title: QT QIODevice equivalent of "a+" (read, but append only)
body: <p>We have a very high performance application - or, more accurately, a scalable application that needs to write to log files.</p>
  <p>Each instance gets it's own log file, but when looking at performance metrics, we occasionally see very slow write times. The log files are going to a shared disk, so that we can review the logs when the VM that spools up goes away (with it's disk)</p>
  <p>In working this through the cloud provider, they advise that the log files should be opened with &quot;a+&quot; mode, per: <a href="https://www.cplusplus.com/reference/cstdio/fopen/" rel="nofollow noreferrer">https://www.cplusplus.com/reference/cstdio/fopen/</a>.</p>
  <blockquote>
  <p>&quot;a+&quot;  append/update: Open a file for update (both for input and output)
  with all output operations writing data at the end of the file.
  Repositioning operations (fseek, fsetpos, rewind) affects the next
  input operations, but output operations move the position back to the
  end of file. The file is created if it does not exist.</p>
  </blockquote>
  <p>This allows the shared disk resource to cache the writes; apparently &quot;write only&quot; mode does not, and that was our problem - thousands of clients, each one of which had to persist to disk before the next could write to it's log file.</p>
  <p>I can't find the equivalent of this with QIODevice's open flags. The best I can do is read/write, which is different than a+.</p>
  <p><a href="https://doc.qt.io/qt-5/qiodevice.html#OpenModeFlag-enum" rel="nofollow noreferrer">https://doc.qt.io/qt-5/qiodevice.html#OpenModeFlag-enum</a></p>
  <p>Is there a better way in QT to open a file for &quot;Append only but read cacheable&quot;?</p>