module AWS::EC2::BlockDeviceMappings

def translate_block_device_mappings(mapping)
  raise ArgumentError.new("block_device_mappings must be a hash") unless
    mapping.kind_of?(Hash)
  mapping.map do |device, dest|
    raise ArgumentError.new("keys of block_device_mappings must be strings") unless
      device.kind_of?(String)
    entry = { :device_name => device }
    case dest
    when :no_device
      # for some reason EC2 rejects boolean values for this seemingly boolean option
      entry[:no_device] = ""
    when Symbol
      raise ArgumentError.new("unrecognized block device mapping: #{dest}")
    when String
      entry[:virtual_name] = dest
    when Hash
      if snapshot = dest.delete(:snapshot)
        dest[:snapshot_id] = snapshot.id
      end
      entry[:ebs] = dest
    else
      raise ArgumentError.new("values of block_device_mappings must "+
                              "be strings, symbols, or hashes")
    end
    entry
  end
end