Comment 4 for bug 1620407

On Thu, Jan 12, 2017 at 01:25:28PM -0000, ChristianEhrhardt wrote:
> On libvirt 1.3 I got:
> error: Failed to start domain testguest-X-on-X
> error: Unable to get index for interface mf_testet: No such device

on xenial, that is the exact error message we get, while on "precise"
kvm hosts (libvirt 0.9.8) the same setup works.

> As well as (other distro but same applies) https://fedoraproject.org/wiki/How_to_debug_Virtualization_problems?rd=Tools/Virtualization/BugReporting#Errors_using_.3Cinterface_type.3D.27ethernet.27.2F.3E
Yes, "ethernet" type networking is made difficult by standard security
settings, and we do have our own infrastructure installed to overcome
these restrictions. One such measure is having a daemon running as root
that does the actual interface creation, triggered by the interface
setup script.

This error message "Unable to get index..." is generated by libvirt,
before qemu is even invoked. While it is perfectly ok for interfaces
with setup scripts to not yet exist before qemu can invoke the script,
libvirt 1.3 nonetheless pre-checks for its existence.

This is what the bug report and the patch is about. With the patch
applied (removal of existence check for scripted interfaces), libvirt
1.3 again does the right thing.

Regards
Matthias