()文件输入输出----APUE2笔记

Unix系统中文件的输入输出只需用5个函数即可：open，read，write，lseek，close。

本章讲的函数称为无缓冲I/O，(在第五章会讲标准的I/O). 无缓冲意味着每一次读或写都调用一个内核里面的系统调用。他们不属于是ISO C的内容，但是是POSIX.1里面的，也是Single Unix Specification里面的内容。

Whenever we describe the sharing of resources among multiple processes, the concept of an atomic operation becomes important. We examine this concept with regard to file I/O and the arguments to the open function. This leads to a discussion of how files are shared among multiple processes and the kernel data structures involved. After describing these features, we describe the dup, fcntl, sync, fsync, and ioctl functions.