class MBR(object):
+ """Represents a Master Boot Record."""
class Partition(object):
format = "<B3sB3sLL"
def __init__(self, raw_part):
-
- ( self.status,
+ (
+ self.status,
self.start,
self.type,
self.end,
def pack(self):
return struct.pack(self.format,
- self.status,
- self.start,
- self.type,
- self.end,
- self.first_sector,
- self.sector_count
- )
-
- def show(self):
+ self.status,
+ self.start,
+ self.type,
+ self.end,
+ self.first_sector,
+ self.sector_count)
+
+ @staticmethod
+ def size():
+ """Returns the size of an MBR partition entry"""
+ return struct.calcsize(MBR.Partition.format)
+
+ def __str__(self):
start = self.unpack_chs(self.start)
end = self.unpack_chs(self.end)
- print "%d %s %d %s %d %d" % (self.status, start, self.type, end,
- self.first_sector, self.sector_count)
+ return "%d %s %d %s %d %d" % (self.status, start, self.type, end,
+ self.first_sector, self.sector_count)
def unpack_chs(self, chs):
+ """Unpacks a CHS address string to a tuple."""
assert len(chs) == 3
return (cylinder, head, sector)
def pack_chs(self, cylinder, head, sector):
+ """Packs a CHS tuple to an address string."""
assert 1 <= sector <= 63
assert 0 <= cylinder <= 1023
"""
def __init__(self, block):
raw_part = {}
- self.code_area, \
- raw_part[0], \
- raw_part[1], \
- raw_part[2], \
- raw_part[3], \
- self.signature = struct.unpack(self.format, block)
+ (self.code_area,
+ raw_part[0],
+ raw_part[1],
+ raw_part[2],
+ raw_part[3],
+ self.signature) = struct.unpack(self.format, block)
self.part = {}
for i in range(4):
self.part[i] = self.Partition(raw_part[i])
+ @staticmethod
+ def size():
+ """Returns the size of a Master Boot Record."""
+ return struct.calcsize(MBR.format)
+
def pack(self):
+ """Packs an MBR to a binary string."""
return struct.pack(self.format,
- self.code_area,
- self.part[0].pack(),
- self.part[1].pack(),
- self.part[2].pack(),
- self.part[3].pack(),
- self.signature
- )
-
- def show(self):
+ self.code_area,
+ self.part[0].pack(),
+ self.part[1].pack(),
+ self.part[2].pack(),
+ self.part[3].pack(),
+ self.signature)
+
+ def __str__(self):
+ ret = ""
for i in range(4):
- print "Part %d: " % i,
- self.part[i].show()
+ ret += "Partition %d: %s\n" % (i, self.part[i])
+ ret += "Signature: %s %s\n" % (hex(ord(self.signature[0])),
+ hex(ord(self.signature[1])))
+ return ret
class GPTPartitionTable(object):
+ """Represents a GUID Partition Table."""
class GPTHeader(object):
+ """Represents a GPT Header of a GUID Partition Table."""
format = "<8s4sII4xQQQQ16sQIII"
"""
Offset Length Contents
"""
def __init__(self, block):
- self.signature, \
- self.revision, \
- self.size, \
- self.header_crc32, \
- self.current_lba, \
- self.backup_lba, \
- self.first_usable_lba, \
- self.last_usable_lba, \
- self.uuid, \
- self.part_entry_start, \
- self.part_count, \
- self.part_entry_size, \
- self.part_crc32 = struct.unpack(self.format, block)
+ (self.signature,
+ self.revision,
+ self.hdr_size,
+ self.header_crc32,
+ self.current_lba,
+ self.backup_lba,
+ self.first_usable_lba,
+ self.last_usable_lba,
+ self.uuid,
+ self.part_entry_start,
+ self.part_count,
+ self.part_entry_size,
+ self.part_crc32) = struct.unpack(self.format, block)
def pack(self):
+ """Packs a GPT Header to a binary string."""
return struct.pack(self.format,
- self.signature, \
- self.revision, \
- self.size, \
- self.header_crc32, \
- self.current_lba, \
- self.backup_lba, \
- self.first_usable_lba, \
- self.last_usable_lba, \
- self.uuid, \
- self.part_entry_start, \
- self.part_count, \
- self.part_entry_size, \
- self.part_crc32
- )
-
- def show(self):
- print "Signature: %s" % self.signature
- print "Revision: %r" % self.revision
- print "Header Size: %d" % self.size
- print "CRC32: %d" % self.header_crc32
- print "Current LBA: %d" % self.current_lba
- print "Backup LBA: %d" % self.backup_lba
- print "First Usable LBA: %d" % self.first_usable_lba
- print "Last Usable LBA: %d" % self.last_usable_lba
- print "Disk GUID: %s" % uuid.UUID(bytes=self.uuid)
- print "Partition entries starting LBA: %d" % self.part_entry_start
- print "Number of Partition entries: %d" % self.part_count
- print "Size of a partition entry: %d" % self.part_entry_size
- print "CRC32 of partition array: %s" % self.part_crc32
+ self.signature,
+ self.revision,
+ self.hdr_size,
+ self.header_crc32,
+ self.current_lba,
+ self.backup_lba,
+ self.first_usable_lba,
+ self.last_usable_lba,
+ self.uuid,
+ self.part_entry_start,
+ self.part_count,
+ self.part_entry_size,
+ self.part_crc32)
+
+ @staticmethod
+ def size():
+ """Returns the size of a GPT Header."""
