Chapter 15. Layered Drivers

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[oR]

CHAPTER OBJECTIVES

An Overview of Intermediate Driver
Writing Layered Drivers
Writing I/O Completion Rules
Allocating Additional IRPs
Writing Filter Drivers
Code Example: A Filter Driver
Writing Tightly Coupled Drivers
Summary

The ability to break a large unit of work into several smaller pieces is the cornerstone of software development. The Windows 2000 device driver model supports this necessary abstraction by allowing the work of a driver to be implemented in multiple layers. Besides simplifying the overall job of writing a driver, this allows different vendors to supply different parts of the implementation.

Indeed, the WDM driver model is based upon layering functional drivers on top of physical drivers, with optional filter drivers surrounding the functional layer. In most cases, a physical driver (that interacts with a standard bus) is never written. And in many cases, only a filter driver must be written to affect the desired behavior from an existing functional driver.

This chapter describes the details of layering a driver design into a hierarchy.

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