img2ext.py

#!/usr/bin/python2

import sys
import mmap

ext4Magic = '\x53\xEF'
ext4MagicOffset = 1080

if len(sys.argv) < 3:
    print("No I/O supplied")
    exit(1)

def copyExt4Image(origin, dest):
    with open(origin, 'rb') as input:
        with open(dest, 'wb') as output:
            input.seek(offset - ext4MagicOffset)
            output.write(input.read())

def findMagic(input):
    with open(input, 'r+b') as f:
        mm = mmap.mmap(f.fileno(), 0)
        return mm.find(ext4Magic, ext4MagicOffset)

systemimg = sys.argv[1]
systemimgout = sys.argv[2]
offset = findMagic(systemimg)
if offset == ext4MagicOffset:
    print('The given file is a proper ext4 image')
elif offset != -1:
    print('ext4 magic number found at byte %d' % offset)
    print('Creating %s...' % systemimgout)
    copyExt4Image(systemimg, systemimgout)
else:
    print("ext4 magic number not found")