protocol:
{
  "driver": "file",
  "filename": "/var/lib/libvirt/images/i.qcow2",
  "size": 4294967296
}

format:
{
  "driver": "qcow2",
  "file": "0123456789ABCDEF0123456789ABCDE",
  "size": 8589934590,
  "backing-file": "json:{\"file\":{\"driver\":\"raw\",\"offset\":9876,\"size\":54321,\"file\":{\"driver\":\"file\",\"filename\":\"/var/lib/libvirt/images/i.img\"}}}",
  "backing-fmt": "raw"
}