I have a USB driver that fetches and sends data to an audio hardware device. I also have a WDM audio driver based on the SimpleAudioSample example.
The USB driver creates a child, and the INF of the audio driver matches on the hardware id of the child. When the child is created I pass a WDF_OBJECT_ATTRIBUTES to allocate some context space. I then allocate an object of type Foo in the context space. When the audio driver is started I retrieve the context space, cast it to the AudioDriverPdoContext struct and then call methods on the object allocated in the USB driver. I also pass object to the USB driver and callback into the audio driver from the USB driver.
The classes that are shared (in the example it’s IBar, Bar and Foo) are built into a separate library, and I link to this library from both the USB and the audio driver. All object are deleted in the same driver that made the allocation.
I wonder if it is ok to share pointers to allocated objectes like this, and call back and fourth between two different drivers using pointer to the objects?
I have looked at using Driver Defined Intefaces, which takes care of versioning and provides a recognisable way of sharing interfaces between drivers, which is of course something good.
class IBar {
public:
virtual ~IBar() = default;
virtual void callback() = 0;
};
class Foo {
public:
void doThings() {
// ...
}
void doOtherThings(IBar* ptr) {
ptr->callback();
}
};
class Bar : public IBar {
public:
void callback() override {
// ...
}
};
struct AudioDriverPdoContext {
Foo* foo = nullptr;
};
WDF_DECLARE_CONTEXT_TYPE_WITH_NAME(AudioDriverPdoContext, getAudioDriverPdoContext)
When the child is created:
WDF_OBJECT_ATTRIBUTES pdoAttributes{};
WDF_OBJECT_ATTRIBUTES_INIT_CONTEXT_TYPE(&pdoAttributes, AudioDriverPdoContext);
WDFDEVICE hChild = nullptr;
if (const auto status = WdfDeviceCreate(&DeviceInit, &pdoAttributes, &hChild);
!NT_SUCCESS(status)) {
return status;
}
// new is implemented to return non-pagable memory
getAudioDriverPdoContext(hChild)->foo = new Foo();
In the StartDevice function of the WDM audio driver
auto bar = new Bar();
if (PDEVICE_OBJECT pdo = nullptr;
NT_SUCCESS(PcGetPhysicalDeviceObject(DeviceObject, &pdo)) && pdo) {
if (auto* const audioDriverPdoContext =
static_cast<AudioDriverPdoContext*>(pdo->DeviceExtension);) {
audioDriverPdoContext->doThings(); // Is this ok?
audioDriverPdoContext->doOtherThings(bar); // Is this ok?
}
}