• 进程控制的函数

    2013-10-26 14:37:18
    pid_t fork( void);  功能:创建一个新进程  返回值: 若成功调用一次则返回两个值,子进程返回0,父进程返回子进程ID;否则,出错返回-1 ...fork之后是父进程还是子进程先执行是不确定的,取决于内核的调度...

    pid_t fork
    void);
              功能:创建一个新进程
             返回值: 若成功调用一次则返回两个值,子进程返回0,父进程返回子进程ID;否则,出错返回-1
    注:
    • fork之后是父进程还是子进程先执行是不确定的,取决于内核的调度算法。
    • 父子进程共享代码段,至于数据段、栈段、堆并不对父进程完全复制,作为替代,使用写时复制技术。这些区域由父子进程共享,内核将他们的访问权限变为只读。如果父子进程中的任何一个试图修改这些区域。则内核只为修改区域的那块内存制作一个副本。通常是虚拟存储系统中的一页。
    • 父进程中所有打开文件描述符都被复制到子进程中。父子进程每个相同的文件描述符共享一个文件表项。
    pid_t vforkvoid);
              功能:创建一个新进程
             返回值: 若成功调用一次则返回两个值,子进程返回0,父进程返回子进程ID;否则,出错返回-1
             注:
    • vfork并不将父进程的地址空间完全复制到子进程中,在调用exec或exit之前它在父进程空间中运行。与父进程共享代码段,数据段,堆栈等。
    • vfork保证子进程先运行,在它调用exec或exit之后父进程才可能被调度运行。
    • 它产生的子进程刚开始暂时与父进程共享地址空间(其实就是线程的概念了),因为这时候子进程在父进程的地址空间中运行,所以子进程不能进行写操作,并且在儿子“霸占”着老子的房子时候,要委屈老子一下了,让他在外面歇着(阻塞),一旦儿子执行了exec或者exit后,相当于儿子买了自己的房子了,这时候就相当于分家了。
    • vfork和fork之间的另一个区别是: vfork保证子进程先运行,在她调用exec或exit之后父进程才可能被调度运行。如果在调用这两个函数之前子进程依赖于父进程的进一步动作,则会导致死锁。由此可见,这个系统调用是用来启动一个新的应用程序。其次,子进程在vfork()返回后直接运行在父进程的栈空间,并使用父进程的内存和数据。这意味着子进程可能破坏父进程的数据结构或栈,造成失败。
    pid_t wait (int * status);
    功能:使父进程阻塞,等待任一子进程结束。一旦任何一个子进程终止,则取得盖子进程的终止状态并立即返回;
    参数:status  保存子进程的终止状态
    返回值:如果它没有任何子进程,则立即出错返回-1.成功返回已终止的子进程PID;
    注:
    • 进程一旦调用了wait,就立即阻塞自己,由wait自动分析是否当前进程的某个子进程已经退出,如果让它找到了这样一个已经变成僵尸的子进程,wait就会收集这个子进程的信息,并把它彻底销毁后返回;如果没有找到这样一个子进程,wait就会一直阻塞在这里,直到有一个出现为止。
    • status是由实现定义的,其中某些位表示退出状态(正常返回),其他位表示信号编号(异常返回)。有一位指示是否产生了core文件。

    pid_t waitpid(pid_t pid,int * status,int options);
    功能:使父进程阻塞,等待特定子进程结束。
    参数:
                   pid:
                     pid==-1 等待任一子进程结束,就这一方面,waitpid和wait等效
                     pid<-1   等待其组ID为pid绝对值的任一子进程。主要是父子进程不在同一组进程中。
                     pid==0   等待其组ID等于调用进程组ID的任一子进程,主要是父进程与子进程在同一组进程中。
                     pid>0     等待其进程ID与pid相等的子进程
                   status:保存子进程的终止状态
                   options:
                        WNOHANG 若pid指定的子进程没有结束,则waitpid()函数返回0,不予以等待。若结束,则返回该子进程的ID。
                        WUNTRACED 若由pid指定的子进程进入暂停状态,并且其状态自暂停以来还未报告过,则马上返回其状态。
                        WCONTINUED 若由pid指定的子进程在暂停后已经继续,但其状态尚未报告,则返回其状态。
             返回值:出错返回-1.成功返回已终止的子进程PID;
             注:
    • 子进程正常结束,exit或_exit或Exit返回其退出状态。异常终止,内核产生一个终止状态
    • 子进程的结束状态返回后存于 status,底下有几个宏可判别结束情况:
    WIFEXITED(status)如果若为正常结束子进程返回的状态,则为真;对于这种情况可执行WEXITSTATUS(status),取子进程传给exit或_eixt的低8位。
    WEXITSTATUS(status)取得子进程 exit()返回的结束代码,一般会先用 WIFEXITED 来判断是否正常结束才能使用此宏。
    WIFSIGNALED(status)若为异常结束子进程返回的状态,则为真;对于这种情况可执行WTERMSIG(status),取使子进程结束的信号编号。
    WTERMSIG(status) 取得子进程因信号而中止的信号代码,一般会先用 WIFSIGNALED 来判断后才使用此宏。
    WIFSTOPPED(status) 若为当前暂停子进程返回的状态,则为真;对于这种情况可执行WSTOPSIG(status),取使子进程暂停的信号编号。
    WSTOPSIG(status) 取得引发子进程暂停的信号代码,一般会先用 WIFSTOPPED 来判断后才使用此宏。




    pid_t getpid(void);
    功能:获得当前进程ID
    返回值:当前进程ID,此函数总是成功
           

    pid_t getppid(void);
    功能:获得父进程ID
    返回值:父进程ID,此函数总是成功

    char *getenv(const char *name)
    功能:获得环境变量
    参数:name:想要获得的环境变量的名字
    返回值:返回指向环境变量的指针,没有匹配的环境变量时返回NULL
    例:getenv("PATH");


    int getdtablesize(void);
           功能:返回当前进程能够打开的最大文件描述符个数。


    pid_t  getpgrp(void);  
            功能:返回调用进程的组ID

    pid_t getpgid(pid_t pid)
             功能:返回进程ID为pid的组ID,若pid=0.则返回调用进程组ID
              返回值:出错返回-1

    int  setpgid(pid_t  pid,pid_t  pgid)
              功能:将pid进程的进程组ID设置为pgid,如果这两个参数相等,则由pid指定的进程变成进程组组长。如果pid是0,则使用调用进程的进程ID。另外,如果pgid是0,则由pid指定的进程ID用作进程组ID。
             一个进程只能为它自己和子进程设置组ID。
             返回值:成功返回0,错误返回-1.





    例程:
    int main()
    {
    pid_t pid;
    int  status;
    int pids[3];
    int i = 0;

    for(i = 0; i < 3; i ++)
    {
    pid = fork();
    if (pid > 0) //father process
    {
    pids[i] = pid;
    printf("new child [%d]\n", pid);
    }
    else if (pid == 0) //child process
    {
    puts("I`m child, I`m going to die");
    if(i == 1)
    sleep(3);
    sleep(1);
    exit(20);
    }
    else
    error(EXIT_FAILURE, errno, "fail to fork --->%s:%s:%d\n",
    __FILE__, __func__, __LINE__);
    }

    for(i = 0; i < 3; i ++)
    printf("%d\n", pids[i]);
    puts("I`m father, waiting for child died ... ...");
    waitpid(pids[1], &status, 0);
    printf("child %d is dead with [%d]\n", pids[1], WEXITSTATUS(status));
    exit(EXIT_SUCCESS);
    }








































































































         

    展开全文
  • #include头文件的理解

    2019-01-02 15:07:46
    该头文件由 POSIX.1 标准(单一UNIX规范的基础)提出,故所有遵循该标准的操作系统和编译器均应提供该头文件(如 Unix 的所有官方版本,包括 Mac OS X、Linux 等)。 对于类 Unix 系统,unistd.h 中所定义的接口...

    1.百度百科定义

      unistd.h 是 C 和 C++ 程序设计语言中提供对 POSIX 操作系统 API 的访问功能的头文件的名称。该头文件由 POSIX.1 标准(单一UNIX规范的基础)提出,故所有遵循该标准的操作系统和编译器均应提供该头文件(如 Unix 的所有官方版本,包括 Mac OS XLinux 等)。

    对于类 Unix 系统,unistd.h 中所定义的接口通常都是大量针对系统调用的封装(英语:wrapper functions),如 fork、pipe 以及各种 I/O 原语(read、write、close 等等)。
     
    我的定义:
    这是一个头文件,封装了类UNIX系统下的很多固定名称的system_call系统调用。所以,这个函数是依赖于编译器,依赖于操作系统的。
    

      

