利用函数fopen(), fread(), fwrite(), fclose() 来实现简单的文件备份， 即将一个文件的内容拷贝到另一个文件中去。

通过一个简单多用户文件系统的设计，加深理解文件系统的内部功能及内部实现

-Function fopen (), fread (), fwrite (), fclose () to implement a simple file backup, and is about to copy the contents of a file to another file. Internal functions and the internal implementation of a simple multi-user file system designed to deepen the understanding of the file system