building kernel module on flatcar

build-wireguard.sh

#!/bin/bash
# more information on building kernel modules https://docs.flatcar-linux.org/os/kernel-modules/

set -ue

. /etc/os-release
. /etc/flatcar/update.conf

rm -f flatcar_developer_container.bin.bz2.DIGESTS ||:
wget "https://${GROUP}.release.flatcar-linux.net/${FLATCAR_BOARD}/${VERSION}/flatcar_developer_container.bin.bz2.DIGESTS"

set +e
sha512sum -c flatcar_developer_container.bin.bz2.DIGESTS
ret="$?"
set -e
if [ "${ret}" -eq 0 ] ; then
  rm -f \
    flatcar_developer_container.bin.bz2 \
    flatcar_developer_container_contents.txt \
    flatcar_developer_container_packages.txt \
    flatcar_developer_container_licenses.json
fi 

if [ ! -f flatcar_developer_container.bin.bz2 ] ; then
  echo "fetching developer image: https://${GROUP}.release.flatcar-linux.net/${FLATCAR_BOARD}/${VERSION}/flatcar_developer_container.bin.bz2"
  wget \
    "https://${GROUP}.release.flatcar-linux.net/${FLATCAR_BOARD}/${VERSION}/flatcar_developer_container.bin.bz2" \
    "https://${GROUP}.release.flatcar-linux.net/${FLATCAR_BOARD}/${VERSION}/flatcar_developer_container_contents.txt" \
    "https://${GROUP}.release.flatcar-linux.net/${FLATCAR_BOARD}/${VERSION}/flatcar_developer_container_packages.txt" \
    "https://${GROUP}.release.flatcar-linux.net/${FLATCAR_BOARD}/${VERSION}/flatcar_developer_container_licenses.json"
  sha512sum -c flatcar_developer_container.bin.bz2.DIGESTS
fi
if [ ! -f flatcar_developer_container.bin ] ; then
  echo "extracting developer image"
  bzcat flatcar_developer_container.bin.bz2 > flatcar_developer_container.bin
fi

dev() {
  systemd-nspawn -q -i ./flatcar_developer_container.bin --bind=/usr/lib64/modules --bind=/:/hostfs ${@}
}

dev -- passwd -d root

dev -- grep ^VERSION= /etc/os-release | cut -d = -f 2
dev -- grep ^GROUP= /etc/flatcar/update.conf | cut -d = -f 2

## /etc/portage/make.conf needs
# PORTAGE_BINHOST="https://storage.googleapis.com/flatcar-jenkins/boards/amd64-usr/2345.3.1/pkgs/
# https://storage.googleapis.com/flatcar-jenkins/boards/amd64-usr/2345.3.1/toolchain/"

dev -- emerge-gitclone
dev -- emerge -gKv coreos-sources ||:
dev -- emerge -gKv sys-fs/squashfs-tools || :
dev -- sh -c 'zcat /proc/config.gz | dd of=/usr/src/linux/.config' || :
dev -- make -C /usr/src/linux modules_prepare || :

if [ ! -d wireguard-linux-compat ] ; then
  git clone https://git.zx2c4.com/wireguard-linux-compat
else
  pushd wireguard-linux-compat
  git pull -r --autostash
  popd
fi
dev --chdir=/hostfs/root/wireguard-linux-compat/src -- make clean
dev --chdir=/hostfs/root/wireguard-linux-compat/src -- make -j$(nproc)
dev --chdir=/hostfs/root/wireguard-linux-compat/src -- make install

if [ ! -d /opt/modules ] ; then
  mkdir -p /opt/modules
fi
systemctl unmask usr-lib64-modules.mount
cat > /etc/systemd/system/usr-lib64-modules.mount <<EOF
# DO NOT EDIT
[Unit]
Description=Custom Kernel Modules
Before=local-fs.target
ConditionPathExists=/opt/modules

[Mount]
Type=overlay
What=overlay
Where=/usr/lib64/modules
Options=lowerdir=/usr/lib64/modules,upperdir=/opt/modules,workdir=/opt/modules.wd

[Install]
WantedBy=local-fs.target
EOF
systemctl enable --now usr-lib64-modules.mount

if [ ! -d wireguard-tools ] ; then
  git clone --recursive https://git.zx2c4.com/wireguard-tools
else
  pushd wireguard-tools
  git pull -r --autostash
  popd
fi
dev --chdir=/hostfs/root/wireguard-tools/src -- make clean
dev --chdir=/hostfs/root/wireguard-tools/src -- make -j$(nproc)
dev --chdir=/hostfs/root/wireguard-tools/src -- make install DESTDIR=/hostfs/opt/


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