    2.源码

      可以从源码中,查看它封装了哪些固定名称的操作系统api。

    #ifndef _UNISTD_H
    #define _UNISTD_H
    #include <features.h>
    #ifdef __cplusplus
    extern "C" {
    #endif
    #include <_ansi.h>
    #include <sys/types.h>
    #include <sys/_types.h>
    #define __need_size_t
    #define __need_ptrdiff_t
    #include <stddef.h>
    extern char **environ;
    void _EXFUN(_exit, (int __status ) _ATTRIBUTE ((noreturn)));
    int _EXFUN(access,(const char *__path, int __amode ));
    unsigned _EXFUN(alarm, (unsigned __secs ));
    int _EXFUN(chdir, (const char *__path ));
    int _EXFUN(chmod, (const char *__path, mode_t __mode ));
    int _EXFUN(chown, (const char *__path, uid_t __owner, gid_t __group ));
    int _EXFUN(chroot, (const char *__path ));
    int _EXFUN(close, (int __fildes ));
    char _EXFUN(*ctermid, (char *__s ));
    char _EXFUN(*cuserid, (char *__s ));
    int _EXFUN(dup, (int __fildes ));
    int _EXFUN(dup2, (int __fildes, int __fildes2 ));
    int _EXFUN(execl, (const char *__path, const char *, ... ));
    int _EXFUN(execle, (const char *__path, const char *, ... ));
    int _EXFUN(execlp, (const char *__file, const char *, ... ));
    int _EXFUN(execv, (const char *__path, char * const __argv[] ));
    int _EXFUN(execve, (const char *__path, char * const __argv[], char * const __envp[] ));
    int _EXFUN(execvp, (const char *__file, char * const __argv[] ));
    int _EXFUN(fchdir, (int __fildes));
    int _EXFUN(fchmod, (int __fildes, mode_t __mode ));
    int _EXFUN(fchown, (int __fildes, uid_t __owner, gid_t __group ));
    pid_t _EXFUN(fork, (void ));
    long _EXFUN(fpathconf, (int __fd, int __name ));
    int _EXFUN(fsync, (int __fd));
    int _EXFUN(ftruncate, (int __fd, off_t __length));
    char _EXFUN(*getcwd, (char *__buf, size_t __size ));
    int _EXFUN(getdomainname ,(char *__name, size_t __len));
    gid_t _EXFUN(getegid, (void ));
    uid_t _EXFUN(geteuid, (void ));
    gid_t _EXFUN(getgid, (void ));
    int _EXFUN(getgroups, (int __gidsetsize, gid_t __grouplist[] ));
    int _EXFUN(__gethostname, (char *__name, size_t __len));
    char _EXFUN(*getlogin, (void ));
    #if defined(_POSIX_THREAD_SAFE_FUNCTIONS)
    int _EXFUN(getlogin_r, (char *name, size_t namesize) );
    #endif
    char _EXFUN(*getpass, (__const char *__prompt));
    int _EXFUN(getpagesize, (void));
    pid_t _EXFUN(getpgid, (pid_t));
    pid_t _EXFUN(getpgrp, (void ));
    pid_t _EXFUN(getpid, (void ));
    pid_t _EXFUN(getppid, (void ));
    uid_t _EXFUN(getuid, (void ));
    char * _EXFUN(getusershell, (void));
    char _EXFUN(*getwd, (char *__buf ));
    int _EXFUN(isatty, (int __fildes ));
    int _EXFUN(lchown, (const char *__path, uid_t __owner, gid_t __group ));
    int _EXFUN(link, (const char *__path1, const char *__path2 ));
    int _EXFUN(nice, (int __nice_value ));
    off_t _EXFUN(lseek, (int __fildes, off_t __offset, int __whence ));
    long _EXFUN(pathconf, (const char *__path, int __name ));
    int _EXFUN(pause, (void ));
    int _EXFUN(pipe, (int __fildes[2] ));
    ssize_t _EXFUN(pread, (int __fd, void *__buf, size_t __nbytes, off_t __offset));
    ssize_t _EXFUN(pwrite, (int __fd, const void *__buf, size_t __nbytes, off_t __offset));
    _READ_WRITE_RETURN_TYPE _EXFUN(read, (int __fd, void *__buf, size_t __nbyte ));
    int _EXFUN(readlink, (const char *path, char *buf, size_t bufsiz));
    int _EXFUN(rmdir, (const char *__path ));
    void * _EXFUN(sbrk, (ptrdiff_t __incr));
    int _EXFUN(setegid, (gid_t __gid ));
    int _EXFUN(seteuid, (uid_t __uid ));
    int _EXFUN(setgid, (gid_t __gid ));
    int _EXFUN(setpgid, (pid_t __pid, pid_t __pgid ));
    int _EXFUN(setpgrp, (void ));
    pid_t _EXFUN(setsid, (void ));
    int _EXFUN(setuid, (uid_t __uid ));
    unsigned _EXFUN(sleep, (unsigned int __seconds ));
    void _EXFUN(swab, (const void *, void *, ssize_t));
    int _EXFUN(symlink, (const char *oldpath, const char *newpath));
    long _EXFUN(sysconf, (int __name ));
    pid_t _EXFUN(tcgetpgrp, (int __fildes ));
    int _EXFUN(tcsetpgrp, (int __fildes, pid_t __pgrp_id ));
    int _EXFUN(truncate, (const char *, off_t __length));
    char * _EXFUN(ttyname, (int __fildes ));
    int _EXFUN(ttyname_r, (int __fildes, char *__buf, size_t __len));
    int _EXFUN(unlink, (const char *__path ));
    int _EXFUN(usleep, (__useconds_t __useconds));
    int _EXFUN(vhangup, (void ));
    _READ_WRITE_RETURN_TYPE _EXFUN(write, (int __fd, const void *__buf, size_t __nbyte ));
    extern char *optarg; /** getopt(3) external variables */
    extern int optind, opterr, optopt;
    int getopt(int, char * const [], const char *);
    extern int optreset; /** getopt(3) external variable */
    #ifndef _POSIX_SOURCE
    pid_t _EXFUN(vfork, (void ));
    extern char *suboptarg; /** getsubopt(3) external variable */
    int getsubopt(char **, char * const *, char **);
    #endif /** _POSIX_SOURCE */
    /** Provide prototypes for most of the _<systemcall> names that are
    provided in newlib for some compilers. */
    int _EXFUN(_close, (int __fildes ));
    pid_t _EXFUN(_fork, (void ));
    pid_t _EXFUN(_getpid, (void ));
    int _EXFUN(_link, (const char *__path1, const char *__path2 ));
    off_t _EXFUN(_lseek, (int __fildes, off_t __offset, int __whence ));
    _READ_WRITE_RETURN_TYPE _EXFUN(_read, (int __fd, void *__buf, size_t __nbyte ));
    void * _EXFUN(_sbrk, (size_t __incr));
    int _EXFUN(_unlink, (const char *__path ));
    _READ_WRITE_RETURN_TYPE _EXFUN(_write, (int __fd, const void *__buf, size_t __nbyte ));
    int _EXFUN(_execve, (const char *__path, char * const __argv[], char * const __envp[] ));
    #define F_OK 0
    #define R_OK 4
    #define W_OK 2
    #define X_OK 1
    # define SEEK_SET 0
    # define SEEK_CUR 1
    # define SEEK_END 2
    #include <sys/features.h>
    #define STDIN_FILENO 0 /** standard input file descriptor */
    #define STDOUT_FILENO 1 /** standard output file descriptor */
    #define STDERR_FILENO 2 /** standard error file descriptor */
    #include <bits/environments.h>
    #include <bits/confname.h>
    # define MAXPATHLEN 1024
    #ifdef __cplusplus
    }
    #endif
    #endif /** _SYS_UNISTD_H */
    

      

     

    展开全文
  • unistd.h

    2019-01-22 21:06:06
    该头文件由 POSIX.1 标准(单一UNIX规范的基础)提出,故所有遵循该标准的操作系统和编译器均应提供该头文件(如 Unix 的所有官方版本,包括 Mac OS X、Linux 等)。 对于类 Unix 系统,unistd.h 中所定义的接口...

    unistd.h 是 C 和 C++ 程序设计语言中提供对 POSIX 操作系统 API 的访问功能的头文件的名称。该头文件由 POSIX.1 标准(单一UNIX规范的基础)提出,故所有遵循该标准的操作系统和编译器均应提供该头文件(如 Unix 的所有官方版本,包括 Mac OS XLinux 等)。

    对于类 Unix 系统,unistd.h 中所定义的接口通常都是大量针对系统调用的封装(英语:wrapper functions),如 fork、pipe 以及各种 I/O 原语(read、write、close 等等)。

    类似于 Cygwin 和 MinGW 的 Unix 兼容层也提供相应版本的 unistd.h。

    unistd.h在linux内核中的源码:

    /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
    /*
     * IA-64 Linux syscall numbers and inline-functions.
     *
     * Copyright (C) 1998-2005 Hewlett-Packard Co
     *	David Mosberger-Tang <davidm@hpl.hp.com>
     */
    #ifndef _UAPI_ASM_IA64_UNISTD_H
    #define _UAPI_ASM_IA64_UNISTD_H
    
