Différentes façons de gérer les IRP - feuille tricher (partie 2 sur 2)

NTSTATUS
MakeSynchronousIoctl(
    IN PDEVICE_OBJECT    TopOfDeviceStack,
    IN ULONG         IoctlControlCode,
    PVOID             InputBuffer,
    ULONG             InputBufferLength,
    PVOID             OutputBuffer,
    ULONG             OutputBufferLength
    )
/*++

Arguments:

    TopOfDeviceStack- 
    
    IoctlControlCode              - Value of the IOCTL request

    InputBuffer        - Buffer to be sent to the TopOfDeviceStack

    InputBufferLength  - Size of buffer to be sent to the TopOfDeviceStack

    OutputBuffer       - Buffer for received data from the TopOfDeviceStack

    OutputBufferLength - Size of receive buffer from the TopOfDeviceStack

Return Value:

    NT status code
    
--*/ 
{
    KEVENT              event;
    PIRP                irp;
    IO_STATUS_BLOCK     ioStatus;
    NTSTATUS status;
    
    // 
    // Creating Device control IRP and send it to the another
    // driver without setting a completion routine.
    // 
    
    KeInitializeEvent(&event, NotificationEvent, FALSE);

    irp = IoBuildDeviceIoControlRequest (
                            IoctlControlCode,
                            TopOfDeviceStack,
                            InputBuffer,
                            InputBufferLength,
                            OutputBuffer,
                            OutputBufferLength,
                            FALSE, // External
                            &event,
                            &ioStatus);

    if (NULL == irp) {
        return STATUS_INSUFFICIENT_RESOURCES;
    }


    status = IoCallDriver(TopOfDeviceStack, irp);

    if (status == STATUS_PENDING) {
        // 
        // You must wait here for the IRP to be completed because:
        // 1) The IoBuildDeviceIoControlRequest associates the IRP with the
        //     thread and if the thread exits for any reason, it would cause the IRP
        //     to be canceled. 
        // 2) The Event and IoStatus block memory is from the stack and we
        //     cannot go out of scope.
        // This event will be signaled by the I/O manager when the
        // IRP is completed.
        // 
        status = KeWaitForSingleObject(
                     &event,
                     Executive, // wait reason
                     KernelMode, // To prevent stack from being paged out.
                     FALSE,     // You are not alertable
                     NULL);     // No time out !!!!

        status = ioStatus.Status;                     
    }

    return status;
}
				

typedef enum {
 
   IRPLOCK_CANCELABLE,
   IRPLOCK_CANCEL_STARTED,
   IRPLOCK_CANCEL_COMPLETE,
   IRPLOCK_COMPLETED
 
} IRPLOCK;
// 
// An IRPLOCK allows for safe cancellation. The idea is to protect the IRP
// while the canceller is calling IoCancelIrp. This is done by wrapping the
// call in InterlockedExchange(s). The roles are as follows:
// 
// Initiator/completion: Cancelable --> IoCallDriver() --> Completed
// Canceller: CancelStarted --> IoCancelIrp() --> CancelCompleted
// 
// No cancellation:
//   Cancelable-->Completed
// 
// Cancellation, IoCancelIrp returns before completion:
//   Cancelable --> CancelStarted --> CancelCompleted --> Completed
// 
// Canceled after completion:
//   Cancelable --> Completed -> CancelStarted
// 
// Cancellation, IRP completed during call to IoCancelIrp():
//   Cancelable --> CancelStarted -> Completed --> CancelCompleted
// 
//  The transition from CancelStarted to Completed tells the completer to block
//  postprocessing (IRP ownership is transferred to the canceller). Similarly,
//  the canceller learns it owns IRP postprocessing (free, completion, etc)
//  during a Completed->CancelCompleted transition.
// 


NTSTATUS
MakeSynchronousIoctlWithTimeOut(
    IN PDEVICE_OBJECT    TopOfDeviceStack,
    IN ULONG         IoctlControlCode,
    PVOID             InputBuffer,
    ULONG             InputBufferLength,
    PVOID             OutputBuffer,
    ULONG             OutputBufferLength,
    IN  ULONG               Milliseconds
    )
/*++

Arguments:

    TopOfDeviceStack   - 

    IoctlControlCode   - Value of the IOCTL request.

