Chris Cant - Writing Windows WDM Device Drivers

Table 9.3 Query device state bits

If any of the state characteristics change after the initial query, a driver notifies the PnP Manager by calling IoInvalidateDeviceState . In response to a call to IoInvalidateDeviceState, the PnP Manager queries the device's PNP_DEVICE_STATE again.

The PnP Manager uses this IRP to get a device's resource requirements list. Bus drivers must handle this request for their child devices that require hardware resources. Function and filter drivers do not handle this IRP.

The PnP Manager uses this IRP to get a device's boot configuration resources. Bus drivers must handle this request for their child devices that require hardware resources. Function and filter drivers do not handle this IRP.

Bus drivers for buses with configuration space must return the relevant information for their child devices. Filter and function drivers do not handle this request.

This request is used to lock or unlock a device. Bus drivers must handle this IRP for a child device that supports device locking. Function and filter drivers do not handle this request.

Bus drivers must write the given information into the configuration space of the child device. Function and filter drivers do not handle this request.

Plug and Play Notification informs Win32 programs and device drivers of device change events that interest them, such as device arrival and removal. They can also refuse requests to remove a device. PnP Notification uses a device interface GUID or a file handle to identify which devices are of interest.

Win32 applications and device drivers register to receive PnP notifications so that they can cope if a device is about to be removed, or if they want to use a device that has just been added. For example, if a program is in the middle of a long transfer, it could refuse permission for a device to be removed. In addition, device drivers can be informed of all devices that expose the required device interface.

A Win32 program calls RegisterDeviceNotification to register that it wants to receive PnP Notification device change messages. You must pass either a window handle or (in W2000 only) a service status handle. The NotificationFilter parameter points a structure that says what type of events you want to receive.

To receive events about devices with a particular device interface, pass a DEV_BROADCAST_DEVICEINTERFACE structure pointer to RegisterDeviceNotification . Set the dbcc_classguid field to the device interface GUID of interest. Set the dbcc_size and dbcc_devicetype fields appropriately.

I have not tried it, but passing a DEV_BROADCAST_HANDLE structure pointer should let you receive events from one open file handle, including custom events.

Do not forget to call UnregisterDeviceNotification when you do not wish to receive any further PnP Notification events.

Device Change Message

Each PnP Notification event is sent to a Win32 program as a WM_DEVICECHANGE message. In MFC applications, this appears in an OnDeviceChange handler.

Table 9.4 lists the main event types returned in wParam. lParam may point to an appropriate structure. For device interface change events, it is a DEV_BROADCAST_DEVICEINTERFACE structure whose dbcc_name field contains the device filename.

For a WM_DEVICECHANGE message that asks permission to remove a device, the handler must return TRUE to agree or BROADCAST_QUERY_DENY [23] BROADCAST_QUERY_DENY has a value of 0x424D5144, ASCII "BMQD", which I presume stands for Broadcast Message Query Deny! to deny the requests. Returning FALSE seems to have the same effect as returning TRUE.

Table 9.4 WM_DEVICECHANGE event types

Wdm2Notify application

Wdm2Notify is a Win32 MFC dialog application that displays any device change events for the Wdm2 device interface. It can be found in the Wdm2\Notify directory of the book software. I had a little difficulty setting up the project so that it would compile and link correctly. As I was using VC++ 5, some of the header files and libraries were out of date. I therefore had to change the project settings to use the Platform SDK include directories first, before the Visual C++ directories. My Platform SDK was installed at D:\MSSDK, so you may need to change the project settings if you want to recompile Wdm2Notify. I also had to link to the version of user32.lib in the Platform SDK. If you are running a later version of Visual Studio, you may be able to undo these project changes.

Some of the device change structures are defined in dbt.h, so I included this header file in the Wdm2Notify main MFC header, stdafx.h. I also had to include the following line in the stdafx.h to ensure that the correct functions were declared.

#define WINVER 0x0500

Listing 9.14 shows the main Wdm2Notify PnP Notification routines in file Wdm2Notif.yDlg.cpp. RegisterDeviceNotification is called in the dialog OnInitDialog routine and unregistered in DestroyWindow. Device change messages are handled in OnDeviceChange. The rest of the source code for Wdm2Notify can be found on the book software disk.