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POUsing QSocketNotifier to select on a char device.
 

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    <p>I wrote a char device driver and am now writing a QT "wrapper" which part of it is to get a signal to fire when the device becomes readable via the poll mechanism. I had tried to do:</p> <pre><code>QFile file("/dev/testDriver"); if(file.open(QFile::ReadOnly)) { QSocketNotifier sn(file.handle(), , QSocketNotifier::Read); sn.setEnabled(true); connect(&amp;sn, SIGNAL(activated(int)), &amp;this, SLOT(readyRead())); } </code></pre> <p>But readyRead was never called and my driver never reported having its poll method called.</p> <p>I was able to get the following code to work so I know my driver is working</p> <pre><code>QFile file("/dev/testDriver"); if(file.open(QFile::ReadOnly)) { struct pollfd fd; fd.fd = file.handle(); fd.events = POLLIN; struct pollfd fds[] = {fd}; int ready; qDebug() &lt;&lt; "Started poll"; ready = poll(fds, 1, -1); qDebug() &lt;&lt; "Poll returned: " &lt;&lt; ready; QTextStream in(&amp;file); QTextStream out(stdout); out &lt;&lt; in.readAll(); } </code></pre> <p>This properly waits for my driver to call wake_up and I can see two poll calls from my driver. One for the initial poll registration and one for when the wake_up happens. </p> <p>Doing it this way I would probably have to spawn a separate thread which all it did was poll on this device and throw a signal and loop. </p> <p>Is it possible to use <a href="http://doc.qt.nokia.com/latest/qsocketnotifier.html" rel="nofollow">QSocketNotifier</a> in this way? The documentation of <a href="http://doc.qt.nokia.com/latest/qfile.html#handle" rel="nofollow">QFile::handle()</a> seems to indicate it should be.</p>
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    1. CODid you ever get this working? I wrote something similar, but I couldn't get `file->read(buf, 1)` to work. It would just hang. However, `read(file->handle(), buf, 1)` worked just fine.
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    2. CO@Harvey Yes the answer I checked worked for me. Turned out to be a simple coding error. Also check out my answer to see if it helps you.
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    3. COTo revise my earlier comment, it was a misunderstanding on my part of how the device driver worked. Both pieces of code worked, it just happened that my other factors caused the entire test to fail when I was using one of them causing me to make the erroneous connection.
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