merge bitmpas:
[
  {
    "type": "block-dirty-bitmap-add",
    "data": {
      "node": "libvirt-5-format",
      "name": "c",
      "persistent": true,
      "disabled": false,
      "granularity": 65536
    }
  },
  {
    "type": "block-dirty-bitmap-merge",
    "data": {
      "node": "libvirt-5-format",
      "target": "c",
      "bitmaps": [
        {
          "node": "libvirt-3-format",
          "name": "c"
        }
      ]
    }
  },
  {
    "type": "block-dirty-bitmap-add",
    "data": {
      "node": "libvirt-5-format",
      "name": "b",
      "persistent": true,
      "disabled": false,
      "granularity": 65536
    }
  },
  {
    "type": "block-dirty-bitmap-merge",
    "data": {
      "node": "libvirt-5-format",
      "target": "b",
      "bitmaps": [
        {
          "node": "libvirt-3-format",
          "name": "b"
        }
      ]
    }
  },
  {
    "type": "block-dirty-bitmap-merge",
    "data": {
      "node": "libvirt-5-format",
      "target": "a",
      "bitmaps": [
        {
          "node": "libvirt-3-format",
          "name": "a"
        },
        {
          "node": "libvirt-4-format",
          "name": "a"
        }
      ]
    }
  }
]