project-edgeos/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": [
        {
            # Kernel for Slot A.
            "num": 2,
            "label": "KERN-A",
            "type": "kernel",
            "size": "128 MiB"
        },
        {
            # Kernel for Slot B.
            "num": 4,
            "label": "KERN-B",
            "type": "kernel",
            "size": "128 MiB"
        },
        {
            # Board specific files, stores persistent configuration.
            "num": 8,
            "label": "OEM",
            "type": "data",
            "fs_format": "ext4",
            "size": "32 MiB",
            "uuid": "random"
        },
        {
            # Used for Legacy Bios, and EFI Bios, not ChromeOS hardware
            "num": 12,
            "label": "EFI-SYSTEM",
            "type": "efi",
            "fs_format": "vfat",
            "size": "128 MiB",
            "uuid": "clear"
        },
        {
            "num": 5,
            "label": "ROOT-B",
            "type": "rootfs",
            "fs_size":"2 GiB",
            "size": "2124 MiB",
            "fs_format": "squashfs",
            "fs_options": {
                "squashfs": "-comp gzip"
            }
        },
        {
            "num": 3,
            "label": "ROOT-A",
            "type": "rootfs",
            "fs_size":"2 GiB",
            "size": "2124 MiB",
            "fs_format": "squashfs",
            "fs_options": {
                "squashfs": "-comp gzip"
            }
        },
        {
          # STATE
          "num": 1,
            "size": "4 GiB",
            "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"
            }
        }
    ]
    }
}