#!/bin/bash

# this is based on:
# https://github.com/scaleway/kernel-tools#how-to-build-a-custom-kernel-module

set -e

# Determine versions
arch="$(uname -m)"
release="$(uname -r)"
upstream="${release%%-*}"
local="${release#*-}"

export PATH="${PATH:+$PATH:}/usr/bin:/bin:/usr/local/bin:/sbin:/usr/sbin:/usr/local/sbin"

# Get kernel sources
mkdir -p /usr/src
rm -f "/usr/src/linux-${upstream}.tar.xz"
rm -rf "/usr/src/linux-${upstream}"
wget -O "/usr/src/linux-${upstream}.tar.xz" "https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-${upstream}.tar.xz"
tar xf "/usr/src/linux-${upstream}.tar.xz" -C /usr/src/
ln -fns "/usr/src/linux-${upstream}" /usr/src/linux
ln -fns "/usr/src/linux-${upstream}" "/lib/modules/${release}/build"

# Prepare kernel
zcat /proc/config.gz > /usr/src/linux/.config
printf 'CONFIG_LOCALVERSION="%s"\nCONFIG_CROSS_COMPILE=""\n' "${local:+-$local}" >> /usr/src/linux/.config
wget -O /usr/src/linux/Module.symvers "http://mirror.scaleway.com/kernel/${arch}/${release}/Module.symvers"
make -C /usr/src/linux prepare modules_prepare