    
    #include <asm/break.h>
    
    #define __BREAK_SYSCALL			__IA64_BREAK_SYSCALL
    
    #define __NR_ni_syscall			1024
    #define __NR_exit			1025
    #define __NR_read			1026
    #define __NR_write			1027
    #define __NR_open			1028
    #define __NR_close			1029
    #define __NR_creat			1030
    #define __NR_link			1031
    #define __NR_unlink			1032
    #define __NR_execve			1033
    #define __NR_chdir			1034
    #define __NR_fchdir			1035
    #define __NR_utimes			1036
    #define __NR_mknod			1037
    #define __NR_chmod			1038
    #define __NR_chown			1039
    #define __NR_lseek			1040
    #define __NR_getpid			1041
    #define __NR_getppid			1042
    #define __NR_mount			1043
    #define __NR_umount			1044
    #define __NR_setuid			1045
    #define __NR_getuid			1046
    #define __NR_geteuid			1047
    #define __NR_ptrace			1048
    #define __NR_access			1049
    #define __NR_sync			1050
    #define __NR_fsync			1051
    #define __NR_fdatasync			1052
    #define __NR_kill			1053
    #define __NR_rename			1054
    #define __NR_mkdir			1055
    #define __NR_rmdir			1056
    #define __NR_dup			1057
    #define __NR_pipe			1058
    #define __NR_times			1059
    #define __NR_brk			1060
    #define __NR_setgid			1061
    #define __NR_getgid			1062
    #define __NR_getegid			1063
    #define __NR_acct			1064
    #define __NR_ioctl			1065
    #define __NR_fcntl			1066
    #define __NR_umask			1067
    #define __NR_chroot			1068
    #define __NR_ustat			1069
    #define __NR_dup2			1070
    #define __NR_setreuid			1071
    #define __NR_setregid			1072
    #define __NR_getresuid			1073
    #define __NR_setresuid			1074
    #define __NR_getresgid			1075
    #define __NR_setresgid			1076
    #define __NR_getgroups			1077
    #define __NR_setgroups			1078
    #define __NR_getpgid			1079
    #define __NR_setpgid			1080
    #define __NR_setsid			1081
    #define __NR_getsid			1082
    #define __NR_sethostname		1083
    #define __NR_setrlimit			1084
    #define __NR_getrlimit			1085
    #define __NR_getrusage			1086
    #define __NR_gettimeofday		1087
    #define __NR_settimeofday		1088
    #define __NR_select			1089
    #define __NR_poll			1090
    #define __NR_symlink			1091
    #define __NR_readlink			1092
    #define __NR_uselib			1093
    #define __NR_swapon			1094
    #define __NR_swapoff			1095
    #define __NR_reboot			1096
    #define __NR_truncate			1097
    #define __NR_ftruncate			1098
    #define __NR_fchmod			1099
    #define __NR_fchown			1100
    #define __NR_getpriority		1101
    #define __NR_setpriority		1102
    #define __NR_statfs			1103
    #define __NR_fstatfs			1104
    #define __NR_gettid			1105
    #define __NR_semget			1106
    #define __NR_semop			1107
    #define __NR_semctl			1108
    #define __NR_msgget			1109
    #define __NR_msgsnd			1110
    #define __NR_msgrcv			1111
    #define __NR_msgctl			1112
    #define __NR_shmget			1113
    #define __NR_shmat			1114
    #define __NR_shmdt			1115
    #define __NR_shmctl			1116
    /* also known as klogctl() in GNU libc: */
    #define __NR_syslog			1117
    #define __NR_setitimer			1118
    #define __NR_getitimer			1119
    /* 1120 was __NR_old_stat */
    /* 1121 was __NR_old_lstat */
    /* 1122 was __NR_old_fstat */
    #define __NR_vhangup			1123
    #define __NR_lchown			1124
    #define __NR_remap_file_pages		1125
    #define __NR_wait4			1126
    #define __NR_sysinfo			1127
    #define __NR_clone			1128
    #define __NR_setdomainname		1129
    #define __NR_uname			1130
    #define __NR_adjtimex			1131
    /* 1132 was __NR_create_module */
    #define __NR_init_module		1133
    #define __NR_delete_module		1134
    /* 1135 was __NR_get_kernel_syms */
    /* 1136 was __NR_query_module */
    #define __NR_quotactl			1137
    #define __NR_bdflush			1138
    #define __NR_sysfs			1139
    #define __NR_personality		1140
    #define __NR_afs_syscall		1141
    #define __NR_setfsuid			1142
    #define __NR_setfsgid			1143
    #define __NR_getdents			1144
    #define __NR_flock			1145
    #define __NR_readv			1146
    #define __NR_writev			1147
    #define __NR_pread64			1148
    #define __NR_pwrite64			1149
    #define __NR__sysctl			1150
    #define __NR_mmap			1151
    #define __NR_munmap			1152
    #define __NR_mlock			1153
    #define __NR_mlockall			1154
    #define __NR_mprotect			1155
    #define __NR_mremap			1156
    #define __NR_msync			1157
    #define __NR_munlock			1158
    #define __NR_munlockall			1159
    #define __NR_sched_getparam		1160
    #define __NR_sched_setparam		1161
    #define __NR_sched_getscheduler		1162
    #define __NR_sched_setscheduler		1163
    #define __NR_sched_yield		1164
    #define __NR_sched_get_priority_max	1165
    #define __NR_sched_get_priority_min	1166
    #define __NR_sched_rr_get_interval	1167
    #define __NR_nanosleep			1168
    #define __NR_nfsservctl			1169
    #define __NR_prctl			1170
    /* 1171 is reserved for backwards compatibility with old __NR_getpagesize */
    #define __NR_mmap2			1172
    #define __NR_pciconfig_read		1173
    #define __NR_pciconfig_write		1174
    #define __NR_perfmonctl			1175
    #define __NR_sigaltstack		1176
    #define __NR_rt_sigaction		1177
    #define __NR_rt_sigpending		1178
    #define __NR_rt_sigprocmask		1179
    #define __NR_rt_sigqueueinfo		1180
    #define __NR_rt_sigreturn		1181
    #define __NR_rt_sigsuspend		1182
    #define __NR_rt_sigtimedwait		1183
    #define __NR_getcwd			1184
    #define __NR_capget			1185
    #define __NR_capset			1186
    #define __NR_sendfile			1187
    #define __NR_getpmsg			1188
    #define __NR_putpmsg			1189
    #define __NR_socket			1190
    #define __NR_bind			1191
    #define __NR_connect			1192
    #define __NR_listen			1193
    #define __NR_accept			1194
    #define __NR_getsockname		1195
    #define __NR_getpeername		1196
    #define __NR_socketpair			1197
    #define __NR_send			1198
    #define __NR_sendto			1199
    #define __NR_recv			1200
    #define __NR_recvfrom			1201
    #define __NR_shutdown			1202
    #define __NR_setsockopt			1203
    #define __NR_getsockopt			1204
    #define __NR_sendmsg			1205
    #define __NR_recvmsg			1206
    #define __NR_pivot_root			1207
    #define __NR_mincore			1208
    #define __NR_madvise			1209
    #define __NR_stat			1210
    #define __NR_lstat			1211
    #define __NR_fstat			1212
    #define __NR_clone2			1213
    #define __NR_getdents64			1214
    #define __NR_getunwind			1215
    #define __NR_readahead			1216
    #define __NR_setxattr			1217
    #define __NR_lsetxattr			1218
    #define __NR_fsetxattr			1219
    #define __NR_getxattr			1220
    #define __NR_lgetxattr			1221
    #define __NR_fgetxattr			1222
    #define __NR_listxattr			1223
    #define __NR_llistxattr			1224
    #define __NR_flistxattr			1225
    #define __NR_removexattr		1226
    #define __NR_lremovexattr		1227
    #define __NR_fremovexattr		1228
    #define __NR_tkill			1229
    #define __NR_futex			1230
    #define __NR_sched_setaffinity		1231
    #define __NR_sched_getaffinity		1232
    #define __NR_set_tid_address		1233
    #define __NR_fadvise64			1234
    #define __NR_tgkill			1235
    #define __NR_exit_group			1236
    #define __NR_lookup_dcookie		1237
    #define __NR_io_setup			1238
    #define __NR_io_destroy			1239
    #define __NR_io_getevents		1240
    #define __NR_io_submit			1241
    #define __NR_io_cancel			1242
    #define __NR_epoll_create		1243
    #define __NR_epoll_ctl			1244
    #define __NR_epoll_wait			1245
    #define __NR_restart_syscall		1246
    #define __NR_semtimedop			1247
    #define __NR_timer_create		1248
    #define __NR_timer_settime		1249
    #define __NR_timer_gettime		1250
    #define __NR_timer_getoverrun		1251
    #define __NR_timer_delete		1252
    #define __NR_clock_settime		1253
    #define __NR_clock_gettime		1254
    #define __NR_clock_getres		1255
    #define __NR_clock_nanosleep		1256
    #define __NR_fstatfs64			1257
    #define __NR_statfs64			1258
    #define __NR_mbind			1259
    #define __NR_get_mempolicy		1260
    #define __NR_set_mempolicy		1261
    #define __NR_mq_open			1262
    #define __NR_mq_unlink			1263
    #define __NR_mq_timedsend		1264
    #define __NR_mq_timedreceive		1265
    #define __NR_mq_notify			1266
    #define __NR_mq_getsetattr		1267
    #define __NR_kexec_load			1268
    #define __NR_vserver			1269
    #define __NR_waitid			1270
    #define __NR_add_key			1271
    #define __NR_request_key		1272
    #define __NR_keyctl			1273
    #define __NR_ioprio_set			1274
    #define __NR_ioprio_get			1275
    #define __NR_move_pages			1276
    #define __NR_inotify_init		1277
    #define __NR_inotify_add_watch		1278
    #define __NR_inotify_rm_watch		1279
    #define __NR_migrate_pages		1280
    #define __NR_openat			1281
    #define __NR_mkdirat			1282
    #define __NR_mknodat			1283
    #define __NR_fchownat			1284
    #define __NR_futimesat			1285
    #define __NR_newfstatat			1286
    #define __NR_unlinkat			1287
    #define __NR_renameat			1288
    #define __NR_linkat			1289
    #define __NR_symlinkat			1290
    #define __NR_readlinkat			1291
    #define __NR_fchmodat			1292
    #define __NR_faccessat			1293
    #define __NR_pselect6			1294
    #define __NR_ppoll			1295
    #define __NR_unshare			1296
    #define __NR_splice			1297
    #define __NR_set_robust_list		1298
    #define __NR_get_robust_list		1299
    #define __NR_sync_file_range		1300
    #define __NR_tee			1301
    #define __NR_vmsplice			1302
    #define __NR_fallocate			1303
    #define __NR_getcpu			1304
    #define __NR_epoll_pwait		1305
    #define __NR_utimensat			1306
    #define __NR_signalfd			1307
    #define __NR_timerfd			1308
    #define __NR_eventfd			1309
    #define __NR_timerfd_create		1310
    #define __NR_timerfd_settime		1311
    #define __NR_timerfd_gettime		1312
    #define __NR_signalfd4			1313
    #define __NR_eventfd2			1314
    #define __NR_epoll_create1		1315
    #define __NR_dup3			1316
    #define __NR_pipe2			1317
    #define __NR_inotify_init1		1318
    #define __NR_preadv			1319
    #define __NR_pwritev			1320
    #define __NR_rt_tgsigqueueinfo		1321
    #define __NR_recvmmsg			1322
    #define __NR_fanotify_init		1323
    #define __NR_fanotify_mark		1324
    #define __NR_prlimit64			1325
    #define __NR_name_to_handle_at		1326
    #define __NR_open_by_handle_at  	1327
    #define __NR_clock_adjtime		1328
    #define __NR_syncfs			1329
    #define __NR_setns			1330
    #define __NR_sendmmsg			1331
    #define __NR_process_vm_readv		1332
    #define __NR_process_vm_writev		1333
    #define __NR_accept4			1334
    #define __NR_finit_module		1335
    #define __NR_sched_setattr		1336
    #define __NR_sched_getattr		1337
    #define __NR_renameat2			1338
    #define __NR_getrandom			1339
    #define __NR_memfd_create		1340
    #define __NR_bpf			1341
    #define __NR_execveat			1342
    #define __NR_userfaultfd		1343
    #define __NR_membarrier			1344
    #define __NR_kcmp			1345
    #define __NR_mlock2			1346
    #define __NR_copy_file_range		1347
    #define __NR_preadv2			1348
    #define __NR_pwritev2			1349
    
    #endif /* _UAPI_ASM_IA64_UNISTD_H */
    

    unistd.h在glibc中的源码:

    /* Copyright (C) 1991-2018 Free Software Foundation, Inc.
       This file is part of the GNU C Library.
    
       The GNU C Library is free software; you can redistribute it and/or
       modify it under the terms of the GNU Lesser General Public
       License as published by the Free Software Foundation; either
       version 2.1 of the License, or (at your option) any later version.
    
       The GNU C Library is distributed in the hope that it will be useful,
       but WITHOUT ANY WARRANTY; without even the implied warranty of
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
       Lesser General Public License for more details.
    
       You should have received a copy of the GNU Lesser General Public
       License along with the GNU C Library; if not, see
       <http://www.gnu.org/licenses/>.  */
    
    /*
     *	POSIX Standard: 2.10 Symbolic Constants		<unistd.h>
     */
    
    #ifndef	_UNISTD_H
    #define	_UNISTD_H	1
    
    #include <features.h>
    
    __BEGIN_DECLS
    
    /* These may be used to determine what facilities are present at compile time.
       Their values can be obtained at run time from `sysconf'.  */
    
    #ifdef __USE_XOPEN2K8
    /* POSIX Standard approved as ISO/IEC 9945-1 as of September 2008.  */
    # define _POSIX_VERSION	200809L
    #elif defined __USE_XOPEN2K
    /* POSIX Standard approved as ISO/IEC 9945-1 as of December 2001.  */
    # define _POSIX_VERSION	200112L
    #elif defined __USE_POSIX199506
    /* POSIX Standard approved as ISO/IEC 9945-1 as of June 1995.  */
    # define _POSIX_VERSION	199506L
    #elif defined __USE_POSIX199309
    /* POSIX Standard approved as ISO/IEC 9945-1 as of September 1993.  */
    # define _POSIX_VERSION	199309L
    #else
    /* POSIX Standard approved as ISO/IEC 9945-1 as of September 1990.  */
    # define _POSIX_VERSION	199009L
    #endif
    
    /* These are not #ifdef __USE_POSIX2 because they are
       in the theoretically application-owned namespace.  */
    
    #ifdef __USE_XOPEN2K8
    # define __POSIX2_THIS_VERSION	200809L
    /* The utilities on GNU systems also correspond to this version.  */
    #elif defined __USE_XOPEN2K
    /* The utilities on GNU systems also correspond to this version.  */
    # define __POSIX2_THIS_VERSION	200112L
    #elif defined __USE_POSIX199506
    /* The utilities on GNU systems also correspond to this version.  */
    # define __POSIX2_THIS_VERSION	199506L
    #else
    /* The utilities on GNU systems also correspond to this version.  */
    # define __POSIX2_THIS_VERSION	199209L
    #endif
    
    /* The utilities on GNU systems also correspond to this version.  */
    #define _POSIX2_VERSION	__POSIX2_THIS_VERSION
    
    /* This symbol was required until the 2001 edition of POSIX.  */
    #define	_POSIX2_C_VERSION	__POSIX2_THIS_VERSION
    
    /* If defined, the implementation supports the
       C Language Bindings Option.  */
    #define	_POSIX2_C_BIND	__POSIX2_THIS_VERSION
    
    /* If defined, the implementation supports the
       C Language Development Utilities Option.  */
    #define	_POSIX2_C_DEV	__POSIX2_THIS_VERSION
    
    /* If defined, the implementation supports the
       Software Development Utilities Option.  */
    #define	_POSIX2_SW_DEV	__POSIX2_THIS_VERSION
    
    /* If defined, the implementation supports the
       creation of locales with the localedef utility.  */
    #define _POSIX2_LOCALEDEF       __POSIX2_THIS_VERSION
    
    /* X/Open version number to which the library conforms.  It is selectable.  */
    #ifdef __USE_XOPEN2K8
    # define _XOPEN_VERSION	700
    #elif defined __USE_XOPEN2K
    # define _XOPEN_VERSION	600
    #elif defined __USE_UNIX98
    # define _XOPEN_VERSION	500
    #else
    # define _XOPEN_VERSION	4
    #endif
    
    /* Commands and utilities from XPG4 are available.  */
    #define _XOPEN_XCU_VERSION	4
    
    /* We are compatible with the old published standards as well.  */
    #define _XOPEN_XPG2	1
    #define _XOPEN_XPG3	1
    #define _XOPEN_XPG4	1
    
    /* The X/Open Unix extensions are available.  */
    #define _XOPEN_UNIX	1
    
    /* The enhanced internationalization capabilities according to XPG4.2
       are present.  */
    #define	_XOPEN_ENH_I18N	1
    
    /* The legacy interfaces are also available.  */
    #define _XOPEN_LEGACY	1
    
    
    /* Get values of POSIX options:
    
       If these symbols are defined, the corresponding features are
       always available.  If not, they may be available sometimes.
       The current values can be obtained with `sysconf'.
    
