kernel_fetcher.sh: use ro for rootfs.image

kernel_fetcher.sh

 #!/bin/bash
 
 # Copyright (c) 2009 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.
 
 # Load common constants.  This should be the first executable line.
 # The path to common.sh should be relative to your script's location.
 . "$(dirname "$0")/common.sh"
 
@@ skipping 29 matching lines @@
 }
 
 trap do_cleanup EXIT
 
 #
 # Set up loop device.  This time it is used to fetch the built kernel from the
 # root image.  This kernel is then written to the fourth partition.
 #
 echo "Fetching kernel from root image..."
 mkdir /tmp/kernel_fetch.$$
-sudo mount -o loop "${FLAGS_from}/rootfs.image" /tmp/kernel_fetch.$$
+sudo mount -o ro,loop "${FLAGS_from}/rootfs.image" /tmp/kernel_fetch.$$
 
 echo "Writing kernel to ${FLAGS_to} at ${FLAGS_offset}..."
 sudo "${SCRIPTS_DIR}"/file_copy.py \
   if=/tmp/kernel_fetch.$$/boot/vmlinux.uimg \
   of="${FLAGS_to}" \
   seek_bytes="${FLAGS_offset}"
 echo "Done."
 
 do_cleanup
 
 trap - EXIT