raspi-config do_expand_rootfs function that uses all of the SDcard

Function for expanding fs

do_expand_rootfs() {
  # Get the starting offset of the root partition
  PART_START=$(parted /dev/mmcblk0 -ms unit s p | grep "^2" | cut -f 2 -d:)
  [ "$PART_START" ] || return 1
  # Return value will likely be error for fdisk as it fails to reload the 
  # partition table because the root fs is mounted
  fdisk /dev/mmcblk0 <<EOF
p
d
2
n
p
2
$PART_START

p
w
EOF
  ASK_TO_REBOOT=1

  # now set up an init.d script
cat <<\EOF > /etc/init.d/resize2fs_once &&
#!/bin/sh
### BEGIN INIT INFO
# Provides:          resize2fs_once
# Required-Start:
# Required-Stop:
# Default-Start: 2 3 4 5 S
# Default-Stop:
# Short-Description: Resize the root filesystem to fill partition
# Description:
### END INIT INFO

. /lib/lsb/init-functions

case "$1" in
  start)
    log_daemon_msg "Starting resize2fs_once" &&
    resize2fs /dev/mmcblk0p2 &&
    rm /etc/init.d/resize2fs_once &&
    update-rc.d resize2fs_once remove &&
    log_end_msg $?
    ;;
  *)
    echo "Usage: $0 start" >&2
    exit 3
    ;;
esac
EOF
  chmod +x /etc/init.d/resize2fs_once &&
  update-rc.d resize2fs_once defaults &&
  whiptail --msgbox "Root partition has been resized.\n\
The filesystem will be enlarged upon the next reboot" 20 60 2
}