MBR (Master Boot Record) partition table: Ruby 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

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.

Usage

Parse a local file and get structure in memory:

data = MbrPartitionTable.from_file("path/to/local/file.MBR (Master Boot Record) partition table")

Or parse structure from a string of bytes:

bytes = "\x00\x01\x02..."
data = MbrPartitionTable.new(Kaitai::Struct::Stream.new(bytes))

After that, one can get various attributes from the structure by invoking getter methods like:

data.bootstrap_code # => get bootstrap code

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

mbr_partition_table.rb

# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

require 'kaitai/struct/struct'

unless Gem::Version.new(Kaitai::Struct::VERSION) >= Gem::Version.new('0.7')
  raise "Incompatible Kaitai Struct Ruby API: 0.7 or later is required, but you have #{Kaitai::Struct::VERSION}"
end


##
# 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.
class MbrPartitionTable < Kaitai::Struct::Struct
  def initialize(_io, _parent = nil, _root = self)
    super(_io, _parent, _root)
    _read
  end

  def _read
    @bootstrap_code = @_io.read_bytes(446)
    @partitions = Array.new(4)
    (4).times { |i|
      @partitions[i] = PartitionEntry.new(@_io, self, @_root)
    }
    @boot_signature = @_io.ensure_fixed_contents([85, 170].pack('C*'))
    self
  end
  class PartitionEntry < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @status = @_io.read_u1
      @chs_start = Chs.new(@_io, self, @_root)
      @partition_type = @_io.read_u1
      @chs_end = Chs.new(@_io, self, @_root)
      @lba_start = @_io.read_u4le
      @num_sectors = @_io.read_u4le
      self
    end
    attr_reader :status
    attr_reader :chs_start
    attr_reader :partition_type
    attr_reader :chs_end
    attr_reader :lba_start
    attr_reader :num_sectors
  end
  class Chs < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @head = @_io.read_u1
      @b2 = @_io.read_u1
      @b3 = @_io.read_u1
      self
    end
    def sector
      return @sector unless @sector.nil?
      @sector = (b2 & 63)
      @sector
    end
    def cylinder
      return @cylinder unless @cylinder.nil?
      @cylinder = (b3 + ((b2 & 192) << 2))
      @cylinder
    end
    attr_reader :head
    attr_reader :b2
    attr_reader :b3
  end
  attr_reader :bootstrap_code
  attr_reader :partitions
  attr_reader :boot_signature
end