netdev - Re: Minimum MTU Mess

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Message-ID: <20160907234451.GZ33916@redhat.com>
Date:   Wed, 7 Sep 2016 19:44:51 -0400
From:   Jarod Wilson <jarod@...hat.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: Minimum MTU Mess

On Wed, Sep 07, 2016 at 01:35:35PM -0700, Stephen Hemminger wrote:
> On Wed, 7 Sep 2016 15:53:56 -0400
> Jarod Wilson <jarod@...hat.com> wrote:
> 
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -6466,9 +6466,17 @@ int dev_set_mtu(struct net_device *dev, int new_mtu)
> >  	if (new_mtu == dev->mtu)
> >  		return 0;
> >  
> > -	/*	MTU must be positive.	 */
> > -	if (new_mtu < 0)
> > +	if (new_mtu < dev->min_mtu) {
> > +		netdev_err(dev, "Invalid MTU %d requested, hw min %d\n",
> > +			   new_mtu, dev->min_mtu);
> >  		return -EINVAL;
> > +	}
> > +
> > +	if (new_mtu > dev->max_mtu) {
> > +		netdev_err(dev, "Invalid MTU %d requested, hw max %d\n",
> > +			   new_mtu, dev->min_mtu);
> > +		return -EINVAL;
> > +	}
> >  
> 
> Maybe don't log something that can be triggered from a user program.
> Or at least rate limit it.

Yeah, I was a little bit on the fence on whether to log anything, make it
netdev_err, netdev_dbg, or what. Quite a few drivers have a netdev_err for
failed MTU changes, while others also have netdev_info spew for successful
MTU changes. Maybe a rate-limited netdev_err is the way to go here.

-- 
Jarod Wilson
jarod@...hat.com