LVM Parser & Block Reader

lvm-parser.rb

# LVM Parser & Block Reader
#
# Copyright (C) 2016 Red Hat Inc

require 'optparse'
require 'ostruct'
require 'binary_struct'

### constants

LVM_PARTITION_TYPE  = 142
SECTOR_SIZE         = 512
LABEL_SCAN_SECTORS  = 4

LVM_ID_LEN          = 8
LVM_TYPE_LEN        = 8
LVM_ID              = "LABELONE"

PV_ID_LEN           = 32
MDA_MAGIC_LEN       = 16
FMTT_MAGIC          = "\040\114\126\115\062\040\170\133\065\101\045\162\060\116\052\076"

# On disk label header.
LABEL_HEADER = BinaryStruct.new([
  "A#{LVM_ID_LEN}",       'lvm_id',
  'Q',                    'sector_xl',
  'L',                    'crc_xl',
  'L',                    'offset_xl',
  "A#{LVM_TYPE_LEN}",     'lvm_type'
])

# On disk physical volume header.
PV_HEADER = BinaryStruct.new([
  "A#{PV_ID_LEN}",        'pv_uuid',
  "Q",                    'device_size_xl'
])

# On disk disk location structure.
DISK_LOCN = BinaryStruct.new([
  "Q",                    'offset',
  "Q",                    'size'
])

# On disk metadata area header.
MDA_HEADER = BinaryStruct.new([
  "L",                    'checksum_xl',
  "A#{MDA_MAGIC_LEN}",    'magic',
  "L",                    'version',
  "Q",                    'start',
  "Q",                    'size'
])

# On disk raw location header, points to metadata.
RAW_LOCN = BinaryStruct.new([
  "Q",                    'offset',
  "Q",                    'size',
  "L",                    'checksum',
  "L",                    'filler'
])

module MD
  HASH_START      = '{'
  HASH_END        = '}'
  ARRAY_START     = '['
  ARRAY_END       = ']'
  STRING_START    = '"'
  STRING_END      = '"'
end

module Thin
  SECTOR_SIZE = 512

  THIN_MAGIC = 27022010

  SPACE_MAP_ROOT_SIZE = 128

  MAX_METADATA_BITMAPS = 255

  SUPERBLOCK = BinaryStruct.new([
   'L',                       'csum',
   'L',                       'flags_',
   'Q',                       'block',
   'A16',                     'uuid',
   'Q',                       'magic',
   'L',                       'version',
   'L',                       'time',

   'Q',                       'trans_id',
   'Q',                       'metadata_snap',

   "A#{SPACE_MAP_ROOT_SIZE}", 'data_space_map_root',
   "A#{SPACE_MAP_ROOT_SIZE}", 'metadata_space_map_root',

   'Q',                       'data_mapping_root',

   'Q',                       'device_details_root',

   'L',                       'data_block_size',     # in 512-byte sectors

   'L',                       'metadata_block_size', # in 512-byte sectors
   'Q',                       'metadata_nr_blocks',

   'L',                       'compat_flags',
   'L',                       'compat_ro_flags',
   'L',                       'incompat_flags'
  ])

  SPACE_MAP = BinaryStruct.new([
    'Q',                      'nr_blocks',
    'Q',                      'nr_allocated',
    'Q',                      'bitmap_root',
    'Q',                      'ref_count_root'
  ])

  DISK_NODE = BinaryStruct.new([
    'L',                      'csum',
    'L',                      'flags',
    'Q',                      'blocknr',

    'L',                      'nr_entries',
    'L',                      'max_entries',
    'L',                      'value_size',
    'L',                      'padding'
    #'Q',                      'keys'
  ])

  INDEX_ENTRY = BinaryStruct.new([
    'Q',                      'blocknr',
    'L',                      'nr_free',
    'L',                      'none_free_before'
  ])

  METADATA_INDEX = BinaryStruct.new([
    'L',                      'csum',
    'L',                      'padding',
    'Q',                      'blocknr'
  ])

  BITMAP_HEADER = BinaryStruct.new([
    'L',                      'csum',
    'L',                      'notused',
    'Q',                      'blocknr'
  ])

  DEVICE_DETAILS = BinaryStruct.new([
    'Q',                      'mapped_blocks',
    'Q',                      'transaction_id',
    'L',                      'creation_time',
    'L',                      'snapshotted_time'
  ])

  MAPPING_DETAILS = BinaryStruct.new([
    'Q',                       'value'
  ])
end

