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Driver Development Part 1: Introduction to Drivers

, 5 Feb 2005
This article will go into the basics of creating a simple driver.
driverdev_src.zip
Programming
development
DEBUG
private
src
drivers
example
makefile
obj
i386
LoadDriver
makefile
obj
i386
usedriver
makefile
obj
i386
/**********************************************************************
 * 
 *  Toby Opferman
 *
 *  Driver Example
 *
 *  This example is for educational purposes only.  I license this source
 *  out for use in learning how to write a device driver.
 *
 *     Driver Functionality
 **********************************************************************/

#define _X86_ 

#include <wdm.h>
#include "example.h"


/**********************************************************************
 * Internal Functions
 **********************************************************************/
BOOLEAN Example_IsStringTerminated(PCHAR pString, UINT uiLength);


#pragma alloc_text(PAGE, Example_Create) 
#pragma alloc_text(PAGE, Example_Close) 
#pragma alloc_text(PAGE, Example_IoControl) 
#pragma alloc_text(PAGE, Example_Read)
#pragma alloc_text(PAGE, Example_WriteDirectIO)
#pragma alloc_text(PAGE, Example_WriteBufferedIO)
#pragma alloc_text(PAGE, Example_WriteNeither)
#pragma alloc_text(PAGE, Example_UnSupportedFunction)
#pragma alloc_text(PAGE, Example_IsStringTerminated)




/**********************************************************************
 * 
 *  Example_Create
 *
 *    This is called when an instance of this driver is created (CreateFile)
 *
 **********************************************************************/
NTSTATUS Example_Create(PDEVICE_OBJECT DeviceObject, PIRP Irp)
{
    NTSTATUS NtStatus = STATUS_SUCCESS;
    DbgPrint("Example_Create Called \r\n");

    return NtStatus;
}

/**********************************************************************
 * 
 *  Example_Close
 *
 *    This is called when an instance of this driver is closed (CloseHandle)
 *
 **********************************************************************/
NTSTATUS Example_Close(PDEVICE_OBJECT DeviceObject, PIRP Irp)
{
    NTSTATUS NtStatus = STATUS_SUCCESS;
    DbgPrint("Example_Close Called \r\n");

    return NtStatus;
}



/**********************************************************************
 * 
 *  Example_IoControl
 *
 *    This is called when an IOCTL is issued on the device handle (DeviceIoControl)
 *
 **********************************************************************/
NTSTATUS Example_IoControl(PDEVICE_OBJECT DeviceObject, PIRP Irp)
{
    NTSTATUS NtStatus = STATUS_SUCCESS;
    DbgPrint("Example_IoControl Called \r\n");

    return NtStatus;
}



/**********************************************************************
 * 
 *  Example_Read
 *
 *    This is called when a read is issued on the device handle (ReadFile/ReadFileEx)
 *
 **********************************************************************/
NTSTATUS Example_Read(PDEVICE_OBJECT DeviceObject, PIRP Irp)
{
    NTSTATUS NtStatus = STATUS_SUCCESS;
    DbgPrint("Example_Read Called \r\n");

    return NtStatus;
}



/**********************************************************************
 * 
 *  Example_WriteDirectIO
 *
 *    This is called when a write is issued on the device handle (WriteFile/WriteFileEx)
 *
 *    This version uses Direct I/O
 *
 **********************************************************************/
NTSTATUS Example_WriteDirectIO(PDEVICE_OBJECT DeviceObject, PIRP Irp)
{
    NTSTATUS NtStatus = STATUS_SUCCESS;
    PIO_STACK_LOCATION pIoStackIrp = NULL;
    PCHAR pWriteDataBuffer;

    DbgPrint("Example_WriteDirectIO Called \r\n");
    
    /*
     * Each time the IRP is passed down the driver stack a new stack location is added
     * specifying certain parameters for the IRP to the driver.
     */
    pIoStackIrp = IoGetCurrentIrpStackLocation(Irp);
    
    if(pIoStackIrp)
    {
        pWriteDataBuffer = MmGetSystemAddressForMdlSafe(Irp->MdlAddress, NormalPagePriority);
    
        if(pWriteDataBuffer)
        {                             
            /*
             * We need to verify that the string is NULL terminated. Bad things can happen
             * if we access memory not valid while in the Kernel.
             */
           if(Example_IsStringTerminated(pWriteDataBuffer, pIoStackIrp->Parameters.Write.Length))
           {
                DbgPrint(pWriteDataBuffer);
           }
        }
    }

    return NtStatus;
}

/**********************************************************************
 * 
 *  Example_WriteBufferedIO
 *
 *    This is called when a write is issued on the device handle (WriteFile/WriteFileEx)
 *
 *    This version uses Buffered I/O
 *
 **********************************************************************/
NTSTATUS Example_WriteBufferedIO(PDEVICE_OBJECT DeviceObject, PIRP Irp)
{
    NTSTATUS NtStatus = STATUS_SUCCESS;
    PIO_STACK_LOCATION pIoStackIrp = NULL;
    PCHAR pWriteDataBuffer;

