QGamePad - Does not detect disconnection - Linux

Caipiblack

Dear guy's

The 11 November 2016 I have reported a problem with QGamePad on Linux (bug report)

Currently (in 2018) it is still not fixed.

The problem:
With the backend "evdev" when the gamepad is disconnected the module doesn't process the event from the driver!

It's a real problem because I have to control a heavy robot and it can be dangerous if the remote controller is disconnected because I have no ways to detect it using QGamePad: Nothing is updated on the module when it happens !

The problem is in qevdevgamepadbackend.cpp the signal deviceRemoved() is not emit!. But if you see in readData(), this signal can be emit ...

void QEvdevGamepadDevice::readData()
{
    input_event buffer[32];
    int events = 0, n = 0;
    for (; ;) {
        events = QT_READ(m_fd, reinterpret_cast<char*>(buffer) + n, sizeof(buffer) - n);
        if (events <= 0)
            goto err;
        n += events;
        if (n % sizeof(::input_event) == 0)
            break;
    }

    n /= sizeof(::input_event);

    for (int i = 0; i < n; ++i)
        processInputEvent(&buffer[i]);

    return;

err:
    if (!events) {
        qWarning("Gamepad: Got EOF from input device");
        return;
    } else if (events < 0) {
        if (errno != EINTR && errno != EAGAIN) {
            qErrnoWarning(errno, "Gamepad: Could not read from input device");
            if (errno == ENODEV) { // device got disconnected -> stop reading
                delete m_notifier;
                m_notifier = 0;
                QT_CLOSE(m_fd);
                m_fd = -1;
            }
        }
    }
}

When the gamepad is disconnected, the message "Gamepad: Could not read from input device" appear.

Maybe we just have to add "emit deviceRemoved()" but you need to pass a QString with the device name, maybe that's the reason why it's not finished since two years

Can someone check it please ?

SGaist

Hi,

You should add your new findings to the bug report.

aha_1980

@Caipiblack

I don't see a signal deviceRemoved() in QtGamePad. The nearest one is connectedChanged(bool) but that looks indeed like a possible signal in this situation.

Have you already tried to patch the code yourself? Due to the lack of a gamepad, I cannot test this myself.

Regards

Edit: Ah, there is a deviceRemoved() signal in QEvdevGamepadBackend which is used within the backend only for housekeeping. What stays, the signal you need outside is connectChanged(bool).