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Hi  Lajos.
Thank you.
I have a progress. I think my fake extension works.

I added 
```
extensions.register_custom_supported_check(
        "vpc_extension", lambda: True, plugin_agnostic=False
    )
```
to
```
class Vpc(api_extensions.ExtensionDescriptor):
    extensions.register_custom_supported_check(
        "vpc_extension", lambda: True, plugin_agnostic=False
    )
    ...
```

and I use ml2 extension driver without any new plugin. https://github.com/openstack/neutron/blob/master/neutron/tests/unit/plugins/ml2/drivers/ext_test.py#L44

I tested it with python neutronclientapi. So I can change my new attribute (neutron.update_network(id, {'network': {'new_attribute': some string }})) 
and I see my changes (neutron.list_networks(name='demo-net'))

I'm close to the end.
Now I'm using modifed `TestExtensionDriver(TestExtensionDriverBase):`. It works but It stores the data locally. 
And I want to use class TestDBExtensionDriver(TestExtensionDriverBase): (https://github.com/openstack/neutron/blob/master/neutron/tests/unit/plugins/ml2/drivers/ext_test.py#L169)

I tried to use it but I got such errors in neutron-server.log: "Table 'neutron.myextension.networkextensions' doesn't exist"
How can I create a new table?
I saw https://docs.openstack.org/neutron/latest/contributor/alembic_migrations.html and https://github.com/openstack/neutron-vpnaas/tree/master/neutron_vpnaas/db but I still don't understand.
I mean I think some of the neutron_vpnaas/db files are generated. Are neutron_vpnaas/db/migration/alembic_migrations/versions generated?
Which files I should create(their names, I think I can copy from neutron_vpnaas/db/) and what commands to type to create one new table: https://github.com/openstack/neutron/blob/master/neutron/tests/unit/plugins/ml2/drivers/ext_test.py#L136-L144 ?


> Hi Igor,The line which is interesting for you: "Extension vpc_extension not supported by any of loaded plugins"
> In core Neutron for ml2 there is a list of supported extension aliases:
> https://opendev.org/openstack/neutron/src/branch/master/neutron/plugins/ml2/plugin.py#L200-L239
> 
> And there is a similar for l3 also:
> https://opendev.org/openstack/neutron/src/branch/master/neutron/services/l3_router/l3_router_plugin.py#L98-L110
> 
> Or similarly for QoS:
> https://opendev.org/openstack/neutron/src/branch/master/neutron/services/qos/qos_plugin.py#L76-L90
> 
> So you need a plugin that uses the extension.
> 
> Good luck :-)
> Lajos Katona (lajoskatona)
> 
> Igor Zhukov <fsb4000 at yandex.ru> ezt írta (időpont: 2022. aug. 23., K, 16:04):
> 
>> Hi again!
>>
>> Do you know how to debug ML2 extension drivers?
>>
>> I created folder with two python files: vpc/extensions/vpc.py and vpc/plugins/ml2/drivers/vpc.py (also empty __init__.py files)
>>
>> I added to neuron.conf
>>
>> api_extensions_path = /path/to/vpc/extensions
>>
>> and I added to ml2_ini.conf
>>
>> extension_drivers = port_security, vpc.plugins.ml2.drivers.vpc:VpcExtensionDriver
>>
>> and my neutron.server.log has:
>>
>> INFO neutron.plugins.ml2.managers [-] Configured extension driver names: ['port_security', 'vpc_neutron.plugins.ml2.drivers.vpc:VpcExtensionDriver']
>>
>> WARNING stevedore.named [-] Could not load vpc_neutron.plugins.ml2.drivers.vpc:VpcExtensionDriver
>>
>> ....
>>
>> INFO neutron.api.extensions [req-fd226631-b0cd-4ff8-956b-9470e7f26ebe - - - - -] Extension vpc_extension not supported by any of loaded plugins
>>
>> How can I find why the extension driver could not be loaded?
>>
>>> Hi,The fake_extension is used only in unit tests to test the extension framework, i.e. :
>>
>>> https://opendev.org/openstack/neutron/src/branch/master/neutron/tests/unit/plugins/ml2/drivers/ext_test.py#L37
>>
>>>
>>
>>> If you would like to write an API extension check neutron-lib/api/definitions/ (and you can find the extensions "counterpart" under neutron/extensions in neutron repository)
>>
>>>
>>
>>> You can also check other Networking projects like networking-bgvpn, neutron-dynamic-routing to have examples of API extensions.
>>
>>> If you have an extension under neutron/extensions and there's somebody who uses it (see [1]) you will see it is loaded in neutron servers logs (something like this: "Loaded extension: address-group") and you can find it in the output of openstack extension list --network
>>
>>>
>>
>>> [1]: https://opendev.org/openstack/neutron/src/branch/master/neutron/plugins/ml2/plugin.py#L200
>>
>>>
>>
>>> Best wishes
>>
>>> Lajos Katona
>>
>>>
>>
>>> Igor Zhukov <fsb4000 at yandex.ru> ezt írta (időpont: 2022. aug. 22., H, 19:41):
>>
>>>
>>
>>>> Hi all!
>>
>>>>
>>
>>>> Sorry for a complete noob question but I can't figure it out 😿
>>
>>>>
>>
>>>> So if I want to add Fake ML2 extension what should I do?
>>
>>>>
>>
>>>> I have neutron server installed and I have the file: https://github.com/openstack/neutron/blob/master/neutron/tests/unit/plugins/ml2/extensions/fake_extension.py
>>
>>>>
>>
>>>> How to configure neutron server, where should I put the file, should I create another files? How can I test that it works?