在内存中开辟一个空间作为文件存储器，在其上实现一个简单的文件系统

退出这个文件系统时，需要该文件系统的内容保存到磁盘上，以便下次可以将其回复到内存中来。-Open up a space in memory as a file store, and implement a simple file system on its

When you exit this file system, you need to save the content of the file system to the disk, so that it can be returned to memory next time..