[Libguestfs] [libvirt-users] couple of questions about virt-v2v

[Richard W.M. Jones]

On Wed, Aug 31, 2016 at 07:28:05PM +0100, cmc wrote:
> Hi Rich,
> 
> Thanks, I'll see if oVirt supports 7.3 yet.
> 
> 
> > What's the actual error?
> >
> 
> -------------8<------------
> 
> virt-v2v: error: libguestfs error: bridge 'virbr0' not found.  Try running:
> 
>   brctl show
> 
> to get a list of bridges on the host, and then selecting the
> bridge you wish the appliance network to connect to using:
> 
>   export LIBGUESTFS_BACKEND_SETTINGS=network_bridge=<bridge name>
> 
> You may also need to allow the bridge in /etc/qemu/bridge.conf.
> For further information see guestfs(3).
> 
> -------------8<------------
> 
> I got around this by just running 'brctl addbr virbr0', but was curious as
> to why it needed a bridge on a host it wasn't going to run on. I couldn't
> find the man page for guestfs(3)

The short answer is that you need to install the
``libvirt-daemon-driver-network'' package (RHEL), or the
``libvirt-daemon-config-network'' package (Fedora).
Or you can avoid using libvirt at all by setting:
export LIBGUESTFS_BACKEND=direct

The long answer is that we have to choose a bridge name in order to
get libvirt to give us a network, but there is no obvious choice of
bridge name so we pick "virbr0" (which happens to be the name of the
libvirt "default" network).  There's not really any good way to choose
the right bridge name, since it depends on your local network config
and the phase of the moon.  So it's a bug / shortcoming in libvirt.

The very long answer is:
https://bugzilla.redhat.com/show_bug.cgi?id=1148012

BTW randomly creating the bridge as you did might get you past the
error, but probably won't work if virt-v2v actually needs to use the
network. YMMV.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-p2v converts physical machines to virtual machines.  Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
http://libguestfs.org/virt-v2v