libvirt-xen: namespaces of interfaces to long by creating instances

Hi there

My environment Ubuntu 17.04 with XEN 4.8 (xenproject) nova 7.1.0, libvirtd 2.5.0, openvswitch 2.6.1. And a almost similar install with Ubuntu 16.04. In short OpenStack Ocata.
I've found an issue by creating HVM guests. The issue by using libvirt, libxenlight and nova is that the namespace of the the name from an virtual interface, is to long by creating an HVM instance on XEN. They should be assigned to an linuxbridge by the porcess of creating. But brctl couldn't work with it because the name ist to long. At the end of the process the bridges would be assigned to an ovs-bridge. Which seems to be the default by using Neutron with OpenVSwitch for networking. The issue with the to long names is only present by creating HVM guests. At last with PVM guests it works well. Anyway the issue exists by setups with linuxbridges or openvswith by using networking with neutron.

Here an posted example configfile to reproduce it

http://paste.openstack.org/show/604857/

Here paste of an logfile where you can see the issue

http://paste.openstack.org/show/604858/

cat /var/log/xen/xen-hotplug.log
Error: argument "tap5b6d941e-50-emu" is wrong: "name" too long

So IMHO it seems that with XEN, libvirt and OpenStack only deployments with PVM guests are currently possibele.

best regards
Darko Hojnik