Introduction to User-Mode Driver Framework

OutlineOutline

What is UMDF?

When should I use UMDF?

When shouldn’t I use UMDF?

What does UMDF give me?What kind of drivers can I write?

What can my drivers do?

What next?

GoalsGoals

How UMDF fits into WDF

Understand UMDF’s capabilities

Current Driver ModelsCurrent Driver Models

Windows has several different driver modelsWindows Driver Model (WDM) is the generic model

Specific driver models for popular devices classesStorage, Networking, Printing, Imaging, etc...

Some built on top of WDM. Others run as user-mode services.

WDM FeaturesAsynchronous, packet-based I/O

I/O Cancellation

Layering of drivers

Dynamic loading and unloading of drivers

Plug and Play & Power management

Low-level high-performance interfaces

WDM AdvantagesLarge device coverage

Flexible

Limitations with Current ModelsLimitations with Current Models

Generic driver model (WDM) is too complexFocuses on very advanced drivers which punishes simple ones

Poor DDI design

Device specific models have complexity of their ownOften this bubbles through from WDM

Developer trapped in device-specific model

Poor knowledge transfer from one to the next

Many drivers must be written in kernel mode Even though much functionality could be user mode

Developers spend too much time driving our softwareCannot concentrate on driving their hardware

Driver quality suffers as a result

Do not allow extension and future growth

Overview of Current Driver ModelsOverview of Current Driver Models

Device/Driver Classes Current ModelDisplay Adapters Video port

Storage Adapters (SCSI & ATA) SCSIport, Storport, ATAport,

Network Adapters NDIS

Video Capture AvStream

Audio Adapters AVStream, PortCls

File System filters FS Mini filter

Printers UniDrv

Scanners,Cameras WIA

PCI, PC Card, generic filter drivers WDM

Modems, Cable Modem WDM & NDIS WDM

Biometric Devices WDM

Smart Card Devices WDM

Keyboard/Mouse Filters WDM

Legacy Devices (Serial, Parallel) WDM

Portable Media Players WMDM

UPnP & Network Connected Devices, Cell Phones No support

USB, 1394, Bluetooth, SD devices WDM (kernel), no support (user)

Others WDM

Windows Driver FoundationWindows Driver Foundation

We need a new generic driver model that ...Scales conceptually from simple to extremely complex drivers

Can be extended to domain specific models

Can be validated at compile-time as well as run-time

Windows Driver Foundation (WDF) consists ofA generic driver model

Implementations of that modelKernel Mode Driver Framework (KMDF)

User Mode Driver Framework (UMDF)

Driver Verification ToolsStatic Driver Verifier

PREfast for Drivers

Windows Driver Foundation GoalsWindows Driver Foundation Goals

SimplicityNo harder than it needs to be to accomplish a task

Fast time to market for driversLet driver developers focus on their domain, not ours

Reduce crashes and blue screens due to driversBetter customer experience helps everyone

Provide complete driver development experienceDevelop and test

Built-in diagnosability, tracing, verification tools

Deployment and InstallSupport versioning

Windows Driver Foundation- ExperienceWindows Driver Foundation- Experience

Overview of Current (User) Driver ModelsOverview of Current (User) Driver Models

Device/Driver Classes Current ModelDisplay Adapters Video port

Storage Adapters (SCSI & ATA) SCSIport, Storport, ATAport,

Network Adapters NDIS

Video Capture AvStream

Audio Adapters AVStream, PortCls

File System filters FS Mini filter

Printers UniDrv

Scanners,Cameras WIA

PCI, PC Card, generic filter drivers WDM

Modems, Cable Modem WDM & NDIS WDM

Biometric Devices WDM

Smart Card Devices WDM

Keyboard/Mouse Filters WDM

Legacy Devices (Serial, Parallel) WDM

Portable Media Players WMDM

UPnP & Network Connected Devices, Cell Phones No support

USB, 1394, Bluetooth, SD devices WDM (kernel), no support (user)

Others WDM

Why Build a User-Mode Framework?Why Build a User-Mode Framework?

Difficult to provide high-quality driversCrash statistics prove this

WDF Framework makes drivers easier to write

Lots of driver models already live in user spacePrinters, Audio, Imaging

Divergent driver models has become a problem

UMDF brings general-purpose model into user-mode

General UMDF provides:Unified facilities

Support for WDF model

What is UMDF?What is UMDF?

Implementation of the WDF Driver Model

Provides ...The infrastructure to run a device driver in user-mode

The WDF I/O Pipeline and PnP/PM State Machine

The core WDF objectsDevices, Files, Queues, Requests, I/O Targets, etc...

