Device driver programming in windows

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To start the hello program, enter the following command:. And what a surprise, it displays the Hello, World! Stop the driver with:. We received another message as well from the so-called Reincarnation Server RS. In Minix as a microkernel , device drivers are separate programs which send and receive message to communicate with the other operating system components.

Device drivers, like any other program, may contain bugs and could crash at any point in time. The Reincarnation server will attempt to restart device drivers when it notices they are abruptly killed by the kernel due to a crash, or in our case when they exit 2 unexpectedly. You can see the Reincarnation Server in the process list as rs , if you use the ps 1 command.

The Reincarnation Server sends keep-a-live messages to each running device driver on the system periodically, to ensure they are still responsible and not i. So how do we deal with this?

We let our hello driver reply to the keep-a-live messages, so RS will correctly detect it is still running. Fortunately, as we will see in the next example, there is a library libchardriver on Minix. This library takes care of various tasks common to all character drivers. For example, it performs the communication with the Reincarnation Server and the operating system components transparently.

In contrast, one functionality that is directly exposed to the device driver developer is the initialization protocol. When a new device driver or any other system service is started, RS will send the driver an initialization message with information on how to initialize properly. The driver is expected to reply back with OK initialization completed successfully or with an error initialization failed.

In the former case, RS will assume the new device driver has been started correctly. In the latter case, RS will immediately shut down the driver without attempting to restart it. The user will be informed with a message on the console.

Fortunately, the initialization protocol is completely hidden in the System Event Framework SEF that exposes library calls to let developers handle initialization in an easy and effective way. Each callback is nothing but a function that receives initialization data as input and returns a status code to determine the result of the initialization process.

As of now, developers can register callbacks for three types of initializations: fresh when a service is started the first time , live update when a service is dynamically updated to a new version , restart when a service is restarted after a crash or a controlled restart.

In this example we will extend the hello driver and re-implement it using libchardriver. Each character and block driver is associated with a major device number. Thus, we need to pick a free major device number for the device—one that is not already in use for another device driver.

As you can see, it contains a pre-processor macro for the message. Now place this source code in the hello. Let's try to understand what the above code does. First, it has several include lines for the required prototypes and functions used in the program.

Then, it declares a struct chardriver. This structure is filled with callback functions which will be invoked by libchardriver at runtime. It has callback functions for performing open, read, write and close operations on the device driver. The operating system will then on behalf of the device driver take care of properly copying the bytes between the two programs.

In the main function there are only two simple calls. This tutorial will describe how to create a simple device driver, dynamically load and unload it, and finally talk to it from user mode. I need to define a starting ground before we begin to explain how to write a device driver. The starting point for this article will be the compiler. The compiler and linker generate a binary in a format that the Operating System understands. In this format, there is an idea called a subsystem.

A subsystem, along with other options specified in the PE header information, describes how to load an executable which also includes the entry point into the binary. This is why a lot of people may not be familiar with this concept even though they are most likely already using it if they have ever written Windows applications.

Have you ever written a console application? Have you ever written a GUI application for Windows? These are different subsystems in Windows. Both of these will generate a PE binary with the appropriate subsystem information.

If you accidentally choose the wrong project, you can simply change this in the linker options menu rather than needing to create a new project. MSDN Subsystem compiler options. The first section lied a little bit about the subsystem.

If we know we want this to be a driver, we simply need to write an entry point whose parameter list and return type matches that of a driver. The system will then load the driver when we install it and tell the system that it is a driver. The name we use can be anything. We can call it BufferFly if we want. The DDK contains an environment that has pre-set options in the common make file directory which makes it simpler to create an application as it specifies the default options. The actual driver developer can then override these settings in the make file or simply use them as a connivance.

The linker builds the final binary, and based on what the options are in the PE header and how the binary is attempting to be loaded run as an EXE through the loader, loaded by LoadLibrary , or attempting to be loaded as a driver will define how the loading system behaves. The loading system attempts to perform some level of verification, that the image being loaded is indeed supposed to be loaded in this manner, for example.

Your job is to simply write the application based on how you want it to be loaded and then set the correct options in the linker so it knows how to properly create the binary. There are various resources on the details of the PE format which you should be able to find if you are interested in further investigation into this area. I know that a lot of people simply want to jump right into writing the driver and seeing it work.

This is generally the case in most programming scenarios as you usually just take the code, change it around, compile it, and test it out. If you remember back to when you were first learning Windows development, it was probably the same way. This was a lot of fun and you probably learned a lot, but you know that with a driver, the adventure is a little different.

Not knowing what to do can end up in blue screening the system, and if your driver is loaded on boot and executes that code, you now have a problem. Hopefully, you can boot in safe mode or restore to a previous hardware configuration. That being the case, we have a few things to go over before you write the driver in order to help educate you on what you are doing before you actually do it. The first rule of thumb is do not just take a driver and compile it with some of your changes.

If you do not understand how the driver is working or how to program correctly in the environment, you are likely to cause problems.

