Quota update should not allow negative headroom

[Eoghan Glynn]

Currently quotas can be reduced to below the current usage level for that resource type, giving negative headroom which seems to me non-sensical.

Was this intended as a deliberate way to "softly" reduce resource usage? i.e. to cause the in use count to slowly approach the new quotas as resources are released as part of their natural lifecycle, e.g. when instances are eventually delete'd, new instances cannot be spun up to replace them.

This however seems a very unreliable way of reducing reducing usage retrospectively, as the resources in question may be held onto indefinitely. A more reliable approach would be to force the release of the excess resource *before* the quota is reduced.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/5952

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/28232
Committed: http://github.com/openstack/nova/commit/77b4012a02c6b4827a7a6b112f35deb9ce94c395
Submitter: Jenkins
Branch: master

commit 77b4012a02c6b4827a7a6b112f35deb9ce94c395
Author: liyingjun <email address hidden>
Date: Mon Apr 29 16:39:22 2013 +0800

    Per-project-user-quotas for more granularity

    Implements blueprint per-user-quotas.

    Fixes bug 968175

    Based on the original quotas structure.

    NOTE:
    quota_instances, quota_cores, quota_ram, quota_key_pairs and
    quota_security_groups are supported per user.

    Add CRUD methods for project user quotas API. DocImpact
     - Shows quotas for a user.
       GET v2/{tenant_id}/os-quota-sets/{tenant_id}?user_id={user_id}
     - Updates quotas for a user.
       POST v2/{tenant_id}/os-quota-sets/{tenant_id}?user_id={user_id}

    Add commands for project user quotas management.
     - Show user quotas:
       nova-manage project quota --project <Project name> --user <User name>
     - Update/Create user quotas:
       nova-manage project quota --project <Project name> --user <User name>
       --key <key> --value <value>

    Change-Id: I24af1f6bc439d5d740303c6fe176a9bffe754579