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    [Solved .. kind of] Getting event when USB is attached/detached

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    • McLion
      McLion last edited by

      Hi

      I am working on a embedded Linux device with Qt4.6.3. When a USB device (i.e. Memorystick) is attached it gets listed as /dev/sda1 and can be mounted manually. So, it basically does the hot-plug which works perfectly for keyboard and mouse, but it it not mounting drives.

      Is there a way I can get a signal in Qt on that event (and the remove event as well). I do not want it to auto-mount because I want to have control over mounting/unmounting. However, if implementing auto-mounting is the easier way, I can handle that as well.

      Thanks
      McL

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      • SGaist
        SGaist Lifetime Qt Champion last edited by

        Hi,

        You can have a look at KDE's Solid library for that. IIRC it's now a tier1 lib which means it doesn't need the full KDE framework to be used.

        Hope it helps

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        Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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        • McLion
          McLion last edited by

          Hi,

          I looked into it ... and it looks promising.
          However, I'm not sure if and how I get this into my Qt.

          For other addings (i.e. QextSerialPort) there was a pri that I simply could include into my pro and compile the sources together with my code.
          For QSerialPort there was a pro which I could use with qmake to build/install libraries and use these now.

          If I look at the sources of solid ... there's nothing alike ?!?
          Any further suggestion highly appreciated.

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          • SGaist
            SGaist Lifetime Qt Champion last edited by

            Indeed you have to build it using cmake

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            Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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            • McLion
              McLion last edited by

              Does somebody know this? http://sourceforge.net/projects/qdevicewatcher/

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              • p3c0
                p3c0 Moderators last edited by

                If you have udisks running on the embedded system then you could use QDbus to get events.

                157

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                • McLion
                  McLion last edited by

                  No udisk and no Dbus ... unfortunately

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                  • McLion
                    McLion last edited by

                    also looked at libusb ...
                    which is listing in TODO:_ notifications of hotplugged/unplugged devices_
                    So, this seems not to work either :(

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                    • SGaist
                      SGaist Lifetime Qt Champion last edited by

                      Do you have udev running ?

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                      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                      • McLion
                        McLion last edited by

                        Nope, running Busybox with mdev.
                        Were you thinking about libudev ... me to ;)

                        How about having QFileSystemWatcher monitoring /dev and getting an event when a sd?? is added .. could that work? ... I never used QFileWatcher before.

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                        • SGaist
                          SGaist Lifetime Qt Champion last edited by

                          IIRC, not all filesystems on linux can be watched, thinking of /dev and /sys if my memory serves well. However, you could also simply poll dev for known device, not really efficient but might be simpler

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                          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                          • McLion
                            McLion last edited by

                            Setting a watcher on /dev works as supposed.
                            Plugging a USB memory stick adds 5 entries in /dev which are removed again if the device is unplugged. The directoryChanged signal is emitted 17 times for plugging and 5 times for unplugging.
                            However, since the signal does not contain the information of what exactly the change in /dev was, I would need to maintain a list of the contents of /dev to be able to compare ... /dev has about 150 entries ... doing this for every emit ... I'm not sure if this is a good idea nor do I already have a solid idea on a efficient solution for doing this.

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                            • SGaist
                              SGaist Lifetime Qt Champion last edited by

                              You could keep a list of /dev's content when starting to watch and then compare it to the current content when getting the directoryChanged signal. You can couple that with a QTimer to avoid a burst of your slot

                              Interested in AI ? www.idiap.ch
                              Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                              • McLion
                                McLion last edited by

                                Just did a test to debug output with this solution which could be a starting point to work something out:

                                @void QTGUI_MainWindow::showModifiedDirectory(QString directory)
                                {
                                qDebug() << "directory changed:" << directory;
                                QDir dir(directory);
                                if(dir.exists("sda1")) { qDebug() << "sda1 found!"; }
                                if(dir.exists("sdb1")) { qDebug() << "sdb1 found!"; }
                                }
                                @

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                                • McLion
                                  McLion last edited by

                                  Just like to add that this works as proposed using QFileSystemWatcher used to monitor the /dev. On the event I do some filtering using QDir … that’s it.

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                                  • A
                                    andreyc last edited by

                                    There is a "a device watcher":http://qt-project.org/forums/viewthread/9605/ library.
                                    I have not tried it.

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                                    • McLion
                                      McLion last edited by

                                      Thanks for the hint. I have already checked this and looked at it. It's based on udev. Since my device uses busybox with mdev, I decided to not try to make this run and try my own solution instead.

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