+ return struct.calcsize(GPTPartitionTable.GPTHeader.format)
+
+ def __str__(self):
+ return "Signature: %s\n" % self.signature + \
+ "Revision: %r\n" % self.revision + \
+ "Header Size: %d\n" % self.hdr_size + \
+ "CRC32: %d\n" % self.header_crc32 + \
+ "Current LBA: %d\n" % self.current_lba + \
+ "Backup LBA: %d\n" % self.backup_lba + \
+ "First Usable LBA: %d\n" % self.first_usable_lba + \
+ "Last Usable LBA: %d\n" % self.last_usable_lba + \
+ "Disk GUID: %s\n" % uuid.UUID(bytes=self.uuid) + \
+ "Partition entries starting LBA: %d\n" % \
+ self.part_entry_start + \
+ "Number of Partition entries: %d\n" % self.part_count + \
+ "Size of a partition entry: %d\n" % self.part_entry_size + \
+ "CRC32 of partition array: %s\n" % self.part_crc32
def __init__(self, disk):
self.disk = disk
with open(disk, "rb") as d:
- #MBR (Logical block address 0)
+ # MBR (Logical block address 0)
lba0 = d.read(BLOCKSIZE)
self.mbr = MBR(lba0)
+
# Primary GPT Header (LBA 1)
- lba1 = d.read(BLOCKSIZE)
- self.primary = self.GPTHeader(lba1[:92])
+ raw_header = d.read(self.GPTHeader.size())
+ self.primary = self.GPTHeader(raw_header)
+
# Partition entries (LBA 2...34)
d.seek(self.primary.part_entry_start * BLOCKSIZE)
entries_size = self.primary.part_count * \
- self.primary.part_entry_size
+ self.primary.part_entry_size
self.part_entries = d.read(entries_size)
+
# Secondary GPT Header (LBA -1)
d.seek(self.primary.backup_lba * BLOCKSIZE)
- lba_1 = d.read(BLOCKSIZE)
- self.secondary = self.GPTHeader(lba_1[:92])
+ raw_header = d.read(self.GPTHeader.size())
+ self.secondary = self.GPTHeader(raw_header)
def size(self):
- return (self.primary.backup_lba + 1) * BLOCKSIZE
+ """Returns the payload size of GPT partitioned device."""
+ return (self.primary.backup_lba + 1) * BLOCKSIZE
- def shrink(self, size):
+ def shrink(self, size, old_size):
+ """Move the secondary GPT Header entries to the address specified by
+ size parameter.
+ """
+
+ # Most partition manipulation programs leave 2048 sector after the last
+ # partition
+ aligned = size + 2048 * BLOCKSIZE
- if size == self.size():
- return size
+ # new_size is at least: size + Partition Entries + Secondary GPT Header
+ new_size = aligned if aligned <= old_size else \
+ size + len(self.part_entries) + BLOCKSIZE
- assert size < self.size()
+ assert new_size <= old_size, "The secodary GPT fits in the device"
+
+ if new_size == self.size():
+ return new_size
- # new_size = size + Partition Entries + Secondary GPT Header
- new_size = size + len(self.part_entries) + BLOCKSIZE
- new_size = ((new_size + 4095) // 4096) * 4096 # align to 4K
lba_count = new_size // BLOCKSIZE
# Correct MBR
- #TODO: Check for hybrid partition tables
+ #TODO: Check if the partition tables is hybrid
self.mbr.part[0].sector_count = (new_size // BLOCKSIZE) - 1
- # Correct Primary header
+ # Fix Primary header
self.primary.header_crc32 = 0
self.primary.backup_lba = lba_count - 1 # LBA-1
self.primary.last_usable_lba = lba_count - 34 # LBA-34
self.primary.header_crc32 = \
- binascii.crc32(self.primary.pack()) & 0xffffffff
+ binascii.crc32(self.primary.pack()) & 0xffffffff
- # Correct Secondary header entries
+ # Fix Secondary header
self.secondary.header_crc32 = 0
self.secondary.current_lba = self.primary.backup_lba
self.secondary.last_usable_lba = lba_count - 34 # LBA-34
self.secondary.part_entry_start = lba_count - 33 # LBA-33
self.secondary.header_crc32 = \
- binascii.crc32(self.secondary.pack()) & 0xffffffff
+ binascii.crc32(self.secondary.pack()) & 0xffffffff
# Copy the new partition table back to the device
with open(self.disk, "wb") as d:
d.write(self.mbr.pack())
- d.write(struct.pack("%ss" % BLOCKSIZE, '\x00' * BLOCKSIZE))
- d.seek(BLOCKSIZE)
d.write(self.primary.pack())
+ d.write('\x00' * (BLOCKSIZE - self.primary.size()))
d.seek(self.secondary.part_entry_start * BLOCKSIZE)
d.write(self.part_entries)
d.seek(self.primary.backup_lba * BLOCKSIZE)
- d.write(struct.pack("%ss" % BLOCKSIZE, '\x00' * BLOCKSIZE))
- d.seek(self.primary.backup_lba * BLOCKSIZE)
d.write(self.secondary.pack())
+ d.write('\x00' * (BLOCKSIZE - self.secondary.size()))
return new_size
if __name__ == '__main__':
ptable = GPTPartitionTable(sys.argv[1])
- print "MBR:"
- ptable.mbr.show()
- print
- print "Primary partition table:"
- ptable.primary.show()
- print
- print "Secondary partition table:"
- ptable.secondary.show()
+ print "MBR:\n%s" % ptable.mbr
+ print "Primary partition table:\n%s" % ptable.primary
+ print "Secondary partition table:\n%s" % ptable.secondary
# vim: set sta sts=4 shiftwidth=4 sw=4 et ai :
projects / snf-image-creator / blobdiff