Allow disk image target for copy machine.

lib/cros_image_common.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.
 
 # This script contains common utility function to deal with disk images,
 # especially for being redistributed into platforms without complete Chromium OS
 # developing environment.
 
@@ skipping 150 matching lines @@
     "$file" \
     "$mount_point"
 }
 
 # Unmounts a partition mount point by mount_partition
 image_umount_partition() {
   local mount_point="$1"
 
   umount -d "$mount_point"
 }
+
+# Copy a partition from one image to another.
+image_partition_copy() {
+  local src="$1"
+  local srcpart="$2"
+  local dst="$3"
+  local dstpart="$4"
+
+  local srcoffset=$(image_part_offset "${src}" "${srcpart}")
+  local dstoffset=$(image_part_offset "${dst}" "${dstpart}")
+  local length=$(image_part_size "${src}" "${srcpart}")
+  local dstlength=$(image_part_size "${dst}" "${dstpart}")
+
+  if [ "${length}" -gt  "${dstlength}" ]; then
+    exit 1
+  fi
+
+  image_dump_partition "${src}" "${srcpart}" |
+      dd of="${dst}" bs=512 seek="${dstoffset}" conv=notrunc
+}