#!/bin/bash

unset MP1 MP2
MKFS_EXT3="mkfs.ext3 -I 128 -F"
MKFS_EXT2="mkfs.ext2 -F"
MKFS_XFS="mkfs.xfs"
MKFS=${MKFS:-${MKFS_EXT3}}

Usage() {
	cat <<EOF
Usage: ${0##*/} existing new size

   Create a new filesystem image in 'new' of size 'size' with same content
   as 'existing'

   New size is specified per truncate(1), e.g. "10G" for 10 gigabyte
EOF
	return 0
}
error() { echo "$@" 1>&2; }
fail() { [ $# -eq 0 ] || error "$@"; exit 1; }

cleanup() {
	for d in "${MP1}" "${MP2}"; do
		[ -n "${d}" ] || continue
		rmdir "${d}"
	done
}

[ "$1" = "-h" -o "$1" = "--help" ] && { Usage; exit 0; }

[ $# -eq 3 ] || { Usage 1>&2; exit 1; }

old="$1"
new="$2"
size="$3"

trap cleanup EXIT

for x in "${old}" "${new}"; do
	[ -f "${x}" ] || fail "${x}: not a file"
done

tmpd=${TMPDIR:-/tmp}
truncate "--size=${size}" "${new}" ||
	fail "failed to create new image at ${new}"

${MKFS} "${new}" || fail "failed to make fs in ${new}"

MP1=$(mktemp -d ${tmpd}/${0##*/}.XXXXXX) &&
	MP2=$(mktemp -d ${tmpd}/${0##*/}.XXXXXX) ||
	fail "failed to make tempdirs"

sudo sh -c 'im1=${1} && mp1=${2} && im2=${3} && mp2=${4} &&
	mount -o loop,ro "${im1}" "${mp1}" &&
	mount -o loop "${im2}" "${mp2}" &&
	rsync -a --hard-links "${mp1}/" "${mp2}";
	ret=$?;
	umount "${mp1}" || ret=$?;
	umount "${mp2}" || ret=$?;
	rmdir "${mp1}" "${mp2}" || ret=$?;
	exit ${ret};' \
	arg0 "${old}" "${MP1}" "${new}" "${MP2}" || {
		[ -d "${MP1}" ] || unset MP1;
		[ -d "${MP2}" ] || unset MP2;
		fail "failed to sync ${old} => ${new}";
	}

[ -d "${MP1}" ] || unset MP1
[ -d "${MP2}" ] || unset MP2

exit