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#!/usr/bin/python3
# Copyright (C) 2021 SUSE LLC
# program to show gpt partition attributes or set attributes of
# partition 1
# only works with 512 sectors and standard GPT header layout (128
# partition entires with 128 bytes each, secondary header at end of
# device)
from struct import unpack_from, pack_into
from zipfile import crc32
import array
import sys
class Gpt:
# Calculate and insert the CRCs of the partition entires and the
# header.
def calc_crcs(self, header, entries):
# compute crc of partition entries
crc2 = crc32(entries) & 0xFFFFFFFF
pack_into('<L', header, 88, crc2)
# compute crc of header
pack_into('<L', header, 16, 0)
crc1 = crc32(header[:92]) & 0xFFFFFFFF
pack_into('<L', header, 16, crc1)
def read(self, name):
self.name = name
file = open(name, 'rb+')
file.seek(512)
self.primary_header = array.array('B', file.read(512))
self.primary_entries = array.array('B', file.read(32 * 512))
file.seek(-33 * 512, 2)
self.secondary_entries = array.array('B', file.read(32 * 512))
self.secondary_header = array.array('B', file.read(512))
def write(self):
file = open(self.name, 'rb+')
self.calc_crcs(self.primary_header, self.primary_entries)
file.seek(512)
file.write(self.primary_header)
file.write(self.primary_entries)
self.calc_crcs(self.secondary_header, self.secondary_entries)
file.seek(-33 * 512, 2)
file.write(self.secondary_entries)
file.write(self.secondary_header)
gpt = Gpt()
gpt.read(sys.argv[1])
if sys.argv[2] == "show":
attrs = unpack_from('<Q', gpt.primary_entries, 48)[0]
print(hex(attrs))
if sys.argv[2] == "set":
attrs = int(sys.argv[3], 0)
pack_into('<Q', gpt.primary_entries, 48, attrs)
pack_into('<Q', gpt.secondary_entries, 48, attrs)
gpt.write()
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