linux-kernel - Re: [PATCH v2 net-next 03/11] net: bridge: don't print in br_switchdev_set_port

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Date:   Tue, 9 Feb 2021 20:26:17 +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 03/11] net: bridge: don't print in
 br_switchdev_set_port_flag

On Tue, Feb 09, 2021 at 07:36:31PM +0200, Vladimir Oltean wrote:
> On Tue, Feb 09, 2021 at 05:19:28PM +0200, Vladimir Oltean wrote:
> > From: Vladimir Oltean <vladimir.oltean@....com>
> >
> > Currently br_switchdev_set_port_flag has two options for error handling
> > and neither is good:
> > - The driver returns -EOPNOTSUPP in PRE_BRIDGE_FLAGS if it doesn't
> >   support offloading that flag, and this gets silently ignored and
> >   converted to an errno of 0. Nobody does this.
> > - The driver returns some other error code, like -EINVAL, in
> >   PRE_BRIDGE_FLAGS, and br_switchdev_set_port_flag shouts loudly.
> >
> > The problem is that we'd like to offload some port flags during bridge
> > join and leave, but also not have the bridge shout at us if those fail.
> > But on the other hand we'd like the user to know that we can't offload
> > something when they set that through netlink. And since we can't have
> > the driver return -EOPNOTSUPP or -EINVAL depending on whether it's
> > called by the user or internally by the bridge, let's just add an extack
> > argument to br_switchdev_set_port_flag and propagate it to its callers.
> > Then, when we need offloading to really fail silently, this can simply
> > be passed a NULL argument.
> >
> > Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> > ---
> 
> The build fails because since I started working on v2 and until I sent
> it, Jakub merged net into net-next which contained this fix:
> https://patchwork.kernel.org/project/netdevbpf/patch/20210207194733.1811529-1-olteanv@gmail.com/
> for which I couldn't change prototype due to it missing in net-next.
> I think I would like to rather wait to gather some feedback first before
> respinning v3, if possible.

It seems that in the sysfs call path br_switchdev_set_port_flag() will
be called with the bridge lock held, which is going to be a problem
given that patch #8 allows this function to block.