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

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Message-ID: <52796722-dfa5-1c1a-c691-9ec86bb7e3dc@nvidia.com>
Date:   Tue, 15 Feb 2022 12:15:46 +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 12:10, Vladimir Oltean wrote:
> On Tue, Feb 15, 2022 at 11:54:05AM +0200, 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.
> 
> Plus, we have call paths that would bypass the "prepare" stage and jump
> to commit, and for good reason. Do we want to change those as well, or
> what would be the benefit?

It's not really prepare (doesn't have any effect), it's a precommit check.
You can keep the would change name, just make sure both wrappers use the
same function so people will be changing just 1 function and won't forget
to update anything. Would be nice to add a comment about it.