fd_table.h

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/*
 * Copyright (c) 2013-2019 Huawei Technologies Co., Ltd. All rights reserved.
 * Copyright (c) 2020-2021 Huawei Device Co., Ltd. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
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 *
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 *    conditions and the following disclaimer.
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 * 2. Redistributions in binary form must reproduce the above copyright notice, this list
 *    of conditions and the following disclaimer in the documentation and/or other materials
 *    provided with the distribution.
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 *    to endorse or promote products derived from this software without specific prior written
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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#ifndef __INCLUDE_FS_FDTABLE_H
#define __INCLUDE_FS_FDTABLE_H
 
#include <limits.h>
#include <sys/select.h>
#include <semaphore.h>
#include "linux/spinlock.h"
 
/**
 * @file fb_table.h
 * @verbatim
    fd:文件描述符（file descriptor）也叫文件句柄.
    为了高效管理已被打开的文件所创建的索引,是一个非负整数,本质上一个凭证.凭证上岗.
    fd只是个索引, 顺藤摸瓜, fd -> file -> vnode -> 块/字符驱动程序
 
    当应用程序请求内核打开/新建一个文件时，内核会返回一个文件描述符用于对应这个打开/新建的文件，
    读写文件也是需要使用这个文件描述符来指定待读写的文件的。
    鸿蒙和LINUX一样,一切皆为文件,系统中，所有的文件操作，都是通过fd来定位资源和状态的
    fd有两个好处, 1.安全,对用户透明,不需要知道具体怎么实现的,凭编号拿结果 2.方便扩展
    -----------------------------------------------------------------------------
 
    int select(int n, fd_set *restrict rfds, fd_set *restrict wfds, fd_set *restrict efds, struct timeval *restrict tv)
    见于..\third_party\musl\src\select\select.c   
    https://blog.csdn.net/starflame/article/details/7860091
 
    理解select模型的关键在于理解fd_set，为说明方便，取fd_set长度为1字节，fd_set中的每一bit可以对应一个文件描述符fd。
    则1字节长的fd_set最大可以对应8个fd。
 
    typedef struct fd_set
    {
    unsigned char fd_bits [(FD_SETSIZE+7)/8];//用一位来表示一个FD
    } fd_set;
 
    fd_set:
    select()机制中提供一fd_set的数据结构，实际上是一long类型的数组，每一个数组元素都能与一打开的文件句柄
    （不管是socket句柄，还是其他文件或命名管道或设备句柄）建立联系，建立联系的工作由程序员完成，当调用select()时，
    由内核根据IO状态修改fd_set的内容，由此来通知执行了select()的进程哪一socket或文件发生了可读或可写事件。
 
    process fd 和 system fd 的区别和联系
    process fd(进程FD):每个进程都有一个属于自己的files_struct
    system fd(系统FD):整个系统共用的fd表
    二者的关系描述为:files_struct->ft_fds[进程FD].sysFd = 系统FD ;
 * @endverbatim 
 * @brief 
 */
 
/* open file table for process fd */
/// 进程fd <--> 系统FD绑定 sysFd的默认值是-1
struct file_table_s {
    intptr_t sysFd; /* system fd associate with the tg_filelist index */
};
/// 进程fd表结构体
struct fd_table_s {
    unsigned int max_fds;///< 进程的文件描述符最多有256个
    struct file_table_s *ft_fds; /* process fd array associate with system fd | 系统分配给进程的FD数组 ,fd 默认是 -1*/
    fd_set *proc_fds;   ///< 进程fd管理位,用bitmap管理FD使用情况,默认打开了 0,1,2           (stdin,stdout,stderr)
    fd_set *cloexec_fds;
    sem_t ft_sem; /* manage access to the file table | 管理对文件表的访问的信号量*/
};
/// 注:系统描述符的使用情况也是用bitmap管理见于 ..\third_party\third_party_NuttX\fs\inode\fs_files.c
/// 进程文件表结构体 ,进程对文件操作在内存的表现 files_struct 为 进程 process->files 字段,包含一个进程的所有和VFS相关的内容 
struct files_struct {
    int count;              ///< 持有的文件数量
    struct fd_table_s *fdt; ///< 持有的文件表
    unsigned int file_lock; ///< 文件互斥锁
    unsigned int next_fd;   ///< 下一个fd
#ifdef VFS_USING_WORKDIR
    spinlock_t workdir_lock;    ///< 工作区目录自旋锁
    char workdir[PATH_MAX];     ///< 工作区路径,最大 256个字符
#endif
};
 
 
typedef struct ProcessCB LosProcessCB;
//
void files_refer(int fd);
 
int files_close_internal(int fd, LosProcessCB *processCB);
///复制FD
struct files_struct *dup_fd(struct files_struct *oldf);
///为进程分配文件管理器，其中包含fd总数，(0,1,2)默认给了stdin,stdout,stderr
struct files_struct *alloc_files(void);
///删除参数进程的文件管理器
void delete_files(struct files_struct *files);
///创建文件管理器快照，所谓快照就是一份拷贝
struct files_struct *create_files_snapshot(const struct files_struct *oldf);
///删除文件管理器快照
void delete_files_snapshot(struct files_struct *files);
///分配一个系统fd，从全局tg_filelist中拿sysFd
int alloc_fd(int minfd);
 
void alloc_std_fd(struct fd_table_s *fdt);
 
void FileTableLock(struct fd_table_s *fdt);
 
void FileTableUnLock(struct fd_table_s *fdt);
 
struct fd_table_s *GetFdTable(void);
#endif