为Linux系统设计一个简单的二级文件系统。要求做到以下几点：

1．可以实现下列几条命令：

login　　用户登录

dir　　　　列目录

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

2．列目录时要列出文件名，物理地址，保护码和文件长度。

3．源文件可以进行读写保护。

-Linux system design for a simple two file system. Requirements do the following : 1. Can be achieved following several commands : login users logged out dir directory create founding documents, delete delete the file open fight Close the file was opened close reading paper documents read write two papers to write. Contents out to be listed name, physical address, the protection code and document length. 3. Source document can read and write protection.