MBR (Master Boot Record) partition table: Lua parsing library

MBR (Master Boot Record) partition table is a traditional way of MS-DOS to partition larger hard disc drives into distinct partitions.

This table is stored in the end of the boot sector (first sector) of the drive, after the bootstrap code. Original DOS 2.0 specification allowed only 4 partitions per disc, but DOS 3.2 introduced concept of "extended partitions", which work as nested extra "boot records" which are pointed to by original ("primary") partitions in MBR.

KS implementation details

License: CC0-1.0

References

This page hosts a formal specification of MBR (Master Boot Record) partition table using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Lua source code to parse MBR (Master Boot Record) partition table

mbr_partition_table.lua

-- This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
--
-- This file is compatible with Lua 5.3

local class = require("class")
require("kaitaistruct")

-- 
-- MBR (Master Boot Record) partition table is a traditional way of
-- MS-DOS to partition larger hard disc drives into distinct
-- partitions.
-- 
-- This table is stored in the end of the boot sector (first sector) of
-- the drive, after the bootstrap code. Original DOS 2.0 specification
-- allowed only 4 partitions per disc, but DOS 3.2 introduced concept
-- of "extended partitions", which work as nested extra "boot records"
-- which are pointed to by original ("primary") partitions in MBR.
MbrPartitionTable = class.class(KaitaiStruct)

function MbrPartitionTable:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function MbrPartitionTable:_read()
  self.bootstrap_code = self._io:read_bytes(446)
  self.partitions = {}
  for i = 0, 4 - 1 do
    self.partitions[i + 1] = MbrPartitionTable.PartitionEntry(self._io, self, self._root)
  end
  self.boot_signature = self._io:read_bytes(2)
  if not(self.boot_signature == "\085\170") then
    error("not equal, expected " ..  "\085\170" .. ", but got " .. self.boot_signature)
  end
end


MbrPartitionTable.PartitionEntry = class.class(KaitaiStruct)

function MbrPartitionTable.PartitionEntry:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function MbrPartitionTable.PartitionEntry:_read()
  self.status = self._io:read_u1()
  self.chs_start = MbrPartitionTable.Chs(self._io, self, self._root)
  self.partition_type = self._io:read_u1()
  self.chs_end = MbrPartitionTable.Chs(self._io, self, self._root)
  self.lba_start = self._io:read_u4le()
  self.num_sectors = self._io:read_u4le()
end


MbrPartitionTable.Chs = class.class(KaitaiStruct)

function MbrPartitionTable.Chs:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function MbrPartitionTable.Chs:_read()
  self.head = self._io:read_u1()
  self.b2 = self._io:read_u1()
  self.b3 = self._io:read_u1()
end

MbrPartitionTable.Chs.property.sector = {}
function MbrPartitionTable.Chs.property.sector:get()
  if self._m_sector ~= nil then
    return self._m_sector
  end

  self._m_sector = (self.b2 & 63)
  return self._m_sector
end

MbrPartitionTable.Chs.property.cylinder = {}
function MbrPartitionTable.Chs.property.cylinder:get()
  if self._m_cylinder ~= nil then
    return self._m_cylinder
  end

  self._m_cylinder = (self.b3 + ((self.b2 & 192) << 2))
  return self._m_cylinder
end