rm $2
truncate -r $1 $2
filefrag -v $1 | grep -v "File" | grep -v " ext logical physical expected length flags" | grep -v "extents found" | while read ext logical physical expected length flags; do
[ -z $logical ] && continue
[ -z $length ] && length=$expected
[ -z $length ] && continue

hole_jump=""
if [ "$length" != "0" ]; then
    hole_jump="seek=$logical skip=$logical conv=notrunc"
fi

dd if=$1 of=$2 \
   count=$length bs=4096 \
   iflag=fullblock oflag=direct,dsync \
   $hole_jump \
   2> /dev/null
done
filefrag -v $2
cmp $1 $2