root / image_creator / gpt.py @ f953c647
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#!/usr/bin/env python
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# -*- coding: utf-8 -*-
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#
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# Copyright 2012 GRNET S.A. All rights reserved.
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#
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# Redistribution and use in source and binary forms, with or
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# without modification, are permitted provided that the following
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# conditions are met:
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#
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# 1. Redistributions of source code must retain the above
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# copyright notice, this list of conditions and the following
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# disclaimer.
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#
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# 2. Redistributions in binary form must reproduce the above
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# copyright notice, this list of conditions and the following
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# disclaimer in the documentation and/or other materials
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# provided with the distribution.
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#
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# THIS SOFTWARE IS PROVIDED BY GRNET S.A. ``AS IS'' AND ANY EXPRESS
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# OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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# PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL GRNET S.A OR
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# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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# AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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# POSSIBILITY OF SUCH DAMAGE.
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#
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# The views and conclusions contained in the software and
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# documentation are those of the authors and should not be
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# interpreted as representing official policies, either expressed
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# or implied, of GRNET S.A.
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"""This module provides the code for handling GUID partition tables"""
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import struct |
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import sys |
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import uuid |
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import binascii |
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BLOCKSIZE = 512
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class MBR(object): |
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"""Represents a Master Boot Record."""
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class Partition(object): |
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"""Represents a partition entry in MBR"""
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format = "<B3sB3sLL"
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def __init__(self, raw_part): |
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"""Create a Partition instance"""
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( |
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self.status,
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self.start,
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self.type,
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self.end,
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self.first_sector,
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self.sector_count
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) = struct.unpack(self.format, raw_part)
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def pack(self): |
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"""Pack the partition values into a binary string"""
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return struct.pack(self.format, |
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self.status,
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self.start,
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self.type,
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self.end,
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self.first_sector,
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self.sector_count)
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@staticmethod
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def size(): |
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"""Returns the size of an MBR partition entry"""
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return struct.calcsize(MBR.Partition.format)
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def __str__(self): |
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start = self.unpack_chs(self.start) |
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end = self.unpack_chs(self.end) |
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return "%d %s %d %s %d %d" % (self.status, start, self.type, end, |
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self.first_sector, self.sector_count) |
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def unpack_chs(self, chs): |
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"""Unpacks a CHS address string to a tuple."""
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assert len(chs) == 3 |
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head = struct.unpack('<B', chs[0])[0] |
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sector = struct.unpack('<B', chs[1])[0] & 0x3f |
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cylinder = (struct.unpack('<B', chs[1])[0] & 0xC0) << 2 | \ |
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struct.unpack('<B', chs[2])[0] |
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return (cylinder, head, sector)
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def pack_chs(self, cylinder, head, sector): |
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"""Packs a CHS tuple to an address string."""
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assert 1 <= sector <= 63 |
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assert 0 <= cylinder <= 1023 |
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assert 0 <= head <= 255 |
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byte0 = head |
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byte1 = (cylinder >> 2) & 0xC0 | sector |
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byte2 = cylinder & 0xff
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return struct.pack('<BBB', byte0, byte1, byte2) |
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format = "<444s2x16s16s16s16s2s"
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"""
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Offset Length Contents
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0 440(max. 446) code area
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440 2(optional) disk signature
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444 2 Usually nulls
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446 16 Partition 0
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462 16 Partition 1
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478 16 Partition 2
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494 16 Partition 3
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510 2 MBR signature
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"""
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def __init__(self, block): |
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"""Create an MBR instance"""
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raw_part = {}
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(self.code_area,
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raw_part[0],
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raw_part[1],
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raw_part[2],
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raw_part[3],
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self.signature) = struct.unpack(self.format, block) |
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self.part = {}
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for i in range(4): |
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self.part[i] = self.Partition(raw_part[i]) |
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@staticmethod
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def size(): |
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"""Return the size of a Master Boot Record."""
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return struct.calcsize(MBR.format)
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def pack(self): |
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"""Pack an MBR to a binary string."""
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return struct.pack(self.format, |
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self.code_area,
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self.part[0].pack(), |
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self.part[1].pack(), |
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self.part[2].pack(), |
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self.part[3].pack(), |
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self.signature)
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def __str__(self): |
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ret = ""
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for i in range(4): |
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ret += "Partition %d: %s\n" % (i, self.part[i]) |
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ret += "Signature: %s %s\n" % (hex(ord(self.signature[0])), |
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hex(ord(self.signature[1]))) |
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return ret
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class GPTPartitionTable(object): |
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"""Represents a GUID Partition Table."""
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class GPTHeader(object): |
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"""Represents a GPT Header of a GUID Partition Table."""
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format = "<8s4sII4xQQQQ16sQIII"
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"""
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Offset Length Contents
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0 8 bytes Signature
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8 4 bytes Revision
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12 4 bytes Header size in little endian
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16 4 bytes CRC32 of header
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20 4 bytes Reserved; must be zero
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24 8 bytes Current LBA
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32 8 bytes Backup LBA
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40 8 bytes First usable LBA for partitions
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48 8 bytes Last usable LBA
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56 16 bytes Disk GUID
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72 8 bytes Partition entries starting LBA
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80 4 bytes Number of partition entries
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84 4 bytes Size of a partition entry
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88 4 bytes CRC32 of partition array
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92 * Reserved; must be zeroes
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LBA size Total
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"""
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def __init__(self, block): |
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"""Create a GPTHeader instance"""
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(self.signature,
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self.revision,
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self.hdr_size,
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self.header_crc32,
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self.current_lba,
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self.backup_lba,
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self.first_usable_lba,
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self.last_usable_lba,
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self.uuid,
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self.part_entry_start,
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self.part_count,
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self.part_entry_size,
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self.part_crc32) = struct.unpack(self.format, block) |
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def pack(self): |
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"""Packs a GPT Header to a binary string."""
