#!/bin/bash

start() {
    DEVICE=$1
    BASE=$(basename $DEVICE)
    OVERLAY=overlay-$BASE
    
    SIZE=$(blockdev --getsize $DEVICE)
    BYTESIZE=$(blockdev --getsize64 $DEVICE)
    
    # Create sparse file as big as possible
    OVLSIZE=$BYTESIZE
    while ! truncate -s${OVLSIZE} $OVERLAY; do
      echo $OVLSIZE failed
      OVLSIZE=$(( OVLSIZE/2 ))
    done
    
    if ! LOOPDEV=$(losetup --show -f -- $OVERLAY); then
      LOOPS=$(ls /dev/loop* | wc -l)
      mknod -m 660 /dev/loop$LOOPS b 7 $LOOPS
      LOOPDEV=$(losetup --show -f -- $OVERLAY)
    fi
    
    echo 0 $SIZE snapshot $DEVICE $LOOPDEV P 8 | dmsetup create $BASE
    echo Overlay device: /dev/mapper/$BASE
    echo Overlay file: $OVERLAY
    echo Stop with:
    echo dmsetup remove $BASE; rm $OVERLAY
    echo losetup -d $LOOPDEV
}

stop() {
    DEVICE=$1
    BASE=$(basename $DEVICE)
    OVERLAY=overlay-$BASE
    dmsetup remove $BASE
    # Find the loop device with $OVERLAY and stop it
    losetup -d $(losetup -j $OVERLAY)
    rm $OVERLAY
}

start $1