       _POSIX_JOB_CONTROL		Job control is supported.
       _POSIX_SAVED_IDS		Processes have a saved set-user-ID
    				and a saved set-group-ID.
       _POSIX_REALTIME_SIGNALS	Real-time, queued signals are supported.
       _POSIX_PRIORITY_SCHEDULING	Priority scheduling is supported.
       _POSIX_TIMERS		POSIX.4 clocks and timers are supported.
       _POSIX_ASYNCHRONOUS_IO	Asynchronous I/O is supported.
       _POSIX_PRIORITIZED_IO	Prioritized asynchronous I/O is supported.
       _POSIX_SYNCHRONIZED_IO	Synchronizing file data is supported.
       _POSIX_FSYNC			The fsync function is present.
       _POSIX_MAPPED_FILES		Mapping of files to memory is supported.
       _POSIX_MEMLOCK		Locking of all memory is supported.
       _POSIX_MEMLOCK_RANGE		Locking of ranges of memory is supported.
       _POSIX_MEMORY_PROTECTION	Setting of memory protections is supported.
       _POSIX_MESSAGE_PASSING	POSIX.4 message queues are supported.
       _POSIX_SEMAPHORES		POSIX.4 counting semaphores are supported.
       _POSIX_SHARED_MEMORY_OBJECTS	POSIX.4 shared memory objects are supported.
       _POSIX_THREADS		POSIX.1c pthreads are supported.
       _POSIX_THREAD_ATTR_STACKADDR	Thread stack address attribute option supported.
       _POSIX_THREAD_ATTR_STACKSIZE	Thread stack size attribute option supported.
       _POSIX_THREAD_SAFE_FUNCTIONS	Thread-safe functions are supported.
       _POSIX_THREAD_PRIORITY_SCHEDULING
    				POSIX.1c thread execution scheduling supported.
       _POSIX_THREAD_PRIO_INHERIT	Thread priority inheritance option supported.
       _POSIX_THREAD_PRIO_PROTECT	Thread priority protection option supported.
       _POSIX_THREAD_PROCESS_SHARED	Process-shared synchronization supported.
       _POSIX_PII			Protocol-independent interfaces are supported.
       _POSIX_PII_XTI		XTI protocol-indep. interfaces are supported.
       _POSIX_PII_SOCKET		Socket protocol-indep. interfaces are supported.
       _POSIX_PII_INTERNET		Internet family of protocols supported.
       _POSIX_PII_INTERNET_STREAM	Connection-mode Internet protocol supported.
       _POSIX_PII_INTERNET_DGRAM	Connectionless Internet protocol supported.
       _POSIX_PII_OSI		ISO/OSI family of protocols supported.
       _POSIX_PII_OSI_COTS		Connection-mode ISO/OSI service supported.
       _POSIX_PII_OSI_CLTS		Connectionless ISO/OSI service supported.
       _POSIX_POLL			Implementation supports `poll' function.
       _POSIX_SELECT		Implementation supports `select' and `pselect'.
    
       _XOPEN_REALTIME		X/Open realtime support is available.
       _XOPEN_REALTIME_THREADS	X/Open realtime thread support is available.
       _XOPEN_SHM			Shared memory interface according to XPG4.2.
    
       _XBS5_ILP32_OFF32		Implementation provides environment with 32-bit
    				int, long, pointer, and off_t types.
       _XBS5_ILP32_OFFBIG		Implementation provides environment with 32-bit
    				int, long, and pointer and off_t with at least
    				64 bits.
       _XBS5_LP64_OFF64		Implementation provides environment with 32-bit
    				int, and 64-bit long, pointer, and off_t types.
       _XBS5_LPBIG_OFFBIG		Implementation provides environment with at
    				least 32 bits int and long, pointer, and off_t
    				with at least 64 bits.
    
       If any of these symbols is defined as -1, the corresponding option is not
       true for any file.  If any is defined as other than -1, the corresponding
       option is true for all files.  If a symbol is not defined at all, the value
       for a specific file can be obtained from `pathconf' and `fpathconf'.
    
       _POSIX_CHOWN_RESTRICTED	Only the super user can use `chown' to change
    				the owner of a file.  `chown' can only be used
    				to change the group ID of a file to a group of
    				which the calling process is a member.
       _POSIX_NO_TRUNC		Pathname components longer than
    				NAME_MAX generate an error.
       _POSIX_VDISABLE		If defined, if the value of an element of the
    				`c_cc' member of `struct termios' is
    				_POSIX_VDISABLE, no character will have the
    				effect associated with that element.
       _POSIX_SYNC_IO		Synchronous I/O may be performed.
       _POSIX_ASYNC_IO		Asynchronous I/O may be performed.
       _POSIX_PRIO_IO		Prioritized Asynchronous I/O may be performed.
    
       Support for the Large File Support interface is not generally available.
       If it is available the following constants are defined to one.
       _LFS64_LARGEFILE		Low-level I/O supports large files.
       _LFS64_STDIO			Standard I/O supports large files.
       */
    
    #include <bits/posix_opt.h>
    
    /* Get the environment definitions from Unix98.  */
    #if defined __USE_UNIX98 || defined __USE_XOPEN2K
    # include <bits/environments.h>
    #endif
    
    /* Standard file descriptors.  */
    #define	STDIN_FILENO	0	/* Standard input.  */
    #define	STDOUT_FILENO	1	/* Standard output.  */
    #define	STDERR_FILENO	2	/* Standard error output.  */
    
    
    /* All functions that are not declared anywhere else.  */
    
    #include <bits/types.h>
    
    #ifndef	__ssize_t_defined
    typedef __ssize_t ssize_t;
    # define __ssize_t_defined
    #endif
    
    #define	__need_size_t
    #define __need_NULL
    #include <stddef.h>
    
    #if defined __USE_XOPEN || defined __USE_XOPEN2K
    /* The Single Unix specification says that some more types are
       available here.  */
    # ifndef __gid_t_defined
    typedef __gid_t gid_t;
    #  define __gid_t_defined
    # endif
    
    # ifndef __uid_t_defined
    typedef __uid_t uid_t;
    #  define __uid_t_defined
    # endif
    
    # ifndef __off_t_defined
    #  ifndef __USE_FILE_OFFSET64
    typedef __off_t off_t;
    #  else
    typedef __off64_t off_t;
    #  endif
    #  define __off_t_defined
    # endif
    # if defined __USE_LARGEFILE64 && !defined __off64_t_defined
    typedef __off64_t off64_t;
    #  define __off64_t_defined
    # endif
    
    # ifndef __useconds_t_defined
    typedef __useconds_t useconds_t;
    #  define __useconds_t_defined
    # endif
    
    # ifndef __pid_t_defined
    typedef __pid_t pid_t;
    #  define __pid_t_defined
    # endif
    #endif	/* X/Open */
    
    #if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K
    # ifndef __intptr_t_defined
    typedef __intptr_t intptr_t;
    #  define __intptr_t_defined
    # endif
    #endif
    
    #if defined __USE_MISC || defined __USE_XOPEN
    # ifndef __socklen_t_defined
    typedef __socklen_t socklen_t;
    #  define __socklen_t_defined
    # endif
    #endif
    
    /* Values for the second argument to access.
       These may be OR'd together.  */
    #define	R_OK	4		/* Test for read permission.  */
    #define	W_OK	2		/* Test for write permission.  */
    #define	X_OK	1		/* Test for execute permission.  */
    #define	F_OK	0		/* Test for existence.  */
    
    /* Test for access to NAME using the real UID and real GID.  */
    extern int access (const char *__name, int __type) __THROW __nonnull ((1));
    
    #ifdef __USE_GNU
    /* Test for access to NAME using the effective UID and GID
       (as normal file operations use).  */
    extern int euidaccess (const char *__name, int __type)
         __THROW __nonnull ((1));
    
    /* An alias for `euidaccess', used by some other systems.  */
    extern int eaccess (const char *__name, int __type)
         __THROW __nonnull ((1));
    #endif
    
    #ifdef __USE_ATFILE
    /* Test for access to FILE relative to the directory FD is open on.
       If AT_EACCESS is set in FLAG, then use effective IDs like `eaccess',
       otherwise use real IDs like `access'.  */
    extern int faccessat (int __fd, const char *__file, int __type, int __flag)
         __THROW __nonnull ((2)) __wur;
    #endif /* Use GNU.  */
    
    
    /* Values for the WHENCE argument to lseek.  */
    #ifndef	_STDIO_H		/* <stdio.h> has the same definitions.  */
    # define SEEK_SET	0	/* Seek from beginning of file.  */
    # define SEEK_CUR	1	/* Seek from current position.  */
    # define SEEK_END	2	/* Seek from end of file.  */
    # ifdef __USE_GNU
    #  define SEEK_DATA	3	/* Seek to next data.  */
    #  define SEEK_HOLE	4	/* Seek to next hole.  */
    # endif
    #endif
    
    #if defined __USE_MISC && !defined L_SET
    /* Old BSD names for the same constants; just for compatibility.  */
    # define L_SET		SEEK_SET
    # define L_INCR		SEEK_CUR
    # define L_XTND		SEEK_END
    #endif
    
    
    /* Move FD's file position to OFFSET bytes from the
       beginning of the file (if WHENCE is SEEK_SET),
       the current position (if WHENCE is SEEK_CUR),
       or the end of the file (if WHENCE is SEEK_END).
       Return the new file position.  */
    #ifndef __USE_FILE_OFFSET64
    extern __off_t lseek (int __fd, __off_t __offset, int __whence) __THROW;
    #else
    # ifdef __REDIRECT_NTH
    extern __off64_t __REDIRECT_NTH (lseek,
    				 (int __fd, __off64_t __offset, int __whence),
    				 lseek64);
    # else
    #  define lseek lseek64
    # endif
    #endif
    #ifdef __USE_LARGEFILE64
    extern __off64_t lseek64 (int __fd, __off64_t __offset, int __whence)
         __THROW;
    #endif
    
    /* Close the file descriptor FD.
    
       This function is a cancellation point and therefore not marked with
       __THROW.  */
    extern int close (int __fd);
    
    /* Read NBYTES into BUF from FD.  Return the
       number read, -1 for errors or 0 for EOF.
    
       This function is a cancellation point and therefore not marked with
       __THROW.  */
    extern ssize_t read (int __fd, void *__buf, size_t __nbytes) __wur;
    
    /* Write N bytes of BUF to FD.  Return the number written, or -1.
    
       This function is a cancellation point and therefore not marked with
       __THROW.  */
    extern ssize_t write (int __fd, const void *__buf, size_t __n) __wur;
    
    #if defined __USE_UNIX98 || defined __USE_XOPEN2K8
    # ifndef __USE_FILE_OFFSET64
    /* Read NBYTES into BUF from FD at the given position OFFSET without
       changing the file pointer.  Return the number read, -1 for errors
       or 0 for EOF.
    
