virt-manager cloning ignores--sparse flag

[Philip Orleans]

Scenario
You have a Virtual Machine where you created the *.img file without clicking in "allocate all the space now", so the virtual disk file is sparse, which is great. Suppose your file is nominally larger than your available space in the Host. Then, if you attempt to clone (right-click clone) that virtual machine, the process will fail because virt-manager does not use the --sparse=always flag when it copies the virtual disk. Virt-manager needs to find out if the original virtual disk to be cloned is sparse, and use the same flag. Instead, it creates a fully-expanded file.

[Philip Orleans (venefax)]

This is obviously not an Ubuntu bug, but any distribution may actually push this change to the virt-manager maintainers.

[Philip Orleans (venefax)]

The way VMware does it is like this: when you are about clone a VM, you need to chose its on-disk format,
a) Sparse, b) Full, c) Same as Source.
Sometimes you clone a VM but you want to change its dosk-format from Sparse to Full.
We should follow the same path.