The process_[create|update]_<resource>() extension driver methods are
intended to validate user input. Exceptions raised by these need to be
returned to users so they know what they did wrong. These exceptions
should not be logged as anything higher than info level, since user
errors generally are not of concern to admins. Also, given that these
methods are called within the create or update transaction, raising an
exception will cause the entire transaction to be rolled back. Once an
exceptions occurs in an extension driver, there is no point in
continuing to call the other extension drivers since only one exception
will be returned to the user at a time.
-Bob
On 8/4/15 2:26 PM, Abhishek Raut wrote:
There is this review[1] trying to solve exactly what you¹re asking for.
I think it makes sense for the exceptions to be propagated all the way
back to the user instead of swallowing them and then roll back the
transaction. Does it even make sense to continue after a failure?
[1] https://review.openstack.org/#/c/202061/
‹Abhishek Raut
On 8/4/15, 3:02 AM, "Ihar Hrachyshka" <ihrac...@redhat.com> wrote:
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Hi all,
in feature/qos, we use ml2 extension drivers to handle additional
qos_policy_id field that can be provided thru API:
http://git.openstack.org/cgit/openstack/neutron/tree/neutron/plugins/ml2
/extensions/qos.py?h=feature/qos
What we do in qos extension is we create a database 'binding' object
between the updated port and the QoS policy that corresponds to
qos_policy_id. So we access the database. It means there may be some
complications there, f.e. the policy object is not available for the
tenant, or just does not exist. In that case, we raise an exception
>from the extension, assuming that ml2 will propagate it to the user in
some form.
But it does not work. This is because _call_on_ext_drivers swallows
exceptions:
http://git.openstack.org/cgit/openstack/neutron/tree/neutron/plugins/ml2
/managers.py#n766
It makes me ask some questions:
- - first, do we use extensions as was expected? Can we extend
extensions to cover our use case?
- - second, what would be the right way to go assuming we want to
support the case? Should we just reraise? Or maybe postpone till all
extension drivers are called, and then propagate an exception top into
the stack? (Probably some extension manager specific exception?) Or
maybe we want extensions to claim whether they may raise, and handle
them accordingly?
- - alternatively, if we abuse the API and should stop doing it, which
other options do we have to achieve similar behaviour without relying
on ml2 extensions AND without polluting ml2 driver with qos specific cod
e?
Thanks for your answers,
Ihar
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