Nova VMwareapi Resize of Volume Backed server fails

[Fabian Wiesel]

Description
===========
More specifically the following tempest test in master fails:
tempest.api.compute.servers.test_server_actions.ServerActionsV293TestJSON.test_rebuild_volume_backed_server

Steps to reproduce
==================
* Install Devstack from master
* Run tempest test `tempest.api.compute.servers.test_server_actions.ServerActionsV293TestJSON.test_rebuild_volume_backed_server`

Expected result
===============
The test succeeds.

Actual result
=============
What happened instead of the expected result?
How did the issue look like?

Environment
===========
1. Git 1858cf18b940b3636e54eb5aafaf4050bdd02939 (master). So essentially this:
 https://review.opendev.org/c/openstack/nova/+/909474
As instance creation is impossible without that patch.

2. Which hypervisor did you use? What's the version of that?

vmwareapi (VSphere 7.0.3 & ESXi 7.0.3)

2. Which storage type did you use?

vmdk on NFS 4.1

3. Which networking type did you use?

networking-nsx-t (https://github.com/sapcc/networking-nsx-t)

Logs & Configs
==============

Can be found here: http://openstack-ci-logs.global.cloud.sap/openstack/nova/1858cf18b940b3636e54eb5aafaf4050bdd02939/index.html

The critical exception for this bug report is (abbreviated and reformatted for clarity):
----
 req-7aa5ded6-ea97-4010-93c8-9e39389cbfe0 tempest-ServerActionsTestOtherA-839537081
[ 865.017199] env[58735]: ERROR nova.compute.manager [instance: b4d9131c-fc91-4fd4-813b-13b4bdfe1647]
Traceback (most recent call last):
  File "/opt/stack/nova/nova/compute/manager.py", line 10856, in _error_out_instance_on_exception
    yield
  File "/opt/stack/nova/nova/compute/manager.py", line 6096, in _resize_instance
    disk_info = self.driver.migrate_disk_and_power_off(
  File "/opt/stack/nova/nova/virt/vmwareapi/driver.py", line 263, in migrate_disk_and_power_off
    return self._vmops.migrate_disk_and_power_off(context, instance,
  File "/opt/stack/nova/nova/virt/vmwareapi/vmops.py", line 1467, in migrate_disk_and_power_off
    self._resize_disk(instance, vm_ref, vmdk, flavor)
  File "/opt/stack/nova/nova/virt/vmwareapi/vmops.py", line 1398, in _resize_disk
    self._volumeops.detach_disk_from_vm(vm_ref, instance, vmdk.device)
  File "/opt/stack/nova/nova/virt/vmwareapi/volumeops.py", line 121, in detach_disk_from_vm
    disk_key = device.key
AttributeError: 'NoneType' object has no attribute 'key'

---

The bug is actually in the function `nova.virt.vmwareapi.vm_util.get_vmdk_info` here:
https://opendev.org/openstack/nova/src/branch/master/nova/virt/vmwareapi/vm_util.py#L690

The code works with the assumption, that the root-disk is named as the instance.
This assumption breaks in several cases, but most for this test-case, the root volume is actually a cinder volume.
It will also break when the the disk gets migrated to another datastore, either through a live-migration with no shared storage, or simply automatically with SDRS..

I have an alternative implementation here: https://github.com/sapcc/nova/blob/stable/xena-m3/nova/virt/vmwareapi/vm_util.py#L997-L1034
I'll provide a bug fix from it.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/nova/+/910627