#!/bin/sh
  # ----------------------------------------------------------------------
  # extract-ikconfig - Extract the .config file from a kernel image
  #
  # This will only work when the kernel was compiled with CONFIG_IKCONFIG.
  #
  # The obscure use of the "tr" filter is to work around older versions of
  # "grep" that report the byte offset of the line instead of the pattern.
  #
  # (c) 2009,2010 Dick Streefland <dick@streefland.net>
  # Licensed under the terms of the GNU General Public License.
  # ----------------------------------------------------------------------
  
  cf1='IKCFG_ST\037\213\010'
  cf2='0123456789'
  
  dump_config()
  {
  	if	pos=`tr "$cf1
  $cf2" "
  $cf2=" < "$1" | grep -abo "^$cf2"`
  	then
  		pos=${pos%%:*}
  		tail -c+$(($pos+8)) "$1" | zcat > $tmp1 2> /dev/null
  		if	[ $? != 1 ]
  		then	# exit status must be 0 or 2 (trailing garbage warning)
  			cat $tmp1
  			exit 0
  		fi
  	fi
  }
  
  try_decompress()
  {
  	for	pos in `tr "$1
  $2" "
  $2=" < "$img" | grep -abo "^$2"`
  	do
  		pos=${pos%%:*}
  		tail -c+$pos "$img" | $3 > $tmp2 2> /dev/null
  		dump_config $tmp2
  	done
  }
  
  # Check invocation:
  me=${0##*/}
  img=$1
  if	[ $# -ne 1 -o ! -s "$img" ]
  then
  	echo "Usage: $me <kernel-image>" >&2
  	exit 2
  fi
  
  # Prepare temp files:
  tmp1=/tmp/ikconfig$$.1
  tmp2=/tmp/ikconfig$$.2
  trap "rm -f $tmp1 $tmp2" 0
  
  # Initial attempt for uncompressed images or objects:
  dump_config "$img"
  
  # That didn't work, so retry after decompression.
  try_decompress '\037\213\010' xy    gunzip
  try_decompress '\3757zXZ\000' abcde unxz
  try_decompress 'BZh'          xy    bunzip2
  try_decompress '\135\0\0\0'   xxx   unlzma
  try_decompress '\211\114\132' xy    'lzop -d'
  
  # Bail out:
  echo "$me: Cannot find kernel config." >&2
  exit 1