safeappend.py

def _safe_append(filename, workspacedir, data):
    """Safely add data to a file to prevent corruption in the case of """
    """power failure. """
    fd, tmp = tempfile.mkstemp(prefix='tmpfile', dir=workspacedir)
    try:
        # close it and open it again so that "with" can be used
        os.close(fd)
        shutil.copyfile(filename, tmp)
        with open(tmp, 'a') as f:
            f.write(data)

        _atomic_copy(tmp, filename)
    finally:
        try:
            os.remove(tmp)
        except OSError:
            pass

def _atomic_copy(old, new):
    old = os.path.realpath(old)
    olddir = os.path.dirname(old)
    new = os.path.realpath(new)

    with open(old, "r") as f:
        fd = f.fileno()
        os.fdatasync(fd)

    # Remember first sync the file AND directory to make sure data
    # is written out
    fd = os.open(os.path.dirname(olddir), os.O_RDONLY)
    os.fsync(fd)
    os.close(fd)

    # Rename should be atomic with respect to disk, yes all of this assumes
    # linux and possibly non-network filesystems.
    os.rename(old, new)


def _enable_devtool_inc(workspacedir, basepath):
    """ Make sure devtool.inc gets added to local.conf """
    local_conf = os.path.join(basepath, 'conf', 'local.conf')

    # Exit if already included
    with open(local_conf, 'r') as f:
        for line in f:
            if re.match(r'^\s*include\s+devtool.inc\s*$', line):
                logger.info("devtool.inc already included skipping")
                return

    _safe_append(local_conf, workspacedir, "include devtool.inc\n")