OSAPI: support 'user' and 'core' extensions paths

[Dan Prince]

The osapi_extensions_path nova flag currently defaults to /var/lib/nova/extensions. This directory is most useful for custom 'user' extensions (stuff that doesn't live in the nova core source tree).

It would be nice to have an extensions directory within the nova tree which we could use for 'core' extensions. This would provide a good place to add extended OS API features that are not part of the official spec but exist within the nova source code base. The core extension mechanism should probably provide a way to make core extensions optional such that they can also be disabled.

[justinsb (justin-fathomdb)]

Hi Dan - not sure if you've started this, but if not, I can probably do it... I need to repackage volumes as an extension.

[justinsb (justin-fathomdb)]

Hi Dan ... I've actually had to go quite far on this to get volumes to work, such that merging would likely be painful. I'd like to grab this if I can. Otherwise, can you put up your branch when it's done so I can merge with it.

The work I'm doing is in my volumes-api branch ... should be pushing in 15 minutes or so (with luck!)

[justinsb (justin-fathomdb)]

Hi Dan... I think I've basically done this in my volumes branch now:

https://code.launchpad.net/~justin-fathomdb/nova/volumes-api/+merge/54464

If you disagree with my approach, let's talk about it, otherwise I think you can re-assign this one to me.

[Dan Prince (dan-prince)]

Hey Justin,

I'll add some comments in your volumes branch as well. I'd really rather this go in as its own feature branch. I can understand the need for this kind of thing with something like /volumes that we want to check into Nova itself but we can certainly do this first (get it right) and then implement volumes to use it.

I really prefer things to go into nova as individual features and not in one big chunk.

In the meantime I'd go for making volumes a 'user' extension which already works great. Just have people that want to use it drop the volumes extension .py file into /var/lib/nova/extensions.

Dan

[Thierry Carrez (ttx)]

@Dan: does the recently-merged branch cover your concerns ? If yes, please feel free to set this bug to "Fix committed".