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Getting Started Writing Windows Drivers

Updated 21 February 2014. Finally!

So you want to write Windows drivers, eh? Well, you've come to the right place. We'll give you some tips and "tell it like it is."

You might also find the article "Getting Starting Writing Windows Drivers" that appeared in the Jan/Feb 2014 Issue of The NT Insiderinteresting and useful... check it out here.

Background

  • What Are Some Of The Key Background Concepts That I Need To Understand Before Learning To Write Drivers?
  • What Are The Most Important Things To Know Abour Writing Drivers?
  • How Do I Learn How To Write A Driver for Windows?=\
  • Getting Help

  • Where Can I Get Help?
  • Suppose I Want To Pay for Help?

  • Tools of the Trade

  • What Tools Do I Need To Write Windows Drivers?
  • Do I have to use Microsoft's Compiler?
  • What Language Can I Write Drivers In?
  • What Debuggers Can Be Used for Driver Debugging?
  • What Testing Tools Are Available?
  • Are There Other Test Tools, Besides Verifier?
  • How Do I Get Started Using The DDK?
  • Where Can I Download, or Were Do I Get, The Latest DDK?
  • What's This Checked Build Stuff?
  • Support Considerations

  • Do I Have To Support PnP In My Driver?
  • Do I Have To Support PnP, Even If My Device Can Never Be Removed From The System?
  • Can I Write My Driver First, and Add PnP Later?
  • Do I Have To Support Power Management In My Driver?

  • Creating Your Driver
  • There Are Many Different Driver Models -- How Do I Know What KIND Of Driver I Should Write?
  • Where Can I Get Driver Samples?
  • How Do I Start Cranking Code?
  • After I Write It, How Do I Install It?
  • What Is WDM? What's This WDF Thing I Keep Hearing/Reading About?
  • Do I Include WDM.H or NTDDK.H?
  • I Want to Change The Way A Standard Driver Works - Can I Modify The DDK Sample and Just Replace The Standard Windows Driver?
  • What Is Windows File Protection?

  • BACKGROUND

    What Are Some Of The Key Concepts In Operating Systems and Computer Science That I Need To Understand Before Learning To Write Drivers?

    You need to understand some basics about operating systems and devices before you can learn to write drivers. Here's a list of things you should know:

    • The difference between wait locks versus spin locks, and why spin locks might be used in an Operating System
    • Threads and processes: What these are in the Windows world versus the Unix world
    • What we mean by "thread safe", fully re-entrant, and MP safe
    • Processor modes -- What's the difference between Ring 0 and Ring 3 in an x86 architecture system
    • Memory management - User mode, versus Kernel Mode. What we mean by "demand paged virtual memory"
    • What are multiple, nested, interrupt levels
    • The difference between I/O port space and memory space
    • Something about how devices work: What a device register looks like, why/when devices interrupt
    • The definition of "direct memory access" (DMA) and the basic differences between DMA and programmed I/O relevant to a driver

    What Are The Most Important Things To Know Abour Writing Drivers?

    THE single most important things you need to know are the basic architecture concepts of the Windows operating system. This means that you must understand threading, serialization and synchronization, IRQLs, the basic objects used in the I/O subsystem (driver, device, etc), and the general flow of an I/O request through the system. Writing drivers is not like writing most applications; you absolutely cannot just find a sample and start hacking away at it to make it do what you want. It simply won't work. You have to put the work in up front to get a basic clue, or you'll be condemned to having problem after problem with no idea of how to fix what you've done.

    To brush-up on your Windows architecture, we recommend you pick up a copy of the latest version of Windows Internals by Russinovich, Solomon, and Ionescu (as we're writing ths, that's the 6th Edition). Read and understand Chapters 1 through 3 (up to bu tnot necessarily including the section entitled "Advanced Local Procedure Calls"). To understand something about the I/O facilities provided by Windows, you can read Windows System Programming by Johnson M. Hart. Chapter 1, 2, 4 and chapter 14 are the most relevant.

