root / snf-image-helper / fix_gpt.py @ 21be5a41
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#!/usr/bin/env python
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# Copyright (C) 2012 GRNET S.A.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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# 02110-1301, USA.
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import struct |
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import sys |
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import binascii |
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import stat |
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import os |
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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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format = "<B3sB3sLL"
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def __init__(self, raw_part): |
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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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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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) |
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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 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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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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"""Returns 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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"""Packs 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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) |
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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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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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) |
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@staticmethod
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def size(): |
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"""Returns the size of a GPT Header."""
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return struct.calcsize(GPTPartitionTable.GPTHeader.format)
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def __init__(self, disk): |
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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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"""Returns the payload size of GPT partitioned device."""
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return (self.primary.backup_lba + 1) * BLOCKSIZE |
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def fix(self, lba_count): |
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"""Move the secondary GPT Header entries to the LBA specified by
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lba_count parameter.
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"""
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assert lba_count * BLOCKSIZE > self.size() |
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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 = lba_count - 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.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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if __name__ == '__main__': |
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usage = "Usage: %s <disk> <sectors>\n" % (sys.argv[0]) |
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if len(sys.argv) != 3: |
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sys.stderr.write(usage) |
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sys.exit(1)
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disk = sys.argv[1]
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mode = os.stat(disk).st_mode |
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if not stat.S_ISBLK(mode): |
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sys.stderr.write("Parameter disk must be a block device\n")
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sys.stderr.write(usage) |
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sys.exit(1)
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try:
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size = int(sys.argv[2]) |
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except ValueError: |
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sys.stderr.write("Parameter new_size must be a number\n")
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sys.stderr.write(usage) |
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sys.exit(1)
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ptable = GPTPartitionTable(disk) |
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if size * BLOCKSIZE == ptable.size():
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sys.stderr.write("Nothing to do...\n")
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elif size * BLOCKSIZE > ptable.size():
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ptable.fix(size) |
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sys.stderr.write("GPT table was fixed\n")
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else:
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sys.stderr.write("Disk is langer than size")
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exit(1) |
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sys.exit(0)
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# vim: set sta sts=4 shiftwidth=4 sw=4 et ai :
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