Calico still uses vif type tap and it causes failures with libvirt 9.5.0

[Arun S A G]

Description
===========
Calico (out of tree) uses vif type tap. But libvirt doesn't like pre-existing tap devices https://github.com/libvirt/libvirt/commit/a2ae3d299cf from libvirt 9.5.0. This causes openstack clusters that run calico networking backend to fail during instance creation.

Steps to reproduce
==================
1. Configure calico
2. Run openstack with libvirt 9.5.0 (latest in centos 9 stream)
3. Boot a VM

Expected result
===============
The VM is able to boot without any problems

Actual result

Other information
=================

13:34:38 < sean-k-mooney> calico is apparently still using vif type tap https://github.com/projectcalico/calico/blob/cf7fa35475eba84f5afcd7f53ac7d07dcb403202/networking-calico/networking_calico/plugins/ml2/drivers/calico/test/lib.py#L66C31-L66C34

13:35:06 < sean-k-mooney> vif type tap is not supported by our os-vif code so its usign the legacy fallback
13:35:51 < sean-k-mooney> https://github.com/openstack/nova/blob/master/nova/virt/libvirt/vif.py#L595-L596
13:36:15 < sean-k-mooney> https://github.com/openstack/nova/blob/master/nova/virt/libvirt/vif.py#L420-L430
13:36:48 < sean-k-mooney> https://github.com/openstack/nova/blob/master/nova/virt/libvirt/designer.py#L44-L55

13:37:40 < sean-k-mooney> zer0c00l: with that said the tap was always ment to be created by libvirt so it sound like calico might have been doing things it shoudl not have been
13:38:03 < zer0c00l> sean-k-mooney: Thanks for looking into this. :(
13:38:36 < sean-k-mooney> we could proably correct this with a bug fix
13:38:52 < sean-k-mooney> jsut setting managed='no'
13:39:13 < sean-k-mooney> here https://github.com/openstack/nova/blob/master/nova/virt/libvirt/vif.py#L427
13:39:54 < sean-k-mooney> the problem is that the there is no way to test this really upstream
13:40:06 < sean-k-mooney> well beyond unit/fucntional tests
13:40:12 < sean-k-mooney> but we dont have any calico ci
13:40:37 < sean-k-mooney> calico should be the only backend using vif_type=tap
13:40:52 < sean-k-mooney> but im not sure if we woudl need a config option in the workarounds section for this or not

Potential patch
===============
diff --git a/nova/virt/libvirt/config.py b/nova/virt/libvirt/config.py
index 47e92e3..5af3ce4 100644
--- a/nova/virt/libvirt/config.py
+++ b/nova/virt/libvirt/config.py
@@ -1749,6 +1749,7 @@
         self.device_addr = None
         self.mtu = None
         self.alias = None
+ self.managed = 'no'

     def __eq__(self, other):
         if not isinstance(other, LibvirtConfigGuestInterface):
@@ -1851,7 +1852,7 @@
             dev.append(vlan_elem)

         if self.target_dev is not None:
- dev.append(etree.Element("target", dev=self.target_dev))
+ dev.append(etree.Element("target", dev=self.target_dev, managed=self.managed))

         if self.vporttype is not None:
             vport = etree.Element("virtualport", type=self.vporttype)