#!/bin/sh
mp=/mnt/root.tmp
fs=/

excludes='--exclude /var/log/ --exclude /tmp/'

devs()
{
  btrfs fi sh "$fs"  | sed -ne 's?^[ \t]*devid[ \t].*/dev?/dev?p'
}

[ $(id -u) = 0 ] || exec sudo "$0" "$@" || exit

if ! [ -e "$mp" ] || ! mountpoint -q "$mp"
then
  mkdir -p "$mp"
  dev=$(devs | tail -n1) || exit
  mount -t btrfs "$dev" -o subvol=/ "$mp" || exit
fi

case $# in
  0) run()
     {
       rsync -xani $excludes "$mp"/root/ "$mp"/root~orig/
     }
     ;;
  *) run()
     {
       for f
       do
         diff "$mp"/root~orig/"$f" "$mp"/root/"$f"
       done
     }
     ;;
esac
if [ -t 0 ]
then
  run "$@" | less
else
  run "$@"
fi

umount "$mp"