### structures

class RawDisk
  def initialize(path)
    @file = File.open(path)
  end

  def seek(pos)
    @file.seek pos
  end

  def read(len)
    @file.read len
  end
end

class LVDisk
  attr_accessor :lv, :block_size, :extent_size

  def initialize(lv)
    self.lv = lv

    self.block_size = 512
    self.extent_size = lv.vg.extent_size * block_size
  end

  def size
    lv.num_blocks
  end

  def read(pos, len)
    return read_thin(pos, len) if lv.thin?

    str = ''
    end_pos = pos + len - 1
    start_seg, end_seg = get_segs(pos, end_pos)

    (start_seg..end_seg).each do |si|
      seg       = lv.segments[si]
      seg_start = seg.block_start
      srs       = seg_start # segment read start
      srl       = seg.size  # segment read length

      if si == start_seg
        srs = pos
        srl = seg.size - (pos - seg_start)
      end

      if si == end_seg
        srl = end_pos - srs + 1
      end

      str << read_seg(seg, srs, srl)
    end

    str
  end

  private

  def read_thin(pos, len)
    str = ''
    device_id = lv.thin_segment.device_id
    thin_pool = lv.thin_pool_volume
    data_blks = thin_pool.metadata_volume.superblock.device_to_data(device_id, pos, len)
    data_blks.each do |offset, len|
      str << thin_pool.data_volume.disk.read(offset, len)
    end

    return str
  end

  def get_segs(pos, end_pos)
    # start / end segment
    ss = nil
    es = nil

    lv.segments.each_with_index do |seg, i|
      ss = i if seg.address_range === pos
      if seg.address_range === end_pos
        raise "Segment sequence error" unless ss
        es = i
        break
      end
    end
    raise "Segment range error" if !ss || !es

    return ss, es
  end

  def read_seg(seg, start, len)
    # TODO: support segment types other than linear (stripeCount = 1)
    stripe = seg.stripes[0]
    pos    = stripe.start_address + start - seg.block_start
    disk   = stripe.physical_volume.disk
    disk.seek pos #, IO::SEEK_SET
    disk.read len
  end
end

class VolumeGroup
  attr_accessor :id, :name,
                :extent_size, :seqno, :status,
                :physical_volumes, :logical_volumes,
                :disk_obj

  def initialize(args={})
    args.keys.each { |k| send("#{k}=".intern, args[k]) }

    physical_volumes.values.each { |pv| pv.vg = self } if physical_volumes
    logical_volumes.values.each  { |lv| lv.vg = self } if logical_volumes
  end
end

class PhysicalVolume
  attr_accessor :id, :name,
                :device, :device_size,
                :pe_start, :pe_count,
                :status, :vg

  def initialize(args={})
    args.keys.each { |k| send("#{k}=".intern, args[k]) }
  end

  def disk
    @disk ||= $volume_groups.find { |vg|
                vg.disk_obj.pv_header.pv_uuid == id
              }.disk_obj.raw_disk
  end
end

class LogicalVolume
  attr_accessor :id, :name,
                :segment_count, :segments,
                :status, :vg

  def initialize(args={})
    args.keys.each { |k| send("#{k}=".intern, args[k]) }

    segments.each  { |seg| seg.lv = self } if segments
  end

  def disk
    @disk ||= begin
      LVDisk.new self
    end
  end

  def num_blocks
    @num_blocks ||= segments.inject(0) { |num, seg| num + seg.num_blocks }
  end

  # will raise exception if LogicalVolume is not thin metadata volume
  def superblock
    @superblock ||= Thin::SuperBlock.get self
  end

  def thin_segments
    @thin_segments ||= segments.select { |segment| segment.thin? }
  end

  def thin_segment
    @thin_segment ||= thin_segments.first
  end

  def thin?
    !thin_segments.empty?
  end

  def thin_pool_volume
    return nil unless thin?
    return thin_segment.thin_pool_volume
  end

  def thin_pool_segments
    @thin_pool_segments ||= segments.select { |segment| segment.thin_pool? }
  end

  def thin_pool_segment
    thin_pool_segments.first
  end

  def thin_pool?
    !thin_pool_segments.empty?
  end

  def metadata_volume
    thin_pool_segment.metadata_volume
  end

  def data_volume
    thin_pool_segment.data_volume
  end

  def set_volumes(lvs)
    segments.each { |seg| seg.set_volumes lvs }
  end
end

class LVSegment
  attr_accessor :start_extent, :extent_count, :type,
                :stripe_count, :stripes, :device_id, :lv