    InputBuffer        - Buffer to be sent to the TopOfDeviceStack.

    InputBufferLength  - Size of buffer to be sent to the TopOfDeviceStack.

    OutputBuffer       - Buffer for received data from the TopOfDeviceStack.

    OutputBufferLength - Size of receive buffer from the TopOfDeviceStack.

    Milliseconds       - Timeout value in Milliseconds

Return Value:

    NT status code
    
--*/ 
{
    NTSTATUS status;
    PIRP irp;
    KEVENT event;
    IO_STATUS_BLOCK ioStatus;
    LARGE_INTEGER dueTime;
    IRPLOCK lock;

    KeInitializeEvent(&event, NotificationEvent, FALSE);

    irp = IoBuildDeviceIoControlRequest (
                    IoctlControlCode,
                    TopOfDeviceStack,
                    InputBuffer,
                    InputBufferLength,
                    OutputBuffer,
                    OutputBufferLength,
                    FALSE, // External ioctl
                    &event,
                    &ioStatus);



    if (irp == NULL) {
        return STATUS_INSUFFICIENT_RESOURCES;
    }

    lock = IRPLOCK_CANCELABLE;

    IoSetCompletionRoutine(
                    irp,
                    MakeSynchronousIoctlWithTimeOutCompletion,
                    &lock,
                    TRUE,
                    TRUE,
                    TRUE
                    );

    status = IoCallDriver(TopOfDeviceStack, irp);

    if (status == STATUS_PENDING) {

        dueTime.QuadPart = -10000 * Milliseconds;

        status = KeWaitForSingleObject(
                            &event,
                            Executive,
                            KernelMode,
                            FALSE,
                            &dueTime
                            );

        if (status == STATUS_TIMEOUT) {

            if (InterlockedExchange((PVOID)&lock, IRPLOCK_CANCEL_STARTED) == IRPLOCK_CANCELABLE) {

                // 
                // You got it to the IRP before it was completed. You can cancel
                // the IRP without fear of losing it, because the completion routine
                // does not let go of the IRP until you allow it.
                // 
                IoCancelIrp(irp);

                // 
                // Release the completion routine. If it already got there,
                // then you need to complete it yourself. Otherwise, you got
                // through IoCancelIrp before the IRP completed entirely.
                // 
                if (InterlockedExchange(&lock, IRPLOCK_CANCEL_COMPLETE) == IRPLOCK_COMPLETED) {
                    IoCompleteRequest(irp, IO_NO_INCREMENT);
                }
            }

            KeWaitForSingleObject(&event, Executive, KernelMode, FALSE, NULL);

            ioStatus.Status = status; // Return STATUS_TIMEOUT

        } else {

            status = ioStatus.Status;
        }
    }

    return status;
}

NTSTATUS
MakeSynchronousIoctlWithTimeOutCompletion(
    IN PDEVICE_OBJECT   DeviceObject,
    IN PIRP             Irp,
    IN PVOID            Context
    )
{
    PLONG lock;

    lock = (PLONG) Context;

    if (InterlockedExchange((PVOID)&lock, IRPLOCK_COMPLETED) == IRPLOCK_CANCEL_STARTED) {
        // 
        // Main line code has got the control of the IRP. It will
        // now take the responsibility of completing the IRP. 
        // Therefore...
        return STATUS_MORE_PROCESSING_REQUIRED;
    }

    return STATUS_CONTINUE_COMPLETION ;
}
				

NTSTATUS
MakeSynchronousNonIoctlRequest (
    PDEVICE_OBJECT   TopOfDeviceStack,
    PVOID               WriteBuffer,
    ULONG               NumBytes
    )
/*++
Arguments:

    TopOfDeviceStack - 
    
    WriteBuffer       - Buffer to be sent to the TopOfDeviceStack.

    NumBytes  - Size of buffer to be sent to the TopOfDeviceStack.

