WMI in Action

The WMl features of the Wdm3 driver can be tested in three ways. In all cases, the DebugPrint output of the checked build gives copious trace information about the requests as they happen.

The first thing I must say is that I could not get the driver to compile or run in Windows 98. I am sure that I could have got the Wdm3 driver to compile if I had copied the correct headers and libraries into the W98 DDK, but that did not seem appropriate. It is possible that the one test Windows 98 computer available had its WBEM/WMI runtime corrupted. In the Windows 2000 beta 2, I obtained an update to the WBEM/WMI SDK. Perhaps this update was not meant for Windows 98 and therefore messed up the runtime environment. Anyway, I was able to do the rest of my testing only in Windows 2000.

The MSPower_DeviceEnable WMI data block is used by the Device Manager to display the Power Management tab in the device properties box, as shown in Figure 10.3 in Chapter 10. It retrieves the Enable property, eventually in a call to QueryWmiDataBlock. If the user changes the setting, it is changed in SetWmiDataBlock when the device properties box is closed.

Alternatively, the standard WBEM Object Browser can be used to inspect the MSPower_ DeviceEnable or Wdm3Information WMI data blocks. Logon to the \Root\WMI namespace as the current user, select the Wdm3Information class, for instance, and select one of the Wdm3 device instances.

Figure 12.1 shows the Wdm3Information display for the Wdm3 device that has an instance name of Root\\Unknown\\0004_0 as its key property. The Wdm3Test application has been run, so the current buffer length is 4. The BufferFirstWord property has a decimal value of 2882400001, which is hex 0xabcdef01.

W2000 Beta 3 includes the WBEMTest tool (System32\WBEM\wbemtest.exe) that can also be used to inspect WBEM classes and instances.

By the way, I found that the WBEM Object Browser seemed a bit sluggish. This is possibly because it is using WQL to query the database. In contrast, the Device Manager's use of WMI when dealing with a device's Power Management tab seems to run quickly.

Figure 12.1 WBEM Object Browser inspecting a Wdm3Information instance

You can use the WBEM CIM Studio to look at the class definitions. If you change a WMI data block, use WBEM CIM Studio to delete the old class definition. A reboot of the computer seems to be necessary to reregister the class correctly.

I could not work out how to use the WBEM Event Registration utility to enable events in the Wdm3 driver.