Multiple device driver? (KMDF/WDF) - windows

Question

I've just written a KMDF USB driver. Now I want to connect several (up to at least four) devices to the PC. Where do I start? I've noted that when I connect the second device to the PC it use the very same instance of the driver as for the first connected device. EvtDeviceAdd(...) runs one time per device and since I don't have any handling for several devices things get weird... Right now my EvtDeviceAdd looks like this:
NTSTATUS EvtDeviceAdd(IN WDFDRIVER Driver, IN PWDFDEVICE_INIT DeviceInit) {
WDF_PNPPOWER_EVENT_CALLBACKS pnpPowerCallbacks;
WDF_OBJECT_ATTRIBUTES attributes;
NTSTATUS status;
WDFDEVICE device;
WDF_DEVICE_PNP_CAPABILITIES pnpCaps;
WDF_IO_QUEUE_CONFIG ioQueueConfig;
PDEVICE_CONTEXT pDevContext;
WDFQUEUE queue;
PWSTR driverRegistryPath;
UNREFERENCED_PARAMETER(Driver);
PAGED_CODE();
DbgPrint("New device was added\n");
WDF_PNPPOWER_EVENT_CALLBACKS_INIT(&pnpPowerCallbacks);
pnpPowerCallbacks.EvtDevicePrepareHardware = EvtDevicePrepareHardware;
WdfDeviceInitSetPnpPowerEventCallbacks(DeviceInit, &pnpPowerCallbacks);
WdfDeviceInitSetIoType(DeviceInit, WdfDeviceIoBuffered);
WDF_OBJECT_ATTRIBUTES_INIT_CONTEXT_TYPE(&attributes, DEVICE_CONTEXT);
status = WdfDeviceCreate(&DeviceInit, &attributes, &device);
if (!NT_SUCCESS(status)) {
DbgPrint("WdfDeviceCreate failed with Status code %!STATUS!\n", status);
return status;
}
pDevContext = GetDeviceContext(device);
WDF_DEVICE_PNP_CAPABILITIES_INIT(&pnpCaps);
pnpCaps.SurpriseRemovalOK = WdfTrue;
WdfDeviceSetPnpCapabilities(device, &pnpCaps);
WDF_IO_QUEUE_CONFIG_INIT_DEFAULT_QUEUE(&ioQueueConfig, WdfIoQueueDispatchParallel);
ioQueueConfig.EvtIoRead = EvtIoRead;
ioQueueConfig.EvtIoWrite = EvtIoWrite;
ioQueueConfig.EvtIoDeviceControl = EvtIoDeviceControl;
ioQueueConfig.PowerManaged = WdfTrue;
status = WdfIoQueueCreate(device, &ioQueueConfig, WDF_NO_OBJECT_ATTRIBUTES, &queue);
if (!NT_SUCCESS(status)) {
DbgPrint("WdfIoQueueCreate failed %!STATUS!\n", status);
return status;
}
pDevContext->DeviceIOControlQueue = queue;
status = WdfDeviceCreateDeviceInterface(device, (LPGUID) &GUID_DEVINTERFACE_MYDEVICE, NULL);
if (!NT_SUCCESS(status)) {
DbgPrint("WdfDeviceCreateDeviceInterface failed %!STATUS!\n", status);
return status;
}
}
Where do I start? Is there any good examples?

Answer 1

There is only one instance of the driver in memory for all the connected devices (it's a singleton). The OS calls to the driver are accompanied with the relevant device context and from that point the devices shouldn't interfere with each other operation. The problems begin if non-constant global/static variables are being used. Since the Kernel space is shared, such variables will be actually shared and accessible from all attached devices. For this reason global/static data shouldn't be device-specific and should be guarded since it's shared resource. There are some samples in the WDK demonstrating multi-device drivers.