Snapshots when using RBD backend make full copy then upload unnecessarily

[Michael H Wilson]

When performing a snapshot a local copy is made. In the case of RBD, it reads what libvirt thinks is a raw block device and then converts that to a local raw file. The file is then uploaded to glance, which reads the whole raw file and stores it in the backend, if the backend is Ceph this is completely unnecessary and defeats the whole point of having a Ceph cluster. The fix should go something like this:

1. Tell Ceph to make a snapshot of the RBD
2. Get Ceph metadata from backend, send that to Glance
3. Glance gets metadata, if it has Ceph backend no download is necessary
4. If it doesn't, download image from Ceph location, store in backend

[Zoltan Arnold Nagy (zoltan)]

I think this is a very serious bug as the local temporary files could overrun the storage space on the hypervisor thus giving an opportunity to perform a denial of service attack.

[Abel Lopez (al592b)]

I think this is a duplicate of 1226351

[Zoltan Arnold Nagy (zoltan)]

It is not. That patch is about getting ceph ephemeral supported _at all_, and this bug is about how to fix the snapshotting issues.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/125963

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/127397

[OpenStack Infra (hudson-openstack)]

Change abandoned by Sean Dague (<email address hidden>) on branch: master
Review: https://review.openstack.org/125963
Reason: This review is > 4 weeks without comment and currently blocked by a core reviewer with a -2. We are abandoning this for now. Feel free to reactivate the review by pressing the restore button and contacting the reviewer with the -2 on this review to ensure you address their concerns.

[Davanum Srinivas (DIMS) (dims-v)]

Fix proposed again.

[OpenStack Infra (hudson-openstack)]

Change abandoned by John Garbutt (<email address hidden>) on branch: master
Review: https://review.openstack.org/125963
Reason: seems like this effort has been abandoned, so abandoning this change in favor of: https://review.openstack.org/#/c/205282/

[Sean Dague (sdague)]

The patch referenced is merged upstream. Assume this addresses it, if not, please reopen

[Ian Cordasco (icordasc)]

This was fixed entirely in Nova and no longer requires work in glance-store.