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--- projects:qtusb [2013/06/04 16:42] – [udev Rules] mkucia
+++ projects:qtusb [2013/06/04 23:10] – [udev Rules] mkucia
@@ Line 209: / Line 209: @@
 TODO
-==== udev Rules ====
+==== udev rules ====
 Create a rule for device by making a new file:
@@ Line 224: / Line 224: @@
 There are more actions that udev rules can implement. For example launching application when device is connected.
+==== Detecting device mount/remove ====
+udev allow user applications to receive messages on changes in devices filesystem.
+One can filter messages by subsystem and type.
+In our case we want to receive USB device notifications from USB subsystem (it also emits USB interface messages).
+Finally monitor is activated and file descriptor ([[wp>Unix_file_types#Socket|socket file]]) retrieved.
+<code=c>
+// Create the udev object
+if (!(udev = udev_new()))
+[..]
+// Set up a monitor to monitor usb devices
+mon = udev_monitor_new_from_netlink(udev, "udev");
+// We want only to receive information about usb devices
+udev_monitor_filter_add_match_subsystem_devtype(mon, "usb", "usb_device");
+udev_monitor_enable_receiving(mon);
+fd = udev_monitor_get_fd(mon);
+</code>
+The messages need to be pooled periodically. I created timer that fires every 250 [ms].
+<code=c>
+// Start timer that will periodicaly check if hardware is connected
+monitorTimer = new QTimer(this);
+connect(monitorTimer, &QTimer::timeout, this, &MainWindow::monitorTimerTick );
+monitorTimer->start(250);
+</code>
+Timer code checks if there is a new message. select() returns amount of messages. In this case function is non-blocking but one can implement timeout easy here.
+<code=c>
+void MainWindow::monitorTimerTick()
+{
+    // Set up select
+    fd_set fds;
+    struct timeval tv;
+    int ret;
+    FD_ZERO(&fds);
+    FD_SET(fd, &fds);
+    tv.tv_sec = 0;
+    tv.tv_usec = 0;
+    ret = select(fd+1, &fds, NULL, NULL, &tv);
+    // Check if our file descriptor has received data.
+    if (ret > 0 && FD_ISSET(fd, &fds))
+    {
+</code>
+When new message is confirmed code check if it from our hardware by looking into vendor id and product id.
+If device matches, code checks type of event and emits appropriate Qt signal.
+<code=c>
+// Get the device
+if ( (dev = udev_monitor_receive_device(mon)) == NULL)
+[...]
+// Now check if the device is our rgb_led launchpad
+const char* str_action = udev_device_get_action(dev);
+const char* str_PID = udev_device_get_property_value(dev, "ID_MODEL_ID");
+const char* str_VID = udev_device_get_property_value(dev, "ID_VENDOR_ID");
+[...]
+// Compare strings and send signals
+if ( (strcmp(STR_PRODUCT_ID,str_PID) == 0) && (strcmp(STR_VENDOR_ID,str_VID) == 0) )
+{
+   if (strcmp("add",str_action) == 0)
+   {
+      emit signal_DeviceConnected();
+   }
+   else if (strcmp("remove",str_action) == 0)
+   {
+      emit signal_DeviceDisconnected();
+   }
+[...]
+    // If there are more events to process, do not wait for next tick!
+    if (ret-1 > 0)
+        monitorTimerTick();
+</code>
 ====== References ======
   * http://www.signal11.us/oss/udev/