GET /servers/details is not always returning the correct number of servers

[Arnaud Morin]

Context
=======
Nova 2024.2 (but master seems affected)

For an unknown reason (yet), we had leftovers in our nova_api/build_requests table:

MariaDB [nova_api]> select instance_uuid from build_requests;
+--------------------------------------+
| instance_uuid |
+--------------------------------------+
| 261bce67-29ec-4e09-a172-f9fca1daa60e |
... (maybe some others)
+--------------------------------------+

The thing is that this instance does exists on the infra:
$ openstack server show 261bce67-29ec-4e09-a172-f9fca1daa60e -c Id
+--------+--------------------------------------+
| Field | Value |
+--------+--------------------------------------+
| id | 261bce67-29ec-4e09-a172-f9fca1daa60e |
| status | ACTIVE |
+--------+--------------------------------------+

Issue
=====

Because it's in both build_requests and one of the nova cell, it's then filtered by def _get_unique_filter_method [1] when requesting instances with a limit:

$ curl -H "X-Auth-Token: $T" "http://nova.57.129.93.86.xip.opensteak.fr/v2.1/servers/detail?limit=7" | jq ".servers[].id" | wc -l
6

AND the marker for next page is missing (servers_links).

The servers_links is missing because def _get_collection_links is not adding it if the number of object is lower than the limit [2] [3]

[1] https://github.com/openstack/nova/blob/a5bcaf69b1a80d4d02fe092900471a6e7a28e292/nova/compute/api.py#L3174-L3200
[2] https://github.com/openstack/nova/blob/a5bcaf69b1a80d4d02fe092900471a6e7a28e292/nova/api/openstack/compute/views/servers.py#L581
[3] https://github.com/openstack/nova/blob/a5bcaf69b1a80d4d02fe092900471a6e7a28e292/nova/api/openstack/common.py#L416

[Arnaud Morin (arnaud-morin)]

fix ongoing https://review.opendev.org/c/openstack/nova/+/947804

[sean mooney (sean-k-mooney)]

the missing marker is a bug, the fact you get less then limit back is not really a bug.
i have set this to low as a result but we can fix it however im not entirly sure that the current fix is correct.

ill need to review it a bit more carefully.