[fedora-virt] Change format of backing file?

[Tom Horsley]

On Tue, 12 Aug 2014 20:57:32 -0600
Eric Blake wrote:

> qemu-img rebase -u -b inner.img -F qcow2 -f qcow2 outer.qcow2

Cool. I never noticed rebase before. It is good to learn new
things - Thanks.

Now I wonder if it would still work if I used virt-sparsify
to zero out the un-used block rather than merely converting
the raw to qcow2? :-).