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

McLion

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

SGaist

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

McLion

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.

SGaist

Indeed you have to build it using cmake

McLion

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

p3c0

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

McLion

No udisk and no Dbus ... unfortunately

McLion

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

SGaist

Do you have udev running ?

McLion

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.

SGaist

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

McLion

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.

SGaist

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

McLion

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!"; }
}
@

McLion

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.

andreyc

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

McLion

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.