User-Mode Driver Framework (UMDF)

The User-Mode Driver Framework (UMDF) is a set of COM interfaces and services that enable you to write and deploy drivers that run in user mode. UMDF simplifies driver development by providing a framework that handles many common driver tasks, allowing you to focus on device-specific functionality.

What is UMDF?

UMDF provides a robust and simplified environment for developing drivers. By running drivers in user mode, UMDF enhances system stability and security. If a user-mode driver encounters an error, it is less likely to crash the entire operating system compared to a kernel-mode driver.

Key Benefits of UMDF:

• Enhanced Stability: Drivers run in isolated user-mode processes, preventing them from destabilizing the kernel.
• Simplified Development: UMDF abstracts away much of the complexity of kernel-mode programming, offering a COM-based interface.
• Improved Security: User-mode drivers have fewer privileges, reducing the attack surface.
• Easier Debugging: Debugging user-mode applications is generally simpler than kernel-mode debugging.
• Hot-Plugging Support: UMDF drivers integrate well with Plug and Play functionality, making hot-plugging devices seamless.

Getting Started with UMDF

To begin developing UMDF drivers, you'll need to set up your development environment. This typically involves installing the Windows Driver Kit (WDK) and Visual Studio. The WDK provides the necessary tools, headers, libraries, and samples for driver development.

Essential Components:

• Windows Driver Kit (WDK): The primary toolkit for driver development.
• Visual Studio: An integrated development environment (IDE) for writing, building, and debugging code.
• Driver Test Framework (DTF): A framework for automating driver testing.

Refer to the Driver Development Environment documentation for detailed setup instructions.

UMDF Architecture

UMDF consists of the UMDF host process and the UMDF driver. The host process (WUDFHost.exe) acts as a mediator between the UMDF driver and the operating system. When a device is connected, the UMDF host process is launched, and your UMDF driver is loaded into this process.

Developing a UMDF Driver

Developing a UMDF driver involves implementing COM interfaces that the framework exposes. Key aspects include:

• Driver Entry Point: The standard entry point for a UMDF driver.
• Device Initialization and Shutdown: Handling the PnP events for device arrival and removal.
• I/O Request Handling: Processing I/O requests from applications.
• Power Management: Managing device power states.
• Property Stores: Reading and writing device properties.

Example of an I/O Request:

When an application sends an I/O request to your device, the UMDF framework receives it and forwards it to your driver. Your driver's implementation of the IWDFIoQueue::OnIoDefault (or a more specific handler) method will be invoked.

// Example: Simplified handler for an I/O request
HRESULT MyDevice::OnIoDefault(IWDFIoQueue* pWdfQueue, IWDFIoRequest* pWdfRequest)
{
    ULONG IoControlCode;
    pWdfRequest->GetIoControlCode(&IoControlCode);

    switch (IoControlCode)
    {
        case IOCTL_MY_CUSTOM_COMMAND:
            // Handle custom command
            break;
        case IOCTL_READ_DATA:
            // Handle read request
            break;
        default:
            // Unrecognized I/O control code
            pWdfRequest->CompleteWithInformation(
                HRESULT_FROM_WIN32(ERROR_INVALID_FUNCTION),
                0);
            return S_FALSE; // Request processed
    }

    // If handled, complete the request
    return S_OK;
}
            

UMDF Samples

The WDK includes numerous sample UMDF drivers that demonstrate various device types and functionalities. These samples are an excellent resource for learning how to implement specific features and understand the UMDF programming model.

Explore the UMDF samples in the WDK installation directory or on the GitHub repository for comprehensive examples.