369     def assert_test_image_in_usb_disk(self, usb_dev=None):  argument
378         if usb_dev:
382             usb_dev = self.servo.probe_host_usb_dev()
383             if not usb_dev:
387         rootfs = '%s%s' % (usb_dev, self._ROOTFS_PARTITION_NUMBER)
388         logging.info('usb dev is %s', usb_dev)
1117     def _modify_usb_kernel(self, usb_dev, from_magic, to_magic):  argument
1131         kernel_part = self._join_part(usb_dev, self.KERNEL_MAP['a'])
1149     def corrupt_usb_kernel(self, usb_dev):  argument
1154         self._modify_usb_kernel(usb_dev, self.CHROMEOS_MAGIC,
1157     def restore_usb_kernel(self, usb_dev):  argument
1162         self._modify_usb_kernel(usb_dev, self.CORRUPTED_MAGIC,