    DbgPrint("Example_WriteBufferedIO Called \r\n");
    
    /*
     * Each time the IRP is passed down the driver stack a new stack location is added
     * specifying certain parameters for the IRP to the driver.
     */
    pIoStackIrp = IoGetCurrentIrpStackLocation(Irp);
    
    if(pIoStackIrp)
    {
        pWriteDataBuffer = (PCHAR)Irp->AssociatedIrp.SystemBuffer;
    
        if(pWriteDataBuffer)
        {                             
            /*
             * We need to verify that the string is NULL terminated. Bad things can happen
             * if we access memory not valid while in the Kernel.
             */
           if(Example_IsStringTerminated(pWriteDataBuffer, pIoStackIrp->Parameters.Write.Length))
           {
                DbgPrint(pWriteDataBuffer);
           }
        }
    }

    return NtStatus;
}

/**********************************************************************
 * 
 *  Example_WriteNeither
 *
 *    This is called when a write is issued on the device handle (WriteFile/WriteFileEx)
 *
 *    This version uses Neither buffered or direct I/O.  User mode memory is
 *    read directly.
 *
 **********************************************************************/
NTSTATUS Example_WriteNeither(PDEVICE_OBJECT DeviceObject, PIRP Irp)
{
    NTSTATUS NtStatus = STATUS_SUCCESS;
    PIO_STACK_LOCATION pIoStackIrp = NULL;
    PCHAR pWriteDataBuffer;

    DbgPrint("Example_WriteNeither Called \r\n");
    
    /*
     * Each time the IRP is passed down the driver stack a new stack location is added
     * specifying certain parameters for the IRP to the driver.
     */
    pIoStackIrp = IoGetCurrentIrpStackLocation(Irp);
    
    if(pIoStackIrp)
    {
        /*
         * We need this in an exception handler or else we could trap.
         */
        __try {
        
                ProbeForRead(Irp->UserBuffer, pIoStackIrp->Parameters.Write.Length, TYPE_ALIGNMENT(char));
                pWriteDataBuffer = Irp->UserBuffer;
            
                if(pWriteDataBuffer)
                {                             
                    /*
                     * We need to verify that the string is NULL terminated. Bad things can happen
                     * if we access memory not valid while in the Kernel.
                     */
                   if(Example_IsStringTerminated(pWriteDataBuffer, pIoStackIrp->Parameters.Write.Length))
                   {
                        DbgPrint(pWriteDataBuffer);
                   }
                }

        } __except( EXCEPTION_EXECUTE_HANDLER ) {

              NtStatus = GetExceptionCode();     
        }

    }

    return NtStatus;
}
                       

/**********************************************************************
 * 
 *  Example_UnSupportedFunction
 *
 *    This is called when a major function is issued that isn't supported.
 *
 **********************************************************************/
NTSTATUS Example_UnSupportedFunction(PDEVICE_OBJECT DeviceObject, PIRP Irp)
{
    NTSTATUS NtStatus = STATUS_NOT_SUPPORTED;
    DbgPrint("Example_UnSupportedFunction Called \r\n");

    return NtStatus;
}


/**********************************************************************
 * 
 *  Example_IsStringTerminated
 *
 *    Simple function to determine a string is NULL terminated.
 *
 **** We could validate also the characters in the string are printable! ***
 *
 **********************************************************************/
BOOLEAN Example_IsStringTerminated(PCHAR pString, UINT uiLength)
{
    BOOLEAN bStringIsTerminated = FALSE;
    UINT uiIndex = 0;

    while(uiIndex < uiLength && bStringIsTerminated == FALSE)
    {
        if(pString[uiIndex] == '\0')
        {
            bStringIsTerminated = TRUE;
        }
        else
        {
           uiIndex++;
        }
    }

    return bStringIsTerminated;
}


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About the Author

Toby Opferman
Engineer Intel
United States United States
Toby Opferman has worked in just about all aspects of Windows development including applications, services and drivers.
 
He has also played a variety of roles professionally on a wide range of projects. This has included pure researching roles, architect roles and developer roles. He also was also solely responsible for debugging traps and blue screens for a number of years.
 
Previously of Citrix Systems he is very experienced in the area of Terminal Services. He currently works on Operating Systems and low level architecture at Intel.

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