Support VHDX differencing images (ie images with backing)

The qemu vhdx driver does not support type 2 (differencing) vhdx images (usually stored with file extension .avhdx). This means that any hyperv images with snapshots are not supported by qemu-img. It would be great to be able to convert to a new qcow image from a backing + set of differencing images from hyperv, and/or convert an individual differencing vhdx image to a qcow2 image with a backing file specified.

The QEMU project is currently considering to move its bug tracking to
another system. For this we need to know which bugs are still valid
and which could be closed already. Thus we are setting older bugs to
"Incomplete" now.

If you still think this bug report here is valid, then please switch
the state back to "New" within the next 60 days, otherwise this report
will be marked as "Expired". Or please mark it as "Fix Released" if
the problem has been solved with a newer version of QEMU already.

Thank you and sorry for the inconvenience.


[Expired for QEMU because there has been no activity for 60 days.]