> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/4.3-bsd-unix-cao-zuo-xi-tong-she-ji-yu-shi-xian/di-san-bu-fen-io-xi-tong/9.10.-xiao-jie.md).

# 9.10 小结

我们考察了 4.3BSD 的终端 I/O 系统。终端处理分在两处：终端所接字符设备的设备驱动，和所有此类驱动共享的行规程。标准终端行规程既支持伯克利的新终端规程，也支持第七版 UNIX 的旧规程。其他行规程支持串行线的非终端用途，如网络连接或数字化硬件的连接。如第 1 章所述，计划中的未来工作包括支持 POSIX 行规程。

## 习题

9.1 终端输入有哪三种可能的模式？用户与交互式屏幕编辑器对话时最常用哪种模式？

9.2 处理终端输入为什么用两个字符队列？描述各自的用途。

9.3 说终端线路“支持调制解调器控制”是什么意思？这类线路通常怎么用？

9.4 用户在会话中途断开调制解调器线路时，与终端关联的进程会收到哪些信号？

9.5 终端输出队列的高水位线如何确定？

9.6 DH-11 终端多路复用器的开销为什么显著低于 DZ-11？

\*9.7 考虑一个让一台终端上的辅导者监视并协助其他终端上学生的设施：学生键入的一切既作为输入传给系统，也作为输出传到辅导者终端；辅导者键入的一切都定向为各学生终端的输入。描述这一设施如何用专门的行规程实现。再描述这一设施有用的进一步推广。

\*9.8 终端行规程支持擦除字符、词和行时的输入文本逻辑擦除。记住用户键入输入行期间其他系统活动仍在继续，解释实现这一特性必须考虑哪些复杂情况。举出三种特例并描述其对实现的影响。

**9.9** 终端多路复用器的设备驱动使用行规程有哪些优点？有哪些局限？对终端 I/O 系统的当前结构提出一种替代方案。

**9.10** 考虑 Berknet 与 SLIP 规程的差异。虽然两者为求效率都使用替代行规程，其中一种用途若不修改内核（例如加一个专门的行规程模块）将极难实现。哪种用途难以实现？解释你的选择。

## 参考文献

Romkey, 1988. J. Romkey, “A Nonstandard for Transmission of IP Datagrams Over Serial Lines: SLIP,” RFC 1055, SRI Network Information Center, Menlo Park, CA (June 1988).

Scheifler & Gettys, 1986. R. W. Scheifler & J. Gettys, “The X Window System,” *ACM Transactions on Graphics* **5**(2), pp. 79–109 (April 1986).


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