#!/bin/bash

# Uncompress LZA-packed firmware kernel. This is a functional, but
# quick & dirty version of the Perl script by Enrik Berkhan shown and explained
# at http://www.wehavemorefun.de/fritzbox/index.php/EVA. There is no CRC
# calculation for the time being and also no other kind of error checking,
# always assuming the source file is okay. The advantage of this version is
# that we do not need Perl and especially no exotic LZMA package which is
# unavailable as a Debian image, for example. The opposite is true for unlzma
# which is installed on most Linux systems in general and part of busybox-tools
# as a part of ds26 in particular.

case $# in
	2)
		;;
	*)
		echo "usage: $(basename "$0") <kernel_img> <uncomp_file>" >&2
		echo "    kernel_img  - file starting with compressed kernel image," >&2
		echo "                  e.g. kernel.image or kernel.raw" >&2
		echo "    uncomp_file - uncompressed kernel output file name" >&2
		exit 1
esac

(
	# Get LZMA properties + dictionary size
	dd if="$1" bs=1 count=5 skip=28
	# Get uncompressed length (32-bit little-endian), pad to 64-bit
	dd if="$1" bs=1 count=4 skip=20
	dd if=/dev/zero bs=1 count=4
	# Jump to compressed data, pipe into output stream
	dd if="$1" bs=36 skip=1
) | $(dirname "$0")/busybox unlzma > "$2"