Teach QXmlInputSource to report progress

Suppose I want to read OpenStreetMaps XML. I want to report progress (how many bytes) of input is read.

Today, QXmlInputSource does not able to report progress.

I can use hack and use QIODevice::pos(), but it is the hack.

Maybe, new member function int progress(), which will return percent of input file (data) read ?
if file is sequental (like socket), progress should return special value (like -1).

Other solution is something like QFuture / QFutureWatcher ....

The main purpose is to show QProgressBar / QProgressDialog