WDM驱动加载方式理解

#pragma PAGEDCODE
NTSTATUS HelloWDMAddDevice(IN PDRIVER_OBJECT DriverObject,
                           IN PDEVICE_OBJECT PhysicalDeviceObject)
{ 
    PAGED_CODE();
    KdPrint(("Enter HelloWDMAddDevice\n"));

    NTSTATUS status;
    PDEVICE_OBJECT fdo;
    UNICODE_STRING devName;
    RtlInitUnicodeString(&devName,L"\\Device\\MyWDMDevice");
    status = IoCreateDevice(
        DriverObject,
        sizeof(DEVICE_EXTENSION),
        &(UNICODE_STRING)devName,
        FILE_DEVICE_UNKNOWN,
        0,
        FALSE,
        &fdo);
    if( !NT_SUCCESS(status))
        return status;
    PDEVICE_EXTENSION pdx = (PDEVICE_EXTENSION)fdo->DeviceExtension;
    pdx->fdo = fdo;
    pdx->NextStackDevice = IoAttachDeviceToDeviceStack(fdo, PhysicalDeviceObject);
    UNICODE_STRING symLinkName;
    RtlInitUnicodeString(&symLinkName,L"\\DosDevices\\HelloWDM");

    pdx->ustrDeviceName = devName;
    pdx->ustrSymLinkName = symLinkName;
    status = IoCreateSymbolicLink(&(UNICODE_STRING)symLinkName,&(UNICODE_STRING)devName);

    if( !NT_SUCCESS(status))
    {
        IoDeleteSymbolicLink(&pdx->ustrSymLinkName);
        status = IoCreateSymbolicLink(&symLinkName,&devName);
        if( !NT_SUCCESS(status))
        {
            return status;
        }
    }

    fdo->Flags |= DO_BUFFERED_IO | DO_POWER_PAGABLE;
    fdo->Flags &= ~DO_DEVICE_INITIALIZING;

    KdPrint(("Leave HelloWDMAddDevice\n"));
    return STATUS_SUCCESS;
}