       This function is a cancellation point and therefore not marked with
       __THROW.  */
    extern ssize_t pread (int __fd, void *__buf, size_t __nbytes,
    		      __off_t __offset) __wur;
    
    /* Write N bytes of BUF to FD at the given position OFFSET without
       changing the file pointer.  Return the number written, or -1.
    
       This function is a cancellation point and therefore not marked with
       __THROW.  */
    extern ssize_t pwrite (int __fd, const void *__buf, size_t __n,
    		       __off_t __offset) __wur;
    # else
    #  ifdef __REDIRECT
    extern ssize_t __REDIRECT (pread, (int __fd, void *__buf, size_t __nbytes,
    				   __off64_t __offset),
    			   pread64) __wur;
    extern ssize_t __REDIRECT (pwrite, (int __fd, const void *__buf,
    				    size_t __nbytes, __off64_t __offset),
    			   pwrite64) __wur;
    #  else
    #   define pread pread64
    #   define pwrite pwrite64
    #  endif
    # endif
    
    # ifdef __USE_LARGEFILE64
    /* Read NBYTES into BUF from FD at the given position OFFSET without
       changing the file pointer.  Return the number read, -1 for errors
       or 0 for EOF.  */
    extern ssize_t pread64 (int __fd, void *__buf, size_t __nbytes,
    			__off64_t __offset) __wur;
    /* Write N bytes of BUF to FD at the given position OFFSET without
       changing the file pointer.  Return the number written, or -1.  */
    extern ssize_t pwrite64 (int __fd, const void *__buf, size_t __n,
    			 __off64_t __offset) __wur;
    # endif
    #endif
    
    /* Create a one-way communication channel (pipe).
       If successful, two file descriptors are stored in PIPEDES;
       bytes written on PIPEDES[1] can be read from PIPEDES[0].
       Returns 0 if successful, -1 if not.  */
    extern int pipe (int __pipedes[2]) __THROW __wur;
    
    #ifdef __USE_GNU
    /* Same as pipe but apply flags passed in FLAGS to the new file
       descriptors.  */
    extern int pipe2 (int __pipedes[2], int __flags) __THROW __wur;
    #endif
    
    /* Schedule an alarm.  In SECONDS seconds, the process will get a SIGALRM.
       If SECONDS is zero, any currently scheduled alarm will be cancelled.
       The function returns the number of seconds remaining until the last
       alarm scheduled would have signaled, or zero if there wasn't one.
       There is no return value to indicate an error, but you can set `errno'
       to 0 and check its value after calling `alarm', and this might tell you.
       The signal may come late due to processor scheduling.  */
    extern unsigned int alarm (unsigned int __seconds) __THROW;
    
    /* Make the process sleep for SECONDS seconds, or until a signal arrives
       and is not ignored.  The function returns the number of seconds less
       than SECONDS which it actually slept (thus zero if it slept the full time).
       If a signal handler does a `longjmp' or modifies the handling of the
       SIGALRM signal while inside `sleep' call, the handling of the SIGALRM
       signal afterwards is undefined.  There is no return value to indicate
       error, but if `sleep' returns SECONDS, it probably didn't work.
    
       This function is a cancellation point and therefore not marked with
       __THROW.  */
    extern unsigned int sleep (unsigned int __seconds);
    
    #if (defined __USE_XOPEN_EXTENDED && !defined __USE_XOPEN2K8) \
        || defined __USE_MISC
    /* Set an alarm to go off (generating a SIGALRM signal) in VALUE
       microseconds.  If INTERVAL is nonzero, when the alarm goes off, the
       timer is reset to go off every INTERVAL microseconds thereafter.
       Returns the number of microseconds remaining before the alarm.  */
    extern __useconds_t ualarm (__useconds_t __value, __useconds_t __interval)
         __THROW;
    
    /* Sleep USECONDS microseconds, or until a signal arrives that is not blocked
       or ignored.
    
       This function is a cancellation point and therefore not marked with
       __THROW.  */
    extern int usleep (__useconds_t __useconds);
    #endif
    
    
    /* Suspend the process until a signal arrives.
       This always returns -1 and sets `errno' to EINTR.
    
       This function is a cancellation point and therefore not marked with
       __THROW.  */
    extern int pause (void);
    
    
    /* Change the owner and group of FILE.  */
    extern int chown (const char *__file, __uid_t __owner, __gid_t __group)
         __THROW __nonnull ((1)) __wur;
    
    #if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K8
    /* Change the owner and group of the file that FD is open on.  */
    extern int fchown (int __fd, __uid_t __owner, __gid_t __group) __THROW __wur;
    
    
    /* Change owner and group of FILE, if it is a symbolic
       link the ownership of the symbolic link is changed.  */
    extern int lchown (const char *__file, __uid_t __owner, __gid_t __group)
         __THROW __nonnull ((1)) __wur;
    
    #endif /* Use X/Open Unix.  */
    
    #ifdef __USE_ATFILE
    /* Change the owner and group of FILE relative to the directory FD is open
       on.  */
    extern int fchownat (int __fd, const char *__file, __uid_t __owner,
    		     __gid_t __group, int __flag)
         __THROW __nonnull ((2)) __wur;
    #endif /* Use GNU.  */
    
    /* Change the process's working directory to PATH.  */
    extern int chdir (const char *__path) __THROW __nonnull ((1)) __wur;
    
    #if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K8
    /* Change the process's working directory to the one FD is open on.  */
    extern int fchdir (int __fd) __THROW __wur;
    #endif
    
    /* Get the pathname of the current working directory,
       and put it in SIZE bytes of BUF.  Returns NULL if the
       directory couldn't be determined or SIZE was too small.
       If successful, returns BUF.  In GNU, if BUF is NULL,
       an array is allocated with `malloc'; the array is SIZE
       bytes long, unless SIZE == 0, in which case it is as
       big as necessary.  */
    extern char *getcwd (char *__buf, size_t __size) __THROW __wur;
    
    #ifdef	__USE_GNU
    /* Return a malloc'd string containing the current directory name.
       If the environment variable `PWD' is set, and its value is correct,
       that value is used.  */
    extern char *get_current_dir_name (void) __THROW;
    #endif
    
    #if (defined __USE_XOPEN_EXTENDED && !defined __USE_XOPEN2K8) \
        || defined __USE_MISC
    /* Put the absolute pathname of the current working directory in BUF.
       If successful, return BUF.  If not, put an error message in
       BUF and return NULL.  BUF should be at least PATH_MAX bytes long.  */
    extern char *getwd (char *__buf)
         __THROW __nonnull ((1)) __attribute_deprecated__ __wur;
    #endif
    
    
    /* Duplicate FD, returning a new file descriptor on the same file.  */
    extern int dup (int __fd) __THROW __wur;
    
    /* Duplicate FD to FD2, closing FD2 and making it open on the same file.  */
    extern int dup2 (int __fd, int __fd2) __THROW;
    
    #ifdef __USE_GNU
    /* Duplicate FD to FD2, closing FD2 and making it open on the same
       file while setting flags according to FLAGS.  */
    extern int dup3 (int __fd, int __fd2, int __flags) __THROW;
    #endif
    
    /* NULL-terminated array of "NAME=VALUE" environment variables.  */
    extern char **__environ;
    #ifdef __USE_GNU
    extern char **environ;
    #endif
    
    
    /* Replace the current process, executing PATH with arguments ARGV and
       environment ENVP.  ARGV and ENVP are terminated by NULL pointers.  */
    extern int execve (const char *__path, char *const __argv[],
    		   char *const __envp[]) __THROW __nonnull ((1, 2));
    
    #ifdef __USE_XOPEN2K8
    /* Execute the file FD refers to, overlaying the running program image.
       ARGV and ENVP are passed to the new program, as for `execve'.  */
    extern int fexecve (int __fd, char *const __argv[], char *const __envp[])
         __THROW __nonnull ((2));
    #endif
    
    
    /* Execute PATH with arguments ARGV and environment from `environ'.  */
    extern int execv (const char *__path, char *const __argv[])
         __THROW __nonnull ((1, 2));
    
    /* Execute PATH with all arguments after PATH until a NULL pointer,
       and the argument after that for environment.  */
    extern int execle (const char *__path, const char *__arg, ...)
         __THROW __nonnull ((1, 2));
    
    /* Execute PATH with all arguments after PATH until
       a NULL pointer and environment from `environ'.  */
    extern int execl (const char *__path, const char *__arg, ...)
         __THROW __nonnull ((1, 2));
    
    /* Execute FILE, searching in the `PATH' environment variable if it contains
       no slashes, with arguments ARGV and environment from `environ'.  */
    extern int execvp (const char *__file, char *const __argv[])
         __THROW __nonnull ((1, 2));
    
    /* Execute FILE, searching in the `PATH' environment variable if
       it contains no slashes, with all arguments after FILE until a
       NULL pointer and environment from `environ'.  */
    extern int execlp (const char *__file, const char *__arg, ...)
         __THROW __nonnull ((1, 2));
    
    #ifdef __USE_GNU
    /* Execute FILE, searching in the `PATH' environment variable if it contains
       no slashes, with arguments ARGV and environment from `environ'.  */
    extern int execvpe (const char *__file, char *const __argv[],
    		    char *const __envp[])
         __THROW __nonnull ((1, 2));
    #endif
    
    
    #if defined __USE_MISC || defined __USE_XOPEN
    /* Add INC to priority of the current process.  */
    extern int nice (int __inc) __THROW __wur;
    #endif
    
    
    /* Terminate program execution with the low-order 8 bits of STATUS.  */
    extern void _exit (int __status) __attribute__ ((__noreturn__));
    
    
    /* Get the `_PC_*' symbols for the NAME argument to `pathconf' and `fpathconf';
       the `_SC_*' symbols for the NAME argument to `sysconf';
       and the `_CS_*' symbols for the NAME argument to `confstr'.  */
    #include <bits/confname.h>
    
    /* Get file-specific configuration information about PATH.  */
    extern long int pathconf (const char *__path, int __name)
         __THROW __nonnull ((1));
    
    /* Get file-specific configuration about descriptor FD.  */
    extern long int fpathconf (int __fd, int __name) __THROW;
    
    /* Get the value of the system variable NAME.  */
    extern long int sysconf (int __name) __THROW;
    
    #ifdef	__USE_POSIX2
    /* Get the value of the string-valued system variable NAME.  */
    extern size_t confstr (int __name, char *__buf, size_t __len) __THROW;
    #endif
    
    
    /* Get the process ID of the calling process.  */
    extern __pid_t getpid (void) __THROW;
    
    /* Get the process ID of the calling process's parent.  */
    extern __pid_t getppid (void) __THROW;
    
    /* Get the process group ID of the calling process.  */
    extern __pid_t getpgrp (void) __THROW;
    
    /* Get the process group ID of process PID.  */
    extern __pid_t __getpgid (__pid_t __pid) __THROW;
    #if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K8
    extern __pid_t getpgid (__pid_t __pid) __THROW;
    #endif
    
    
    /* Set the process group ID of the process matching PID to PGID.
       If PID is zero, the current process's process group ID is set.
       If PGID is zero, the process ID of the process is used.  */
    extern int setpgid (__pid_t __pid, __pid_t __pgid) __THROW;
    
    #if defined __USE_MISC || defined __USE_XOPEN_EXTENDED
    /* Both System V and BSD have `setpgrp' functions, but with different
       calling conventions.  The BSD function is the same as POSIX.1 `setpgid'
       (above).  The System V function takes no arguments and puts the calling
       process in its on group like `setpgid (0, 0)'.
    
