failed to create and initialize its net_device is
> basically for consistency with the ports that are statically disabled in
> the device tree. Since devlink is a mechanism through which we gain
> insight into the hardware, and disabled ports are still physically
> present, just, you know, disabled and not used, their devlink ports
> still exist and can be used for things like dumping port regions.
> We treat ports that fail to find their PHY during probing as
> 'dynamically disabled', and the expectation is for them to behave just
> the same as ports that were statically disabled through the device tree.
> 
> My change is entirely about how to properly structure the code such that
> we unregister the port regions that a devlink port might have, before
> unregistering the devlink port itself, and how to re-register those port
> regions then, after the new devlink port was registered.