  attr_accessor :thin_pool, :metadata, :pool

  attr_accessor :thin_pool_volume, :metadata_volume, :data_volume

  def initialize(args={})
    args.keys.each { |k| send("#{k}=".intern, args[k]) }

    stripes.each  { |stripe| stripe.seg = self } if stripes
  end

  def start_address
    @start_address ||= start_extent * lv.disk.extent_size
  end

  def end_address
    @end_address ||= (start_extent + extent_count) * lv.disk.extent_size - 1
  end

  def address_range
    @address_range ||= Range.new start_address, end_address, false
  end

  def block_start
    @block_start ||= address_range.begin
  end

  def size
    @size ||= end_address - start_address + 1
  end

  def num_blocks
    @num_blocks ||= size / lv.disk.block_size
  end

  def thin?
    type == 'thin'
  end

  def thin_pool?
    type == 'thin-pool'
  end

  def set_metadata_volume(lvs)
    @metadata_volume = lvs.find { |lv| lv.name == metadata }
  end

  def set_data_volume(lvs)
    @data_volume = lvs.find { |lv| lv.name == pool }
  end

  def set_thin_pool_volume(lvs)
    @thin_pool_volume = lvs.find { |lv| lv.name == thin_pool }
  end

  def set_volumes(lvs)
    set_metadata_volume lvs
    set_data_volume lvs
    set_thin_pool_volume lvs
  end
end

class LVSegStripe
  attr_accessor :pvn, :ext, :seg

  def initialize(pvn, ext)
    self.pvn = pvn
    self.ext = ext
  end

  def physical_volume
    @physical_volume ||= begin
      pv = seg.lv.vg.physical_volumes[pvn]
      raise "Physical volume object (#{pvn}) not found in volume group" if pv.nil?
      pv
    end
  end

  def start_address
    @start_address ||= (physical_volume.pe_start * seg.lv.disk.block_size) +
                       (ext * seg.lv.disk.extent_size)
  end
end

### thin structures

module Thin
  class BTree
    FLAGS = { :internal => 1, :leaf => 2}

    attr_accessor :root_address

    def initialize(superblock, root_address, value_type)
      @superblock   = superblock
      @root_address = root_address
      @value_type   = value_type
    end

    def root
      @root ||= begin
        @superblock.seek root_address
        @superblock.read_struct DISK_NODE
      end
    end

    def internal?
      (root['flags'] & FLAGS[:internal]) != 0
    end

    def leaf?
      (root['flags'] & FLAGS[:leaf]) != 0
    end

    def num_entries
      @num_entries ||= root['nr_entries']
    end

    def max_entries
      @max_entries ||= root['max_entries']
    end

    def key_base
      root_address + DISK_NODE.size
    end

    def key_address(i)
      key_base + i * 8
    end

    def value_base
      key_address(max_entries)
    end

    def value_address(i)
      value_base + @value_type.size * i
    end

    def keys
      @keys ||= begin
        @superblock.seek key_base
        @superblock.read(num_entries * 8).unpack("Q#{num_entries}")
      end
    end

    def entries
      @entries ||= begin
        @superblock.seek value_base
        @superblock.read_structs @value_type, num_entries
      end
    end

    def entry_for(key)
      entries[keys.index(key)]
    end

    def to_h
      @h ||=
        Hash[0.upto(num_entries-1).collect do |i|
          k = keys[i]
          e = entries[i].kind_of?(BTree) ? entries[i].to_h : entries[i]
          [k, e]
        end]
    end

    def [](key)
      return to_h[key]
    end
  end # class BTree

  class DataMap < BTree
    TIME_MASK = (1 << 24) - 1

    def initialize(superblock, root_address)
      super superblock, root_address, MAPPING_DETAILS
    end

    alias :device_blocks :keys

    def entries
      @dmentries ||= begin
        super.collect do |entry|
          value = entry['value']
          internal? ? DataMap.new(@superblock, @superblock.md_block_address(value)) :
                      [extract_data_block(value), extract_time(value)]
        end
      end
    end

    def data_block(device_block)
      device_blocks.reverse.each do |map_device_block|
        if map_device_block <= device_block
          entry = entry_for(map_device_block)
          return entry.data_block(device_block) if entry.is_a?(DataMap)
          raise RuntimeError, "LVM2Thin cannot find device block: #{device_block} (closest: #{map_device_block})" unless map_device_block == device_block
          return entry.first
        end
      end

