IoAllocateIrp(IN CCHAR StackSize,
              IN BOOLEAN ChargeQuota)
{
  ....
  IoInitializeIrp(Irp, Size, StackSize);

IoInitializeIrp(IN PIRP Irp,
                IN USHORT PacketSize,
                IN CCHAR StackSize)
{
    /* Clear it */
    IOTRACE(IO_IRP_DEBUG,
            "%s - Initializing IRP %p\n",
            __FUNCTION__,
            Irp);
    RtlZeroMemory(Irp, PacketSize);

    /* Set the Header and other data */
    Irp->Type = IO_TYPE_IRP;
    Irp->Size = PacketSize;
    Irp->StackCount = StackSize;
    [COLOR="Red"]Irp->CurrentLocation = StackSize + 1[/COLOR];

IofCallDriver(IN PDEVICE_OBJECT DeviceObject,
              IN PIRP Irp)
{
    PDRIVER_OBJECT DriverObject;
    PIO_STACK_LOCATION StackPtr;
    DriverObject = DeviceObject->DriverObject;
    Irp->CurrentLocation--;