IRP调用IoSkipCurrentIrpStackLocation与IoCopyCurrentIrpStackLocationToNext的区别

当IPR需要传递给下层设备时，一般的操作有两种。
第一种是直接下传：

 IoCopyCurrentIrpStackLocationToNext(irp);
 status = IoCallDriver(parentFdoExt->fdo, irp);

这种情况下是保留当前驱动栈对该IRP的IO_STACK_LOCATION，这是因为：

FORCEINLINE
VOID
IoCopyCurrentIrpStackLocationToNext(
    _Inout_ PIRP Irp
)
/*--

Routine Description:

    This routine is invoked to copy the IRP stack arguments and file
    pointer from the current IrpStackLocation to the next
    in an I/O Request Packet (IRP).

    If the caller wants to call IoCallDriver with a completion routine
    but does not wish to change the arguments otherwise,
    the caller first calls IoCopyCurrentIrpStackLocationToNext,
    then IoSetCompletionRoutine, then IoCallDriver.

Arguments:

    Irp - Pointer to the I/O Request Packet.

Return Value:

    None.

--*/
{
    PIO_STACK_LOCATION irpSp;
    PIO_STACK_LOCATION nextIrpSp;
    irpSp = IoGetCurrentIrpStackLocation(Irp);
    nextIrpSp = IoGetNextIrpStackLocation(Irp);
    RtlCopyMemory( nextIrpSp, irpSp, FIELD_OFFSET(IO_STACK_LOCATION, CompletionRoutine));
    nextIrpSp->Control = 0;
}

可以以看到IoCopyCurrentIrpStackLocationToNext只是将当前的栈信息复制到下一层中（不包括完成例程）

而第二种是：

 IoSkipCurrentIrpStackLocation(irp);
 status = IoCallDriver(parentFdoExt->topDevObj, irp);

跳过当前栈，让下层驱动使用当前的驱动栈。所以使用IoSkipCurrentIrpStackLocation函数先使IRP的IO_STACK_LOCATION上移，上移Irp->Tail.Overlay.CurrentStackLocation指针的上移和当前位置层位置CurrentLocation的上移：

ORCEINLINE
VOID
IoSkipCurrentIrpStackLocation (
    _Inout_ PIRP Irp
)
/*--
Routine Description:

    This routine is invoked to increment the current stack location of
    a given IRP.

    If the caller wishes to call the next driver in a stack, and does not
    wish to change the arguments, nor does he wish to set a completion
    routine, then the caller first calls IoSkipCurrentIrpStackLocation
    and the calls IoCallDriver.

Arguments:

    Irp - Pointer to the I/O Request Packet.

Return Value:

    None
--*/
{
    NT_ASSERT(Irp->CurrentLocation <= Irp->StackCount);
    Irp->CurrentLocation++;
    Irp->Tail.Overlay.CurrentStackLocation++;
}

最终它们都是调用的是IoCalldriver函数：http://www.pnpon.com/article/detail-361.html
从源代码可以看到：
其仅是检查当前位直CurrentLocation。然后获取下一层的IO_STACK_LOCATION并赋于Irp->Tail.Overlay.CurrentStackLocation，然后执行DeviceObject对应的DriverObject对应的函数。

其实从这里也可以看出，IoCallDriver这个函数的调用是需要一些准备工作的，而且比较重要。这些准备工作是根据用户的需求而设置不同。所以IoCallDriver函数有点像半个函数。