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Re: [libvirt] Libvirtd default.xml (in qemu/networks/autostart) breaks XEN

On Fri, Jul 18, 2008 at 01:13:30PM +0100, Daniel P. Berrange wrote:
> On Fri, Jul 18, 2008 at 12:33:22PM +0200, Stefan de Konink wrote:
> > The desire to automatically install the autostarted network configuration
> > of libvirt broke my (and some other users on xen-users) setup. I suggest
> > to *remove* this network configuration as default and *not* put it into
> > xenstore as a stateful config.
> > 
> > *It does not work by default*
> It works just fine by default. If anything is breaking networking it is
> XenD.

You don't mention which version of Xen you have, but make sure you have
this changeset in it..

changeset:   16625:44a98411d230
user:        Keir Fraser <keir fraser citrix com>
date:        Sat Dec 15 18:26:52 2007 +0000
files:       tools/python/xen/xend/XendNetwork.py
xend: Prevent XenD touching externally managed bridges

With current XenD 3.0.4 or later try the following:

    brctl addbr demo
    ifconfig demo up

    /etc/init.d/xend start
    /etc/init.d/xend stop

    ifconfig demo down
    brctl delbr demo

Now, start XenD again....

    /etc/init.d/xend start

And watch in horror as it re-creates your 'demo' bridge.

The problem is that the 'XendNetwork' class does not distinguish
between bridge devices that it is managing (ie those created via
XenAPI) and those which it does not manage (ie those created by OS
distro init scripts, or by apps like  libvirt).

While initially I thought I could just make XenD ignore
externally-managed bridges completely, it seems to needs to know about
them otherwise it can't hook up guest VIFs to them correctly. So the
attached patch adds a 'managed' flag to the XendNetwork
class. Externally managed bridges have this set to False. At startup
XenD will now only re-create bridge devices which have the 'managed'
flag set to 'True'  - ie those created via XenAPI.

Signed-off-by: Daniel P. Berrange <berrange redhat com>

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