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

From: Andrew Morton <[email-masked]>
Date: Tue, 11 Dec 2007 14:59:21 -0800

On Tue, 11 Dec 2007 14:52:43 -0800
Stephen Hemminger <[email-masked]> wrote:

> On Tue, 11 Dec 2007 13:26:14 -0800
> Andrew Morton <[email-masked]> wrote:
> 
> > 
> > (please respond via emailed reply-to-all, not via the bugzilla web
> > interface).
> > 
> > On Tue, 11 Dec 2007 11:04:55 -0800 (PST)
> > [email-masked] 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: [email-masked]
> > >         ReportedBy: [email-masked]
> > > 
> > > 
> > > 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.
> 

If the fix to make bridge compatible with 2.6.23 behaviour isn't too
gruesome then I'd have thought it'd be worth doing it?