Return Value:

    NT status code


--*/ 
{
    NTSTATUS        status;
    PIRP            irp;
    LARGE_INTEGER   startingOffset;
    KEVENT          event;
    IO_STATUS_BLOCK     ioStatus;
    PVOID context;
    
    startingOffset.QuadPart = (LONGLONG) 0;
    // 
    // Allocate memory for any context information to be passed
    // to the completion routine.
    // 
    context = ExAllocatePoolWithTag(NonPagedPool, sizeof(ULONG), 'ITag');
    if(!context) {
        return STATUS_INSUFFICIENT_RESOURCES;
    }

    KeInitializeEvent(&event,  NotificationEvent,   FALSE);

    irp = IoBuildSynchronousFsdRequest(
                IRP_MJ_WRITE,
                TopOfDeviceStack,
                WriteBuffer,
                NumBytes,


                &startingOffset, // Optional
                &event,
                &ioStatus
                ); 
    
    if (NULL == irp) {
        ExFreePool(context);
        return STATUS_INSUFFICIENT_RESOURCES;
    }

    IoSetCompletionRoutine(irp,
                   MakeSynchronousNonIoctlRequestCompletion,
                   context,
                   TRUE,
                   TRUE,
                   TRUE);

    status = IoCallDriver(TopOfDeviceStack, irp);

    if (status == STATUS_PENDING) {

       status = KeWaitForSingleObject(
                            &event,
                            Executive,
                            KernelMode,
                            FALSE, // Not alertable
                            NULL);
        status = ioStatus.Status;
    }

    return status;
}
NTSTATUS
MakeSynchronousNonIoctlRequestCompletion(
    IN PDEVICE_OBJECT   DeviceObject,
    IN PIRP             Irp,
    IN PVOID            Context
    )
{
    if (Context) {
        ExFreePool(Context);
    }
    return STATUS_CONTINUE_COMPLETION ;

}

NTSTATUS MakeSynchronousNonIoctlRequest2(
    PDEVICE_OBJECT TopOfDeviceStack,
    PVOID WriteBuffer,
    ULONG NumBytes
    )
/*++ Arguments:
    TopOfDeviceStack

    WriteBuffer     - Buffer to be sent to the TopOfDeviceStack.

    NumBytes        - Size of buffer to be sent to the TopOfDeviceStack.

Return Value:
    NT status code
--*/
{
    NTSTATUS        status;
    PIRP            irp;
    LARGE_INTEGER   startingOffset;
    KEVENT          event;
    IO_STATUS_BLOCK ioStatus;
    BOOLEAN         isSynchronous = TRUE;

    startingOffset.QuadPart = (LONGLONG) 0;
    KeInitializeEvent(&event, NotificationEvent, FALSE);
    irp = IoBuildSynchronousFsdRequest(
                IRP_MJ_WRITE,
                TopOfDeviceStack,
                WriteBuffer,
                NumBytes,
                &startingOffset, // Optional
                &event,
                &ioStatus
                );

    if (NULL == irp) {
        return STATUS_INSUFFICIENT_RESOURCES;
    }

    IoSetCompletionRoutine(irp,
                MakeSynchronousNonIoctlRequestCompletion2,
                (PVOID)&event,
                TRUE,
                TRUE,
                TRUE);

    status = IoCallDriver(TopOfDeviceStack, irp);

    if (status == STATUS_PENDING) {

        KeWaitForSingleObject(&event,
                              Executive,
                              KernelMode,
                              FALSE, // Not alertable
                              NULL);
        status = irp->IoStatus.Status;
        isSynchronous = FALSE;
    }

    //
    // Because you have stopped the completion of the IRP, you must
    // complete here and wait for it to be completed by waiting
    // on the same event again, which will be signaled by the I/O
    // manager.
    // NOTE: you cannot queue the IRP for
    // reuse by calling IoReuseIrp because it does not break the
    // association of this IRP with the current thread.
    //

    KeClearEvent(&event);
    IoCompleteRequest(irp, IO_NO_INCREMENT);

