build_image: avoid losetup -c because older kernels seem to balk

build_image

 #!/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.
 
 # Script to build a bootable keyfob-based chromeos system image from within
 # a chromiumos setup. This assumes that all needed packages have been built into
 # the given target's root with binary packages turned on. This script will
 # build the Chrome OS image using only pre-built binary packages.
@@ skipping 514 matching lines @@
   fi
 
   # Create root file system disk image to fit on a 1GB memory stick.
   # 1 GB in hard-drive-manufacturer-speak is 10^9, not 2^30.  950MB < 10^9 bytes.
   if [[ ${FLAGS_factory_install} -eq ${FLAGS_TRUE} ]] ; then
     ROOT_SIZE_BYTES=$((1024 * 1024 * 300))
   else
     ROOT_SIZE_BYTES=$((1024 * 1024 * ${FLAGS_rootfs_size}))
   fi
 
-  dd if=/dev/zero of="${ROOT_FS_IMG}" bs=1 count=1 seek=$((ROOT_SIZE_BYTES - 1))
-  sudo losetup "${LOOP_DEV}" "${ROOT_FS_IMG}"
-  sudo mkfs.ext3 "${LOOP_DEV}"
-
-  # Pad out 10% for the hash tree.  This currently _exact_ for
-  # default configuration.  More space may be needed for different options.
+  # Pad out for the hash tree.
   ROOT_HASH_PAD=$((FLAGS_rootfs_hash_pad * 1024 * 1024))
   info "Padding the rootfs image by ${ROOT_HASH_PAD} bytes for hash data"
+
   dd if=/dev/zero of="${ROOT_FS_IMG}" bs=1 count=1 \
      seek=$((ROOT_SIZE_BYTES + ROOT_HASH_PAD - 1))
-  # Update to reflect the new capacity in the loop device.
-  sudo losetup -c "${LOOP_DEV}"
+  sudo losetup "${LOOP_DEV}" "${ROOT_FS_IMG}"
+  # Specify a block size and block count to avoid using the hash pad.
+  sudo mkfs.ext3 -b 4096 "${LOOP_DEV}" "$((ROOT_SIZE_BYTES / 4096))"
 
   # Tune and mount rootfs.
   # TODO(wad) rename the disk label to match the GPT since we
   #           can't change it later.
   DISK_LABEL="C-KEYFOB"
   sudo tune2fs -L "${DISK_LABEL}" -U "${UUID}" -c 0 -i 0 "${LOOP_DEV}"
   sudo mount "${LOOP_DEV}" "${ROOT_FS_DIR}"
 
   # Create stateful partition of the same size as the rootfs.
   STATEFUL_LOOP_DEV=$(sudo losetup -f)
@@ skipping 211 matching lines @@
   echo "Developer image created as ${DEVELOPER_IMAGE_NAME}"
 fi
 
 print_time_elapsed
 
 echo "To copy to USB keyfob, OUTSIDE the chroot, do something like:"
 echo "  ./image_to_usb.sh --from=${OUTSIDE_OUTPUT_DIR} --to=/dev/sdX"
 echo "To convert to VMWare image, OUTSIDE the chroot, do something like:"
 echo "  ./image_to_vm.sh --from=${OUTSIDE_OUTPUT_DIR}"
 echo "from the scripts directory where you entered the chroot."