Create an image with filesystem, copies a local directory content to it

dir2img.py

#!/usr/bin/python3
"""Create image from a directory

This script creates image whose contents are a given directoy on the filesystem.

Example usage:

    $ mkdir mydir
    $ echo A > mydir/a
    $ ./dir2img.py -d mydir -i myimage.img
    $ virt-ls -a myimage.img /
    a
    $ virt-cat -a myimage.img /a
    A

Requirements:

command line utilities:

 - losetup
 - rsync
 - mount
 - umount

root permissions for creating the loopback device and mounting the image

"""

import argparse
import os
import subprocess
import tempfile

def main():
    parser = argparse.ArgumentParser("create a filesystem from directory to image file")
    parser.add_argument('-d' ,'--dir', required=True, help='directory to pack in image')
    parser.add_argument('-i', '--image', required=True, help='image file name')
    parser.add_argument('-s' ,'--size', default='*2', help='size of the image, prefix with * or + to set it to directory size + or * a ratio')
    args = parser.parse_args()

    size = get_size(args.dir)
    if args.size.startswith('*'):
        size *= float(args.size[1:])
    elif args.size.startswith('+'):
        size += int(args.size[1:])
    elif size > int(args.size):
        size = args.size
    else:
        raise ErrorException('Cannot create image smaller than directory size')
    # round to nearest sector size
    size = ((size-1)/512 + 1)*512
    # ensure tiny ext4 can fit image
    size = max(size, 100*1024)
    print('creating file of size %d bytes' % size)

    with open(args.image, 'w') as fp:
        fp.truncate(size)

    subprocess.check_call(['mkfs.ext4', args.image])

    lodevice = subprocess.check_output(['losetup', '-f']).strip()
    subprocess.check_call(['losetup', lodevice, args.image])
    tempdir = None
    try:

        tempdir = tempfile.mkdtemp(prefix='losetup_mounted_dir')
        subprocess.check_call(['mount', lodevice, tempdir])

        try:
            subprocess.check_call(['rsync', '-aP', args.dir+'/', tempdir])
        finally:
            subprocess.check_call(['umount', tempdir])
    finally:
        if tempdir:
            os.removedirs(tempdir)
        subprocess.check_call(['losetup', '-d', lodevice])


class ErrorException(Exception):
    pass

def get_size(start_path):
    total_size = 0
    for dirpath, dirnames, filenames in os.walk(start_path):
        for f in filenames:
            fp = os.path.join(dirpath, f)
            total_size += os.path.getsize(fp)
    return total_size

if __name__ == '__main__':
    try:
        main()
    except ErrorException as e:
        print(e)