netdev - Re: [PATCH v2 net-next 04/11] net: bridge: offload initial and final port flags through switchdev

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Date:   Wed, 10 Feb 2021 00:01:24 +0200
From:   Ido Schimmel <idosch@...sch.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bridge@...ts.linux-foundation.org, Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        UNGLinuxDriver@...rochip.com, Vadym Kochan <vkochan@...vell.com>,
        Taras Chornyi <tchornyi@...vell.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Ivan Vecera <ivecera@...hat.com>, linux-omap@...r.kernel.org
Subject: Re: [PATCH v2 net-next 04/11] net: bridge: offload initial and final
 port flags through switchdev

On Tue, Feb 09, 2021 at 10:20:45PM +0200, Vladimir Oltean wrote:
> On Tue, Feb 09, 2021 at 08:51:00PM +0200, Ido Schimmel wrote:
> > On Tue, Feb 09, 2021 at 05:19:29PM +0200, Vladimir Oltean wrote:
> > > So switchdev drivers operating in standalone mode should disable address
> > > learning. As a matter of practicality, we can reduce code duplication in
> > > drivers by having the bridge notify through switchdev of the initial and
> > > final brport flags. Then, drivers can simply start up hardcoded for no
> > > address learning (similar to how they already start up hardcoded for no
> > > forwarding), then they only need to listen for
> > > SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS and their job is basically done, no
> > > need for special cases when the port joins or leaves the bridge etc.
> > 
> > How are you handling the case where a port leaves a LAG that is linked
> > to a bridge? In this case the port becomes a standalone port, but will
> > not get this notification.
> 
> Apparently the answer to that question is "I delete the code that makes
> this use case work", how smart of me. Thanks.

Not sure how you expect to interpret this.

> 
> Unless you have any idea how I could move the logic into the bridge, I
> guess I'm stuck with DSA and all the other switchdev drivers having this
> forest of corner cases to deal with. At least I can add a comment so I'm
> not tempted to delete it next time.

There are too many moving pieces with stacked devices. It is not only
LAG/bridge. In L3 you have VRFs, SVIs, macvlans etc. It might be better
to gracefully / explicitly not handle a case rather than pretending to
handle it correctly with complex / buggy code.

For example, you should refuse to be enslaved to a LAG that already has
upper devices such as a bridge. You are probably not handling this
correctly / at all. This is easy. Just a call to
netdev_has_any_upper_dev().

The reverse, during unlinking, would be to refuse unlinking if the upper
has uppers of its own. netdev_upper_dev_unlink() needs to learn to
return an error and callers such as team/bond need to learn to handle
it, but it seems patchable.