qcow2: Prohibit backing file changes in 'qemu-img amend'
This was deprecated back in
bc5ee6da7 (qcow2: Deprecate use of
qemu-img amend to change backing file), and no one in the meantime has
given any reasons why it should be supported. Time to make change
attempts a hard error (but for convenience, specifying the _same_
backing chain is not forbidden). Update a couple of iotests to match.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <
20210503213600.569128-2-eblake@redhat.com>
Reviewed-by: Connor Kuehl <ckuehl@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>