#!/bin/bash

# update-kernel.sh - automatically compile and install new kernel sources
# Licensed under the terms of the GNU GPLv3 or later
# Proprietary Software Must Perish!

# AUTHOR: Johannes Truschnigg ( johannes.truschnigg@gmx.at || http://johannes.truschnigg.info )

SCRIPTNAME="${0##*/}";

die() {
	printf "${SCRIPTNAME}: Fatal: %s\n" "${1:-reason undefined.}" 2>&1;
	exit ${2:-1};
}

goon() {
	read -sp "${1:-Continue executing ${SCRIPTNAME}?} (^C->no || [ENTER]->yes)" DUMMY;
	echo;
}

[[ "${UID}" > 0 ]] && die "must be run as root.";

fgrep -q /boot /etc/fstab && (mount | fgrep -q /boot || mount /boot);

unset ESELECT;
ESELECT=$(which eselect 2>/dev/null);

if [[ -n "${ESELECT}" ]];
then
	# Gentoo specific way
	"${ESELECT}" kernel set \
	"$(${ESELECT} --no-colour kernel list | tail -n1 | grep -o [0-9] | head -n1)";
else
	# hopefully works anywhere
	cd /usr/src/;
	unset KERNELS;
	declare -a KERNELS;
	KERNELS=(linux-*);
	[[ -z "${KERNELS}" ]] && die "no kernel-source-dir candidates found.";

	unset TARGET;
	for candidate in ${KERNELS[*]};
	do
		[[ -d "${candidate}" && -f "${candidate}/Kbuild" ]] && TARGET="${candidate}";
	done

	[[ -z "${TARGET}" ]] && die "no suitable kernel-source-dir found.";

	rm -f /usr/src/linux;
	ln -s "${TARGET}" linux;
fi

printf "Selected kernel-source-dir: %s\n" "$(readlink /usr/src/linux)";

goon "Continue configuring kernel-source?";
cd /usr/src/linux;
#TODO: make this more clever/reliable
unset CONFIG_FOUND;
[[ -e "/usr/src/linux-$(uname -r)/.config" ]] && cp "/usr/src/linux-$(uname -r)/.config" .config && CONFIG_FOUND=1;
[[ -e "/proc/config.gz" ]] && zcat /proc/config.gz > .config && CONFIG_FOUND=1;
[[ "${CONFIG_FOUND}" != 1 ]] && die "could not find a suitable .config.";
make oldconfig;

goon "Continue compiling kernel?";
unset JOBS_IN_PARALLEL;
JOBS_IN_PARALLEL=$(($(fgrep -c vendor_id /proc/cpuinfo) + 1) 2>/dev/null);
make -j${JOBS_IN_PARALLEL:-2};

goon "Continue installing kernel-image and modules (if any)?";
make install &&\
make modules_install &&\
exit 0;