http://doc.qt.nokia.com/4.7-snapshot/qfile.html#flush
does not say about fsync() sync() fdatasync() syscalls.
I don't understand - after flush() does my data will be written to the disk? ot just to FS cache ?

man fflush():

NOTES
Note that fflush() only flushes the user space buffers provided by the C library. To ensure that the data is physically stored on
disk the kernel buffers must be flushed too, for example, with sync(2) or fsync(2).

I think, flush() should be extended with QFile::flush(bool sync=false)