Read images

from bcachefs import Bcachefs

with Bcachefs('disk.img', 'r') as image:
    file_names = image.namelist()

    for filename in file_names:
        with image.open(filename, 'rb') as file:
            for line in file.lines():
                print(line)

Multiprocessing

import multiprocessing as mp

def count_size(fs, name):
    with fs:
        try:
            with fs.open(name, 'rb') as f:
                return len(f.read())
        except FileNotFoundError:
            return 0

with Bcachefs(image) as fs:
    files = fs.namelist()

    with mp.Pool(4) as p:
        sizes = p.starmap(count_size, [(fs, n) for n in files])

size = sum(sizes)