    //
    // We must wait here to prevent the event from going out of scope.
    // I/O manager will signal the event and copy the status to our
    // IoStatus block for synchronous IRPs only if the return status is not
    // an error. For asynchronous IRPs, the above mentioned copy operation
    // takes place regardless of the status value.
    //

    if (!(NT_ERROR(status) && isSynchronous)) {
        KeWaitForSingleObject(&event,
                              Executive,
                              KernelMode,
                              FALSE, // Not alertable
                              NULL);
    }
    return status;
}

NTSTATUS MakeSynchronousNonIoctlRequestCompletion2(
    IN PDEVICE_OBJECT   DeviceObject,
    IN PIRP             Irp,
    IN PVOID            Context )
{
    if (Irp->PendingReturned) {
        KeSetEvent ((PKEVENT) Context, IO_NO_INCREMENT, FALSE);
    }
    return STATUS_MORE_PROCESSING_REQUIRED;
}

NTSTATUS
MakeAsynchronousRequest (
    PDEVICE_OBJECT   TopOfDeviceStack,
    PVOID               WriteBuffer,
    ULONG               NumBytes
    )
/*++
Arguments:

    TopOfDeviceStack - 
    
    WriteBuffer       - Buffer to be sent to the TopOfDeviceStack.

    NumBytes  - Size of buffer to be sent to the TopOfDeviceStack.

--*/ 
{
    NTSTATUS        status;
    PIRP            irp;
    LARGE_INTEGER   startingOffset;
    PIO_STACK_LOCATION  nextStack;
    PVOID context;
    
    startingOffset.QuadPart = (LONGLONG) 0;

    irp = IoBuildAsynchronousFsdRequest(
                IRP_MJ_WRITE,
                TopOfDeviceStack,
                WriteBuffer,
                NumBytes,
                &startingOffset, // Optional
                NULL
                ); 
    
    if (NULL == irp) {
       
        return STATUS_INSUFFICIENT_RESOURCES;
    }

    // 
    // Allocate memory for context structure to be passed to the completion routine.
    // 
    context = ExAllocatePoolWithTag(NonPagedPool, sizeof(ULONG_PTR), 'ITag');
    if (NULL == context) {
        IoFreeIrp(irp);   
        return STATUS_INSUFFICIENT_RESOURCES;
    }

    IoSetCompletionRoutine(irp,
                   MakeAsynchronousRequestCompletion,
                   context,
                   TRUE,
                   TRUE,
                   TRUE);
    // 
    // If you want to change any value in the IRP stack, you must
    // first obtain the stack location by calling IoGetNextIrpStackLocation.
    // This is the location that is initialized by the IoBuildxxx requests and  
    // is the one that the target device driver is going to view.
    // 
    nextStack = IoGetNextIrpStackLocation(irp);
    // 
    // Change the MajorFunction code to something appropriate.
    // 
    nextStack->MajorFunction = IRP_MJ_SCSI;

    (void) IoCallDriver(TopOfDeviceStack, irp);

    return STATUS_SUCCESS;
}
NTSTATUS
MakeAsynchronousRequestCompletion(
    IN PDEVICE_OBJECT   DeviceObject,
    IN PIRP             Irp,
    IN PVOID            Context
    )
{
    PMDL mdl, nextMdl;
    
    // 
    // If the target device object is set up to do buffered i/o 
    // (TopOfDeviceStack->Flags and DO_BUFFERED_IO), then 
    // IoBuildAsynchronousFsdRequest request allocates a system buffer
    // for read and write operation. If you stop the completion of the IRP
    // here, you must free that buffer.
    // 

    if(Irp->AssociatedIrp.SystemBuffer && (Irp->Flags & IRP_DEALLOCATE_BUFFER) ) {
            ExFreePool(Irp->AssociatedIrp.SystemBuffer);
    }
    
