Description of problem:

When cloning a VM disk we want it to complete quickly but it can revert back to the slower host-assisted method for many different reasons. The logic is complex enough that a KCS article was written to help diagnose the reason:

https://access.redhat.com/articles/7021609

Since the diagnostic steps are concrete we should be able to automatically provide a reason that host-assisted cloning is used so that the issue can be resolved.

Version-Release number of selected component (if applicable):

4.14.0 and earlier

How reproducible:

Variable, depending on storage configuration.

Steps to Reproduce:
One way to reproduce this is by cloning to a PVC with a different volume mode

1. Determine the volume mode of the source PVC
2. Ensure "smart" cloning works when cloning a source PVC to a PVC with the same volume mode.
3. Create a DV to clone the source PVC and specify a different volume mode

Actual results:

The clone completes successfully but uses host-assisted cloning. There is no clear information available (in the PVC nor in events) to explain why host-assisted cloning was used.

Expected results:

The PVC is annotated with a clone fallback reason and an event is generated.

Additional info: