netdev - Re: [Bugme-new] [Bug 9545] New: Cannot bring up a bridge interface without a MAC address set

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Date:	Tue, 11 Dec 2007 14:52:43 -0800
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	netdev@...r.kernel.org, bugme-daemon@...zilla.kernel.org,
	berrange@...hat.com, Jeff Garzik <jeff@...zik.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [Bugme-new] [Bug 9545] New: Cannot bring up a bridge interface
 without a MAC address set

On Tue, 11 Dec 2007 13:26:14 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:

> 
> (please respond via emailed reply-to-all, not via the bugzilla web
> interface).
> 
> On Tue, 11 Dec 2007 11:04:55 -0800 (PST)
> bugme-daemon@...zilla.kernel.org wrote:
> 
> > http://bugzilla.kernel.org/show_bug.cgi?id=9545
> > 
> >            Summary: Cannot bring up a bridge interface without a MAC address
> >                     set
> >            Product: Networking
> >            Version: 2.5
> >      KernelVersion: 2.6.24-0.81.rc4.git7.fc9
> >           Platform: All
> >         OS/Version: Linux
> >               Tree: Fedora
> >             Status: NEW
> >           Severity: normal
> >           Priority: P1
> >          Component: Other
> >         AssignedTo: acme@...stprotocols.net
> >         ReportedBy: berrange@...hat.com
> > 
> > 
> > Most recent kernel where this bug did not occur: Any 2.6.23 or earlier
> > Distribution: Fedora 9 rawhide
> > Hardware Environment: Intel(R) Core(TM)2 Duo CPU     E6850, x86_64
> > Software Environment:  2.6.24-0.81.rc4.git7.fc9 #1 SMP  x86_64 GNU/Linux
> > Problem Description:
> > It is not possible to bring up a bridge interface unless one first assigns a
> > MAC address to it. This is a regression from earlier kernels where one could
> > always bring up a bridge device immediately after creating it. The bridge
> > should not require a MAC address because it is not going to be configured with
> > any IP addr - in my scenario I merely wish to use it to connect a number of
> > 'tap' devices associated with KVM guests.
> > 
> > Steps to reproduce:
> > # brctl addbr demobr
> > # ifconfig demobr up
> > SIOCSIFFLAGS: Invalid argument

The tap devices have to have addresses don't they. So bringing up an empty
bridge is meaningless. If you just add the device first then it will work.

Could be fixed to prevent errors from existing scripts but it is not a complete showstopper.
The problem is that when device is brought up it propogates events up to
other layers and applications, these layers will then query and see a bogus
address.

-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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