    Trust me on this one. There are very few shortcuts. Learn about the O/S. Then start to learn about how to write drivers.

    How Do I Learn How To Write A Driver for Windows?

    If you've written drivers for Linux or one of the UNIX variants, and you're familiar with Windows O/S concepts, you might be able to learn what you need to know by reading the documentation provided with the Windows Driver Kit (WDK). Get the most recent version of the WDK (see later question), and read the section entitled Getting Started with Windows Drivers. This documentation is surprising good, and covers a very broad range of topics. Over the years, the MSDN online docs on how to write Windows drivers have evolved to the point that they are actually both quite clear and helpful.

    Probably the best way to come up to speed on Windows drivers fast is to take a seminar on the topic. Don't be too quick to dismiss this option, even if you consider yourself pretty smart. Sure, it costs some money. But Windows drivers are both complicated and confusing enough that it can be extremely helpful to have somebody brain-dump you with just the required information. Also, if the person teaching the class has real hands-on knowledge, they can probably save you lots of time by helping you avoid some of the better-known "gotchas" that lurk in this space.

    If you do opt to take a seminar, we don't recommend you take one from a "local" company. ?Ask around. ?We admit that we're partially to the seminars we here at OSR teach (you can check them out here. (Almost nobody (even experienced Windows driver writers) takes one of these seminars and says it was a waste of time. ?We?teach both private and public seminars all over the world on a variety of topics.

    TOOLS OF THE TRADE

    What Tools Do I Need To Write Windows Drivers?

    A new version of the Windows Driver Kit (WDK) is released with each new version of Windows. You can use the new WDK version to build drivers for that new version of Windows, and certain older Windows systems.

    For example, the WDK released with Windows 8.1 will allow you to build drivers for Windows 7, Windows 8, and Windows 8.1 -- The Win 8 WDK lets you build drivers for Windows versions back to Vista.

    The tools for building Windows drivers changed dramatically starting with the Win 8 WDK. ?At that time, driver development took a vast leap into the future (er, well, actually, the present) and became fully integrated with Visual Studio. The only catch is that you need Visual Studio Professional or better. Visual Studio Express Edition (the one that's available free) will not work. Assuming you have the right version of Visual Studio, you can download the WDK and install it as an add-in to Visual Studio. That's all you need! You can find all the info, including download links, at http://www.microsoft.com/wdk/ .

    Do I have to use Microsoft's Compiler?

    Face it: There is very little that you really have to do in this world, besides breathe and die. Strictly speaking, you do not have to use the MS VC++ compiler. A few brave souls over the past years have used other compilers. But trying to use another compiler is best described as an exquisitely painful exercise. The WDK header files use a significant number of Microsoft specific features (such as language extensions, pragmas, and the like). Writing drivers is hard enough. Trying to write drivers using something other than the Microsoft compiler is really not something that you want to try.

    What Language Can I Write Drivers In?

    You write drivers for Windows in either C or C++. C++ was only officially supported for most drivers starting with Windows 8. ?And only a subset of C++ functionality is supported.?

    Don't even think about trying to use another language. All the functions and data types are only defined in C/C++ header files. There are no assembly language definitions provided, so you can't use assembly language, either.
    ?

    What Debuggers Can Be Used for Driver Debugging?

    WinDbg, Microsoft's standard kernel mode debugger, comes with the WDK. If you want to download WinDbg for stand-alone use, like for use in your test lab, you can also download the latest version from?http://www.microsoft.com/wdk/. In general, WinDbg is a powerful and reliable tool.

    If you're just starting out in the world of drivers, you probably should use WinDbg. You'll hear lots of whining and carping about WinDbg from some of the "old hands" that have been doing Windows driver development for years. While WinDbg is quite reliable now, this has not always been the case.