       New programs should always use `setpgid' instead.
    
       GNU provides the POSIX.1 function.  */
    
    /* Set the process group ID of the calling process to its own PID.
       This is exactly the same as `setpgid (0, 0)'.  */
    extern int setpgrp (void) __THROW;
    
    #endif	/* Use misc or X/Open.  */
    
    /* Create a new session with the calling process as its leader.
       The process group IDs of the session and the calling process
       are set to the process ID of the calling process, which is returned.  */
    extern __pid_t setsid (void) __THROW;
    
    #if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K8
    /* Return the session ID of the given process.  */
    extern __pid_t getsid (__pid_t __pid) __THROW;
    #endif
    
    /* Get the real user ID of the calling process.  */
    extern __uid_t getuid (void) __THROW;
    
    /* Get the effective user ID of the calling process.  */
    extern __uid_t geteuid (void) __THROW;
    
    /* Get the real group ID of the calling process.  */
    extern __gid_t getgid (void) __THROW;
    
    /* Get the effective group ID of the calling process.  */
    extern __gid_t getegid (void) __THROW;
    
    /* If SIZE is zero, return the number of supplementary groups
       the calling process is in.  Otherwise, fill in the group IDs
       of its supplementary groups in LIST and return the number written.  */
    extern int getgroups (int __size, __gid_t __list[]) __THROW __wur;
    
    #ifdef	__USE_GNU
    /* Return nonzero iff the calling process is in group GID.  */
    extern int group_member (__gid_t __gid) __THROW;
    #endif
    
    /* Set the user ID of the calling process to UID.
       If the calling process is the super-user, set the real
       and effective user IDs, and the saved set-user-ID to UID;
       if not, the effective user ID is set to UID.  */
    extern int setuid (__uid_t __uid) __THROW __wur;
    
    #if defined __USE_MISC || defined __USE_XOPEN_EXTENDED
    /* Set the real user ID of the calling process to RUID,
       and the effective user ID of the calling process to EUID.  */
    extern int setreuid (__uid_t __ruid, __uid_t __euid) __THROW __wur;
    #endif
    
    #ifdef __USE_XOPEN2K
    /* Set the effective user ID of the calling process to UID.  */
    extern int seteuid (__uid_t __uid) __THROW __wur;
    #endif /* Use POSIX.1-2001.  */
    
    /* Set the group ID of the calling process to GID.
       If the calling process is the super-user, set the real
       and effective group IDs, and the saved set-group-ID to GID;
       if not, the effective group ID is set to GID.  */
    extern int setgid (__gid_t __gid) __THROW __wur;
    
    #if defined __USE_MISC || defined __USE_XOPEN_EXTENDED
    /* Set the real group ID of the calling process to RGID,
       and the effective group ID of the calling process to EGID.  */
    extern int setregid (__gid_t __rgid, __gid_t __egid) __THROW __wur;
    #endif
    
    #ifdef __USE_XOPEN2K
    /* Set the effective group ID of the calling process to GID.  */
    extern int setegid (__gid_t __gid) __THROW __wur;
    #endif /* Use POSIX.1-2001.  */
    
    #ifdef __USE_GNU
    /* Fetch the real user ID, effective user ID, and saved-set user ID,
       of the calling process.  */
    extern int getresuid (__uid_t *__ruid, __uid_t *__euid, __uid_t *__suid)
         __THROW;
    
    /* Fetch the real group ID, effective group ID, and saved-set group ID,
       of the calling process.  */
    extern int getresgid (__gid_t *__rgid, __gid_t *__egid, __gid_t *__sgid)
         __THROW;
    
    /* Set the real user ID, effective user ID, and saved-set user ID,
       of the calling process to RUID, EUID, and SUID, respectively.  */
    extern int setresuid (__uid_t __ruid, __uid_t __euid, __uid_t __suid)
         __THROW __wur;
    
    /* Set the real group ID, effective group ID, and saved-set group ID,
       of the calling process to RGID, EGID, and SGID, respectively.  */
    extern int setresgid (__gid_t __rgid, __gid_t __egid, __gid_t __sgid)
         __THROW __wur;
    #endif
    
    
    /* Clone the calling process, creating an exact copy.
       Return -1 for errors, 0 to the new process,
       and the process ID of the new process to the old process.  */
    extern __pid_t fork (void) __THROWNL;
    
    #if (defined __USE_XOPEN_EXTENDED && !defined __USE_XOPEN2K8) \
        || defined __USE_MISC
    /* Clone the calling process, but without copying the whole address space.
       The calling process is suspended until the new process exits or is
       replaced by a call to `execve'.  Return -1 for errors, 0 to the new process,
       and the process ID of the new process to the old process.  */
    extern __pid_t vfork (void) __THROW;
    #endif /* Use misc or XPG < 7. */
    
    
    /* Return the pathname of the terminal FD is open on, or NULL on errors.
       The returned storage is good only until the next call to this function.  */
    extern char *ttyname (int __fd) __THROW;
    
    /* Store at most BUFLEN characters of the pathname of the terminal FD is
       open on in BUF.  Return 0 on success, otherwise an error number.  */
    extern int ttyname_r (int __fd, char *__buf, size_t __buflen)
         __THROW __nonnull ((2)) __wur;
    
    /* Return 1 if FD is a valid descriptor associated
       with a terminal, zero if not.  */
    extern int isatty (int __fd) __THROW;
    
    #ifdef __USE_MISC
    /* Return the index into the active-logins file (utmp) for
       the controlling terminal.  */
    extern int ttyslot (void) __THROW;
    #endif
    
    
    /* Make a link to FROM named TO.  */
    extern int link (const char *__from, const char *__to)
         __THROW __nonnull ((1, 2)) __wur;
    
    #ifdef __USE_ATFILE
    /* Like link but relative paths in TO and FROM are interpreted relative
       to FROMFD and TOFD respectively.  */
    extern int linkat (int __fromfd, const char *__from, int __tofd,
    		   const char *__to, int __flags)
         __THROW __nonnull ((2, 4)) __wur;
    #endif
    
    #if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K
    /* Make a symbolic link to FROM named TO.  */
    extern int symlink (const char *__from, const char *__to)
         __THROW __nonnull ((1, 2)) __wur;
    
    /* Read the contents of the symbolic link PATH into no more than
       LEN bytes of BUF.  The contents are not null-terminated.
       Returns the number of characters read, or -1 for errors.  */
    extern ssize_t readlink (const char *__restrict __path,
    			 char *__restrict __buf, size_t __len)
         __THROW __nonnull ((1, 2)) __wur;
    #endif /* Use POSIX.1-2001.  */
    
    #ifdef __USE_ATFILE
    /* Like symlink but a relative path in TO is interpreted relative to TOFD.  */
    extern int symlinkat (const char *__from, int __tofd,
    		      const char *__to) __THROW __nonnull ((1, 3)) __wur;
    
    /* Like readlink but a relative PATH is interpreted relative to FD.  */
    extern ssize_t readlinkat (int __fd, const char *__restrict __path,
    			   char *__restrict __buf, size_t __len)
         __THROW __nonnull ((2, 3)) __wur;
    #endif
    
    /* Remove the link NAME.  */
    extern int unlink (const char *__name) __THROW __nonnull ((1));
    
    #ifdef __USE_ATFILE
    /* Remove the link NAME relative to FD.  */
    extern int unlinkat (int __fd, const char *__name, int __flag)
         __THROW __nonnull ((2));
    #endif
    
    /* Remove the directory PATH.  */
    extern int rmdir (const char *__path) __THROW __nonnull ((1));
    
    
    /* Return the foreground process group ID of FD.  */
    extern __pid_t tcgetpgrp (int __fd) __THROW;
    
    /* Set the foreground process group ID of FD set PGRP_ID.  */
    extern int tcsetpgrp (int __fd, __pid_t __pgrp_id) __THROW;
    
    
    /* Return the login name of the user.
    
       This function is a possible cancellation point and therefore not
       marked with __THROW.  */
    extern char *getlogin (void);
    #ifdef __USE_POSIX199506
    /* Return at most NAME_LEN characters of the login name of the user in NAME.
       If it cannot be determined or some other error occurred, return the error
       code.  Otherwise return 0.
    
       This function is a possible cancellation point and therefore not
       marked with __THROW.  */
    extern int getlogin_r (char *__name, size_t __name_len) __nonnull ((1));
    #endif
    
    #ifdef	__USE_MISC
    /* Set the login name returned by `getlogin'.  */
    extern int setlogin (const char *__name) __THROW __nonnull ((1));
    #endif
    
    
    #ifdef	__USE_POSIX2
    /* Get definitions and prototypes for functions to process the
       arguments in ARGV (ARGC of them, minus the program name) for
       options given in OPTS.  */
    # include <bits/getopt_posix.h>
    #endif
    
    
    #if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K
    /* Put the name of the current host in no more than LEN bytes of NAME.
       The result is null-terminated if LEN is large enough for the full
       name and the terminator.  */
    extern int gethostname (char *__name, size_t __len) __THROW __nonnull ((1));
    #endif
    
    
    #if defined __USE_MISC
    /* Set the name of the current host to NAME, which is LEN bytes long.
       This call is restricted to the super-user.  */
    extern int sethostname (const char *__name, size_t __len)
         __THROW __nonnull ((1)) __wur;
    
    /* Set the current machine's Internet number to ID.
       This call is restricted to the super-user.  */
    extern int sethostid (long int __id) __THROW __wur;
    
    
    /* Get and set the NIS (aka YP) domain name, if any.
       Called just like `gethostname' and `sethostname'.
       The NIS domain name is usually the empty string when not using NIS.  */
    extern int getdomainname (char *__name, size_t __len)
         __THROW __nonnull ((1)) __wur;
    extern int setdomainname (const char *__name, size_t __len)
         __THROW __nonnull ((1)) __wur;
    
    
    /* Revoke access permissions to all processes currently communicating
       with the control terminal, and then send a SIGHUP signal to the process
       group of the control terminal.  */
    extern int vhangup (void) __THROW;
    
    /* Revoke the access of all descriptors currently open on FILE.  */
    extern int revoke (const char *__file) __THROW __nonnull ((1)) __wur;
    
    
    /* Enable statistical profiling, writing samples of the PC into at most
       SIZE bytes of SAMPLE_BUFFER; every processor clock tick while profiling
       is enabled, the system examines the user PC and increments
       SAMPLE_BUFFER[((PC - OFFSET) / 2) * SCALE / 65536].  If SCALE is zero,
       disable profiling.  Returns zero on success, -1 on error.  */
    extern int profil (unsigned short int *__sample_buffer, size_t __size,
    		   size_t __offset, unsigned int __scale)
         __THROW __nonnull ((1));
    
    
    /* Turn accounting on if NAME is an existing file.  The system will then write
       a record for each process as it terminates, to this file.  If NAME is NULL,
       turn accounting off.  This call is restricted to the super-user.  */
    extern int acct (const char *__name) __THROW;
    
    
    /* Successive calls return the shells listed in `/etc/shells'.  */
    extern char *getusershell (void) __THROW;
    extern void endusershell (void) __THROW; /* Discard cached info.  */
    extern void setusershell (void) __THROW; /* Rewind and re-read the file.  */
    
    
    /* Put the program in the background, and dissociate from the controlling
       terminal.  If NOCHDIR is zero, do `chdir ("/")'.  If NOCLOSE is zero,
       redirects stdin, stdout, and stderr to /dev/null.  */
    extern int daemon (int __nochdir, int __noclose) __THROW __wur;
    #endif /* Use misc.  */
    
    
    #if defined __USE_MISC || (defined __USE_XOPEN && !defined __USE_XOPEN2K)
    /* Make PATH be the root directory (the starting point for absolute paths).
       This call is restricted to the super-user.  */
    extern int chroot (const char *__path) __THROW __nonnull ((1)) __wur;
    
    /* Prompt with PROMPT and read a string from the terminal without echoing.
       Uses /dev/tty if possible; otherwise stderr and stdin.  */
    extern char *getpass (const char *__prompt) __nonnull ((1));
    #endif /* Use misc || X/Open.  */
    
    
    /* Make all changes done to FD actually appear on disk.
    
