Async Call struct method in DriverKit doesn't return the data assigned

Question

I'm using DriverKit in iPadOS.

I've got a call to read data synchronously, which is working fine.

So I'm trying to do the asynchronous one.

For this I'm calling IOConnectCallAsyncStructMethod with

ret = IOConnectCallAsyncStructMethod(connection, MessageType_AsyncReadRequest, callback_port, asynRequestRef, kIOAsyncCalloutCount, nullptr, 0, output, &outputSizeT);

Where:

arraySize = 248
uint64_t output[arraySize] = {}; 
size_t outputSizeT = sizeof(uint64_t) * arraySize;

When I got the data from the USB device, I return it with AsyncCompletion

With:

    uint64_t *read // This will contain the data from the device

    const uint32_t size = 32;
    
    uint64_t asyncData[size] = { };
    memcpy(asyncData, read, (sizeof(uint64_t) * size));


        AsyncCompletion(ivars->readSampleCallbackAction, kIOReturnSuccess, asyncData, size);
        ivars->readSampleCallbackAction->release();

My problem is when the call of IOConnectCallAsyncStructMethod returns. ret would be 0 as successful but output won't contain the data.

I know there is data in asyncData because if I inspect the variable in debug mode I can see the data I expect.

Any ideas?

Thanks

score 0 · Answer 1 · answered Aug 08 '23 at 10:42

Ok, I had two problems here.

One the data is not returned in the output variable. The data is returned in the AsyncCallback method.

Also I think there is another problem in my call to asynccompletion

Because I'm passing an array of uint64_t of size 32, probably that's producing a problem because the maximum is 16 ( https://developer.apple.com/documentation/driverkit/3325601-arguments_array_maximum/kiouserclientasyncargumentscountmax )

https://developer.apple.com/documentation/driverkit/iouserclient/3325613-asynccompletion

If I change the size from const uint32_t size = 32; to const uint32_t size = 8;

I would get the call in AsyncCallback

Async Call struct method in DriverKit doesn't return the data assigned

1 Answers1