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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# Copyright 2018 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Converts a Chromium OS GPT disk image into a single rootfs/kernel"""
import argparse
import os
import shutil
import struct
import subprocess
import sys
import tempfile
from pathlib import Path
from termina_util import extract_vmlinux, mount_disk
def extract_squashfs_partition(dest_path, disk_path, part_num):
base_cmd = ['sudo', 'partx', '--raw', '--noheadings', '--nr', str(part_num)]
part_start_sectors = subprocess.check_output(base_cmd + ['--output', 'START', disk_path])
part_start_bytes = int(part_start_sectors) * 512
part_size_sectors = subprocess.check_output(base_cmd + ['--output', 'SECTORS', disk_path])
part_size_bytes = int(part_size_sectors) * 512
with open(disk_path, 'rb') as disk:
magic, = struct.unpack('<I',
if magic != 0x73717368:
print('this does not look like a squashfs partition')
with open(dest_path, 'wb') as output:
count = part_size_bytes
while count > 0:
buf =
if len(buf) == 0:
print('no more disk to read')
to_write = count
if to_write > 4096:
to_write = 4096
count -= output.write(buf[:to_write])
def can_hardlink(src_path, target_path):
src_stat = src_path.stat()
target_stat = target_path.stat()
return src_stat.st_mode == target_stat.st_mode and \
src_stat.st_uid == target_stat.st_uid and \
src_stat.st_gid == target_stat.st_gid
def dedupe_hardlinks(target_dir):
dupes = subprocess.check_output(['fdupes', '--recursive', str(target_dir)]).decode('utf-8')
src_file = ''
for line in dupes.splitlines():
# Empty line means we're at the end of a set of dupes.
if not line:
src_file = ''
# No src_file means we're at a new dupe source file.
if not src_file:
src_file = line
# Check that we can perform the hard link.
src_path = Path(src_file)
target_path = Path(line)
if not can_hardlink(src_path, target_path):
# This file is a dupe - perform a hard link.
target_path.unlink(), str(target_path))
def create_fs_image(img_path, src_path):
# Create image at 200% of source size.
# resize2fs will shrink it to the minimum size later.
du_output = subprocess.check_output(['du', '-bsx', src_path]).decode('utf-8')
src_size = int(du_output.split()[0])
img_size = int(src_size * 2.00)
with'wb+') as vm_rootfs:
'-m', '0',
'-i', '16384',
'-b', '4096',
'-O', '^has_journal',
stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, check=True)
with tempfile.TemporaryDirectory() as tempdir_path:
mnt_dir = Path(tempdir_path)
with mount_disk(str(img_path), str(mnt_dir)) as mntpoint:
['sudo', 'rsync', '-aH', str(src_path) + '/', str(mnt_dir)],
stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, check=True)
['/sbin/e2fsck', '-y', '-f', str(img_path)],
stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, check=True)
['/sbin/resize2fs', '-M', str(img_path)],
stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, check=True)
def repack_rootfs(output_dir, disk_path):
with tempfile.TemporaryDirectory() as tempdir_path:
tempdir = Path(tempdir_path)
rootfs_img_path = tempdir / 'rootfs.img'
extract_squashfs_partition(str(rootfs_img_path), str(disk_path), 3)
stateful_img_path = tempdir / 'stateful.img'
extract_squashfs_partition(str(stateful_img_path), str(disk_path), 1)
# Unsquash the rootfs and stateful partitions.
rootfs_dir = tempdir / 'rootfs'['unsquashfs', '-d', str(rootfs_dir), str(rootfs_img_path)], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, check=True)
stateful_dir = tempdir / 'stateful'['unsquashfs', '-d', str(stateful_dir), str(stateful_img_path)], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, check=True)
# Extract the kernel. For ARM we just grab the Image-* file. For x86, we
# grab the vmlinuz (bzImage).
images = list(rootfs_dir.glob('boot/Image-*'))
output_kernel = output_dir / 'vm_kernel'
if len(images) > 0:
shutil.copy(str(images[0]), str(output_kernel))
shutil.copy(str(rootfs_dir / 'boot' / 'vmlinuz'), str(output_kernel))
# Remove cruft we don't need.
cruft_dirs = ['boot', 'lib/firmware', 'mnt/stateful_partition']
for cruft_dir in cruft_dirs:
shutil.rmtree(str(rootfs_dir / cruft_dir), ignore_errors=True)
# Add new mnt dirs.
(rootfs_dir / 'mnt' / 'stateful').mkdir()
(rootfs_dir / 'mnt' / 'shared').mkdir()
(rootfs_dir / 'mnt' / 'external').mkdir()
# Copy the dev_image into its location at /usr/local.
usr_local = rootfs_dir / 'usr' / 'local'
dev_image = stateful_dir / 'dev_image'
shutil.copytree(str(dev_image), str(usr_local), symlinks=True, ignore_dangling_symlinks=True)
# Copy lsb-release and credits into place.
shutil.copy(str(rootfs_dir / 'etc' / 'lsb-release'), str(output_dir))
credits_path = rootfs_dir / 'opt/google/chrome/resources/about_os_credits.html'
shutil.copy(str(credits_path), str(output_dir))
# Create vm_tools.img if /opt/google/cros-containers exists.
tools_dir = rootfs_dir / 'opt' / 'google' / 'cros-containers'
if tools_dir.exists():
create_fs_image(output_dir / 'vm_tools.img', tools_dir)
# Remove contents of tools_dir so they are not included in vm_rootfs.img.
# Leave the top-level /opt/google/cros-containers directory in place
# as a mount point.
for child in tools_dir.iterdir():
# Create vm_rootfs.img.
create_fs_image(output_dir / 'vm_rootfs.img', rootfs_dir)
def main():
parser = argparse.ArgumentParser(description='Build a Termina image')
parser.add_argument('image', help='source disk image to build the Termina image from')
parser.add_argument('output', help='output directory')
args = parser.parse_args()
disk_path = Path(args.image)
if not disk_path.is_file():
print('please provide the path to the termina image')
output_dir = Path(args.output)
if output_dir.exists():
print('refusing to overwrite output directory')
repack_rootfs(output_dir, disk_path)
if __name__ == '__main__':