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

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Message-ID: <a38ac2a6-d9b9-190a-f144-496be1768b98@nvidia.com>
Date:   Tue, 15 Feb 2022 12:12:11 +0200
From:   Nikolay Aleksandrov <nikolay@...dia.com>
To:     Vladimir Oltean <vladimir.oltean@....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 15/02/2022 11:54, Vladimir Oltean wrote:
> 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.
> 

Hence the wrappers for commit == false and commit == true. You could name the precommit
one __vlan_flags_would_change or something more appropriate. The point is to make
sure we always update both when flags are changed.

>>>  
>>>  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.