说明：  完整的文件系统模拟 基本功能 （1）多用户 （2）多级目录：具有树形目录结构；（3）具有login (用户登录)和用户身份认证功能；（4）文件的创建： create （5）文件的打开：open（6）文件的读：read（7）文件的写：write（8）文件关闭：close（9）删除文件：delete （12）列出文件目录：dir（列目录时要列出文件名、物理地址和文件长度） （13）退出：logout （14）文件保护机制
(integrity of the file system simulation basic functions (1) Multi-user (2) Multi-level directory : with the tree structure; (3) having a login (user login) and user authentication functions; (4) Documentation of the founders : create (5) documents the open : open (6) the documents read : read (7) of the document reads : write (8) documents Close : close (9) delete the file : delete (12) provides directory : dir (listed directory to list name, physical address and length of documents) (13) withdrew : logout (14) document protection mechanisms)