      raise RuntimeError, "LVM2Thin could not find data block for #{device_block}"
    end

    private

    def extract_data_block(value)
      value >> 24
    end

    def extract_time(value)
      value & TIME_MASK
    end
  end # class DataMap

  class MappingTree < BTree
    def initialize(superblock, root_address)
      super superblock, root_address, MAPPING_DETAILS
    end

    def entries
      @mtentries ||= begin
        super.collect do |entry|
          DataMap.new @superblock, @superblock.md_block_address(entry['value'])
        end
      end
    end

    def map_for(device_id)
      entry_for(device_id)
    end
  end # class MappingTree

  class DataSpaceMap
    attr_accessor :struct

    def initialize(superblock, struct)
      @superblock = superblock
      @struct = struct
    end

    def btree_root_address
      @btree_root_address ||= @superblock.md_block_address(struct['bitmap_root'])
    end

    def btree
      @btree ||= BTree.new @superblock, btree_root_address, INDEX_ENTRY
    end
  end

  class MetadataSpaceMap
    def metadata_root_address
      @metadata_root_address ||= @superblock.md_block_address(struct['bitmap_root'])
    end

    def root
      @metadata_root ||= begin
        @superblock.seek metadata_root_address
        @superblock.read_struct METADATA_INDEX
      end
    end

    def indices
      @metadata_indices ||= (struct['nr_blocks'].to_f / @superblock.entries_per_block).ceil
    end

    def index_entries
      @index_entries ||=
        0.upto(indices-1).collect do |i|
          address = metadata_root_address + METADATA_INDEX.size + i * INDEX_ENTRY.size
          @superblock.seek address
          @superblock.read_struct INDEX_ENTRY
        end
    end

    def bitmaps
      @bitmaps ||= index_entries.collect do |index_entry|
        @superblock.seek @superblock.md_block_address(index_entry['blocknr'])
        @superblock.read_struct BITMAP_HEADER
      end
    end

    attr_accessor :struct

    def initialize(superblock, struct)
      @superblock = superblock
      @struct     = struct
    end
  end # class DataSpaceMap

  class SuperBlock
    attr_accessor :metadata_volume

    attr_accessor :struct

    def self.get(metadata_volume)
      @superblock ||= begin
        superblock = SuperBlock.new
        superblock.metadata_volume = metadata_volume
        superblock.seek 0
        superblock.struct = superblock.read_struct SUPERBLOCK
        raise "unknown lvm2 thin metadata magic number" if superblock.struct.magic != THIN_MAGIC
        superblock
      end
    end

    ### superblock properties:

    def md_block_size
      @md_block_size ||= struct['metadata_block_size'] * 512 # = 4096
    end

    def md_block_address(blk_addr)
      blk_addr * md_block_size
    end

    def entries_per_block
      @entries_per_block ||= (md_block_size - BITMAP_HEADER.size) * 4
    end

    def data_block_size
      @data_block_size ||= struct['data_block_size'] * 512
    end

    def data_block_address(blk_addr)
      blk_addr * data_block_size
    end

    ### lvm thin structures:

    def data_space_map
      @data_space_map ||= begin
        seek SUPERBLOCK.offset('data_space_map_root')
        DataSpaceMap.new self, read_struct(SPACE_MAP)
      end
    end

    def metadata_space_map
      @metadata_space_map ||= begin
        seek SUPERBLOCK.offset('metadata_space_map_root')
        MetadataSpaceMap.new self, read_struct(SPACE_MAP)
      end
    end

    def data_mapping_address
      @data_mapping_address ||= md_block_address(struct['data_mapping_root'])
    end

    def data_mapping
      @data_mapping ||= MappingTree.new self, data_mapping_address
    end

    def device_details_address
      @device_details_address ||= md_block_address(struct['device_details_root'])
    end

    def device_details
      @device_details ||= BTree.new self, device_details_address, DEVICE_DETAILS
    end

    ### address resolution / mapping:

    def device_block(device_address)
      (device_address / data_block_size).to_i
    end

    def device_block_offset(device_address)
      device_address % data_block_size
    end