       This function is a cancellation point and therefore not marked with
       __THROW.  */
    extern int fsync (int __fd);
    
    
    #ifdef __USE_GNU
    /* Make all changes done to all files on the file system associated
       with FD actually appear on disk.  */
    extern int syncfs (int __fd) __THROW;
    #endif
    
    
    #if defined __USE_MISC || defined __USE_XOPEN_EXTENDED
    
    /* Return identifier for the current host.  */
    extern long int gethostid (void);
    
    /* Make all changes done to all files actually appear on disk.  */
    extern void sync (void) __THROW;
    
    
    # if defined __USE_MISC || !defined __USE_XOPEN2K
    /* Return the number of bytes in a page.  This is the system's page size,
       which is not necessarily the same as the hardware page size.  */
    extern int getpagesize (void)  __THROW __attribute__ ((__const__));
    
    
    /* Return the maximum number of file descriptors
       the current process could possibly have.  */
    extern int getdtablesize (void) __THROW;
    # endif
    
    #endif /* Use misc || X/Open Unix.  */
    
    
    #if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K8
    
    /* Truncate FILE to LENGTH bytes.  */
    # ifndef __USE_FILE_OFFSET64
    extern int truncate (const char *__file, __off_t __length)
         __THROW __nonnull ((1)) __wur;
    # else
    #  ifdef __REDIRECT_NTH
    extern int __REDIRECT_NTH (truncate,
    			   (const char *__file, __off64_t __length),
    			   truncate64) __nonnull ((1)) __wur;
    #  else
    #   define truncate truncate64
    #  endif
    # endif
    # ifdef __USE_LARGEFILE64
    extern int truncate64 (const char *__file, __off64_t __length)
         __THROW __nonnull ((1)) __wur;
    # endif
    
    #endif /* Use X/Open Unix || POSIX 2008.  */
    
    #if defined __USE_POSIX199309 \
        || defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K
    
    /* Truncate the file FD is open on to LENGTH bytes.  */
    # ifndef __USE_FILE_OFFSET64
    extern int ftruncate (int __fd, __off_t __length) __THROW __wur;
    # else
    #  ifdef __REDIRECT_NTH
    extern int __REDIRECT_NTH (ftruncate, (int __fd, __off64_t __length),
    			   ftruncate64) __wur;
    #  else
    #   define ftruncate ftruncate64
    #  endif
    # endif
    # ifdef __USE_LARGEFILE64
    extern int ftruncate64 (int __fd, __off64_t __length) __THROW __wur;
    # endif
    
    #endif /* Use POSIX.1b || X/Open Unix || XPG6.  */
    
    
    #if (defined __USE_XOPEN_EXTENDED && !defined __USE_XOPEN2K) \
        || defined __USE_MISC
    
    /* Set the end of accessible data space (aka "the break") to ADDR.
       Returns zero on success and -1 for errors (with errno set).  */
    extern int brk (void *__addr) __THROW __wur;
    
    /* Increase or decrease the end of accessible data space by DELTA bytes.
       If successful, returns the address the previous end of data space
       (i.e. the beginning of the new space, if DELTA > 0);
       returns (void *) -1 for errors (with errno set).  */
    extern void *sbrk (intptr_t __delta) __THROW;
    #endif
    
    
    #ifdef __USE_MISC
    /* Invoke `system call' number SYSNO, passing it the remaining arguments.
       This is completely system-dependent, and not often useful.
    
       In Unix, `syscall' sets `errno' for all errors and most calls return -1
       for errors; in many systems you cannot pass arguments or get return
       values for all system calls (`pipe', `fork', and `getppid' typically
       among them).
    
       In Mach, all system calls take normal arguments and always return an
       error code (zero for success).  */
    extern long int syscall (long int __sysno, ...) __THROW;
    
    #endif	/* Use misc.  */
    
    
    #if (defined __USE_MISC || defined __USE_XOPEN_EXTENDED) && !defined F_LOCK
    /* NOTE: These declarations also appear in <fcntl.h>; be sure to keep both
       files consistent.  Some systems have them there and some here, and some
       software depends on the macros being defined without including both.  */
    
    /* `lockf' is a simpler interface to the locking facilities of `fcntl'.
       LEN is always relative to the current file position.
       The CMD argument is one of the following.
    
       This function is a cancellation point and therefore not marked with
       __THROW.  */
    
    # define F_ULOCK 0	/* Unlock a previously locked region.  */
    # define F_LOCK  1	/* Lock a region for exclusive use.  */
    # define F_TLOCK 2	/* Test and lock a region for exclusive use.  */
    # define F_TEST  3	/* Test a region for other processes locks.  */
    
    # ifndef __USE_FILE_OFFSET64
    extern int lockf (int __fd, int __cmd, __off_t __len) __wur;
    # else
    #  ifdef __REDIRECT
    extern int __REDIRECT (lockf, (int __fd, int __cmd, __off64_t __len),
    		       lockf64) __wur;
    #  else
    #   define lockf lockf64
    #  endif
    # endif
    # ifdef __USE_LARGEFILE64
    extern int lockf64 (int __fd, int __cmd, __off64_t __len) __wur;
    # endif
    #endif /* Use misc and F_LOCK not already defined.  */
    
    
    #ifdef __USE_GNU
    
    /* Evaluate EXPRESSION, and repeat as long as it returns -1 with `errno'
       set to EINTR.  */
    
    # define TEMP_FAILURE_RETRY(expression) \
      (__extension__							      \
        ({ long int __result;						      \
           do __result = (long int) (expression);				      \
           while (__result == -1L && errno == EINTR);			      \
           __result; }))
    
    /* Copy LENGTH bytes from INFD to OUTFD.  */
    ssize_t copy_file_range (int __infd, __off64_t *__pinoff,
    			 int __outfd, __off64_t *__poutoff,
    			 size_t __length, unsigned int __flags);
    #endif /* __USE_GNU */
    
    #if defined __USE_POSIX199309 || defined __USE_UNIX98
    /* Synchronize at least the data part of a file with the underlying
       media.  */
    extern int fdatasync (int __fildes);
    #endif /* Use POSIX199309 */
    
    #ifdef __USE_MISC
    /* One-way hash PHRASE, returning a string suitable for storage in the
       user database.  SALT selects the one-way function to use, and
       ensures that no two users' hashes are the same, even if they use
       the same passphrase.  The return value points to static storage
       which will be overwritten by the next call to crypt.  */
    extern char *crypt (const char *__key, const char *__salt)
         __THROW __nonnull ((1, 2));
    #endif
    
    #ifdef	__USE_XOPEN
    /* Swab pairs bytes in the first N bytes of the area pointed to by
       FROM and copy the result to TO.  The value of TO must not be in the
       range [FROM - N + 1, FROM - 1].  If N is odd the first byte in FROM
       is without partner.  */
    extern void swab (const void *__restrict __from, void *__restrict __to,
    		  ssize_t __n) __THROW __nonnull ((1, 2));
    #endif
    
    
    /* Prior to Issue 6, the Single Unix Specification required these
       prototypes to appear in this header.  They are also found in
       <stdio.h>.  */
    #if defined __USE_XOPEN && !defined __USE_XOPEN2K
    /* Return the name of the controlling terminal.  */
    extern char *ctermid (char *__s) __THROW;
    
    /* Return the name of the current user.  */
    extern char *cuserid (char *__s);
    #endif
    
    
    /* Unix98 requires this function to be declared here.  In other
       standards it is in <pthread.h>.  */
    #if defined __USE_UNIX98 && !defined __USE_XOPEN2K
    extern int pthread_atfork (void (*__prepare) (void),
    			   void (*__parent) (void),
    			   void (*__child) (void)) __THROW;
    #endif
    
    #ifdef __USE_MISC
    /* Write LENGTH bytes of randomness starting at BUFFER.  Return 0 on
       success or -1 on error.  */
    int getentropy (void *__buffer, size_t __length) __wur;
    #endif
    
    /* Define some macros helping to catch buffer overflows.  */
    #if __USE_FORTIFY_LEVEL > 0 && defined __fortify_function
    # include <bits/unistd.h>
    #endif
    
    __END_DECLS
    
    #endif /* unistd.h  */
    

     

    展开全文
  • 操作系统(Linux)

    2020-06-14 20:22:56
    目录补充第四周vfork在进程当中运行新代码回收进程资源第五周同步机制--锁第七周无名管道1无名管道2有名管道 FIFO双重模式Linux系统调用Linux 可执行文件结构 补充 第四周 vfork 系统调用 vfork和它创建的子进程和...

    补充

    第四周

    vfork

    1. 系统调用
      vfork和它创建的子进程和父进程共享地址空间
      fork创建独立的地址空间
    2. pid_t vfork(void)
      共享包括栈空间

    3. 在这里插入图片描述
      例2:栈错误,内存错误
      在这里插入图片描述
      在这里插入图片描述
      exit(0); 终止进程,不返回

    在进程当中运行新代码

    1. 替换进程映像
      exec()
      在这里插入图片描述

    2. 3.
      在这里插入图片描述
      在这里插入图片描述
    3. system()函数
      在这里插入图片描述
    4. 如果使用新映像完全取代,使用exec

    5. ‘新建进程system
      在这里插入图片描述
      在这里插入图片描述
      加&变为后台进程
      在这里插入图片描述
      ps:查看进程信息
      在这里插入图片描述
    6. 用exec执行命令
      在这里插入图片描述
      down没有被打印,本进程被已经被替换掉。

    回收进程资源

    1. 两部分资源
      在这里插入图片描述
    2. 回收用户空间资源
      在这里插入图片描述
    3. return 和 exit区别
      在这里插入图片描述
      在这里插入图片描述
    4. exit 和 _exit区别
      在这里插入图片描述

    5. 在这里插入图片描述
      用return返回,循环会一直进行。
      用exit返回,会终止当前进程
    6. 例2
      在这里插入图片描述
      在这里插入图片描述
      exit刷新文件缓冲区
      _exit不刷新文件缓冲区
    7. 注册退出函数
      int atexit (void (*function)(void))
      (1)先进后出:先注册的后执行
      (2)等到exit(0)执行时执行才退出函数
      (3)_exit不执行退出函数,return执行。
      在这里插入图片描述
      在这里插入图片描述
    8. 回收内核空间资源
      在这里插入图片描述
      waitpid:
      在这里插入图片描述
      在这里插入图片描述

    第五周

    同步机制–锁

    1. 同步互斥方法
      在这里插入图片描述
    2. 关锁 lock 和开锁 unlock
      在这里插入图片描述
      关锁时忙等待,开销大。
      非忙等(让权等待) -等待队列、阻塞-唤醒
      饥饿、死锁

