Problems receiving Notifications from IOKit (CoreFoundation) for plugged Devices

Question

I'm currently developing an application on 10.6.7 which should receive notifications when a new usb device is plugged in. I found out that there is a IOKit function which handles such stuff 'IOServiceAddMatchingNotification'. Because the return value from this specific function is 0, I think that the problem perhaps is in my matching Dictionary, which is given into this function. I declare the Dictionary that way:

CFMutableDictionaryRef matchingDict = IOServiceMatching(kIOUSBDeviceClassName);

Because I wan't to receive a notification for each device, I don't know if this is the right way to create this particular dictionary.

My complete code look like this:

ioKitNotificationPort = IONotificationPortCreate(kIOMasterPortDefault);
notificationRunLoopSource = IONotificationPortGetRunLoopSource(ioKitNotificationPort);

CFRunLoopAddSource(CFRunLoopGetCurrent(), notificationRunLoopSource, kCFRunLoopDefaultMode);

CFMutableDictionaryRef matchingDict = IOServiceMatching(kIOUSBDeviceClassName);


addMatchingNotificationResult = IOServiceAddMatchingNotification(ioKitNotificationPort,
                                                                 kIOPublishNotification,
                                                                 matchingDict,
                                                                 deviceAdded,
                                                                 NULL,

Does anyone has a idea why this won't work? (Note: The Callback function is a static void c function and the rest is wrapped ins ide a Obj-C class).

Thanks

Xcode 4, 10.6.7

I'm not terribly familiar with the user space side of IOKit yet, but on the kernel side, matching happens first for the most specific matching dictionary and only if that fails are more general matches tried. Are you trying this with devices that would already be matched by existing drivers? Also, maybe this will help: developer.apple.com/library/mac/#qa/qa1076/_index.html — pmdj
I tried this with a usb stick that I'm using a couple of time now. Finder finds that stick, so I think I don't need to write a entry in the driver directory from OS X. Also I like to get notifications for sticks that were never before attached to my mac, so there should be a way to handle this... I still can't find that way... — Andi

Mattie Mattie · Accepted Answer · 2011-08-09T00:48:48

Weirdly, you must empty the iterator returned by IOServiceAddMatchingNotification before the notification will be armed. I don't see that in the code provided, so that could be in the issue. That iterator is actually what you need to keep around to keep the notification running.

io_iterator_t ioNotification;

addMatchingNotificationResult = IOServiceAddMatchingNotification(ioKitNotificationPort,
                                                                 kIOPublishNotification,
                                                                 matchingDict,
                                                                 deviceAdded,
                                                                 NULL,
                                                                 &ioNotification);

while ((service = IOIteratorNext(ioNotification)))
{
    NSLog(@"Hey, I found a service!");

    IOObjectRelease(service); // yes, you have to release this
}

Problems receiving Notifications from IOKit (CoreFoundation) for plugged Devices

4 Answers