Книга: Writing Windows WDM Device Drivers

Driver Language and Libraries

Driver Language and Libraries

A driver is a Dynamic Link Library (DLL) with the file extension .sys. It is usually written in C or C++ and can include resources, such as a version block, event messages, and Windows Management Instrumentation (WMI) class definitions. In Windows 98, a driver executable must have an 8.3 filename.

Although drivers were traditionally written just in C, it is quite straightforward to use C++. The main requirement is to use the extern "C" directive in a couple of important places. However, do not use the new keyword in C++. The new keyword may be implemented using malloc, which is not available to kernel mode drivers.

In fact, most standard libraries and classes are not available to driver writers in either language, because they make inappropriate use of memory. If you are using one of the proprietary driver development kits, these provide various useful classes, including safe memory allocators.

Instead, you can use any of the routines provided by the operating system to kernel mode devices, as described in Chapter 3. While these are useful, it takes a while to get used to the different set of routines that are available.

Assembly code can be used if absolutely necessary. Obviously, this makes for more work if you port the driver to the Windows 2000 Alpha platform.

A resource .rc file should include a standard version block. Increment the version numbers as new builds are released. Make sure that you keep a full source backup of each version you release. Many version control packages can help you manage this task.

If you generate NT or Windows 2000 events, you should write these in an .mc file that is compiled using the mc utility and included in a driver's resource file. More details of this process are in Chapter 13.

Similarly, if you generate custom WMI classes, you need to write a .mof file that is compiled using the mofcomp tool and included in the driver's resource file. See Chapter 12 for more information.

A sophisticated driver might need to download microcode to its device and so would include the microcode as a binary resource in its executable.

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