UMDF and KMDF both share the WDF ModelSo learning how to use one will apply to the other

But they are not source or binary compatibleHave similar but not identical DDIs

Each has additional functionality applicable to its domain

Device Stack

Overview of the ArchitectureOverview of the Architecture

Provided by:

Microsoft

ISV

IHV

Driver Manager

Host ProcessUser

Kernel

Framework

UM driverFramework

UM driver

Reflector

...

CoInstaller

Kernel Driver

Kernel Driver

Who Should Use UMDF?Who Should Use UMDF?

Existing driver developers…Who want to move drivers to user space

Who already have the “driver mindset”

New driver developers…Coming from application development

Who need to provide device support

Who are learning new skills

Anyone who wants to...Build a driver without a lot of development overhead

Reduce the risks associated with traditional drivers

Stop causing blue screens

Where can you use UMDF?Where can you use UMDF?

Primary Scenarios“Protocol Bus” devices

Devices attached to USB, 1394, TCP/IP, etc...

Software-only driversFilter drivers, virtualized serial port, etc…

Current DevicesPortable Media Players, Cell Phones, PDAs/ActiveSync, Auxiliary Display, Cameras

Future DevicesDevices on future protocol busses

Devices where driver can be split into ...Small kernel-mode component to do hardware access

Larger user-mode driver to provide complex functionality

When and How To Use UMDFWhen and How To Use UMDF

UMDF is a standard Windows codenamed “Longhorn” feature

Support in WDK

Build with the WDK Build EnvironmentStandard device driver build environment

No integration with Visual Studio

Why Use UMDF?Why Use UMDF?

Uses the WDF Driver ModelCan learn a single model that applies to KM and UM drivers

Faster development cycleEasier debugging on a single machine

Crashes during development don’t require a reboot

Access to user-mode servicesWin32 file I/O, Function Discovery, WINSOCK, RPC, Crypto

But you have to be careful…

Why Use UMDF?Why Use UMDF?

Improved stabilityUser-Mode Drivers are isolated from other drivers

Kernel is isolated from user-mode drivers

Increased securityCompromised driver does not crash the system

Lower privileges restrain a compromised driver

RecoverabilitySystem can recover after a driver crash – no blue-screens

The driver can be restarted without rebooting

Kernel-Mode or User-Mode Driver?Kernel-Mode or User-Mode Driver?

You must use kernel mode when you:

Need direct hardware access, for example,Require DMA

Must handle interrupts

Need access to device registers

Have strict timing requirementsUMDF will have increased latency

Need kernel-only resourcesOr kernel components need access to your driver

Features You Can Use in Your DriverFeatures You Can Use in Your Driver

General WDF capabilitiesPnP/PM provides “opt-in” callbacks for various events

Object model has context management & flow control

I/O Targets allow driver to send new I/O requestsRegardless of where the target device driver is running

Coordinated with cancellation and cleanup

Escape to Win32 and user-mode services

Standard facilities for Windows I/O modelPnP Device Discovery

Synchronous & Asynchronous I/O with Cancellation

Buffered and Direct I/O transfers

Standard INF Driven setup

Common ConcernsCommon Concerns

Will a user-mode driver be fast enough?UMDF driver can already flood a portable media device

UMDF may increase latency, but throughput remains high

Performance is one of our top priorities

But it’s not always the top priority for driver developersBalanced with improvements in quality, stability, security, etc...

Will a user-mode driver be secure?As secure as any other user-mode service

RPC, LSASS, WinLogon, etc...

A compromised user-mode driver is more containedCannot crash the system or expose kernel secrets

Will user-mode drivers be high quality drivers?We’ll continue to push to improve driver quality in all models

UMDF will prevent badly behaved drivers from crashing the system

What’s Next?What’s Next?

Development platform is the WDK/LDK

Currently allows developing drivers for Longhorn

But we know that’s not enough…Plan to support Windows XP in Longhorn time-frame

Versioning supportSupport for side-by-side installation

Beta programWindows Driver Foundation Beta Program Invitation

http://www.microsoft.com/whdc/driver/wdf/beta.mspx

Call To ActionCall To Action

Install the Windows Driver Kit

Join the WDF Beta ProgramAt http://beta.microsoft.com

Guest ID: Guest4WDF

Evaluate UMDF for your driver projectsConsider development time, customer support for system crashes, etc.

Send Us Feedback - We want to knowIf UMDF will meet your needs

What stops you from writing your drivers with UMDF

Email: umdffdbk @ microsoft.com

Additional ResourcesAdditional Resources

Web Resources:WDF Information:

http://www.microsoft.com/whdc/driver/wdf/default.mspx

Windows Debugger:http://www.microsoft.com/whdc/devtools/debugging/default.mspx

External Resources“Introduction to the Windows Driver Foundation: How To Develop Device Drivers Using the Kernel Mode Driver Framework” from OSR Press

Release date is September 2005

Focuses on KMDF but provides general WDF information as well

© 2005 Microsoft Corporation. All rights reserved.This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.