docs: public static final long getLongAttribute(Path path, String attribute, long def, LinkOption... options) throws IOException
      {
          attribute = attribute.startsWith("user:") ? attribute : "user:"+attribute;
          byte[] attr = (byte[]) Files.getAttribute(path, attribute, options);
          if (attr == null)
          {
              return def;
          }      
          if (attr.length != 8)
          {
              throw new IllegalArgumentException(attribute+" not correct type");
          }
          return Primitives.readLong(attr);
      }