    # return array of tuples containing data volume addresses and lengths to
    # read from them to read the specified device offset & length
    def device_to_data(device_id, pos, len)
      dev_blk = device_block(pos)
      dev_off = device_block_offset(pos)

      total_len = 0
      data_blks = []

      num_data_blks = (len / data_block_size).to_i + 1
      0.upto(num_data_blks - 1) do |i|
        data_blk = data_mapping.map_for(device_id).data_block(dev_blk + i)

        blk_start = data_blk * data_block_size
        blk_len   = 0

        if i == 0
          blk_start += dev_off
          blk_len    = data_block_size - dev_off - 1

        elsif i == num_data_blks - 1
          blk_len = len - total_len

        else
          blk_len    = data_block_size
        end

        total_len += blk_len
        data_blks << [blk_start, blk_len]
      end

      data_blks
    end

    ### metadata volume disk helpers:

    def seek(pos)
      @seek_pos = pos
    end

    def read(n)
      @metadata_volume.disk.read @seek_pos, n
    end

    def read_struct(struct)
      OpenStruct.new(struct.decode(@metadata_volume.disk.read(@seek_pos, struct.size)))
    end

    def read_structs(struct, num)
      Array.new(num) do
        read_struct struct
      end
    end
  end # class SuperBlock
end # module Thin


### processing

def disks
  @disks ||= []
end

optparse = OptionParser.new do |opts|
  opts.on('-h', '--help', 'Display this help screen') do
    puts opts
    exit
  end

  opts.on('-d', '--disk |path|') do |disk|
    disks << disk
  end
end

optparse.parse!

if disks.empty?
  puts "need at least one disk"
  exit 1
end

$volume_groups = []

disks.each do |disk|
  $disk_obj = OpenStruct.new
  $disk_obj.raw_disk = RawDisk.new disk

  def disk_obj
    $disk_obj
  end

  def seek(pos)
    disk_obj.raw_disk.seek pos
  end

  def read(len)
    disk_obj.raw_disk.read len
  end

  def read_struct(struct)
    OpenStruct.new(struct.decode(read(struct.size)))
  end

  ### label scanner / metadata extractor

  def label_sectors
    (0...LABEL_SCAN_SECTORS).collect do |s|
      s * SECTOR_SIZE
    end
  end

  def is_label?(struct)
    struct.lvm_id == LVM_ID
  end

  def labels
    disk_obj.labels ||=
      label_sectors.collect do |s|
        seek s
        struct = read_struct LABEL_HEADER
        is_label?(struct) ? struct : nil
      end.compact
  end

  def label
    disk_obj.label ||= labels.first
  end

  def pv_header_address
    disk_obj.pv_header_address ||=
      (label.sector_xl * SECTOR_SIZE) + label.offset_xl
  end

  def _pv_header
    disk_obj._pv_header ||= begin
      seek pv_header_address
      read_struct PV_HEADER
    end
  end

  def _disk_locations
    _pv_header.disk_locations ||= begin
      locations = []
      loop do
        location   = read_struct DISK_LOCN
        break if location.offset == 0
        locations << location
      end
      locations
    end
  end

  def _metadata_disk_locations
    _pv_header.metadata_disk_locations ||= begin
      locations = []
      loop do
        location   = read_struct DISK_LOCN
        break if location.offset == 0
        locations << location
      end
      locations
    end
  end

  def pv_header
    disk_obj.pv_header ||= begin
      ph = _pv_header
      _disk_locations
      _metadata_disk_locations
      ph
    end
  end

  def _metadata_locations(md)
    locations = []
    loop do
      location = read_struct RAW_LOCN
      break if location.offset == 0
      location.base = md.start
      locations << location
    end
    locations
  end

  def metadata_headers
    disk_obj.metadata_headers ||= begin
      pv_header.metadata_disk_locations.collect do |loc|
        seek loc.offset
        md = read_struct MDA_HEADER
        raise "Unknown LVM2 Magic" if md.magic != FMTT_MAGIC
        md.raw_locations = _metadata_locations(md)
        md
      end
    end
  end

  def _sanitize_raw_metadata(md)
    md.gsub(/#.*$/, "")
      .gsub("[",    "[ ")
      .gsub("]",    " ]")
      .gsub('"',    ' " ')
      .delete("=,")
      .gsub(/\s+/,  " ")
      .split(' ')
  end

  def raw_metadata
    disk_obj.raw_metadata ||= begin
      metadata_headers.collect { |hdr| hdr.raw_locations }
                      .flatten.collect do |location|
        seek location.base + location.offset
        _sanitize_raw_metadata read(location.size)
      end
    end
  end

  def num_vgs
    @num_vgs ||= raw_metadata.size
  end

  ### metadata parser

  $raw_metadata   = nil
  $raw_metadata_i = nil

  def _raw_metadata
    $raw_metadata ||= Array.new(raw_metadata[$raw_metadata_i])
  end

