# $conffiles is a list of patters of the form
# ^[XO-] <pattern> [<value>]
# X means enable, O disable, and - removes it
# pattern can use '*' as a wildcard for [^ #]
# optionaly can set a value different that y
apply_conffiles() {
	local f x; 
	rm -f /tmp/$$.sed
	for f in $conffiles; do if [ -f "$f" ]; then
		while read a c v; do
			x="${c//\\*/[^ #]*}"
			x="^\(# \)\?\($x\)[= ].*\$"
			
			# value
			if [ -z "$v" ]; then
				v='y'
			fi
			case "$a" in
				X)	echo "apply_conffiles: rule $c=$v."
					echo "s,$x,\2=$v,g" >> /tmp/$$.sed
					;;
				O)	echo "apply_conffiles: rule unset $c."
					echo "s,$x,# \2 is not set,g" >> /tmp/$$.sed
					;;
				-)	echo "apply_conffiles: rule remove $c."
					echo "s,$x,,g" >> /tmp/$$.sed
					;;
				*)
					echo "apply_conffiles: bad rule $a $c $v"
					;;
			esac
		done < <( cat $f ); 
	fi ; done
	sed -f /tmp/$$.sed .config > $1
	rm /tmp/$$.sed
}

# get default config, and filter considering <n>
# levels, because new options can appear and other disappear
auto_config() {
	local j=1 n="${1:-1}"

	# defconfig
	eval "$MAKE defconfig $makeopt"
	cp -v .config .config.$j

	j=2 ; for (( i=1 ; i<n ; i++, j++ )) {
		apply_conffiles .config.$j
		cp -v .config.$j .config
		
		eval "$MAKE oldconfig $makeopt"
		(( j++ )) ; cp -v .config .config.$j
		}

	# second round
	apply_conffiles .config.$j
	cp -v .config.$j .config
}