#!/bin/sh
#
# Generate a filesystem-based image

set -e
set -u

# Print usage message
#
help() {
    echo "usage: ${0} [OPTIONS] foo.lkrn|foo.efi [bar.lkrn|bar.efi,...]"
    echo
    echo "where OPTIONS are:"
    echo " -h       show this help"
    echo " -o FILE  save image to file"
    echo " -p PAD   pad filesystem (in kB)"
}

# Get hex byte from binary file
#
get_byte() {
    local FILENAME
    local OFFSET

    FILENAME="${1}"
    OFFSET="${2}"

    od -j "${OFFSET}" -N 1 -A n -t x1 -- "${FILENAME}" | tr -d " "
}

# Get hex word from binary file
#
get_word() {
    local FILENAME
    local OFFSET

    FILENAME="${1}"
    OFFSET="${2}"

    od -j "${OFFSET}" -N 2 -A n -t x1 -- "${FILENAME}" | tr -d " "
}

# Get appropriate EFI boot filename for CPU architecture
#
efi_boot_name() {
    local FILENAME
    local PESIG
    local ARCH

    FILENAME="${1}"

    MZSIG=$(get_word "${FILENAME}" 0)
    if [ "${MZSIG}" != "4d5a" ] ; then
	echo "${FILENAME}: invalid MZ header" >&2
	exit 1
    fi
    PEOFF=$(get_byte "${FILENAME}" 0x3c)
    PESIG=$(get_word "${FILENAME}" "0x${PEOFF}")
    if [ "${PESIG}" != "5045" ] ; then
	echo "${FILENAME}: invalid PE header" >&2
	exit 1
    fi
    ARCH=$(get_word "${FILENAME}" $(( "0x${PEOFF}" + 4 )) )
    case "${ARCH}" in
	"4c01" )
	    echo "BOOTIA32.EFI"
	    ;;
	"6486" )
	    echo "BOOTX64.EFI"
	    ;;
	"c201" )
	    echo "BOOTARM.EFI"
	    ;;
	"64aa" )
	    echo "BOOTAA64.EFI"
	    ;;
	* )
	    echo "${FILENAME}: unrecognised EFI architecture ${ARCH}" >&2
	    exit 1
    esac
}

# Copy syslinux file
#
copy_syslinux_file() {
    local FILENAME
    local DESTDIR
    local SRCDIR

    FILENAME="${1}"
    DESTDIR="${2}"

    for SRCDIR in \
	/usr/lib/syslinux \
	/usr/lib/syslinux/bios \
	/usr/lib/syslinux/modules/bios \
	/usr/share/syslinux \
	/usr/share/syslinux/bios \
	/usr/share/syslinux/modules/bios \
	/usr/local/share/syslinux \
	/usr/local/share/syslinux/bios \
	/usr/local/share/syslinux/modules/bios \
	/usr/lib/ISOLINUX \
	; do
	if [ -e "${SRCDIR}/${FILENAME}" ] ; then
	    cp "${SRCDIR}/${FILENAME}" "${DESTDIR}/"
	    break
	fi
    done
}

# Parse command-line options
#
OUTFILE=
PAD=0
while getopts "hlo:p:" OPTION ; do
    case "${OPTION}" in
	h)
	    help
	    exit 0
	    ;;
	o)
	    OUTFILE="${OPTARG}"
	    ;;
	p)
	    PAD="${OPTARG}"
	    ;;
	*)
	    help
	    exit 1
	    ;;
    esac
done
if [ -z "${OUTFILE}" ]; then
    echo "${0}: no output file given" >&2
    help
    exit 1
fi
shift $(( OPTIND - 1 ))

# Create temporary working directory
#
WORKDIR=$(mktemp -d "${OUTFILE}.XXXXXX")
ISODIR="${WORKDIR}/iso"
FATDIR="${WORKDIR}/fat"
mkdir -p "${ISODIR}" "${FATDIR}"

# Configure output
#
case "${OUTFILE}" in
    *.iso)
	ISOIMG="${OUTFILE}"
	FATIMG="${ISODIR}/esp.img"
	BIOSDIR="${ISODIR}"
	SYSLINUXCFG="${ISODIR}/isolinux.cfg"
	;;
    *)
	ISOIMG=
	FATIMG="${OUTFILE}"
	BIOSDIR="${FATDIR}"
	SYSLINUXCFG="${FATDIR}/syslinux.cfg"
	;;
esac
ISOARGS=