    Note that the general model for debugging Windows drivers is to use two systems. Do not try to do it any other way. Just get a second system, and connect the debugger to it across the network (or using a 1394 or serial cable). ?Or user a VM on your development system if you're writing a software only driver. But, to repeat, do not bother trying to develop a driver using one system. Computers are cheap these days. Yes, even in countries outside the US and Western Europe. Get a second system.

    What Testing Tools Are Available?

    The Windows operating system contains the most powerful testing tool available, Driver Verifier.

    Driver Verifier (usually, referred to as just "Verifier") comprises special set of modules in the operating system that carefully monitor the execution of specific drivers. If Verifier detects an inconsistency, or any incorrect operation, it will display a diagnostic message in the debugger and then crash the system.

    Driver Verifier is setup and controlled using the utility verifier.exe, located in the Windows system directory. Using verifier.exe, you can configure Driver Verifier to monitor specific drivers (such as a driver that you are writing) for problems.

    Driver Verifier is best when it's used throughout your entire debugging process. That is, you should always have Verifier enabled for your driver on your test machine. As you go through the process of adding functionality to or modifying your driver, Driver Verifier will be there to watch your driver's actions.

    It's important to realize that Driver Verifier is essentially a passive monitor. That means that while it might occasionally modify the information sent to your driver, it mostly just watches what your driver does. Driver Verifier itself is not a tester. It doesn't send any I/O requests to your driver. Therefore, in order to make use of Driver Verifier, you will have to send the broadest range of both valid and invalid I/O requests to your driver. This will allow Driver Verifier to monitor your driver's behavior in the broadest possible set of conditions.


    Are There Other Test Tools, Besides Verifier?

    Absolutely. A bunch of them.

    Visual Studio has a powerful Code Analysis feasture built-in. This will check to ensure you aren't making all sorts of silly (and dangerous) coding areas. The WDK header files are specially annotated to enhance the checking the Code Analysis provides.

    The WDK plug-in for Visual Stuido includes another helpful tool called Static Driver Verifier. This tool examines your code and models its behavior to see if it conforms to the various interface and architecture rules for Windows drivers.

    Windows even provides, for free, an entire suite of tests call the Hardware Certification Kit. This is a pretty big kit, and its rather cumbersome and annoying to use. We therefore don't recommend you set this up for basic driver testing.

    How Do I Get Started Using The DDK?

    Just like you'd do for any Visual Studio project:?Install Visual Studio and the WDK on your development machine. ?Start by building a sample project. We suggest starting with a sample KMDF project, because KMDF is almost certainly going to be the framework you'll be using for driver development.

    Where Can I Get The Latest DDK?

    Didn't I already answer this? Go to ?http://www.microsoft.com/wdk/ and you'll find the links there.

    What's This Checked Build Stuff?

    Windows comes in two basic flavors: (a) The normal distribution kit that everybody uses, and (b) A special build that has debugging information in it. The build with debugging information is for use by driver writers, and for diagnosing serious system problems. This debug build is called the "Checked Build."

    See the WDK's Getting Started section, Guide to Using the Free and Checked Builds, for a full run-down on what the checked build is, where you get it, and how to best make use of it.

    CREATING YOUR DRIVER

    There Are Many Different Driver Models -- How Do I Know What KIND Of Driver I Should Write?

    There are many different "models" for writing drivers on Windows. Chosing a driver model will be the most important decision you'll make abaout how your driver will be developed.

    In short, there are special models and general purpose models. Special models apply to specific types of devices. For example, there's a specific model for network adapters, one for storage controllers, and a different one for graphcis drivers. If the device you'll be writing a driver for has a model that's specific to that device type, you basically have to use that model.

    If the device for which you'll be writing a driver does NOT have a dedicated driver model you want to use KMDF. ?KMDF is the WIndows Driver Foundation, Kernel Mode Driver Framework. KMDF is the modern model for writing drivers for most types of "generic" devices: USB, PCIe, and the like.