    // 
    // If the target device object is set up do direct i/o (DO_DIRECT_IO), then 
    // IoBuildAsynchronousFsdRequest creates an MDL to describe the buffer
    // and locks the pages. If you stop the completion of the IRP, you must unlock
    // the pages and free the MDL.
    // 
    
    else if (Irp->MdlAddress != NULL) {
        for (mdl = Irp->MdlAddress; mdl != NULL; mdl = nextMdl) {
            nextMdl = mdl->Next;
            MmUnlockPages( mdl ); IoFreeMdl( mdl ); // This function will also unmap pages.
        }
        Irp->MdlAddress = NULL;
    }

    if(Context) {
        ExFreePool(Context);
    }
    


    // 
    // If you intend to queue the IRP and reuse it for another request,
    // make sure you call IoReuseIrp(Irp, STATUS_SUCCESS) before you reuse.
    // 
    IoFreeIrp(Irp);
   
    // 
    // NOTE: this is the only status that you can return for driver-created asynchronous IRPs.
    // 
    return STATUS_MORE_PROCESSING_REQUIRED;
}
				

NTSTATUS
MakeAsynchronousRequest2(
    PDEVICE_OBJECT   TopOfDeviceStack,
    PVOID               WriteBuffer,
    ULONG               NumBytes
    )
/*++
Arguments:

    TopOfDeviceStack - 
    
    WriteBuffer       - Buffer to be sent to the TopOfDeviceStack.

    NumBytes  - Size of buffer to be sent to the TopOfDeviceStack.

--*/ 
{
    NTSTATUS        status;
    PIRP            irp;
    LARGE_INTEGER   startingOffset;
    KEVENT          event;
    PIO_STACK_LOCATION  nextStack;

    startingOffset.QuadPart = (LONGLONG) 0;
    
    // 
    // Start by allocating the IRP for this request.  Do not charge quota
    // to the current process for this IRP.
    // 

    irp = IoAllocateIrp( TopOfDeviceStack->StackSize, FALSE );
    if (NULL == irp) {
       
        return STATUS_INSUFFICIENT_RESOURCES;
    }

     // 
    // Obtain a pointer to the stack location of the first driver that will be
    // invoked.  This is where the function codes and the parameters are set.
    // 

    nextStack = IoGetNextIrpStackLocation( irp );
    nextStack->MajorFunction = IRP_MJ_WRITE;
    nextStack->Parameters.Write.Length = NumBytes;
    nextStack->Parameters.Write.ByteOffset= startingOffset;

 
    if(TopOfDeviceStack->Flags & DO_BUFFERED_IO) {
        
        irp->AssociatedIrp.SystemBuffer = WriteBuffer;
        irp->MdlAddress = NULL;
        
    } else if (TopOfDeviceStack->Flags & DO_DIRECT_IO) {
        // 
        // The target device supports direct I/O operations.  Allocate
        // an MDL large enough to map the buffer and lock the pages into
        // memory.
        // 
        irp->MdlAddress = IoAllocateMdl( WriteBuffer,
                                         NumBytes,
                                         FALSE,
                                         FALSE,
                                         (PIRP) NULL );
        if (irp->MdlAddress == NULL) {
            IoFreeIrp( irp );
            return STATUS_INSUFFICIENT_RESOURCES;
        }

        try {
            
            MmProbeAndLockPages( irp->MdlAddress,
                                 KernelMode,
                                 (LOCK_OPERATION) (nextStack->MajorFunction == IRP_MJ_WRITE ? IoReadAccess : IoWriteAccess) );
            
        } except(EXCEPTION_EXECUTE_HANDLER) {
        
              if (irp->MdlAddress != NULL) {
                  IoFreeMdl( irp->MdlAddress );
              }
              IoFreeIrp( irp );
              return  GetExceptionCode();
              
        }
    }   

    IoSetCompletionRoutine(irp,
                   MakeAsynchronousRequestCompletion2,
                   NULL,
                   TRUE,
                   TRUE,
                   TRUE);

    (void) IoCallDriver(TargetDeviceObject, irp);

    return STATUS_SUCCESS;
}

NTSTATUS
MakeAsynchronousRequestCompletion2(
    IN PDEVICE_OBJECT   DeviceObject,
    IN PIRP             Irp,
    IN PVOID            Context
    )
{
    PMDL mdl, nextMdl;