# Locate required tools
#
if [ -n "${ISOIMG}" ] ; then
    MKISOFS=
    for CMD in genisoimage mkisofs xorrisofs ; do
	if ${CMD} --version >/dev/null 2>/dev/null ; then
	    MKISOFS="${CMD}"
	    break
	fi
    done
    if [ -z "${MKISOFS}" ] ; then
	echo "${0}: cannot find mkisofs or equivalent" >&2
	exit 1
    fi
fi

# Copy files to temporary working directory
#
LKRN=
EFI=
for FILENAME ; do
    case "${FILENAME}" in
	*.lkrn)
	    DESTDIR="${BIOSDIR}"
	    DESTFILE=$(basename "${FILENAME}")
	    if [ -z "${LKRN}" ] ; then
		echo "SAY iPXE boot image" > "${SYSLINUXCFG}"
		echo "TIMEOUT 30" >> "${SYSLINUXCFG}"
		echo "DEFAULT ${DESTFILE}" >> "${SYSLINUXCFG}"
	    fi
	    echo "LABEL ${DESTFILE}" >> "${SYSLINUXCFG}"
	    echo " KERNEL ${DESTFILE}" >> "${SYSLINUXCFG}"
	    LKRN=1
	    ;;
	*.efi)
	    DESTDIR="${FATDIR}/EFI/BOOT"
	    DESTFILE=$(efi_boot_name "${FILENAME}")
	    if [ -z "${EFI}" ] ; then
		mkdir -p "${DESTDIR}"
	    fi
	    EFI=1
	    ;;
	*)
	    echo "${0}: unrecognised input filename ${FILENAME}" >&2
	    help
	    exit 1
	    ;;
    esac
    if [ -e "${DESTDIR}/${DESTFILE}" ] ; then
	echo "${0}: duplicate ${DESTFILE} from ${FILENAME}" >&2
	exit 1
    fi
    cp "${FILENAME}" "${DESTDIR}/${DESTFILE}"
done

# Configure ISO image, if applicable
#
# Note that the BIOS boot files are required even for an EFI-only ISO,
# since isohybrid will refuse to work without them.
#
if [ -n "${ISOIMG}" ] ; then
    copy_syslinux_file "isolinux.bin" "${ISODIR}"
    copy_syslinux_file "ldlinux.c32" "${ISODIR}" || true
    ISOARGS="${ISOARGS} -no-emul-boot -eltorito-boot isolinux.bin"
    ISOARGS="${ISOARGS} -boot-load-size 4 -boot-info-table"
    if [ -n "${EFI}" ] ; then
	ISOARGS="${ISOARGS} -eltorito-alt-boot -no-emul-boot -e esp.img"
    else
	FATIMG=
    fi
fi

# Create FAT filesystem image, if applicable
#
if [ -n "${FATIMG}" ] ; then
    FATSIZE=$(du -s -k ${FATDIR} | cut -f1)
    FATSIZE=$(( FATSIZE + PAD + 256 ))
    touch "${FATIMG}"
    if [ "${FATSIZE}" -le "1440" ] ; then
	truncate -s 1440K "${FATIMG}"
	mformat -f 1440 -i "${FATIMG}" ::
    else
	truncate -s "${FATSIZE}K" "${FATIMG}"
	mformat -i "${FATIMG}" ::
    fi
    mcopy -i "${FATIMG}" -s "${FATDIR}"/* ::
    if [ "${BIOSDIR}" = "${FATDIR}" ] ; then
	syslinux "${FATIMG}"
    fi
fi

# Create ISO filesystem image, if applicable
#
if [ -n "${ISOIMG}" ] ; then
    "${MKISOFS}" -quiet -volid "iPXE" -preparer "iPXE build system" \
	    -appid "iPXE - Open Source Network Boot Firmware" \
	    -publisher "ipxe.org" -sysid "iPXE" -J -R -o "${ISOIMG}" \
	    ${ISOARGS} "${ISODIR}"
    if isohybrid --version >/dev/null 2>/dev/null ; then
	isohybrid "${ISOIMG}"
    fi
fi

# Clean up temporary working directory
#
rm -rf "${WORKDIR}"