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

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Message-ID: <25bc3bf2-0dea-5667-8aae-c57a2a693bec@cumulusnetworks.com>
Date:   Thu, 26 Mar 2020 14:19:25 +0200
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Ido Schimmel <idosch@...sch.org>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        murali.policharla@...adcom.com,
        Stephen Hemminger <stephen@...workplumber.org>,
        Jiri Pirko <jiri@...nulli.us>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net-next 10/10] net: bridge: implement
 auto-normalization of MTU for hardware datapath

On 26/03/2020 14:18, Vladimir Oltean wrote:
> On Thu, 26 Mar 2020 at 14:06, Nikolay Aleksandrov
> <nikolay@...ulusnetworks.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@...sch.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.