Synnefo » snf-ganeti » ganeti-local

def WriteFile(file_name, fn=None, data=None,

              mode=None, uid=-1, gid=-1,

              atime=None, mtime=None):

  """(Over)write a file atomically.

  The file_name and either fn (a function taking one argument, the

  file descriptor, and which should write the data to it) or data (the

  contents of the file) must be passed. The other arguments are

  optional and allow setting the file mode, owner and group, and the

  mtime/atime of the file.

  If the function doesn't raise an exception, it has succeeded and the

  target file has the new contents. If the file has raised an

  exception, an existing target file should be unmodified and the

  temporary file should be removed.

  """

  if not os.path.isabs(file_name):

    raise errors.ProgrammerError("Path passed to WriteFile is not"

                                 " absolute: '%s'" % file_name)

  if [fn, data].count(None) != 1:

    raise errors.ProgrammerError("fn or data required")

  if [atime, mtime].count(None) == 1:

    raise errors.ProgrammerError("Both atime and mtime must be either"

                                 " set or None")

  dir_name, base_name = os.path.split(file_name)

  fd, new_name = tempfile.mkstemp('.new', base_name, dir_name)

  # here we need to make sure we remove the temp file, if any error

  # leaves it in place

  try:

    if uid != -1 or gid != -1:

      os.chown(new_name, uid, gid)

    if mode:

      os.chmod(new_name, mode)

    if data is not None:

      os.write(fd, data)

    else:

      fn(fd)

    os.fsync(fd)

    if atime is not None and mtime is not None:

      os.utime(new_name, (atime, mtime))

    os.rename(new_name, file_name)

  finally:

    os.close(fd)

    RemoveFile(new_name)