Книга: Writing Windows WDM Device Drivers

Debugging Notes

Debugging Notes

Here are some notes on how to deal with some common debugging problems.

Updating a driver is fairly straightforward. The makefile for the examples in this book copy the new driver to the Windows System32drivers directory. However, the old version will still be running in memory.

To use the new version you have to update the drivers for your device(s). Use the Update/Change driver option in the Device Manager properties for a device. Opt to "display a list of drivers in a specific location, so you can select the driver you want".

For the Wdm1 driver, select "Other Devices". You should see the list of book software drivers that you have installed. Select the one you want from this list. You do not have to select the Have Disk button (unless you want to install the checked version, say).

If asked, opt to use the new driver even if the Device Manager suggests that the current version may be newer. Windows 98 will force you to browse for the driver files. W2000 uses the driver files in the System32drivers directory.

As noted above, if the new driver returns an error during its initialization then Windows will say that the system needs to reboot. Rebooting may not cure the problem.

NT Style Drivers

As mentioned in an earlier chapter you must update NT style drivers in a different way. As usual, you must get your driver into the Windows System32drivers directory.

Run the Control Panel Devices applet. Find your driver, stop it, and start it again. You can also run the book software Servicer applet; type in the name of your driver, press Stop and then Start. If you run an NT style driver in Windows 98 you must reboot the computer to use an updated driver.

If your driver fails catastrophically during system boot, the system will not load, which makes it tricky to delete or change the offending driver.

There are three solutions to this problem. In a dual boot system, simply reboot in the other operating system and delete or change the driver. Alternatively, both W2000 and W98 have "Safe mode" boot options that should allow you to start Windows, while only loading the most basic system drivers. Delete the offending driver and restart. A final option is to have a bootable floppy disk with a copy of Windows 98. Use this as a quick boot to delete the offending driver files.

Watch out for one driver depending on another. The Wdm1 driver opens a handle to the DebugPrint driver during its initialization, and releases it only when the driver unloads. This means that the DebugPrint driver cannot be replaced while Wdm1 is running. To change the DebugPrint driver, Wdm1 has to be unloaded. Only when the new DebugPrint is safely running, can a Wdm1 device be installed again. 

If a driver queues IRPs but does not provide suitable cancel or cleanup routines, a Win32 program could hang up if it calls CancelIo or exits with file handles open. In this case, the Win32 program appears to have exited but it is still locked in memory, so you will not be able to update it.

The I/O Manager gives a driver five minutes to cancel IRPs. After this time, it displays a message to the user and any pending IRPs are dissociated from the terminating thread.

A reboot is usually necessary to clear this situation.

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