crosutils/make_factory_package.sh: support full SSD image as target outside chroot

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 167 matching lines @@
 
   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
 
+  # Try to use larger buffer if offset/size can be re-aligned.
+  # 2M / 512 = 4096
+  local buffer_ratio=4096
+  local bs=512
+  if [ $((dstoffset % buffer_ratio)) -eq 0 -a \
+       $((length % buffer_ratio)) -eq 0 ]; then
+    dstoffset=$((dstoffset / buffer_ratio))
+    bs=$((bs * buffer_ratio))
+  fi
+
   image_dump_partition "${src}" "${srcpart}" |
-      dd of="${dst}" bs=512 seek="${dstoffset}" conv=notrunc
+      dd of="${dst}" bs="${bs}" seek="${dstoffset}" conv=notrunc oflag=dsync
 }