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#!/usr/bin/python3
# This example can be used to compute the checksum of each
# block in a disk image. eg:
#
# $ ./checksum.py disk.qcow2
# block @ 0 (size 1073741824) sha1 587b1dec5c55d2a2845e18c08bd135135396eb52
#
# The disk image can be in any format that is supported by qemu-nbd.
# You can change the block size and checksum (hash) type using command
# line parameters.
import argparse
import hashlib
import nbd
p = argparse.ArgumentParser(
description="Compute checksums of blocks in a disk image")
p.add_argument('filename', metavar='FILENAME',
help='disk image')
p.add_argument('--format', dest='format',
help='disk image format, eg. qcow2 or raw')
p.add_argument('--blocksize', dest='blocksize', type=int,
default=1024*1024*1024,
help='block size')
p.add_argument('--hash', dest='hash', default='sha1',
help='hash to use, eg. sha1, sha256, etc.')
arg = p.parse_args()
max_read = 32*1024*1024
h = nbd.NBD()
# Set up the qemu-nbd command line.
cmd = ["qemu-nbd", "--read-only", "--persistent", arg.filename]
if arg.format is not None:
cmd += ["-f", arg.format]
h.connect_systemd_socket_activation(cmd)
size = h.get_size()
offset = 0
while offset < size:
hh = hashlib.new(arg.hash)
start = offset
got = 0
while offset < size and got < arg.blocksize:
c = min(max_read, arg.blocksize - got)
c = min(c, size-offset)
hh.update(h.pread(c, offset))
got += c
offset += c
print("block @ %d (size %d)" % (start, got), end=" ")
print("%s %s" % (arg.hash, hh.hexdigest()))
h.shutdown()
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