mount-img

#!/bin/bash

#
# SPDX-License-Identifier: Apache-2.0
#
# Name:
#	Mount image utility
#
# Authors:
#	2017	Zack YL Shih	<ZackYL.Shih@moxa.com>
#	2018	Fero JD Zhou	<FeroJD.Zhou@moxa.com>
#	2019	Ken CJ Chou	<KenCJ.Chou@moxa.com>
#

set -e

VERSION=1.3.0

usage() {
	echo -e "Usage:"
	echo -e "  Mount image"
	echo -e "    # ${0} m|mount <image_file> <mount_dir>"
	echo -e "  Unmount image"
	echo -e "    # ${0} u|umount <mount_dir>"
	echo -e ""
	echo -e "Parameters:"
	echo -e "  image_file"
	echo -e "    A image format file, usually with \".img\" file extension"
	echo -e ""
	echo -e "  mount_dir"
	echo -e "    The path of directory for the image to be mounted"
	echo -e ""
	echo -e "Examples:"
	echo -e "  Mount an image file named \"example.img\" at \"/tmp/mnt\""
	echo -e "  # ./mount-img mount example.img /tmp/mnt"
	echo -e ""
	echo -e "  Unmount the image which mounted at \"/tmp/mnt\""
	echo -e "  # ./mount-img umount /tmp/mnt"
	echo -e ""
	return 0
}

get_value() {
	local tmp
	tmp="$(echo "${1}" | grep "^${2}=")"
	echo "${tmp##*=}"
	return 0
}

get_image_info() {
	local imgfile=${1}
	local fdisk_l_output sec_size num_part part_info
	local line count tmp

	echo "IMAGE_FILE=${imgfile}"
	echo "IMAGE_FILENAME=${imgfile##*/}"

	fdisk_l_output="$(fdisk -l ${imgfile})"

	# get sector size
	sec_size="$(echo "${fdisk_l_output}" | grep "^Units:")"
	sec_size="${sec_size##*= }"
	sec_size="${sec_size%% bytes}"
	echo "IMAGE_SECTOR_SIZE=${sec_size}"

	# get partition information
	part_info="$(echo "${fdisk_l_output}" | grep "^${imgfile}[0-9]")"
	num_part=$(echo "${part_info}" | wc -l)
	echo "IMAGE_NUM_OF_PARTITIONS=${num_part}"

	count=0
	while read -r line; do
		count=$((count + 1))
		# bootflag is set if the line contains '*'
		if echo "${line}" | grep -q "*"; then
			line="$(echo "${line}" | sed 's/*//')"
			echo "IMAGE_P${count}_BOOTFLAG=y"
		else
			echo "IMAGE_P${count}_BOOTFLAG=n"
		fi
		tmp="$(echo "${line}" | awk '{print $1}')"
		echo "IMAGE_P${count}_NUMBER=${tmp##*${imgfile}}"
		tmp="$(echo "${line}" | awk '{print $2}')"
		echo "IMAGE_P${count}_OFFSET=$((tmp * sec_size))"
		tmp="$(echo "${line}" | awk '{print $4}')"
		echo "IMAGE_P${count}_SIZE=$((tmp * sec_size))"
		tmp="$(echo "${line}" | awk '{print $6}')"
		echo "IMAGE_P${count}_FSTYPE=${tmp}"
	done <<< "${part_info}"
	return 0
}

get_device_for_mountpoint() {
	local mnt_point=${1}
	local src tgt

	while read -r src tgt; do
		if [ "${tgt}" == "${mnt_point}" ]; then
			echo "${src}"
			return 0
		fi
	done <<< "$(df --output=source,target)"
	echo "Error: \"${mnt_point}\" is not a mount point"
	return 1
}

mount_img() {
	local img=${1}
	local mnt_dir=${2}
	local img_info i n_part

	if ! [ -f "${img}" ]; then
		echo "image file not found: ${img}" >&2
		exit 2
	fi
	img_info="$(get_image_info "${img}")"

	mkdir -p ${mnt_dir}
	if [ -n "$(ls -A ${mnt_dir})" ]; then
		echo "Error: target directory is not empty" >&2
		exit 2
	fi

	n_part=$(get_value "${img_info}" "IMAGE_NUM_OF_PARTITIONS")
	for i in $(seq 1 ${n_part}); do
		local p_no=$(get_value "${img_info}" "IMAGE_P${i}_NUMBER")
		local p_offset=$(get_value "${img_info}" "IMAGE_P${i}_OFFSET")
		local p_size=$(get_value "${img_info}" "IMAGE_P${i}_SIZE")
		local mnt_point=${mnt_dir}/p${p_no}
		local loopdev

		loopdev="$(losetup -f)"
		losetup -o ${p_offset} --sizelimit ${p_size} ${loopdev} ${img}

		# do nothing for Empty disk type
		if [ "${part_type}" != "0" ]; then
			mkdir -p "${mnt_point}"
			mount "${loopdev}" "${mnt_point}" || true
		fi
	done
	return 0
}

unmount_img() {
	local mnt_dir=${1}
	local part_mnt loopdev

	if ! [ -d "${mnt_dir}" ]; then
		echo "directory not exist: ${mnt_dir}" >&2
		exit 2
	fi
	mnt_dir="$(realpath ${mnt_dir})"

	for part_mnt in ${mnt_dir}/*; do
		if mountpoint -q ${part_mnt}; then
			loopdev="$(get_device_for_mountpoint "${part_mnt}")"
			umount "${part_mnt}" || true
			losetup -d ${loopdev}
		else
			echo "Warning: a non-mountpoint found \"${part_mnt}\"" >&2
		fi
	done
	rm -rf ${mnt_dir}
	return 0
}

main() {
	case "${1}" in
	"-v"|"--version")
		echo ${VERSION}
		;;
	"m"|"mount")
		if [ $# -ne 3 ]; then
			usage >&2
			return 1
		fi

		mount_img "${2}" "${3}"		
		;;
	"u"|"umount")
		if [ $# -ne 2 ]; then
			usage >&2
			return 1
		fi

		unmount_img "${2}"		
		;;
	*)
		echo "Unknown action: \"${1}\"" >&2
		usage >&2
		return 1
		;;
	esac
}

if [ "${EUID}" -ne 0 ]; then
	echo "Please run as root" >&2
	exit 1
fi

main "$@"
exit 0