How to use the tern.utils.rootfs.undo_mount function in tern

# mount diff layers from 0 till the current layer
                target = mount_overlay_fs(image_obj, curr_layer)
                # mount dev, sys and proc after mounting diff layers
                rootfs.prep_rootfs(target)
            # for each command look up the snippet library
            for command in command_list:
                pkg_listing = command_lib.get_package_listing(command.name)
                if isinstance(pkg_listing, str):
                    common.add_base_packages(
                        image_obj.layers[curr_layer], pkg_listing, shell)
                else:
                    common.add_snippet_packages(
                        image_obj.layers[curr_layer], command, pkg_listing,
                        shell)
            if command_list:
                rootfs.undo_mount()
                rootfs.unmount_rootfs()
        # update the master list
        common.update_master_list(master_list, image_obj.layers[curr_layer])
        curr_layer = curr_layer + 1
    common.save_to_cache(image_obj)

try:
                        common.add_base_packages(
                            image_obj.layers[curr_layer], pkg_listing, shell)
                    except KeyboardInterrupt:
                        logger.critical(errors.keyboard_interrupt)
                        abort_analysis()
                else:
                    try:
                        common.add_snippet_packages(
                            image_obj.layers[curr_layer], command, pkg_listing,
                            shell)
                    except KeyboardInterrupt:
                        logger.critical(errors.keyboard_interrupt)
                        abort_analysis()
            if command_list:
                rootfs.undo_mount()
                rootfs.unmount_rootfs()
        # update the master list
        common.update_master_list(master_list, image_obj.layers[curr_layer])
        curr_layer = curr_layer + 1

info_list = look_up_lib(args.keys)
            info_dict = command_lib.check_for_unique_package(
                info_list, args.package)[last]
        else:
            info_dict = look_up_lib(args.keys)
        # try to invoke the commands
        try:
            result = command_lib.get_pkg_attr_list(
                args.shell, info_dict, args.package)
            print('Output list: ' + ' '.join(result[0]))
            print('Error messages: ' + result[1])
            print('Number of elements: ' + str(len(result[0])))
        except subprocess.CalledProcessError as error:
            print(error.output)
        # undo the mounts
        rootfs.undo_mount()
        rootfs.unmount_rootfs()
    else:
        print("Something when wrong in loading the image")
    report.teardown()
    report.clean_image_tars(image_obj)
    report.clean_working_dir(False)

add_shell_message = errors.no_listing_for_base_key.format(
            listing_key='shell')
        image_obj.layers[0].origins.add_notice_to_origins(
            origin_command_lib, Notice(add_shell_message, 'hint'))
        shell = constants.shell
    # only extract packages if there is a known binary and the layer is not
    # cached
    if binary:
        if not common.load_from_cache(image_obj.layers[0], redo):
            # Determine pacakge/os style from binary in the image layer
            common.get_os_style(image_obj.layers[0], binary)
            # get the packages of the first layer
            rootfs.prep_rootfs(target)
            common.add_base_packages(image_obj.layers[0], binary, shell)
            # unmount proc, sys and dev
            rootfs.undo_mount()
    else:
        logger.warning(errors.no_package_manager)
        # /etc/os-release may still be present even if binary is not
        common.get_os_style(image_obj.layers[0], None)
        image_obj.layers[0].origins.add_notice_to_origins(
            origin_first_layer, Notice(errors.no_package_manager, 'warning'))
        # no binary means there is no shell so set to default shell
        logger.warning('Unknown filesystem. Using default shell')
        shell = constants.shell
    # unmount the first layer
    rootfs.unmount_rootfs()
    # populate the master list with all packages found in the first layer
    for p in image_obj.layers[0].packages:
        master_list.append(p)
    # get packages for subsequent layers
    curr_layer = 1

origin_first_layer = 'Layer: ' + image_obj.layers[0].fs_hash[:10]
    # only extract packages if there is a known binary and the layer is not
    # cached
    if binary:
        if not common.load_from_cache(image_obj.layers[0], redo):
            # Determine pacakge/os style from binary in the image layer
            common.get_os_style(image_obj.layers[0], binary)
            # get the packages of the first layer
            try:
                rootfs.prep_rootfs(target)
                common.add_base_packages(image_obj.layers[0], binary, shell)
            except KeyboardInterrupt:
                logger.critical(errors.keyboard_interrupt)
                abort_analysis()
            # unmount proc, sys and dev
            rootfs.undo_mount()
    else:
        logger.warning(errors.no_package_manager)
        # /etc/os-release may still be present even if binary is not
        common.get_os_style(image_obj.layers[0], None)
        image_obj.layers[0].origins.add_notice_to_origins(
            origin_first_layer, Notice(errors.no_package_manager, 'warning'))
        # no binary means there is no shell so set to default shell
        logger.warning('Unknown filesystem. Using default shell')
        shell = constants.shell
    # unmount the first layer
    rootfs.unmount_rootfs()
    # populate the master list with all packages found in the first layer
    for p in image_obj.layers[0].packages:
        master_list.append(p)
    return shell

def unmount():
    """Go through unmounting the working directory"""
    # try to unmount proc, sys and dev
    try:
        rootfs.undo_mount()
    except subprocess.CalledProcessError:
        pass
    try:
        rootfs.unmount_rootfs()
    except subprocess.CalledProcessError:
        pass