    A few words on other driver models: This is being written in 2014. ?There is an old, annoying, model for writing drivers for "generic" devices that has been around since when Windows was born. This old model is called WDM, the Windows Driver Model.You do not want to write a WDM driver. Did you hear what I said? Really. You don't. KMDF has been around for 7 years now. It's proven. It's reliable. It works. And it's waaaay easier to use than WDM. So forget the whole WDM thing.

    Another framework that you probably don't want to use is UMDF. Microsoft's guidance differs from our on this, but we have good reasons. ?UMDF V1 is a difficult scheme that uses C++ and a COM-Lite programming pattern. It's also effectively being deprecated. ?UMDF V2 is great, it's just like KMDF. In fact, UMDF V2 and KMDF share 95% of the same syntax. The problem with UMDF V2 is, as of this writing, it only supports Windows 8.1 and later.

    So... Our advice is, stick with KMDF if you're writing drivers for generic devices that don't have their own "dedicated" Windows driver model.

    Where Can I Get Driver Samples?

    There are almost 150 sample drivers downloadable from MSDN. ?You can find them at http://code.msdn.microsoft.com/windowshardware. ?One things that's nice about these samples is that their licenses are pretty lenient, meaning the license allows you to use the sample as a starting place for your driver. ?On the other hand, these samples are just like the typical sample code you download from MSDN: They are very useful and highly instructive, even if some of the code provided isn't always exactly "the best." Samples are provided for all sorts of hardware drivers, filter drivers, and software-only drivers. Heck, they even give you the source code to a few of the drivers that are part of the Windows OS? including sources for the FAT file system.

    If you take a seminar, especially a lab seminar, you'll undoubtedly walk away with one or more sample drivers.

    If you don't see a sample that's similar to the type of driver you need to write, ask one of the sources listed in "Where Do I Get Help."

    How Do I Start Cranking Code?

    Get the source code sample driver for a device of similar type to the one that you need to support. Assuming your license allows it, start by modifying this driver.

    After I Write It, How Do I Install It?

    You'll need to create an installation control file (AKA a ".inf file") to get your driver installed in the system. The .INF file is used by the setup program, which is invoked from the "Add/Remove Hardware" option in Control Panel. Yes, even if you're writing a driver that isn't directly associated with any hardware, it's still installed from "Add/Remove Hardware." Of course, if you want to get really fancy, you could write an attractive GUI program that invokes your .INF file to do the installation.

    What Is WDM? WDF?

    WDM stands for Windows Driver Model. It's the old, crufty, annoying model that was used for building Windows drivers in the old days (before 2005). ?You don't want to use this for creating new drivers if you can help it.

    WDF is the Windows Driver Foundation. It's the modern and easier way to write drivers for generic devices that don't have their own dedicated device model. ?If you use it, you will like it.

    Do I Include WDM.H or NTDDK.H?

    You want to include WDM.H. Though the definition has changed over the years, this header contains all the definitions for the Windows Driver Model. WDM is the "forward moving" model by which drivers are built. If it's not in WDM, it's probably a legacy driver type or function, and you should probably stay away from it.

    I Want to Change The Way A Standard Driver Works - Can I Modify The WDK Sample and Just Replace The Standard Windows Driver?

    No! A million times no. This causes nothing but trouble.

    The right way to modify the behavior of a standard Windows driver is to write a filter driver. This driver can sit either above or below the standard driver, and modify its behavior. You can even use this approach to provide additional functionality.


    What Is Windows File Protection?

    This is also called System File Protection. It is the mechanism used insome versions of WIndows by which Windows ensures that standard system files (files in %systemroot% and below) are not modified. It's generally not something you have to worry about these days..


    SUPPORT CONSIDERATIONS

    Do I Have To Support PnP In My Driver?

    Why wouldn't you? There are some weird types of drivers that strictly speaking do not fall into the Plug and Play category (like file systems and software-only drivers for monitoring things that happen in kernel mode). But in general your driver has to support PnP. Even if you're writing a driver for an ISA bus device on a dedicated process control system, believe it or not... you'll be writing a PnP compatible KMDF driver.

