linux-kernel - Re: [PATCH] net: core: Fix to store new mtu setting in netdevice.

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Message-ID: <7fe3a751-ffac-c46a-44f9-a1659e3c6947@gmail.com>
Date:   Wed, 2 Jan 2019 07:27:17 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Kirill Tkhai <ktkhai@...tuozzo.com>,
        Murali Krishna Policharla <murali.policharla@...adcom.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "amritha.nambiar@...el.com" <amritha.nambiar@...el.com>,
        "ecree@...arflare.com" <ecree@...arflare.com>,
        "alexander.h.duyck@...el.com" <alexander.h.duyck@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: core: Fix to store new mtu setting in netdevice.

On 02.01.2019 00:36, Andrew Lunn wrote:
>>> Is there a .ndo_change_mtu callback, which does not assign a new mtu itself?
>>>
>> So far all drivers have to do it themselves. But IMO this is more a workaround
>> for the core not doing it. It's something the core should do.
>> Now we can remove this from drivers.
> 
> Hi Heiner
> 
> I think somebody first needs to review all the ndo_change_mtu
> implementations and check that none do something funny like round to
> multiple of 2 or 4 to satisfy DMA restrictions, etc. If there is such
> a thing, we cannot easily move this into the core.
> 
>     Andrew
> .
> 
Good point. I briefly grepped over all drivers and it's not that many
drivers not using the standard assignment dev->mtu = new_mtu.
Some are doing things like dev->mtu = max(new_mtu, xx) what could be
achieved easier with an appropriate max_mtu setting. But that's a
different story.
And I was under the impression that such things had been checked
because the patch had a "Reviewed-by" from Florian (although he
wasn't on cc).

Heiner