  def _raw_vg_name
    $raw_metadata = nil
    _raw_metadata.shift
  end

  def _parse_metadata_hash
    hash = {}
    name = _raw_metadata.shift
    while name && name != MD::HASH_END
      hash[name] = _parse_metadata_obj
      name = _raw_metadata.shift
    end
    hash
  end

  def _parse_metadata_array
    array = []
    val = _raw_metadata.shift
    while val && val != MD::ARRAY_END
      array << _parse_metadata_val(val)
      val = _raw_metadata.shift
    end
    array
  end

  def _parse_metadata_val(val)
    if val == MD::STRING_START
      return _parse_metadata_string
    else
      return val
    end
  end

  def _parse_metadata_string
    str = ''
    word = _raw_metadata.shift
    while word && word != MD::STRING_END
      str << word + " "
      word = _raw_metadata.shift
    end
    str.chomp(" ")
  end

  def _parse_metadata_obj
    val = _raw_metadata.shift

    case val
    when MD::HASH_START
      _parse_metadata_hash
    when MD::ARRAY_START
      _parse_metadata_array
    else
      _parse_metadata_val(val)
    end
  end

  def metadata
    disk_obj.metadata ||= begin
      md = {}
      0.upto(num_vgs-1) do |i|
        $raw_metadata_i = i
        md[_raw_vg_name] = _parse_metadata_obj
      end
      md
    end
  end

  def vg_objs
    disk_obj.vg_objs ||= begin
      metadata.collect do |vg_name, vgobj|
        VolumeGroup.new :id               => vgobj['id'],
                        :name             => vg_name,
                        :extent_size      => vgobj['extent_size'].to_i,
                        :seqno            => vgobj['seqno'],
                        :status           => vgobj["status"],
                        :physical_volumes => _pv_objs(vgobj["physical_volumes"]),
                        :logical_volumes  => _lv_objs(vgobj["logical_volumes"]),
                        :disk_obj         => disk_obj
      end
    end
  end

  def _pv_objs(pv_metadata)
    pvobjs = {}
    pv_metadata.each do |name, pvobj|
      pvobjs[name] = _pv_obj(name, pvobj)
    end
    pvobjs
  end

  def _pv_obj(name, pvobj)
    PhysicalVolume.new :id          => pvobj['id'].delete('-'),
                       :name        => name,
                       :device      => pvobj['device'],
                       :device_size => pvobj['dev_size'],
                       :pe_start    => pvobj['pe_start'].to_i,
                       :pe_count    => pvobj['pe_count'].to_i,
                       :status      => pvobj["status"]
  end

  def _lv_objs(lv_metadata)
    lvobjs = {}
    lv_metadata.each do |name, lvobj|
      lvobjs[name] = _lv_obj(name, lvobj)
    end
    lvobjs
  end

  def _lv_obj(name, lvobj)
    LogicalVolume.new :id            => lvobj['id'],
                      :name          => name,
                      :segment_count => lvobj['segment_count'].to_i,
                      :status        => lvobj['status'],
                      :segments      => _lv_segments(lvobj)
  end

  def _lv_segments(lvobj)
    (1..lvobj['segment_count'].to_i).collect { |s| _lv_segment(lvobj["segment#{s}"]) }
  end

  def _lv_segment(segobj)
    LVSegment.new :start_extent => segobj['start_extent'].to_i,
                  :extent_count => segobj['extent_count'].to_i,
                  :type         => segobj['type'],
                  :stripe_count => segobj['stripe_count'].to_i,
                  :device_id    => _lv_seg_device_id(segobj),
                  :thin_pool    => segobj['thin_pool'],
                  :metadata     => segobj['metadata'],
                  :pool         => segobj['pool'],
                  :stripes      => _lv_seg_stripes(segobj)
  end

  def _lv_seg_device_id(segobj)
    segobj['device_id'] ? segobj['device_id'].to_i : nil
  end
  
  def _lv_seg_stripes(segobj)
    segobj['stripes'] ? (segobj['stripes'].each_slice(2).collect { |pv, o| LVSegStripe.new(pv, o.to_i) }) : nil
  end

  ### 

  $volume_groups += vg_objs
end

logical_volumes = $volume_groups.collect { |vg| vg.logical_volumes.values }.flatten
logical_volumes.each { |lv| lv.set_volumes logical_volumes }

#puts $volume_groups.first.logical_volumes["root"].disk.read 7929824, 512