Qemu: Could not open backing file: Cannot reference an existing block device with additional options or a new filename
When trying to revert to a snapshot QEMU dies with the following error or something similar:
-blockdev driver=qcow2,node-name=hd0-overlay1,file=hd0-overlay1-file,cache.no-flush=on,backing=hd0: Could not open backing file: Cannot reference an existing block device with additional options or a new filename
The backing file is the hd0 block device which is specified on the command line. Possibly we should not specify block devices used as backing files on the command line and just allow them to be read from the overlay file. It is not clear what the expected usage is.