Framework Aims to Increase Driver Reliability

A forthcoming set of APIs aims to reduce the amount of boilerplate code Windows developers must write and increase device driver reliability. The new Windows Driver Foundation (WDF) APIs offer improvements to the current kernel-mode drivers and enable some drivers to run in user mode, isolating the OS from errant drivers. However, at its Apr. 2005 Windows Hardware Engineering Conference (WinHEC), Microsoft reiterated that while the API improvements for kernel-mode drivers will be supported on Windows 2000 and later, its current plans support only user-mode drivers on the next version of Windows (code-named Longhorn).

Existing Model Fragile, Hard to Program

Current Windows device drivers are built on a set of APIs known as the Windows Driver Model (WDM), a complex API that is error-prone and requires developers to include hundreds, and in some cases thousands, of lines of boilerplate code to support OS features such as advanced power management and Plug and Play.

To help developers build drivers, Microsoft has over the years introduced a number of device-specific APIs known as “miniports.” Each miniport offers its own API tailored for a specific class of devices, such as network cards and storage devices. However, as new features were added to the base OS, they appeared as different APIs in the various miniports. Further complicating matters is the move toward multifunction devices, such as a music player that also functions as a mass storage device. It’s difficult to create drivers for such devices because the miniport APIs were not designed with multifunction devices in mind.