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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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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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        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 __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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        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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    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" % (
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                    hex(ord(self.signature[0])), 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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            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 __str__(self):
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            return \
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            "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" % 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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        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 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.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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