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return struct.pack(self.format, |
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self.signature,
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self.revision,
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self.hdr_size,
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self.header_crc32,
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self.current_lba,
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self.backup_lba,
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self.first_usable_lba,
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self.last_usable_lba,
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self.uuid,
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self.part_entry_start,
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self.part_count,
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self.part_entry_size,
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self.part_crc32)
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@staticmethod
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def size(): |
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"""Return the size of a GPT Header."""
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return struct.calcsize(GPTPartitionTable.GPTHeader.format)
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def __str__(self): |
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"""Print a GPTHeader"""
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return "Signature: %s\n" % self.signature + \ |
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"Revision: %r\n" % self.revision + \ |
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"Header Size: %d\n" % self.hdr_size + \ |
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"CRC32: %d\n" % self.header_crc32 + \ |
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"Current LBA: %d\n" % self.current_lba + \ |
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"Backup LBA: %d\n" % self.backup_lba + \ |
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"First Usable LBA: %d\n" % self.first_usable_lba + \ |
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"Last Usable LBA: %d\n" % self.last_usable_lba + \ |
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"Disk GUID: %s\n" % uuid.UUID(bytes=self.uuid) + \ |
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"Partition entries starting LBA: %d\n" % \
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self.part_entry_start + \
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"Number of Partition entries: %d\n" % self.part_count + \ |
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"Size of a partition entry: %d\n" % self.part_entry_size + \ |
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"CRC32 of partition array: %s\n" % self.part_crc32 |
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def __init__(self, disk): |
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"""Create a GPTPartitionTable instance"""
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self.disk = disk
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with open(disk, "rb") as d: |
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# MBR (Logical block address 0)
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lba0 = d.read(BLOCKSIZE) |
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self.mbr = MBR(lba0)
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# Primary GPT Header (LBA 1)
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raw_header = d.read(self.GPTHeader.size())
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self.primary = self.GPTHeader(raw_header) |
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# Partition entries (LBA 2...34)
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d.seek(self.primary.part_entry_start * BLOCKSIZE)
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entries_size = self.primary.part_count * \
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self.primary.part_entry_size
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self.part_entries = d.read(entries_size)
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# Secondary GPT Header (LBA -1)
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d.seek(self.primary.backup_lba * BLOCKSIZE)
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raw_header = d.read(self.GPTHeader.size())
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self.secondary = self.GPTHeader(raw_header) |
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def size(self): |
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"""Return the payload size of GPT partitioned device."""
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return (self.primary.backup_lba + 1) * BLOCKSIZE |
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def shrink(self, size, old_size): |
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"""Move the secondary GPT Header entries to the address specified by
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size parameter.
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"""
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# Most partition manipulation programs leave 2048 sector after the last
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# partition
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aligned = size + 2048 * BLOCKSIZE
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# new_size is at least: size + Partition Entries + Secondary GPT Header
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new_size = aligned if aligned <= old_size else \ |
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size + len(self.part_entries) + BLOCKSIZE |
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assert new_size <= old_size, "The secodary GPT fits in the device" |
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if new_size == self.size(): |
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return new_size
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lba_count = new_size // BLOCKSIZE |
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# Correct MBR
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#TODO: Check if the partition tables is hybrid
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self.mbr.part[0].sector_count = (new_size // BLOCKSIZE) - 1 |
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# Fix Primary header
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self.primary.header_crc32 = 0 |
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self.primary.backup_lba = lba_count - 1 # LBA-1 |
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self.primary.last_usable_lba = lba_count - 34 # LBA-34 |
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self.primary.header_crc32 = \
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binascii.crc32(self.primary.pack()) & 0xffffffff |
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# Fix Secondary header
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self.secondary.header_crc32 = 0 |
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self.secondary.current_lba = self.primary.backup_lba |
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self.secondary.last_usable_lba = lba_count - 34 # LBA-34 |
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self.secondary.part_entry_start = lba_count - 33 # LBA-33 |
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self.secondary.header_crc32 = \
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binascii.crc32(self.secondary.pack()) & 0xffffffff |
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# Copy the new partition table back to the device
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with open(self.disk, "wb") as d: |
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d.write(self.mbr.pack())
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d.write(self.primary.pack())
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d.write('\x00' * (BLOCKSIZE - self.primary.size())) |
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d.write(self.part_entries)
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d.seek(self.secondary.part_entry_start * BLOCKSIZE)
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d.write(self.part_entries)
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d.seek(self.primary.backup_lba * BLOCKSIZE)
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d.write(self.secondary.pack())
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d.write('\x00' * (BLOCKSIZE - self.secondary.size())) |
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return new_size
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if __name__ == '__main__': |
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ptable = GPTPartitionTable(sys.argv[1])
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print "MBR:\n%s" % ptable.mbr |
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print "Primary partition table:\n%s" % ptable.primary |
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print "Secondary partition table:\n%s" % ptable.secondary |
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# vim: set sta sts=4 shiftwidth=4 sw=4 et ai :
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