dockerfiles/kernel-builder/build_kernel

#!/bin/bash
set -e
set -o pipefail

linux_next(){
	local dir="/usr/src/linux-next"

	# Check if we already have the source for linux-next checked out.
	if [[ -d "$dir" ]]; then
		echo "Updating linux-next tree git remotes..."
		(
		cd "$dir"

		git checkout master
		git remote update
		)
	else
		echo "Cloning the git source for linux..."
		git clone https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git "$dir"

		echo "Adding the linux-next git remote..."
		(
		cd "$dir"

		git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
		)
	fi

	echo "Fetching the linux-next remote and updating tags..."
	(
	cd "$dir"

	git fetch linux-next
	git fetch --tags linux-next
	)

	local branch
	branch="next-$(date +%Y%m%d)"
	echo "Checking out the correct branch ${branch}..."
	(
	cd "$dir"

	git checkout -b "$branch" "$branch"
	)
}

install_kernel(){
	local VERSION=$1
	local OPT=$2
	local DIR="/usr/src/linux-${VERSION}"

	if [[ -z $VERSION ]]; then
		echo "Please specify a kernel version."
		exit 1
	elif [[ "$VERSION" == "next" ]]; then
		DIR="/usr/src/linux-next"
		linux_next
	fi

	if [[ "$VERSION" != "next" ]]; then
		local MAJOR_VERSION=${VERSION:0:1}
		local V=( "${VERSION//./ }" )
		local MAJOR_MINOR_VERSION="${V[0]}.${V[1]}"

		# Get the kernel source.
		echo "Getting the kernel source for linux-${VERSION}..."
		echo "This might take a bit to download. Hang tight!"
		if [[ "$VERSION" == *-rc* ]]; then
			[ -d "$DIR" ] || curl -sSL "https://git.kernel.org/torvalds/t/linux-${VERSION}.tar.gz" | tar -C /usr/src -xz

			MAJOR_MINOR_VERSION="${MAJOR_VERSION}.x-rcN"
		else
			[ -d "/usr/src/linux-${VERSION}" ] || curl -sSL "https://cdn.kernel.org/pub/linux/kernel/v${MAJOR_VERSION}.x/linux-${VERSION}.tar.xz" | tar -C /usr/src -xJ
		fi

		# Git clone and apply the patches for the aufs filesystem.
		if [[ "$OPT" == "aufs" ]] && [[ ! -d "${DIR}/fs/aufs" ]]; then
			aufsdir=/aufs4-standalone

			echo "Cloning the git patches for the aufs filesystem..."
			git clone --depth 1 --branch "aufs${MAJOR_MINOR_VERSION}" --single-branch https://github.com/sfjro/aufs4-standalone.git "$aufsdir"

			(
			cd "$DIR"

			echo "Applying patch for the aufs filesystem..."
			git apply $aufsdir/aufs4-kbuild.patch
			git apply $aufsdir/aufs4-base.patch
			git apply $aufsdir/aufs4-mmap.patch
			cp -r $aufsdir/{Documentation,fs} .
			cp $aufsdir/include/uapi/linux/aufs_type.h include/uapi/linux/
			)
		fi
	fi


	# Install Wireguard VPN into the kernel.
	if [[ "$OPT" == "wireguard" ]] && [[ ! -f "${DIR}/net/wireguard/allowedips.c" ]]; then
		echo "Applying patch for Wireguard VPN..."
		(
		cd "$DIR"
		/wireguard/contrib/kernel-tree/create-patch.sh | patch -p1
		)
		echo "Patch for Wireguard VPN successfully applied!"
	fi

	# Copy the config from /usr/src/config if it does not already exist.
	if [[ ! -f "${DIR}/.config" ]] && [[ -f "/usr/src/config" ]]; then
		(
		cd "$DIR"

		cp ../config .config

		# Add the config options for the aufs filesystem.
		if [[ "$OPT" == "aufs" ]]; then
			echo "CONFIG_AUFS_FS=y" >> .config
		fi

		# Add the config options for Wireguard VPN.
		if [[ "$OPT" == "wireguard" ]]; then
			echo "CONFIG_WIREGUARD=y" >> .config
		fi
		)
	fi

	(
	cd "$DIR"

	echo "Building the kernel..."
	make -j"$JOBS"
	echo "Installing the modules..."
	make modules_install
	echo "Installing the kernel..."
	make install
	)
	(
	echo "Stripping the modules..."
	find /lib/modules/ -name "*.ko" -exec strip --strip-unneeded {} +
	)
}

# shellcheck disable=SC2068
install_kernel $@

echo "Kernel successfully installed!"
echo "You will now want to run:"
echo "    update-initramfs -u -k all"
echo "and"
echo "    update-grub2"
echo "or the equivalent for your system."