    // 
    // Free any associated MDL.
    // 
      
    if (Irp->MdlAddress != NULL) {
        for (mdl = Irp->MdlAddress; mdl != NULL; mdl = nextMdl) {
            nextMdl = mdl->Next;
            MmUnlockPages( mdl ); IoFreeMdl( mdl ); // This function will also unmap pages.
        }
        Irp->MdlAddress = NULL;
    }

    // 
    // If you intend to queue the IRP and reuse it for another request,
    // make sure you call IoReuseIrp(Irp, STATUS_SUCCESS) before you reuse.
    // 
    
    IoFreeIrp(Irp);
    
    return STATUS_MORE_PROCESSING_REQUIRED;
}
				

typedef struct _DEVICE_EXTENSION{
    ..
    PDEVICE_OBJECT TopOfDeviceStack;
    PIRP PendingIrp; 
    IRPLOCK IrpLock; // You need this to track the state of the IRP.
    KEVENT IrpEvent; // You need this to synchronize various threads.
    ..
} DEVICE_EXTENSION, *PDEVICE_EXTENSION;
				

InitializeDeviceExtension( PDEVICE_EXTENSION  DeviceExtension)
{
    KeInitializeEvent(&DeviceExtension->IrpEvent, SynchronizationEvent, TRUE); 
}

NTSTATUS
MakeASynchronousRequest3(
    PDEVICE_EXTENSION  DeviceExtension,
    PVOID               WriteBuffer,
    ULONG               NumBytes
    )
/*++
Arguments:

    DeviceExtension - 
    
    WriteBuffer       - Buffer to be sent to the TargetDeviceObject.

    NumBytes  - Size of buffer to be sent to the TargetDeviceObject.

--*/ 
{
    NTSTATUS        status;
    PIRP            irp;
    LARGE_INTEGER   startingOffset;
    PIO_STACK_LOCATION  nextStack;

    // 
    // Wait on the event to make sure that PendingIrp
    // field is free to be used for the next request. If you do
    // call this function in the context of the user thread,
    // make sure to call KeEnterCriticialRegion before the wait to protect 
    // the thread from getting suspended while holding a lock.
    // 
    KeWaitForSingleObject( &DeviceExtension->IrpEvent,
                           Executive,
                           KernelMode,
                           FALSE,
                           NULL );

    startingOffset.QuadPart = (LONGLONG) 0;
    // 
    // If the IRP is used for the same purpose every time, you can just create the IRP in the
    // Initialization routine one time and reuse it by calling IoReuseIrp. 
    // The only thing that you have to do in the routines in this article 
    // is remove the lines that call IoFreeIrp and set the PendingIrp
    // field to NULL. If you do so, make sure that you free the IRP 
    // in the PNP remove handler.
    // 
    irp = IoBuildAsynchronousFsdRequest(
                IRP_MJ_WRITE,
                DeviceExtension->TopOfDeviceStack,
                WriteBuffer,
                NumBytes,
                &startingOffset, // Optional
                NULL
                ); 
    
    if (NULL == irp) {
       
        return STATUS_INSUFFICIENT_RESOURCES;
    }

    // 
    // Initialize the fields relevant fields in the DeviceExtension
    // 
    DeviceExtension->PendingIrp = irp;
    DeviceExtension->IrpLock = IRPLOCK_CANCELABLE;

    IoSetCompletionRoutine(irp,
                   MakeASynchronousRequestCompletion3,
                   DeviceExtension,
                   TRUE,
                   TRUE,
                   TRUE);
    // 
    // If you want to change any value in the IRP stack, you must
    // first obtain the stack location by calling IoGetNextIrpStackLocation.
    // This is the location that is initialized by the IoBuildxxx requests and  
    // is the one that the target device driver is going to view.
    // 

    nextStack = IoGetNextIrpStackLocation(irp);

    // 
    // You could change the MajorFunction code to something appropriate.
    // 
    nextStack->MajorFunction = IRP_MJ_SCSI;

