pmon-update

#!/bin/bash
## PMON Bootloader Menu Updater For Debian
## Copyright (C) 2020 Boyue Zhang <boyue.zhang@pzhang.net>
## Copyright (C) 2020 Jiaxun Yang <jiaxun.yang@flygoat.com>
##
## Based on u-boot-update, which is:
## Copyright (C) 2006-2012 Daniel Baumann <daniel.baumann@progress-technologies.net>
## Copyright (C) 2016-2017 Riku Voipio    <riku.voipio@linaro.org>
##
## This program comes with ABSOLUTELY NO WARRANTY; for details see COPYING.
## This is free software, and you are welcome to redistribute it
## under certain conditions; see COPYING for details.

set -e

_PMON_DIRECTORY="/boot"

Update ()
{
	 # Upate target file using source content
	_TARGET="${1}"
	_SOURCE="${2}"

	_TMPFILE="${_TARGET}.tmp"
	rm -f "${_TMPFILE}"

	echo "${_SOURCE}" > "${_TMPFILE}"

	if [ -e "${_TARGET}" ] && cmp -s "${_TARGET}" "${_TMPFILE}"
	then
		rm -f "${_TMPFILE}"
	else
		# FIXME: should use fsync here
		echo "P: Updating ${_TARGET}..."
		mv -f "${_TMPFILE}" "${_TARGET}"
	fi
}

detect_linux_images()
{
	unset _KERNELS
	cd /boot
	for kernel in vmlinuz-* vmlinux-*; do
		if ! readelf -h $kernel; then
			# Not a valid ELF file, skip.
			continue
		else
			export _KERNELS="${_KERNELS} $kernel"
		fi
	done
}

# FIXME: switch to check boot.cfg file can be written to
# User is unprivileged
if [ "$(id -u)" -ne 0 ]
then
	echo "E: need root privileges"
	exit 1
fi

# Redirect stdout to stderr due Debconf usage
exec 1>&2

# Reading the default file
if [ -e /etc/default/pmon-update ]
then
	. /etc/default/pmon-update
fi

PMON_UPDATE="${PMON_UPDATE:-true}"

if [ "${PMON_UPDATE}" != "true" ]
then
	echo "P: pmon-update is disabled in /etc/default/pmon-update."

	exit 0
fi


# Setting defaults if /etc/default/pmon-update is missing

PMON_ALTERNATIVES="${PMON_ALTERNATIVES}"
PMON_BOOTDEV="${PMON_BOOTDEV:-(wd0,0)}"
PMON_DEFAULT="${PMON_DEFAULT:-0}"
PMON_ENTRIES="${PMON_ENTRIES:-all}"
PMON_TIMEOUT="${PMON_TIMEOUT:-5}"
PMON_MENU_LABEL="${PMON_MENU_LABEL:-Linux}"
PMON_PARAMETERS="${PMON_PARAMETERS:-ro quiet}"

# Find parameter for root from fstab
if [ -z "${PMON_ROOT}" ]
then
	# Use findmnt(8) to determine system root
	if command -v findmnt > /dev/null
	then
		PMON_ROOT="findmnt -n -o SOURCE /"
	elif [ -e /etc/fstab ]
	then
		# Find system root from /etc/fstab
		while read _LINE
		do

read _FS_SPEC _FS_FILE _FS_VFSTYPE _FS_MNTOPS _FS_FREQ _FS_PASSNO << EOF
${_LINE}
EOF

			if [ "${_FS_FILE}" = "/" ]
			then
				case "${_FS_SPEC}" in
					"#"*)
						;;
					*)
						PMON_ROOT="root=${_FS_SPEC}"
						break
						;;
				esac
			fi
		done < /etc/fstab
	else
		echo "E: Unable to detect root device! Please install util-linux or record your system root partition in /etc/fstab."
		exit 1
	fi
fi

# if not in fsrab, try from current kernel arguments
if [ -z "${PMON_ROOT}" ]
then
	for param in `cat /proc/cmdline`
	do
		if [[ $param == root=* ]]
		then
			PMON_ROOT="$param"
			break
		fi
	done
fi


# Create extlinux.conf
_CONFIG="\
## ${_PMON_DIRECTORY}/boot.cfg
##
## IMPORTANT WARNING
##
## The configuration of this file is generated automatically.
## Do not edit this file manually, use: pmon-update

default ${PMON_DEFAULT}
timeout ${PMON_TIMEOUT}
showmenu 1
"

# Find linux versions
detect_linux_images

# Find boot directory as seen in pmon, and path prefix while in linux
if [ "$(stat --printf %d /)" = "$(stat --printf %d /boot)" ]
then
	# / and /boot are on the same filesystem
	_BOOT_PATH="${PMON_BOOTDEV}/boot"
else
	# / and /boot are not on the same filesystem
	_BOOT_PATH="${PMON_BOOTDEV}"
fi


for _KERNEL in ${_KERNELS}
do
	# Strip kernel prefix to derive version.
	_VERSION=${_KERNEL#*-}
	echo "P: Writing config for ${_KERNEL}..."

	_ENTRY="${_ENTRY:-1}"

	if [ -e /boot/initrd.img-${_VERSION} ]
	then
		_INITRD="initrd ${_BOOT_PATH}/initrd.img-${_VERSION}"
	else
		_INITRD=""
	fi

	if echo ${PMON_ALTERNATIVES} | grep -q default
	then

	# Writing default entry
	_CONFIG="${_CONFIG}

title ${PMON_MENU_LABEL} ${_VERSION}
	kernel ${_BOOT_PATH}/${_KERNEL}
	${_INITRD}
	args ${PMON_ROOT} ${PMON_PARAMETERS}"

	fi

	if echo ${PMON_ALTERNATIVES} | grep -q recovery
	then

	# Writing recovery entry
	_CONFIG="${_CONFIG}

title ${PMON_MENU_LABEL} ${_VERSION} (Rescue Target)
	kernel ${_BOOT_PATH}/${_KERNEL}
	${_INITRD}
	args ${PMON_ROOT} $(echo ${PMON_PARAMETERS} | sed -e 's| quiet||') single
	"

	fi

	if [ "${PMON_ENTRIES}" = "${_ENTRY}" ]
	then
		break
	fi
done

# Append extra custom config
if [ -e /boot/pmon/custom.cfg ]
then
	_CONFIG="${_CONFIG}

$(cat /boot/pmon/custom.cfg)
"
fi

Update "${_PMON_DIRECTORY}/boot.cfg" "${_CONFIG}"