Allocation candidates do not interpret provider trees in Devstack

[Dominik Danelski]

Steps to reproduce
==================
* I installed clean Devstack with 3 fake-virt resource providers.
* I confirmed that it is possible to allocate a single CPU by command $ openstack allocation candidate list --os-placement-api-version=1.17 --resource VCPU=1
* I created one child resource provider (under a fake-virt one listed above)
* I set the new resource provider to provide 'VGPU'
* I confirmed that it is possible to allocate a single GPU by command $ openstack allocation candidate list --os-placement-api-version=1.17 --resource VGPU=1
* I checked whether it's possible to allocate both CPU and GPU by command $ openstack allocation candidate list --os-placement-api-version=1.17 --resource VCPU=1 --resource VGPU=1 and the returned list was empty

Expected result
===============
One allocation candidate should be presented to me.

Actual result
=============
No allocation candidates were returned.

Environment
===========
I performed the test for Devstack Ussuri as well as the master branch downloaded on 29.06.2023.
Master: Ubuntu 22.04.2, commit 27568ea33460b9ea4635a7d0a0bb06d32654150b
Ussuri: Ubuntu 18.04.6, commit b11a403c37f9873cdaaa6afc31619ab72b0fd8c2

Logs & Configs
==============
Full list of commands and their results (for Ussuri):
eouser@test-resource-providers:~$ openstack allocation candidate list --os-placement-api-version=1.17 --resource VCPU=1
+---+------------+--------------------------------------+-------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| # | allocation | resource provider | inventory used/capacity | traits |
+---+------------+--------------------------------------+-------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 1 | VCPU=1 | 0f2df6c9-802c-4752-80f8-cdff31676eeb | VCPU=0/16000 | COMPUTE_VOLUME_EXTEND,COMPUTE_DEVICE_TAGGING,COMPUTE_ACCELERATORS,COMPUTE_NET_ATTACH_INTERFACE_WITH_TAG,COMPUTE_NODE,COMPUTE_IMAGE_TYPE_RAW,COMPUTE_VOLUME_ATTACH_WITH_TAG,COMPUTE_NET_ATTACH_INTERFACE,COMPUTE_VOLUME_MULTI_ATTACH,COMPUTE_TRUSTED_CERTS |
| 2 | VCPU=1 | 9475b42a-a7ad-4849-8c6f-133e3ead12c6 | VCPU=0/16000 | COMPUTE_VOLUME_EXTEND,COMPUTE_DEVICE_TAGGING,COMPUTE_ACCELERATORS,COMPUTE_NET_ATTACH_INTERFACE_WITH_TAG,COMPUTE_NODE,COMPUTE_IMAGE_TYPE_RAW,COMPUTE_VOLUME_ATTACH_WITH_TAG,COMPUTE_NET_ATTACH_INTERFACE,COMPUTE_VOLUME_MULTI_ATTACH,COMPUTE_TRUSTED_CERTS |
| 3 | VCPU=1 | 176f3fee-25e2-4201-8320-1433467dfde6 | VCPU=0/16000 | COMPUTE_VOLUME_EXTEND,COMPUTE_DEVICE_TAGGING,COMPUTE_ACCELERATORS,COMPUTE_NET_ATTACH_INTERFACE_WITH_TAG,COMPUTE_NODE,COMPUTE_IMAGE_TYPE_RAW,COMPUTE_VOLUME_ATTACH_WITH_TAG,COMPUTE_NET_ATTACH_INTERFACE,COMPUTE_VOLUME_MULTI_ATTACH,COMPUTE_TRUSTED_CERTS |
+---+------------+--------------------------------------+-------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

eouser@test-resource-providers:~$ openstack resource provider create --os-placement-api-version=1.17 --parent-provider 0f2df6c9-802c-4752-80f8-cdff31676eeb VGPUtest
+----------------------+--------------------------------------+
| Field | Value |
+----------------------+--------------------------------------+
| uuid | 3ec43c70-8342-41e7-b4e8-491ba4067829 |
| name | VGPUtest |
| generation | 0 |
| root_provider_uuid | 0f2df6c9-802c-4752-80f8-cdff31676eeb |
| parent_provider_uuid | 0f2df6c9-802c-4752-80f8-cdff31676eeb |
+----------------------+--------------------------------------+

eouser@test-resource-providers:~$ openstack resource provider list
+--------------------------------------+--------------------------+------------+
| uuid | name | generation |
+--------------------------------------+--------------------------+------------+
| 176f3fee-25e2-4201-8320-1433467dfde6 | test-resource-providers1 | 2 |
| 0f2df6c9-802c-4752-80f8-cdff31676eeb | test-resource-providers2 | 2 |
| 9475b42a-a7ad-4849-8c6f-133e3ead12c6 | test-resource-providers3 | 2 |
| 3ec43c70-8342-41e7-b4e8-491ba4067829 | VGPUtest | 0 |
+--------------------------------------+--------------------------+------------+

eouser@test-resource-providers:~$ openstack resource provider inventory set --os-placement-api-version=1.17 --resource VGPU=1 3ec43c70-8342-41e7-b4e8-491ba4067829
+----------------+------------------+----------+------------+----------+-----------+-------+
| resource_class | allocation_ratio | min_unit | max_unit | reserved | step_size | total |
+----------------+------------------+----------+------------+----------+-----------+-------+
| VGPU | 1.0 | 1 | 2147483647 | 0 | 1 | 1 |
+----------------+------------------+----------+------------+----------+-----------+-------+

eouser@test-resource-providers:~$ openstack allocation candidate list --os-placement-api-version=1.17 --resource VGPU=1
+---+------------+--------------------------------------+-------------------------+--------+
| # | allocation | resource provider | inventory used/capacity | traits |
+---+------------+--------------------------------------+-------------------------+--------+
| 1 | VGPU=1 | 3ec43c70-8342-41e7-b4e8-491ba4067829 | VGPU=0/1 | |
+---+------------+--------------------------------------+-------------------------+--------+

eouser@test-resource-providers:~$ openstack allocation candidate list --os-placement-api-version=1.17 --resource VCPU=1 --resource VGPU=1

[Dominik Danelski (dominikdanelski)]

I found the possible cause of the bug.
Previously, I used Devstack Ussuri, but I noticed that the error doesn't manifest itself on Devstack Yoga. Then, I manually made calls to Placement's API on Devstack Yoga with different API versions specified in header. The query results for the same call were empty for version 1.25, but non-empty for 1.29, which is odd, since docs do not mention any changes for calls to /placement_candidates between these 2 versions.