module UnionFSProbe
  UNIONFS_SUPER_OFFSET  = 1024
  UNIONFS_MAGIC_OFFSET  = 52
  UNIONFS_MAGIC_SIZE    = 4
  UNIONFS_MAGIC         = 0xf15f083d

  def self.probe(dobj)
    return false unless dobj.kind_of?(MiqDisk)

    # Assume UnionFS - read magic at offset.
    dobj.seek(UNIONFS_SUPER_OFFSET + UNIONFS_MAGIC_OFFSET)
    magic = dobj.read(UNIONFS_MAGIC_SIZE).unpack('L')
    raise "UnionFS is Not Supported" if magic == UNIONFS_MAGIC

    # No UnionFS.
    false
  end
end