custom-kernel-gen

#!/bin/bash

set -e

trap '
    ret=$?;
    set +e;
    if [[ $ROOTFS ]]; then
        rm -rf $ROOTFS
    fi
    if [[ $ret -ne 0 ]]; then
        echo FAILED TO GENERATE CUSTOM KERNEL >&2
    fi
    exit $ret;
    ' EXIT

# clean up after ourselves no matter how we die.
trap 'exit 1;' SIGINT

usage() {
    echo "
Usage: $(basename $0) [OPTIONS] [dir]
Pack a kernel to be installed in another board

OPTIONS
    -x             generate auto-extract script
    -c [J|z|zstd]  pass flag to tar while packing

ARGUMENTS
    dir		   directory with the build. If not specified, CWD is used
" 1>&$1;
    exit $(($1 - 1));
}

SCRIPT_DIR=$(dirname $(realpath ${BASH_SOURCE[0]}))

OPT_AUTOEXTRACT=0
OPT_COMPRESS="zstd"
EXT=""
while getopts "xc:h" o; do
    case "${o}" in
        x) OPT_AUTOEXTRACT=1; shift ;;
        c) OPT_COMPRESS=${OPTARG}; shift 2 ;;
        h) usage 1; shift ;;
        \?) usage 2; shift ;;
    esac
done

OPT_UNCOMPRESS=$OPT_COMPRESS

if [ $# -gt 0 ]; then
	cd $1
fi

case "$OPT_COMPRESS" in
    J) EXT="tar.xz"; OPT_COMPRESS=-J;;
    z) EXT="tar.gz"; OPT_COMPRESS=-z;;
    zstd) EXT="tar.zstd"; OPT_COMPRESS=--zstd;;
    "") EXT=".tar";;
    \?) usage 2;;
esac

KVER=$(make kernelrelease)
ROOTFS=$(mktemp -d --tmpdir custom-kernel.XXXXXXXX)

# workaround for make modules_install installing in /lib, which will be created
# as a dir if the directory didn't exit
mkdir -p $ROOTFS/usr/lib/modules
ln -s usr/lib $ROOTFS/lib

make modules_install INSTALL_MOD_PATH=$ROOTFS

# on target this will mean nothing
rm -f $ROOTFS/usr/lib/modules/$KVER/build || true
rm -f $ROOTFS/usr/lib/modules/$KVER/source || true

# copy the kernel image over to /usr/lib/custom-kernel - only one kernel will
# be kept there... user is supposed to call kernel-install on target (which
# copies this kernel to /boot) before installing another kernel
mkdir -p $ROOTFS/usr/lib/custom-kernel/
cp arch/x86/boot/bzImage $ROOTFS/usr/lib/custom-kernel/vmlinuz
cp System.map $ROOTFS/usr/lib/custom-kernel/
echo $KVER > $ROOTFS/usr/lib/custom-kernel/VERSION

# target doesn't need the workaround, so now remove it
rm $ROOTFS/lib

if [ $OPT_AUTOEXTRACT -eq 1 ]; then
    s=${PWD}/linux-${KVER}${EXT}.sh
    sed "s/^OPT_COMPRESS=.*/OPT_COMPRESS=$OPT_UNCOMPRESS/" $SCRIPT_DIR/custom-kernel-install > "$s"
    echo -e "\nexit 0" >> "$s"
    echo -e "\n__CUSTOM_KERNEL_BELLOW__" >> "$s"
    ( cd $ROOTFS && tar -c ${OPT_COMPRESS} * >> "$s" )
    chmod +x "$s"
else
    D=${PWD}
    s=linux-${KVER}-config.xz
    ( cd $ROOTFS && tar -cf $D/linux-${KVER}${EXT} ${OPT_COMPRESS} * )
    xz --stdout .config > "$s"
fi

echo "Done: $s"