mount ext2/3/4 in chromeos scripts should be in /usr/local/bin First run "/usr/local/bin/mountextfs setup" to setup the udev rule.

cleanuploop

#!/bin/sh
while [ "x`cat /proc/mounts|grep /dev/loop )`" != "x" -a "x`cat /proc/mounts|grep /media/removable )`" != "x" ];do 
cat /proc/mounts|grep /dev/loop|while read line;do
  mountpoint=`echo "$line"|cut -d " " -f 2`
  loopdevice=`echo "$line"|cut -d " " -f 1` 
  # check if our ext2/3/4 device is still mounted
  device=`cat /proc/mounts|grep $mountpoint|grep -v $loopdevice`
  if [ "x$device" = "x" ];then
    umount -d $loopdevice
    # Be sure the directory is empty before deleting. 
    if [ "x`ls -A $mountpoint`" = "x" ];then
      rm -r $mountpoint
    fi
  fi
done
sleep 1
done
exit 0

mountextfs

#!/bin/sh
# check if script is run as root
uid=`id -u $USERNAME`
if [ $uid -ne 0 ]; then
  echo "$0 must be run as root"
  exit 1
fi
# Use this to create a unique name for the loop file.
kernel_devname=$2
# Magic seems to be happening here.
mount_extfs() {
  loopfile_path="/usr/local/"
  if [ "${ID_FS_TYPE##ext*}" != "$ID_FS_TYPE" ];then
    # Creating loop file 
    dd if=/dev/zero of=$loopfile_path$kernel_devname bs=1KB count=40
    mkfs.vfat $loopfile_path$kernel_devname -n $ID_FS_LABEL
    # Find unused loop device 
    loop=`losetup -f` 
    losetup $loop $loopfile_path$kernel_devname
    # Send mount command to crosdisk 
    dbus-send --print-reply --system --dest=org.chromium.CrosDisks /org/chromium/CrosDisks org.chromium.CrosDisks.Mount string:$loop string:"" array:string:"ro" 
    found=0 
    first=0 
    dbus-monitor --system --monitor 'interface=org.chromium.CrosDisks, member=MountCompleted'|while read line;do 
      loop_mount=`echo $line|grep "string \"/"`
      if [ $first -eq 0 ];then
        dbus-send --print-reply --system --dest=org.chromium.CrosDisks /org/chromium/CrosDisks org.chromium.CrosDisks.Mount string:$loop string:"" array:string:"ro"
        first=1
      fi 

      if [ "x$loop_mount" != "x" ];then
        loop_mount=`echo $loop_mount|cut -d " " -f 2|sed -e s/\"//g`
        if [ $found -eq 1 ];then
          # TODO: add mount options for permissions and error check 
          mount $DEVNAME "$loop_mount"
          # I guess we should start monitoring /proc/mounts which seems to be the only option.
          if [ "x`ps -aux|grep cleanuploop|grep -v grep`" = "x" ];then
            /usr/local/bin/cleanuploop
          fi 
          exit 0
        fi
        if [ "x$loop_mount" = "x$loop" ];then
          # we found our loop device next string will be the mountpoint. 
          found=1
        fi 
      else
        # We should add a time restriction so it can't run forever. 
        continue
      fi 
    done 
  fi
}

setup_udevrule() {
  mkdir -p /run/udev/rules.d
  rules_file="/run/udev/rules.d/10-mountextfs.rules" 
  if [ ! -f "$rules_file" ];then
    echo "# udev rule for mounting ext2/3/4 formatted usb devices and sd-cards" > "$rules_file" 
    echo 'ACTION=="add", SUBSYSTEM=="block", KERNEL=="sd??", RUN+="/usr/local/bin/mountextfs start %k"' >> "$rules_file"
    # Update the udev rules 
    udevadm control --reload-rules
  else
    echo "$rules_file already exists nothing todo."
    exit 0 
  fi
}
# Just for now everything in one script file.
case "$1" in
  start)
    mount_extfs
    ;;
  setup)
    setup_udevrule 
    echo "done" 
    exit 0 
    ;;

  *)
    echo "Usage: $0 {setup}"
esac
exit 0