osi-tools/osi-mount

#!/usr/bin/env bash
# 2018 Luke Shumaker
declare -r NAME=osi-mount
declare -r VERSION=20180812

set -euE
source "${BASH_SOURCE[0]%/*}/lib/osi.sh"

main() {
	needs_root

	local arg_mode=outside
	local arg_user=
	local args
	if ! args="$(getopt -n "${0##*/}" -o hV -l inside:,user,root,help,version -- "$@")"; then
		arg_mode=error
	else
		eval "args=($args)"
		set -- "${args[@]}"
		while true; do
			case "$1" in
				--inside) shift; arg_mode=$1; shift;;
				--user|--root)
					if [[ -n $arg_user ]]; then
						error 0 "Multiple --user/--root flags given"
						arg_mode=error
					fi
					arg_user=${1#--}
					shift
					;;

				-V|--version) shift; arg_mode=version;;
				-h|--help) shift; arg_mode=usage;;
				--) shift; break;;
				*) error 1 'Internal error.  The programmer writing this tool screwed up.';;
			esac
		done
		case "$arg_mode" in
			outside)
				case "$#" in
					0) error 0 "Must specify an image, mountpoint, and a command"; arg_mode=error;;
					1) error 0 "Must specify a mountpoint and a command"; arg_mode=error;;
					2) error 0 "Must specify a command"; arg_mode=error;;
				esac
				if [[ -z $arg_user ]]; then
					error 0 "Must specify either --root or --user"
					arg_mode=error
				fi
				;;
		esac
	fi
	arg_device=$1
	arg_mountpoint=$2
	arg_cmd=("${@:3}")

	case "$arg_mode" in
		error) print "Try '%q --help' for more information" "${0##*/}" >&2; return 2;;
		version)
			print "%s (notsystemd) %s" "$NAME" "$VERSION"
			return 0
			;;
		usage)
			print 'Usage: %s [OPTIONS] --<user|root> FILENAME.img COMMAND...' "${0##*/}"
			print 'Operating System Image: Mount'
			echo
			print 'OPTIONS:'
			# --inside is internal-only; undocumented
			print '  --user  mount the image RO, run COMMAND as SUDO_USER'
			print '  --root  mount the image RW, run COMMAND as root, protect the rest of the system'
			echo
			print '  -h, --help     display this help'
			print '  -V, --version  output version information'
			return 0
			;;

		outside)
			if out="$(losetup --associated "$arg_device")" && [[ -n $out  ]]; then
				error 0 "Seems to already be mounted somewhere: %s" "$arg_device"
				printf '%s\n' "$out"
				exit 1
			fi
			unshare --mount	"${BASH_SOURCE[0]}"  --inside="$arg_user" "${args[@]}"
			if out="$(losetup --associated "$arg_device")" && [[ -n $out  ]]; then
				error 0 "umount'ed, but file is still associated with a loop device: %s" "$arg_device"
				printf '%s\n' "$out"
				exit 1
			fi
			;;
		user|root)
			needs_sudo
			mount --make-rslave /
			case "$arg_mode" in
				user)
					mount_opt=ro
					losetup_flags=(--read-only)
					;;
				root)
					mount_opt=rw
					losetup_flags=()
					# TODO: make the rest of the system RO
					;;
			esac

			cmd=(mount --no-mtab -o "${mount_opt},discard" -- "$arg_device" "$arg_mountpoint")
			r=0
			out=$("${cmd[@]}" 2>&1) || r=$?
			if (( r != 0)); then
				error $r '%s: %s' "${cmd[*]@Q}" "$out"
			fi
			trap "umount --no-mtab -- ${arg_mountpoint@Q}" EXIT

			case "$arg_mode" in
				user) sudo -u "#${SUDO_UID}" -- "${arg_cmd[@]}";;
				root) command -- "${arg_cmd[@]}";;
			esac
			;;

		*) error 1 'Internal error.  The programmer writing this tool screwed up.';;
	esac
}

main "$@"