MSDN Documentation

Windows Drivers: User Mode

This section provides comprehensive documentation for developing user-mode device drivers for Windows operating systems. User-mode drivers offer enhanced stability and security by running in a less privileged process space compared to kernel-mode drivers.

Overview

User-mode drivers are ideal for devices that do not require direct hardware access at the kernel level. They leverage the Windows Driver Frameworks (WDF) and specific user-mode driver frameworks like the User-Mode Driver Framework (UMDF). Developing in user mode significantly simplifies driver development, debugging, and maintenance.

Key Benefits of User-Mode Drivers

• Stability: Driver crashes do not bring down the entire operating system.
• Security: Runs with restricted privileges, reducing the attack surface.
• Simplified Development: Easier to debug and develop using standard user-mode tools.
• Reduced Complexity: Less concern about kernel-mode complexities like memory management and synchronization.
• Faster Deployment: Can be installed and updated without requiring a system reboot in many cases.

Getting Started with UMDF

The User-Mode Driver Framework (UMDF) provides a COM-based programming model that simplifies the development of user-mode drivers. It abstracts many low-level details, allowing developers to focus on device functionality.

Core Concepts

• Driver Object: Represents the driver itself.
• Device Object: Represents a physical or logical device.
• Framework: Manages the driver and its interaction with the system.
• COM Interfaces: UMDF drivers are built using COM.

Example: A Simple UMDF Driver Structure (Conceptual)

// Header files
#include <windows.h>
#include <wudfddi.h>
#include <wudfddi_1.h>

// Driver Entry Point
HRESULT WINAPI DriverEntry(_In_ WDFDRIVER Driver, _In_ PCWSTR RegistryPath);

// Device Initialization Callback
VOID OnDeviceAdd(_In_ IWDFDriver* Driver, _In_ IWDFDeviceInitialize* DeviceToInitialize);

// Other interfaces and callbacks for device I/O, power management, etc.
                

Key APIs and Frameworks

When developing user-mode drivers, you will primarily interact with the following:

• User-Mode Driver Framework (UMDF): The core framework for building user-mode drivers. Available in UMDF 1.x and UMDF 2.x (integrated with KMDF).
• Windows Driver Kit (WDK): Contains the necessary headers, libraries, and tools for driver development.
• Visual Studio: The integrated development environment (IDE) used for writing, building, and debugging drivers.

Common Tasks and Scenarios

Device Enumeration and Installation

Learn how to declare your driver in the INF file, how the system enumerates devices, and how UMDF binds to these devices.

I/O Operations

Understand how to handle I/O requests (IRPs) in user mode using UMDF callbacks for reading, writing, and device-specific control codes.

Power Management

Implement device power states (D0, D1, D2, D3) and handle system power transitions to conserve energy.

Plug and Play (PnP)

Handle PnP events such as device arrival, removal, and surprise removal.

Interacting with Hardware

While UMDF runs in user mode, it can still interact with hardware through various mechanisms, including:

• DirectMemory Access (DMA) using the WDF DMA framework.
• Port I/O and Memory-Mapped I/O through specific UMDF interfaces or via kernel-mode driver intermediaries.

Resources and Further Reading

Note: This documentation is intended for developers creating drivers for the Windows operating system. Ensure you have the latest Windows Driver Kit (WDK) installed for development.