谦虚求教，慷慨赠分！

PDEVICE_OBJECT
  IoAttachDeviceToDeviceStack(
  IN PDEVICE_OBJECT  SourceDevice,
  IN PDEVICE_OBJECT  TargetDevice
  );
ddk中解释为：
IoAttachDeviceToDeviceStack attaches the caller\'s device object to the highest device object in the chain and returns a pointer to the previously highest device object. I/O requests bound for the target device are routed first to the caller.
现在感到迷惑不解的是：
TargetDevice和返回值都是the highest device object ，那位
来解惑？

看漏了“previously”吧 ;)

TargetDevice 指的是 PDO (PhysicalDeviceObject,由总线创建），而函数返回值是当前驱动程序栈的顶（一般是FDO),也就是你的 IoCallDriver(...)要调用的。