mount-image

#! /usr/bin/env python3

import json
import sys

from contextlib import contextmanager, ExitStack
from os import chdir, getcwd
from pty import spawn
from sh import ErrorReturnCode_32, ErrorReturnCode_12
from sh import losetup, lsblk, mkdir, mount, rmdir, umount
from tempfile import mkdtemp
from time import sleep

@contextmanager
def losetup_context_manager(image):
    print("image", image, losetup)
    device = losetup("-f", "--show", "-P", image).stdout.decode("utf8").strip()
    yield device
    losetup("-d", device)


@contextmanager
def mount_context_manager(parent_folder, part):
    folder = parent_folder + "/" + part["name"]
    mkdir(folder)
    mounted = False
    try:
        mount(part["device"], folder)
        mounted = True
    except (ErrorReturnCode_32, ErrorReturnCode_12):
        print("Warning: couldn't mount", part["name"])
    yield folder
    if mounted:
        umount(folder)
    rmdir(folder)


@contextmanager
def chdir_context_manager(path):
    old_dir = getcwd()
    chdir(path)
    yield
    chdir(old_dir)


def part_name(part):
    result = part["name"][part["name"].rfind("p") + 1:]
    label = part["label"]
    if label is not None:
        result += "_" + label
    return result


def part_device(part):
    return "/dev/" + part["name"]


def main():
    with losetup_context_manager(sys.argv[1]) as device:
        # sleep requied for labels
        sleep(1)
        parts = json.loads(lsblk("--json", "-o", "name,label", device).stdout)
        parts = parts["blockdevices"][0]["children"]
        tmpdir = mkdtemp()
        parts = [
            {"name": part_name(part), "device": part_device(part)}
            for part in parts
        ]
        with ExitStack() as stack:
            for part in parts:
                stack.enter_context(mount_context_manager(tmpdir, part))
            print("All image partitons mounted in", tmpdir, "exit this shell to umount.")
            try:
                with chdir_context_manager(tmpdir):
                    spawn("/bin/bash")
            except:
                pass
        rmdir(tmpdir)

main()

The python 'sh' package needs to be installed. On Ubuntu 20.04, it can be installed with:

$ sudo apt-get update && sudo apt-get -y install python3 python3-pip
$ sudo pip3 install sh
$ chmod +x ./mount-image
$ sudo ./mount-image balena.img