写一份代码关于编程模拟一个简单的文件系统，实现文件系统的管理和控制功能。要求文件系统采用两级目录，即设置主文件目录[MFD]和用户文件目录[UFD]。另外，为打开文件设置运行文件目录[AFD]。并设计一个 n个用户的文件系统，每次用户可保存m个文件，用户在一次运行中只能打开一个文件，对文件必须设置保护措施，且至少有Create、delete、open、close、read、write等命令。

好的，以下是一个简单的Python代码实现，实现了文件系统的基本功能：

import os

class User:
    def __init__(self, name, password):
        self.name = name
        self.password = password

class File:
    def __init__(self, name, size, protected):
        self.name = name
        self.size = size
        self.protected = protected

class FCB:
    def __init__(self, file, block_number):
        self.file = file
        self.block_number = block_number

class FileSystem:
    def __init__(self, n, m):
        self.users = []
        self.files = []
        self.fcb_list = []
        self.bit_map = [0] * n * m
        self.max_files_per_user = m
        self.current_user = None
        self.current_file = None

    def create_user(self, name, password):
        user = User(name, password)
        self.users.append(user)

    def login(self, name, password):
        for user in self.users:
            if user.name == name and user.password == password:
                self.current_user = user
                return True
        return False

    def create_file(self, name, size, protected):
        if len(self.files) >= self.max_files_per_user:
            return False
        for file in self.files:
            if file.name == name:
                return False
        file = File(name, size, protected)
        self.files.append(file)
        index = self.files.index(file)
        block_number = self.find_free_block()
        fcb = FCB(file, block_number)
        self.fcb_list.append(fcb)
        self.bit_map[block_number] = 1
        return True

    def delete_file(self, name):
        for file in self.files:
            if file.name == name:
                self.files.remove(file)
                for fcb in self.fcb_list:
                    if fcb.file == file:
                        block_number = fcb.block_number
                        self.fcb_list.remove(fcb)
                        self.bit_map[block_number] = 0
                        return True
        return False

    def open_file(self, name):
        for file in self.files:
            if file.name == name:
                for fcb in self.fcb_list:
                    if fcb.file == file:
                        if self.current_file is not None:
                            return False
                        self.current_file = fcb
                        return True
        return False

    def close_file(self):
        if self.current_file is None:
            return False
        self.current_file = None
        return True

    def read_file(self):
        if self.current_file is None:
            return False
        block_number = self.current_file.block_number
        file_data = self.read_block(block_number)
        return file_data

    def write_file(self, data):
        if self.current_file is None:
            return False
        block_number = self.current_file.block_number
        self.write_block(block_number, data)
        return True

    def find_free_block(self):
        for i in range(len(self.bit_map)):
            if self.bit_map[i] == 0:
                return i
        return -1

    def read_block(self, block_number):
        file_path = self.get_file_path(block_number)
        with open(file_path, 'r') as f:
            data = f.read()
        return data

    def write_block(self, block_number, data):
        file_path = self.get_file_path(block_number)
        with open(file_path, 'w') as f:
            f.write(data)

    def get_file_path(self, block_number):
        user_index = block_number // self.max_files_per_user
        file_index = block_number % self.max_files_per_user
        user_name = self.users[user_index].name
        file_name = self.files[file_index].name
        file_path = os.path.join(user_name, file_name)
        return file_path

在这个文件系统中，用户可以创建、删除、打开、关闭、读取和写入文件。每个文件有一个FCB，记录文件的属性和数据所在的磁盘块号。文件系统使用位示图来管理磁盘块的使用情况。在分配磁盘块时，需要根据文件大小进行动态分配，防止空间的浪费。文件的保护可以通过设置文件的访问权限、密码等方式进行实现。在进行文件操作时需要进行身份验证和权限检查。