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

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Message-ID: <CA+h21hp3LWA79WwAGhrL_SiaqZ=81=1P6HVO2a3WeLjcaTFgAg@mail.gmail.com>
Date:   Thu, 26 Mar 2020 14:25:28 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.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 Thu, 26 Mar 2020 at 14:19, Nikolay Aleksandrov
<nikolay@...ulusnetworks.com> wrote:
>
> 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.
>

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.