1. The error prompt may be misleading. I guess your backing image should
be running. It should report that "failed to get the lock of backing
image". The operation will be allowed in the future.
2. Check the help doc of qemu-img, the you can get the support sub-command by
force share option "-U".
The behaviour should be expected. Since qemu 2.10, image locking is
enabled which make multiple QEMU processes cannot write to the same
image, even if boot snapshot and backing file at the same time are
not allowed.
You could get image info with the option "-U" as below:
$qemu-img info -U $ImageNa
Currently, qemu-img 'amend' subcommand would fail to adjust image's backing file
which was moved into different path.
For example, parent.qcow2, the backing file of leaf.qcow2, first is at /home/a/,
then moved into /home/b/. Originally this command,
"qemu-img amend -f qcow2 -o
backing_fmt=qcow2,b
