common/process-layout.py

#!/usr/bin/python2
# Copyright 2015 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.

"""Helper tools related to the layout text file.

First create a directory with the paths in it:
$ %(progs)s make common/fs-layout.txt stagedir/

Then create a reduced layout for later inclusion:
$ %(progs)s filter common/fs-layout.txt new-layout.txt
"""

from __future__ import print_function

import argparse
import errno
import os
import sys


def makedirs(path):
  """Like os.makedirs, but ignore existing errors"""
  try:
    os.makedirs(path)
  except OSError as e:
    if e.errno != errno.EEXIST:
      raise


def symlink(src, dst):
  """Like os.symlink, but handle existing errors"""
  try:
    os.symlink(src, dst)
    return
  except OSError as e:
    if e.errno != errno.EEXIST:
      raise
    # Assume the symlink has changed to make our lives simple.
    os.unlink(dst)
    os.symlink(src, dst)


def ProcessLayout(layout):
  """Yield each valid line in |layout| as a tuple of each element"""
  # The number of elements expected for each object type.
  valid_lens = {
      'file': (6, 7),
      'dir': (5,),
      'nod': (8,),
      'slink': (6,),
      'pipe': (5,),
      'sock': (5,),
  }

  with open(layout) as f:
    for line in f:
      line = line.split('#', 1)[0].strip()
      if not line:
        continue

      elements = line.split()

      etype = elements[0]
      if etype not in valid_lens:
        raise ValueError('Invalid line: unknown type "%s":\n%s' %
                         (etype, line))

      valid_len = valid_lens[etype]
      if len(elements) not in valid_len:
        raise ValueError('Invalid line: wanted %r elements; got %i:\n%s' %
                         (valid_len, len(elements), line))

      yield elements


def GetParser():
  parser = argparse.ArgumentParser(description=__doc__)
  parser.add_argument('mode', choices=('make', 'filter'),
                      help='operation to perform')
  parser.add_argument('layout', help='path to the filesystem layout file')
  parser.add_argument('output', help='path to operate on')
  return parser


def main(argv):
  parser = GetParser()
  opts = parser.parse_args(argv)

  if opts.mode == 'make':
    # Create all the requested directories/files in the output directory.
    # These paths are needed so we can install all files into the right
    # layout w/out creating conflicts (e.g. /usr being a dir or a symlink).
    for elements in ProcessLayout(opts.layout):
      etype = elements.pop(0)
      try:
        if etype == 'dir':
          path, mode, uid, gid = elements
          assert ('0', '0') == (uid, gid)
          mode = int(mode, 8)
          path = os.path.join(opts.output, path.lstrip('/'))
          makedirs(path)
          os.chmod(path, mode)
        elif etype == 'slink':
          path, target, mode, uid, gid = elements
          mode = int(mode, 8)
          assert ('0', '0', 0o755) == (uid, gid, mode)
          path = os.path.join(opts.output, path.lstrip('/'))
          makedirs(os.path.dirname(path))
          symlink(target, path)
      except Exception:
        print('While processing line: %s %s' % (etype, elements))
        raise

  elif opts.mode == 'filter':
    # Filter out all the paths that 'make' above created.  The stuff that is
    # left often requires root access (which we don't have), but the cpio gen
    # tool can take care of this for us.
    with open(opts.output, 'a') as f:
      for elements in ProcessLayout(opts.layout):
        if elements[0] not in ('dir', 'slink'):
          f.write(' '.join(elements) + '\n')


if __name__ == '__main__':
  main(sys.argv[1:])