netdev - Re: [PATCH] net: rmnet: Adjust virtual device MTU on real device capability

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Message-ID: <20201207121654.17fac0ef@kicinski-fedora-pc1c0hjn.DHCP.thefacebook.com>
Date:   Mon, 7 Dec 2020 12:16:54 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Loic Poulain <loic.poulain@...aro.org>
Cc:     subashab@...eaurora.org, stranche@...eaurora.org,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: rmnet: Adjust virtual device MTU on real device
 capability

On Mon, 7 Dec 2020 17:45:17 +0100 Loic Poulain wrote:
> > This would need similar checks in the NETDEV_PRECHANGEMTU
> > netdev notifier.  
> 
> What about just returning an error on NETDEV_PRECHANGEMTU notification
> to prevent real device MTU change while virtual rmnet devices are
> linked? Not sure there is a more proper and thread safe way to manager
> that otherwise.

Can't you copy what vlan devices do?  That'd seem like a reasonable and
well tested precedent, no?