    Do I Have To Support PnP, Even If My Device Can Never Be Removed From The System?

    Yes. PnP is the basic process by which Windows finds devices. So even if your device is soldered to the computer main board, or within the SoC, you're writing a PnP driver.

    Can I Write My Driver First, and Add PnP Later?

    No.

    Do I Have To Support Power Management In My Driver?

    Yes..

    GETTING HELP

    Where Can I Get Help?

    You mean where can you get free help, right?

    There are a surprising number of peer help forums. Check out the NTDEV (for driver developers), NTFSD (for file system developers), and WINDBG (for WinDbg debugger users) lists
    here at OSR Online. You must subscribe to contribute. Note that you can choose to join these groups either as traditional list server mailing lists, online or as private usenet news groups. To do the latter, point your news reader to lists.osr.com. You will be required to log in to these groups by providing your username and password (that you specified when you joined) in order to post to the group.

    The people in all of these forums are generally very helpful. Surprisingly often, the MS support folks or developers informally answer questions on all these lists. All the lists expect you to do your homework: Check the WDK documentation and the Microsoft Knowledge Base, and be sure to read the group archives before asking your question. Don't expect people in these groups to write your driver for you.

    A very useful publication is The NT Insider, published every few months by OSR. One of the best things about it is that it's free. Visit http://www.osr.com/ for your free subscription.

    Suppose I Want To Pay for Help?

    One option is per-incident support from Microsoft's WDK Developer Support group. It's relatively inexpensive, and the support people are typically very helpful and know what they're doing.

    There are also a significant number of companies that provide services ranging from per-incident consulting to per-project design/build/test pricing. The costs range from pretty inexpensive to stratospheric, depending on whom you choose. In general (assuming you want to write the driver yourself), we advise you to first exhaust the (free) peer-support options and all possibility of help from Microsoft WDK Developer Support before even considering paying anybody else for assistance.

    Question any company carefully as to their real hands-on skills and experience in your specific type of driver before forking over your money. Don't pay somebody who develops printer drivers for a living to help you with your driver for a mass storage device. These two types of drivers have fundamentally nothing in common. On the other hand, don't engage a high-end expert firm to help you with your garden variety simple driver. This is a bit like taking your Ford to a Ferrari mechanic for a tune up. He can do it, but you'll wind up paying Ferrari prices.

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    User Comments
    Rate this article and give us feedback. Do you find anything missing? Share your opinion with the community!
    Post Your Comment

    "nice site to learn"
    if you fallow this site it will clarify your doubts about windows device drivers development. It is easy to learn things if you fallow in this way.

    Rating:
    31-Jul-14, naresh pirati


    "Very good article"
    Thanks for this excellent article.

    I want to develop a Windows driver for Virtual CD Drive. from where should I start? As mentioned in the article that DDK provided sample source codes for some drivers - are the Virtual Drive drivers included also?

    Rating:
    14-Jul-11, Ravi Gautam


    "Most Important Things To Know..."
    In the article: "What Are The Most Important Things To Know About Writing Drivers?"

    It is mentioned: "...you need to read Inside Windows whatever-is-the-most-recent-version."

    Please note that most recent version of the "Inside Windows whatever-is-the-most-recent-version" book is currently titled: "Microsoft Windows Internals (4th Edition)..." This edition doesn't cover Windows Vista. However, the 5th Edition should be release in a week or two. that edition does cover Windows Vista.

    Rating:
    07-May-09, Bruce Olney


    "Useful information"
    This article is useful for new beginner.

    Rating:
    29-Oct-06, Mike Dawn


    "'windowsupdate' for checked build"
    Is there such a thing as windowsupdate.microsoft.com for the checked build? Or does that site cater to updating both normal and check builds?

    Rating:
    06-Feb-04, Richard Chan


    "test tools"
    Are there not newer test tools available in the DDK? Looking for that "comprehensive list" you mention in Q22...

    Rating:
    16-May-03, James Covey


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