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 13:10:06 +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 13:08, Nikolay Aleksandrov wrote:
> On 15/02/2022 12:30, Vladimir Oltean wrote:
>> On Tue, Feb 15, 2022 at 12:12:11PM +0200, Nikolay Aleksandrov wrote:
>>> 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.
>>
>> I still have a little doubt that I understood you properly.
>> Do you mean like this?
>>
> 
> By the way I just noticed that __vlan_flags_would_change has another bug, it's testing
> vlan's flags against themselves without any change (old_flags == v->flags).
> 
> I meant something similar to this (quickly hacked, untested, add flags probably
> could be renamed to something more appropriate):
> 
> diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
> index 1402d5ca242d..1de69090d3cb 100644
> --- a/net/bridge/br_vlan.c
> +++ b/net/bridge/br_vlan.c
[snip]
> +}
> +
> +static bool __vlan_flags_would_change(struct net_bridge_vlan *v, u16 flags)
> +{
> +       return __vlan_add_flags(v, flags, false);
> +}
> +
> +static bool __vlan_flags_commit(struct net_bridge_vlan *v, u16 flags)
> +{

blah, obviously should be void here and ignore the return value

> +       return __vlan_add_flags(v, flags, true);
>  }
>  
>  static int __vlan_vid_add(struct net_device *dev, struct net_bridge *br,