问个关于串口过滤的问题

请教高手：我想做一个串口的过滤驱动。其实就是拦截CreateFile和Write、Read操作。参考各种例程我的AddDevice例程是这么写的：
NTSTATUS SerAddDevice(IN PDRIVER_OBJECT DriverObject,IN PDEVICE_OBJECT pdo)
{
NTSTATUS status;
PDEVICE_OBJECT fdo;

status = IoCreateDevice (DriverObject,
sizeof(DEVICE_EXTENSION),
NULL, // No Name
FILE_DEVICE_SERIAL_PORT,
FILE_DEVICE_SECURE_OPEN,
FALSE, // Not exclusive
&fdo);

// Remember fdo in our device extension
PDEVICE_EXTENSION dx = (PDEVICE_EXTENSION)fdo->DeviceExtension;
dx->fdo = fdo;

// Attach to the driver stack below us
dx->NextStackDevice = IoAttachDeviceToDeviceStack(fdo,pdo);

  fdo->Flags |= dx->NextStackDevice->Flags & (DO_BUFFERED_IO | DO_DIRECT_IO |
                            DO_POWER_PAGABLE  | DO_POWER_INRUSH);

  fdo->DeviceType = dx->NextStackDevice->DeviceType;
  fdo->Characteristics = dx->NextStackDevice->Characteristics;

fdo->Flags &= ~DO_DEVICE_INITIALIZING;
return STATUS_SUCCESS;
}

但是，当我在应用程序中调用CreateFile(\"\\\\\\\\.\\\\COM1\"...)的时候，驱动根本拦截不到，请问高手是不是AddDevice的那个地方写错了？

挂了上去后我会去处理相关IRP的

[编辑 -  5/24/05 by  KMK]