netdev - Re: [PATCH v2 net-next 1/8] net: bridge: vlan: notify switchdev only when something changed

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Date:   Tue, 15 Feb 2022 09:54:06 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Nikolay Aleksandrov <nikolay@...dia.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Roopa Prabhu <roopa@...dia.com>, Jiri Pirko <jiri@...dia.com>,
        Ido Schimmel <idosch@...dia.com>,
        Rafael Richter <rafael.richter@....de>,
        Daniel Klauer <daniel.klauer@....de>,
        Tobias Waldekranz <tobias@...dekranz.com>
Subject: Re: [PATCH v2 net-next 1/8] net: bridge: vlan: notify switchdev only
 when something changed

On Tue, Feb 15, 2022 at 10:54:26AM +0200, Nikolay Aleksandrov wrote:
> > +/* return true if anything will change as a result of __vlan_add_flags,
> > + * false otherwise
> > + */
> > +static bool __vlan_flags_would_change(struct net_bridge_vlan *v, u16 flags)
> > +{
> > +	struct net_bridge_vlan_group *vg;
> > +	u16 old_flags = v->flags;
> > +	bool pvid_changed;
> >  
> > -	return ret || !!(old_flags ^ v->flags);
> > +	if (br_vlan_is_master(v))
> > +		vg = br_vlan_group(v->br);
> > +	else
> > +		vg = nbp_vlan_group(v->port);
> > +
> > +	if (flags & BRIDGE_VLAN_INFO_PVID)
> > +		pvid_changed = (vg->pvid == v->vid);
> > +	else
> > +		pvid_changed = (vg->pvid != v->vid);
> > +
> > +	return pvid_changed || !!(old_flags ^ v->flags);
> >  }
> 
> These two have to depend on each other, otherwise it's error-prone and
> surely in the future someone will forget to update both.
> How about add a "commit" argument to __vlan_add_flags and possibly rename
> it to __vlan_update_flags, then add 2 small helpers like __vlan_update_flags_precommit
> with commit == false and __vlan_update_flags_commit with commit == true.
> Or some other naming, the point is to always use the same flow and checks
> when updating the flags to make sure people don't forget.

You want to squash __vlan_flags_would_change() and __vlan_add_flags()
into a single function? But "would_change" returns bool, and "add"
returns void.

> >  
> >  static int __vlan_vid_add(struct net_device *dev, struct net_bridge *br,
> > @@ -672,9 +685,13 @@ static int br_vlan_add_existing(struct net_bridge *br,
> >  {
> >  	int err;
> >  
> > -	err = br_switchdev_port_vlan_add(br->dev, vlan->vid, flags, extack);
> > -	if (err && err != -EOPNOTSUPP)
> > -		return err;
> > +	*changed = __vlan_flags_would_change(vlan, flags);
> > +	if (*changed) {
> > +		err = br_switchdev_port_vlan_add(br->dev, vlan->vid, flags,
> > +						 extack);
> > +		if (err && err != -EOPNOTSUPP)
> > +			return err;
> > +	}
> 
> You should revert *changed to false in the error path below,
> otherwise we will emit a notification without anything changed
> if the br_vlan_is_brentry(vlan)) { } block errors out.

Ok.