osi-tools/bin/osi-mount

#!/usr/bin/env bash
# Copyright (C) 2018  Luke Shumaker
# Copyright (C) 2023-2024  Umorpha Systems
# SPDX-License-Identifier: AGPL-3.0-or-later
declare -r NAME=osi-mount
declare -r VERSION=20231023

set -euE

install_prefix="$(realpath --logical --canonicalize-missing -- "${BASH_SOURCE[0]}/../..")"
readonly install_prefix

source "${install_prefix}/lib/osi.sh"
source "${install_prefix}/lib/argparse.sh"

main() {
	opt_specs+=(': --inside : : internal-use only')
	opt_visit:inside() { argparse:setmode inside; }
	opt_final:inside() { :; }

	opt_specs+=(': --user : : mount the image RO, run COMMAND as SUDO_USER')
	opt_specs+=(': --root : : mount the image RW, run COMMAND as root, protect the rest of the system')
	local arg_user=
	opt_visit:user() { set_arg_user 'user'; }
	opt_visit:root() { set_arg_user 'root'; }
	set_arg_user() {
		if [[ -n $arg_user ]]; then
			argparse:error "Multiple --user/--root flags given"
		fi
		arg_user=$1
	}
	opt_final:user() { :; }
	opt_final:root() {
		if [[ -z $arg_user ]]; then
			argparse:error "Must specify either --root or --user"
		fi
	}

	opt_specs+=(': --rwdir : DIR : keep DIR read+write, even when --root')
	local arg_rwdirs=()
	opt_visit:rwdir() { arg_rwdirs+=("$1"); }
	opt_final:rwdir() { :; }

	opt_specs+=('-o : --options : LIST : comma-separated list of mount options')
	opt_visit:options() { arg_mountopt="$1"; }
	opt_final:options() { :; }

	local arg_device=
	local arg_mountopt=
	local arg_cmd=()
	opt_positional() {
		case "$#" in
			0) osi.sh:error 0 "Must specify an image, mountpoint, and a command"; return;;
			1) osi.sh:error 0 "Must specify a mountpoint and a command"; return;;
			2) osi.sh:error 0 "Must specify a command"; return;;
		esac
		arg_device=$(realpath -- "$1")
		arg_mountpoint=$2
		arg_cmd=("${@:3}")
	}

	local arg_orig=("$@")
	argparse outside "$@"

	case "$opt_mode" in
		error)
			osi.sh:print "Try '%q --help' for more information" "${0##*/}" >&2
			return $EXIT_INVALIDARGUMENT
			;;
		version)
			osi.sh:print "%s (osi-tools) %s" "$NAME" "$VERSION"
			return $EXIT_SUCCESS
			;;
		help)
			osi.sh:print 'Usage: sudo %s [OPTIONS] --<user|root> FILENAME.img MOUNTPOINT COMMAND...' "${0##*/}"
			osi.sh:print 'Operating System Image: Mount'
			echo
			#     000000000011111111112222222222333333333344444444445555555555666666666677777777778
			#     012345678901234567890123456789012345678901234567890123456789012345678901234567890
			osi.sh:print 'Run COMMAND with FILENAME.img mounted at MOUNTPOINT.'
			echo
			osi.sh:print 'OPTIONS:'
			echo "${opt_flaghelp}" | grep -v -e --inside
			return $EXIT_SUCCESS
			;;

		outside)
			osi.sh:needs_root
			osi.sh:needs_sudo
			if out="$(losetup --associated "$arg_device")" && [[ -n $out  ]]; then
				osi.sh:error 0 "Seems to already be mounted somewhere: %s" "$arg_device"
				printf '%s\n' "$out"
				exit $EXIT_FAILURE
			fi

			# I feel guilty pulling in the hugeness of systemd-run
			# just for `--property=ProtectSystem=strict`, but I
			# don't want to implement my own protection system.
			flags=(
				--pty --same-dir --wait --collect --quiet
				--setenv=SUDO_UID="$SUDO_UID"
				${SOURCE_DATE_EPOCH:+"--setenv=SOURCE_DATE_EPOCH=$SOURCE_DATE_EPOCH"}
				${TMPDIR:+"--setenv=TMPDIR=$TMPDIR"}
				--property=PrivateMounts=true
			)
			case "$arg_user" in
				user) :;;
				root)
					flags+=(
						--property=ProtectSystem=strict
						--property=ProtectHome=read-only
						--property=ReadWritePaths="$arg_device"
						"${arg_rwdirs[@]/#/--property=ReadWritePaths=}"
					)
					;;
			esac
			systemd-run "${flags[@]}" -- "${BASH_SOURCE[0]}" --inside "${arg_orig[@]}"

			if out="$(losetup --associated "$arg_device")" && [[ -n $out  ]]; then
				osi.sh:error 0 "umount'ed, but file is still associated with a loop device: %s" "$arg_device"
				printf '%s\n' "$out"
				exit $EXIT_FAILURE
			fi
			;;
		inside)
			osi.sh:needs_root
			osi.sh:needs_sudo

			case "$arg_user" in
				user) arg_mountopt+="${arg_mountopt:+,}ro";;
				root) arg_mountopt+="${arg_mountopt:+,}rw,discard";;
			esac

			cmd=(mount --no-mtab -o "$arg_mountopt" -- "$arg_device" "$arg_mountpoint")
			r=0
			out=$("${cmd[@]}" 2>&1) || r=$?
			if (( r != 0 )); then
				osi.sh:error $r '%s: %s' "${cmd[*]@Q}" "$out"
			fi

			case "$arg_user" in
				user) osi.sh:sudo -u "#${SUDO_UID}" -- "${arg_cmd[@]}";;
				root) command -- "${arg_cmd[@]}";;
			esac
			;;

		*) osi.sh:bug 'unknown opt_mode: %s' "$opt_mode";;
	esac
}

main "$@"