说明：  通过一个简单的二级文件系统设计，加深对文件系统的内部功能以及内部实现的理解。要求模拟采用二级目录结构的磁盘文件系统的文件操作，能实现以下几条命令，用输入命令来模拟用户程序中调用的文件操作： Login 用户登录 Dir 列文件目录（列出文件名、物理地址、保护码和文件长度） Create 创建文件 Delete 删除文件 Open 打开文件 Close 关闭文件 Read 读文件 Write 写文件
(Through a simple secondary file system design, deepen the understanding of the internal functions and internal implementation of the file system.It is required to simulate the file operation of the disk file system with a two-level directory structure, which can realize the following commands, and use the input command to simulate the file operation called by the user program: Login Dir column file directory (lists filename, physical address, protection code, and file length) Create Delete Open file Close file Read to Read the file The Write Write files)