# File lib/mongo/util/write_concern.rb, line 49
    def get_write_concern(opts, parent=nil)
      write_concern_from_legacy(opts) if opts.key?(:safe) || @legacy_write_concern
      write_concern = {
        :w        => 1,
        :j        => false,
        :fsync    => false,
        :wtimeout => nil
      }
      write_concern.merge!(parent.write_concern) if parent
      write_concern.merge!(opts.reject {|k,v| !write_concern.keys.include?(k)})
      write_concern
    end