netdev - Re: question on random MAC in usbnet

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Message-ID: <d089926c25a2c5e4593dbe6db9250843badc9771.camel@redhat.com>
Date: Mon, 20 Nov 2023 10:48:22 -0600
From: Dan Williams <dcbw@...hat.com>
To: David Laight <David.Laight@...LAB.COM>, 'Bjørn
 Mork' <bjorn@...k.no>, Oliver Neukum <oneukum@...e.com>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, USB list
	 <linux-usb@...r.kernel.org>
Subject: Re: question on random MAC in usbnet

On Sun, 2023-11-19 at 11:09 +0000, David Laight wrote:
> From: Bjørn Mork
> > Sent: 16 November 2023 11:32
> ...
> > > Do you think that behavior should be changed to using
> > > a separate random MAC for each device that requires it?
> > 
> > I'm in favour.
> > 
> > I could be wrong, but I don't expect anything to break if we did
> > that.
> > The current static address comes from eth_random_addr() in any
> > case, so
> > the end result as seen from the mini drivers should be identical. 
> > The
> > difference will be seen in userspace and surrounding equipment, And
> > those should be for the better.
> 
> It might cause grief when a USB device 'bounces' [1].
> At the moment it will pick up the same 'random' MAC address.
> But afterwards it will change.

Can that be achieved with userspace helpers too? They can match against
USB device details (or just use a static MAC for everything like the
driver does today) and set that on the device before anything else in
userspace starts using it.

Dan

> 
> So you might want to save the MAC on device removal and
> re-use it on the next insert.
> 
> [1] We ended up putting the USB interface inside a 'bond'
> in order to stop the interface everything was using
> randomly disappearing due to common-mode noise on the
> USB data lines causing a disconnect.
> 
>         David
> 
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