[openstack-dev] [nova] [glance] Getting the ball rolling on glance v2 in nova in newton cycle

Sean Dague sean at dague.net
Fri Apr 1 13:45:44 UTC 2016

The glance v2 work is currently blocked as there is no active spec,
would be great if someone from the glance team could get that rolling again.

I started digging back through the patches in detail to figure out if
there are some infrastructure bits we could get in early regardless.

#1 - new methods for glance xenserver plugin

Let's take a simplified approach on this patch -
https://review.openstack.org/#/c/266933 and only change the
xenapi/etc/xapi.d/plugins/ content in the following ways.

- add upload/download_vhd_glance2 methods. Don't add an api parameter.
Add these methods mostly via copy/paste as we're optimizing for deleting
v1 not for fixing v1.

That will put some infrastructure in place so we can just call the v2
actions based on decision from higher up the stack.

#2 - move discover major version back to glanceclient -

I don't understand why this was ever in nova. This really should be

glanceclient.discover... something. It uses internal methods from
glanceclient and internal structures of the content returned.

Catching, if desired, should also be on the glanceclient side.
glanceclient.reset_version() could exist to clear any caching.

#3 - Ideally we'd also have a

client = glanceclient.AutoClient(endpoint, ... ) which basically does
glanceclient.discover and returns us the right client automatically.
client.version provides access to the version information if you need to
figure out what version of a client you have.

This starts to get to a point where the parts of versioning that
glanceclient should know about are in glanceclient, and when nova still
needs to know things it can as for client.version.

For instance make _extract_query_params -
become and instance method that can

if self._client.version >= 2:

This isn't the whole story to get us home, however chunking up some of
these pieces I think makes getting the rest of the story in much
simpler. In nearly every case (except for the alt link in the image
view) we can easily have access to a real glance client. And the code
will be a ton easier to understand with some of the glanceclient
specific details behind the glanceclient interface.


Sean Dague

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