Application programs can have the same type of bugs in behavior but not in root cause. As an example, there are times when you cannot access memory that is pagable. If you know how Virtual Memory works, you know that the Operating System will remove pages from memory to pull in pages that are needed, and this is how more applications can run than would have been physically possible given the memory limitations of the machine.

There are places, however, when pages cannot be read into memory from disk. Where am I going with this? If you close an application that was running, it may still be in memory, for example! This is why a bug like this may go undetected unless you try doing things like driver verifier and eventually may trap. When it does, if you do not understand the basic concepts like this, you would be lost as to what the problem is and how to fix it.

There are a lot of concepts behind everything that will be described in this document. I will not attempt to duplicate this information nor point out every single little detail.

What I will attempt to do is give a basic summary and point you in the direction of where to find more information.

The processor will be executing code in a thread at a particular IRQL. The IRQL of the processor essentially helps determine how that thread is allowed to be interrupted.

The thread can only be interrupted by code which needs to run at a higher IRQL on the same processor. In a multi-processor system, each processor operates independently at its own IRQL. This is the lowest IRQL. No interrupts are masked off and this is the level in which a thread executing in user mode is running. Pagable memory is accessible. In a processor running at this level, only APC level interrupts are masked.

This is the level in which Asynchronous Procedure Calls occur. Pagable memory is still accessible. This, in turn, also disables other APCs from occurring. The processor running at this level has DPC level interrupts and lower masked off.

Pagable memory cannot be accessed, so all memory being accessed must be non-paged. If you are running at Dispatch Level, the APIs that you can use greatly decrease since you can only deal with non-paged memory. Generally, higher level drivers do not deal with IRQLs at this level, but all interrupts at this level or less are masked off and do not occur. This is actually a range of IRQLs, and this is a method to determine which devices have priority over other devices.

However, it is necessary for you to be aware of what IRQL is, if you intend to continue writing device drivers. For more information on IRQLs and thread scheduling, refer to the following documentation , and another good source of information is here. This is a data structure that allows drivers to communicate with each other and to request work to be done by the driver. The IRP includes information about the operation that is being requested.

A description of the IRP data structure can be found here. The description and usage of an IRP can go from simple to complex very easily, so we will only be describing, in general, what an IRP will mean to you. That article can be found here. If they were going to build a house, they could have a common overall design and perhaps a common set of tools like their tool box.

This includes things like power drills, etc. All of these common tools and overall design of building a house would be the IRP. Each of them has an individual piece they need to work on to make this happen, for example, the plumber needs the plans on where to put the pipe, how much pipe he has, etc. Once everyone has completed their job, they then complete the IRP.

The device driver we will be building will not be that complex and will basically be the only driver in the stack. There are a lot of pitfalls that you will need to avoid but they are mostly unrelated to our simple driver.

It is hard to digest theory or even how code is supposed to work, without actually doing anything. You need some hands on experience so you can bring these ideas out of space and into reality. The prototype for the DriverEntry is the following. We will simply be creating one device. The driver can use this location to store driver specific information. The next part is to actually put things in the DriverEntry routine.

The first thing we will do is create the device. You may be wondering how we are going to create a device and what type of device we should create. This is generally because a driver is usually associated with hardware but this is not the case.

There are a variety of different types of drivers which operate at different levels, not all drivers work or interface directly with hardware. Generally, you maintain a stack of drivers each with a specific job to do. The highest level driver is the one that communicates with user mode, and the lowest level drivers generally just talk to other drivers and hardware. There are network drivers, display drivers, file system drivers, etc.

Each place in the stack breaks up a request into a more generic or simpler request for the lower level driver to service. The highest level drivers are the ones which communicate themselves to user mode, and unless they are a special device with a particular framework like display drivers , they can behave generally the same as other drivers just as they implement different types of operations.

As an example, take the hard disk drive. The driver which communicates to user mode does not talk directly to hardware. The high level driver simply manages the file system itself and where to put things. It then communicates where it wants to read or write from the disk to the lower level driver which may or may not talk directly to hardware. There may be another layer which then communicates that request to the actual hardware driver which then physically reads or writes a particular sector off a disk and then returns it to the higher level.

It could then determine what sector read requests to service, however, it has no idea what the data is and does not interpret it. The first thing you will notice is the DbgPrint function. This data structure contains basically three entries. The first is the size of the current Unicode string, the second is the maximum size that the Unicode string can be, and the third is a pointer to the Unicode string.

This is used to describe a Unicode string and used commonly in drivers. Most Unicode strings passing into your driver will not be NULL terminated, so this is something you need to be aware of. Devices have names just like anything else. The second parameter we passed 0, and it says to specify the number of bytes to create for the device extension.

In the search box on the taskbar, enter device manager , then select Device Manager. If Windows doesn't find a new driver, you can try looking for one on the device manufacturer's website and follow their instructions. Right-click or press and hold the name of the device, and select Uninstall.

If you can't see the desktop and instead see a blue, black, or blank screen, see Troubleshoot blue screen errors or Troubleshoot black or blank screen errors. Check for Windows updates. Windows 11 Windows 10 More Need more help?

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