    (void) IoCallDriver(DeviceExtension->TopOfDeviceStack, irp);

    return STATUS_SUCCESS;
}

NTSTATUS
MakeASynchronousRequestCompletion3(
    IN PDEVICE_OBJECT   DeviceObject,
    IN PIRP             Irp,
    IN PVOID            Context
    )
{
    PMDL mdl, nextMdl;
    PDEVICE_EXTENSION deviceExtension = Context;

    // 
    // If the target device object is set up to do buffered i/o 
    // (TargetDeviceObject->Flags & DO_BUFFERED_IO), then 
    // IoBuildAsynchronousFsdRequest request allocates a system buffer
    // for read and write operation. If you stop the completion of the IRP
    // here, you must free that buffer.
    // 

    if(Irp->AssociatedIrp.SystemBuffer && (Irp->Flags & IRP_DEALLOCATE_BUFFER) ) {
            ExFreePool(Irp->AssociatedIrp.SystemBuffer);
    }

    // 
    // If the target device object is set up to do direct i/o (DO_DIRECT_IO), then 
    // IoBuildAsynchronousFsdRequest creates an MDL to describe the buffer
    // and locks the pages. If you stop the completion of the IRP, you must unlock
    // the pages and free the MDL.
    // 

    if (Irp->MdlAddress != NULL) {
        for (mdl = Irp->MdlAddress; mdl != NULL; mdl = nextMdl) {
            nextMdl = mdl->Next;
            MmUnlockPages( mdl ); IoFreeMdl( mdl ); // This function will also unmap pages.
        }
        Irp->MdlAddress = NULL;
    }

    if (InterlockedExchange((PVOID)&deviceExtension->IrpLock, IRPLOCK_COMPLETED) 
                    == IRPLOCK_CANCEL_STARTED) {
        // 
        // Main line code has got the control of the IRP. It will
        // now take the responsibility of freeing the IRP. 
        // Therefore...
        return STATUS_MORE_PROCESSING_REQUIRED;
    }

    // 
    // If you intend to queue the IRP and reuse it for another request, make
    // sure you call IoReuseIrp(Irp, STATUS_SUCCESS) before you reuse.
    // 
    IoFreeIrp(Irp);
    deviceExtension->PendingIrp = NULL; // if freed
    // 
    // Signal the event so that the next thread in the waiting list
    // can send the next request.
    // 
    KeSetEvent (&deviceExtension->IrpEvent, IO_NO_INCREMENT, FALSE);
    
    return STATUS_MORE_PROCESSING_REQUIRED;
}

VOID
CancelPendingIrp(
    PDEVICE_EXTENSION DeviceExtension
    )
/*++
    This function tries to cancel the PendingIrp if it is not already completed.
    Note that the IRP may not be completed and freed when the
    function returns. Therefore, if you are calling this from your PNP Remove device handle,
    you must wait on the IrpEvent to make sure the IRP is indeed completed
    before successfully completing the remove request and allowing the driver to unload.
--*/ 
{ 
     if (InterlockedExchange((PVOID)&DeviceExtension->IrpLock, IRPLOCK_CANCEL_STARTED) == IRPLOCK_CANCELABLE) {

        // 
        // You got it to the IRP before it was completed. You can cancel
        // the IRP without fear of losing it, as the completion routine
        // will not let go of the IRP until you say so.
        // 
        IoCancelIrp(DeviceExtension->PendingIrp);
        // 
        // Release the completion routine. If it already got there,
        // then you need to free it yourself. Otherwise, you got
        // through IoCancelIrp before the IRP completed entirely.
        // 
        if (InterlockedExchange((PVOID)&DeviceExtension->IrpLock, IRPLOCK_CANCEL_COMPLETE) == IRPLOCK_COMPLETED) {
            IoFreeIrp(DeviceExtension->PendingIrp);
            DeviceExtension->PendingIrp = NULL;
            KeSetEvent(&DeviceExtension->IrpEvent, IO_NO_INCREMENT, FALSE);
        }

     }
     
    return ;
}