overlay-lakitu/scripts/disk_layout.json

{
  "parent": "legacy_disk_layout.json",

  "layouts": {
  # The following number for size (4966) is determined such that the
  # size of image with "base" disk layout is exactly 10GiB. GCE images
  # are expected to be multiple of 1GiB. We choose 10GiB because it's
  # the default boot disk size on GCE.
  #
  # For now, we determine the starting sector number of the stateful
  # partition with cgpt (see below) on a built image. But ideally
  # we should arrive at this number based on legacy_disk_layout.json.
  #
  # Partitions are expected to be aligned to 4096 block boundary,
  # that is, 2 MiB.
  #
  # Starting with crrev.com/c/528047, 1GiB will always be added
  # to the stateful partition size. Therefore, we leave room
  # for it in the computation below to prevent the image size
  # growing beyond 10GiB.
  #
  # number of 512-byte sectors in 10GiB:    20,971,520
  # stateful partition starting sector:      8,704,000 (cgpt show /dev/sda)
  # stateful partition size in MiB:              5,990 (2MiB aligned)
  # stateful partition size less 1GiB in MiB:    4,966 (crrev.com/c/528047)
   "common": [
      {
        # STATE
        "num": 1,
        "size": "4966 MiB",
        "fs_options": {
          # A consequence of this option is that some file system
          # structures are initialized lazily when resizing,
          # resulting in much faster resize2fs invocations.
          "ext4": "-O metadata_csum"
        }
      }
    ]
  }
}