Re: [PATCH v2 net-next 10/10] net: bridge: implement auto-normalization of MTU for hardware datapath

[Nikolay Aleksandrov <nikolay@cumulusnetworks.com>]

On 26/03/2020 14:25, Vladimir Oltean wrote:
> On Thu, 26 Mar 2020 at 14:19, Nikolay Aleksandrov
> <nikolay@cumulusnetworks.com> wrote:
>>
>> On 26/03/2020 14:18, Vladimir Oltean wrote:
>>> On Thu, 26 Mar 2020 at 14:06, Nikolay Aleksandrov
>>> <nikolay@cumulusnetworks.com> wrote:
>>>>
>>>> On 26/03/2020 13:35, Ido Schimmel wrote:
>>>>> On Thu, Mar 26, 2020 at 12:25:20PM +0200, Vladimir Oltean wrote:
>>>>>> Hi Ido,
>>>>>>
>>>>>> On Thu, 26 Mar 2020 at 12:17, Ido Schimmel <idosch@idosch.org> wrote:
>>>>>>>
>>> [snip]
>>>>>
>>>>> I think you should be more explicit about it. Did you consider listening
>>>>> to 'NETDEV_PRECHANGEMTU' notifications in relevant drivers and vetoing
>>>>> unsupported configurations with an appropriate extack message? If you
>>>>> can't veto (in order not to break user space), you can still emit an
>>>>> extack message.
>>>>>
>>>>
>>>> +1, this sounds more appropriate IMO
>>>>
>>>
>>> And what does vetoing gain me exactly? The practical inability to
>>> change the MTU of any interface that is already bridged and applies
>>> length check on RX?
>>>
>>
>> I was referring to moving the logic to NETDEV_PRECHANGEMTU, the rest is up to you.
>>
> 
> If I'm not going to veto, then I don't see a lot of sense in listening
> on this particular notifier either. I can do the normalization just
> fine on NETDEV_CHANGEMTU.
> 

I should've been more explicit - I meant I agree that this change doesn't belong in
the bridge, and handling it in a notifier in the driver seems like a better place.
Yes - if it's not going to be a vetto, then CHANGEMTU is fine.