linux-kernel - Re: [PATCH v6] r8152: Add support for setting pass through MAC address on RTL8153-AD

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Message-Id: <201606141847.36109@pali>
Date:	Tue, 14 Jun 2016 18:47:36 +0200
From:	Pali Rohár <pali.rohar@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	David Miller <davem@...emloft.net>, andrew@...n.ch,
	mario_limonciello@...l.com, hayeswang@...ltek.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org, anthony.wong@...onical.com
Subject: Re: [PATCH v6] r8152: Add support for setting pass through MAC address on RTL8153-AD

On Tuesday 14 June 2016 18:40:17 Greg KH wrote:
> On Tue, Jun 14, 2016 at 06:28:10PM +0200, Pali Rohár wrote:
> > On Saturday 11 June 2016 19:42:26 David Miller wrote:
> > > From: Andrew Lunn <andrew@...n.ch>
> > > Date: Sat, 11 Jun 2016 17:39:21 +0200
> > > 
> > > > What is still open is do we want to accept it at all? Do we
> > > > accept the concept of putting the same MAC address on multiple
> > > > interfaces at hotplug time? Do we trust BIOS vendors to not
> > > > keep changing DSDT property name, since it is not
> > > > standardised?
> > > > 
> > > > Do we want this at all should be decided by somebody more
> > > > senior then those passing comments on the code.
> > > 
> > > Indeed, I think the behavior of using the same MAC address on
> > > multiple interfaces if we plug several of these in at once is not
> > > good.
> > > 
> > > We shouldn't behave this way just because the Microsoft driver
> > > does.
> > 
> > I agree, but in some cases it is night mare for local admins when
> > booting different OS cause changing MAC address on local network.
> > 
> > Another similar situation: Imagine that you have two USB network
> > cards and both have "burned" into their registers same MAC
> > address. If you connect both those USB network cards, linux kernel
> > bind appropriate driver which read MAC address for both those
> > cards. But those addresses are same. What will linux kernel do in
> > this case?
> 
> If you can find such a broken USB device, try it and see :)

What do you mean by broken USB device?

You have never seen two ethernet cards with same MAC addresses? Right I 
have not seen two USB, but there is non zero chance that could happen. 
Specially now when more and more people starts using USB network cards.

> (hint, might be hard to find, I've never seen such a device before.)
> 
> I don't see how that pertains to this issue, sorry, how does broken
> USB hardware compare to a working Dell device?

It is same, how to handle two network cards which tell us, that they 
have same MAC addresses.

-- 
Pali Rohár
pali.rohar@...il.com

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