[allocation_pools] Need re-generation new pools from cidr and gateway-ip after update one subnet with empty 'allocation_pools'

[Liu Xie]

We found that allocation_pools is empty list after update subnet with empty 'allocation_pools':
 neutron subnet-show f84d8c24-251c-4a28-83a0-6c7f147c3da1
+-------------------+--------------------------------------+
| Field | Value |
+-------------------+--------------------------------------+
| allocation_pools | |
| cidr | 192.168.123.0/24 |

In my opinion, if we clear the allocation_pools of one subnet, it should re-generation new allocation_pools by the cidr and gateway-ip of the subnet.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/neutron/+/899373

[Miguel Lavalle (minsel)]

If the user wants to update allocation pools to empty and the API allows it, why should we change this behavior?

[Liu Xie (liushy)]

Hi Miguel, thanks for your reply. I know what you mean.
I'm a bit confused, why did the user create a subnet but not allow IP address allocation?

[Miguel Lavalle (minsel)]

As you can see in the unit test failures of your proposed patch (https://739b5b5aed9a6d447975-907323b417218f46df6192f35c6995f8.ssl.cf2.rackcdn.com/899373/1/check/openstack-tox-py39/5433f4e/testr_results.html), the possibility of having subnet empty allocation pools has long been assumed as valid behavior in the Neutron API. That expected behavior should not be changed just because in "your opinion", as indicated in your comment above, another behavior is desirable.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Slawek Kaplonski <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/neutron/+/899373
Reason: This review is > 4 weeks without comment and currently blocked by a core reviewer with a -2. We are abandoning this for now. Feel free to reactivate the review by pressing the restore button and contacting the reviewer with the -2 on this review to ensure you address their concerns.