Open Stack

Hey all,

Jordan wrote a patch which has led to a fairly lengthy review message
from me:

https://review.openstack.org/#/c/393884

It's beefy enough that it's worth raising for people who aren't
necessarily following review notes.

tl;dr ...

* API compat trumps efficiency for the old methods.

* list_ and search_ should get collapsed

* filtering needs to happen on normalized dicts

* push-down filtering needs to be able to only push down non-normalized
keys appropriate for the backend and reserve other filters for client-side