Libguestfs - Oct 2018 - virt-builder fail with "bridge ‘virbr0’ not found" (fixed by LIBGUESTFS_BACKEND=direct ?!)

I'm trying to build fedora-27 image for testing uploads:

$ virt-builder fedora-27 -o /var/tmp/fedora-27.img
...
[  25.2] Opening the new disk
virt-builder: 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 _SETTINGS=network_bridge=<bridge name>


I don't want to add bridges to my new fresh oVirt test host, and
remember that this used to work previously without the bridge.

So I tried the usual "fix" (I know it should not be used in
production):

$ export LIBGUESTFS_BACKEND=direct

And for some reason this works now:

$ virt-builder fedora-27 -o /var/tmp/fedora-27.img
...
[  41.2] Finishing off
                   Output file: /var/tmp/fedora-27.img
                   Output size: 6.0G
                 Output format: raw
            Total usable space: 5.3G
                    Free space: 4.4G (81%)

How LIBGUESTFS_BACKEND is related to the bridge? why do we need
the bridge for building an image?

Nir

On Tuesday, 9 October 2018 20:16:04 CEST Nir Soffer
wrote:
> I'm trying to build fedora-27 image for testing uploads:
> 
> $ virt-builder fedora-27 -o /var/tmp/fedora-27.img
> ...
> [  25.2] Opening the new disk
> virt-builder: 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 _SETTINGS=network_bridge=<bridge name>
The libvirt backend uses a network bridge on the host to setup the
networking in the guest, which is enabled by default in virt-builder.
> I don't want to add bridges to my new fresh oVirt test host, and
> remember that this used to work previously without the bridge.
"used to work" which version with? And which version are you using
now?

-- 
Pino Toscano

On Wed, Oct 10, 2018 at 10:18 AM Pino Toscano <ptoscano@redhat.com> wrote:
> On Tuesday, 9 October 2018 20:16:04 CEST Nir Soffer wrote:
> > I'm trying to build fedora-27 image for testing uploads:
> >
> > $ virt-builder fedora-27 -o /var/tmp/fedora-27.img
> > ...
> > [  25.2] Opening the new disk
> > virt-builder: 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 _SETTINGS=network_bridge=<bridge name>
>
> The libvirt backend uses a network bridge on the host to setup the
> networking in the guest, which is enabled by default in virt-builder.
>
OK, now it is clear why bypassing libvirt avoids this issue.

So maybe I'm missing some libvirt package required for creating the
bridge?

libvirt is installed by vdsm, which requires:
libvirt-client
libvirt-daemon-config-nwfilter
libvirt-daemon-kvm
libvirt-lock-sanlock
libvirt-python

>
> > I don't want to add bridges to my new fresh oVirt test host, and
> > remember that this used to work previously without the bridge.
>
> "used to work" which version with?

What was available in Fedora 28 2-3 month ago. The vm used for
running this was lost, so I don't have more specific info.

> And which version are you using now?
>
$ rpm -q libguestfs-tools-c
libguestfs-tools-c-1.38.4-1.fc28.x86_64

 Nir