merge bitmpas:
[
  {
    "type": "block-dirty-bitmap-merge",
    "data": {
      "node": "libvirt-5-format",
      "target": "a",
      "bitmaps": [
        {
          "node": "libvirt-4-format",
          "name": "a"
        }
      ]
    }
  }
]