    第七周

    无名管道1

    1. 无名管道PIPE
      “ | ” 为 管道
      在这里插入图片描述
      在这里插入图片描述
      在这里插入图片描述
      无亲缘关系不能使用无名管道
    2. 管道为内核中的一段特殊的内存空间
      以文件的方式进行操作
      在这里插入图片描述
    3. 管道和文件的区别
      (1)无名管道的内核资源在通信两进程退出后会自动释放
      (2)大小有限制,不能像文件那样存储大量常规信息
      (3)不能使用lseek函数修改当前读写位置
    4. 创建无名管道
      int pipe (int pipefd[2]);
      单项操作
      在这里插入图片描述
    5. 测试无名管道的大小
      在这里插入图片描述
    6. 无名管道的读写
      在这里插入图片描述
      在这里插入图片描述
    7. 父子进程管道通信
      在这里插入图片描述
      在这里插入图片描述
      Q:子进程关闭了读端,为什么还可以读写?
      子进程继承父进程的所有资源,所以父子进程拥有各自独立的读写端。互不影响。

    无名管道2

    1. 以阻塞的方式读无名管道,如果当前没有一个进程和写端关联,读操作立即返回,按如下操作
      无论管道有无数据:
      在这里插入图片描述
    2. 如果写端有关联,管道无数据,读进程会阻塞
      在这里插入图片描述
      在这里插入图片描述
    3. 以阻塞的方式写无名管道
      在这里插入图片描述
      signal :注册信号
      在这里插入图片描述
      执行结果
      没有进程读管道
      在这里插入图片描述
      在这里插入图片描述
      在这里插入图片描述
    4. 以非阻塞的方式读写管道
      在这里插入图片描述
      在这里插入图片描述
      写操作
      在这里插入图片描述
      灰色有数据,白色无数据
      在这里插入图片描述
      在这里插入图片描述
      在这里插入图片描述

    有名管道 FIFO

    1. 有名管道,命名管道 在这里插入图片描述
    2. 创建文件节点 mknod pipetest p
      cat test.txt > pipetest&
    3. 创建有名管道
      在这里插入图片描述
      pathname :必须系统中不存在
      mode_t mod :权限
      在这里插入图片描述
      在这里插入图片描述
      -l F后面多出红色 “ | ”,表示有名管道
      在这里插入图片描述
      echo:写入
      在这里插入图片描述
      cat:读出
    4. 读写有名管道
      在这里插入图片描述
      在这里插入图片描述
      读写进程
      在这里插入图片描述
      在这里插入图片描述
      在这里插入图片描述
      在这里插入图片描述
    5. 非亲缘关系进程使用有名管道通信
      在这里插入图片描述
      在这里插入图片描述
      示例
      在这里插入图片描述
      在这里插入图片描述
    6. 管道的进本特点
      在这里插入图片描述

    双重模式

    内核模式 用户模式

    Linux

    对已经释放的函数栈空间的访问,是非法的 访问,是不允许的。

    系统调用

    系统调用的 实现 --软中断,可编程中断在这里插入图片描述
    中断Interrupts
    – 外部中断 External (hardware generated) interrupts 串口、硬盘、网卡、时钟、…
    软件产生的中断 Software generated interrupts int 0x80指令,用于系统调用
    • 异常Exceptions – 程序错误 – 软件产生的异常 – 机器检查出的异常

    程序访问 – 通过高层次的API接口 – 而不是直接进行系统调用
    • 三种最常用的应用程序编程接口
    API
    Win32 API 用于 Windows – POSIX API 用于 POSIX-based systems (包括UNIX LINUX,Mac OS X 的所有版本) – Java API 用于JAVA虚拟机(JVM)*

    Linux 可执行文件结构

    1. BSS段: 全局或静态未初始化的变量
    2. 数据段: 全局或静态已初始化的变量
    3. 代码段指令代码操作码,操作数),常量, const声明的变量, 字符串常量

    第十三周

    页面置换算法–FIFO

    1. 算法过程
      在这里插入图片描述
      增加物理块(物理块增多,缺页次数增加情况–异常Belady’s Anomaly)
      在这里插入图片描述
      异常原因:
      在这里插入图片描述

    最近最久未使用算法–LRU

    1. 算法过程
      在这里插入图片描述
    2. LRU算法的可能实现方法
      在这里插入图片描述
      在这里插入图片描述
      在这里插入图片描述
    3. 活动页面栈
      在这里插入图片描述
      7被抽出,栈底为将要被淘汰的
      在这里插入图片描述
    展开全文
  • 单内核与微内核Windows NT和Mac OS X的Mach都是微内核,Linux是单内核,但是吸取了微内核的精华:模块化设计,抢占式内核,支持内核线程及动态装载模块。第二章  从内核出发1.  编译内核时会在内核代码树的...

     

    Robert love

     

    第一章   Linux内核简介

     

    1.       处理器活动范围为:

    运行于内核空间,处于进程上下文

    运行于内核空间,处于中断上下文

    运行于用户空间,执行用户进程。

     

    2.       单内核与微内核

    Windows NTMac OS XMach都是微内核,Linux是单内核,但是吸取了微内核的精华:模块化设计,抢占式内核,支持内核线程及动态装载模块。

     

     

    第二章   从内核出发

     

    1.       编译内核时会在内核代码树的根目录下创建一个System.map文件,是一份符号对照表,用以将内核符号和他们的起始地址对应起来。

    2.       内联函数需要在使用前定义好,例如static inline void foo()

    3.       Gcc中可以使用likely()unlikely()分别标记出发生频率较高和较低的分支,以优化程序执行效率。

    4.       不要在内核使用浮点数。

     

     

    第三章   进程管理

     

    1.       进程是Unix操作系统最基本的抽象之一,另一个是文件。

    2.       每个线程有一个独立的程序计数器,进程栈和一组进程寄存器,内核调度对象是线程,不是进程。

    3.       进程存放在叫做任务队列的双向循环链表中,链表每一项都是task_struct类型,称为进程描述符。

    4.       在进程上下文中,current宏获得当前进程是有效的。

    5.       写时拷贝(COW)是一种推迟甚至免除在fork调用时所需要的数据拷贝操作。内核不复制整个进程地址空间,而是让父进程和子进程共享同一个拷贝,只有在需要写入时,所涉及到的页才被复制。因此在fork之后子进程如果马上调用exec,系统开销就只是复制父进程的页表以及给子进程创建唯一的进程描述符。

    6.       Clone是一个实现fork的系统调用,通过一系列参数来指明父,子进程之间需要共享的资源。

    7.       在创建子进程后,内核有意首先执行子进程。

    8.       Vforkfork相同,唯一不同在于vfork只拷贝父进程页表,不拷贝页表项,他们共享数据,父进程被阻塞直到子进程退出或执行execl

    9.       Linux中线程同样被当作进程,只是他们之间共享资源。

    10.   内核线程只在内核空间运行,但是与普通进程一样可以被调度,被抢占。

     

     

    第四章   进程调度

     

    1.       进程调度来决定什么时候停止一个进程的运行以便其他进程能够得到执行的机会,这个强制的停止,挂起动作叫做抢占。

    2.       进程可以被分为I/O消耗型和处理器消耗型。I/O消耗型应该多被调度,而处理器消耗型应该降低其运行频率,延长运行时间。

    3.       基于进程优先级的调度,Linux实现了基于动态优先级的调度方法:一开始进程设置基本的优先级,然后根据执行情况来加,减优先级。常常处于等待I/OI/O消耗型增加,常常迅速用完处理器时间片的处理器消耗型减少优先级。

    4.       Linux使用-20+19nice值,以及099的实时优先级来决定一个进程的优先级。

    5.       当一个进程时间片耗尽时,就不会再运行,除非其他所有进程都耗尽了时间片,那是,所有进程的时间片被重新计算。

    6.       一个进程进入TASK_RUNNING状态时,内核会检查其优先级是否高于当前进程优先级,如果高于,调度进程被唤醒,抢占发生;或者当进程时间片为0时,同样会唤醒调度进程,将其抢占。

    7.       调度程序最基本的是运行队列,每个处理器一个,表示该处理器上可执行进程的链表。

    8.       Cpu_rq(processor)宏用于返回指定CPU上的运行队列,this_rq()返回当前CPU的。

    9.       在对可执行队列操作前需要用task_rq_lock等函数对其加锁。

    10.   每个运行队列都有2个优先级数组,一个活跃的,一个过期的。每个数组都有一个优先级位图,可以提高查找当前系统内最高优先级的可执行进程的效率。每个数组还都有一个list_head队列,包含有多个链表,每个链表与一个给定的优先级对应,即一个链表表示一个优先级上的所有可执行进程,这样能快速找到某个优先级上的进程。

    11.   每个运行队列的2个优先级数组:活动和过期数组。活动数组内的可执行队列上的进程都还有时间片剩余,没有时间片的都被移至过期数组,在移动前已经对进程算好了下一轮执行的时间片。最后当活动数组可执行队列没进程时,只需要与过期数组切换就可以了。

    12.   调度程序由schedule()完成,独立于每个处理器运行,每个CPU都要使用它来判断下一个要执行的进程。调度基本过程为:在活动数组中找到第一个被设置的位,选择这个级别链表的第一个进程,这时比较调度前后2个进程是否相同,如果不同,调用context_switch()切换上下文。

    13.   时间片计算方式:静态优先级nice值和动态优先级同时作用。Nice值越小,优先级越高,交互性越强。动态优先级通过一个关于静态优先级和进程交互性的函数关系计算而来。一般是nice值为基础,根据交互性有-5+5的一个偏移。

    14.   判断交互性的方式:记录一个进程用于休眠和用于执行的时间,保存在task_structsleep_avg域,休眠时数值增加,执行时数值减少,由此判断进程是交互性高的还是处理器消耗型。

    15.   进程创建时,父,子进程平分父进程剩余的时间片。防止不断建立进程来获取时间片。

    16.   如果一个进程交互性非常强,时间片用完后仍被放回活动数组。

    17.   休眠分为可中断和不可中断2种。区别在于可中断休眠如果接收到一个信号会被提前唤醒并相应该信号。

    18.   内核中休眠—唤醒的一般过程:

        DECLARE_WAITQUEUE (wait, current);

        Add_wait_queue (q, &wait);//添加入等待队列

        While (! condition) {//如果条件没发生

            Set_current_state (TASK_INTERRUPTABLE);//设置为可中断或不中断休眠

            If(signal_panding(current)) {//如果可中断,就需要判断并处理信号

                 /* 处理信号 */

            }

            Schedule ();//继续休眠

        }

        Set_current_state (TASK_RUNNING);//事件发生,设置进程运行

        Remove_wait_queue (q, &wait);//移出等待队列


    19.   负载平衡load_balance(),在对称多处理器中有2种调用方法:在schedule()执行时,如果可执行队列为空,调用。或者被定时器调用,系统空闲时间隔1毫秒一次,其他情况下200毫秒一次。

    20.   上下文切换context_swith()完成的工作:调用switch_mm(),把虚拟内存从上一个进程映射切换到新进程中;调用switch_to(),从上一个处理器状态切换到新的,包括保存,恢复堆栈信息和寄存器信息。

    21.   Need_resched标志标明是否需要重新执行一次调度,每个进程都包含这个标志。某个进程耗尽时间片或者优先级高的进程进入可执行状态时,都这个标志被设置。

    22.   用户抢占:在完成系统调用返回用户空间或者从中断返回用户空间时,内核会检查need_resched标志,如果被设置,则发生用户抢占。

    23.   只要重新调度是安全的(没有持有锁),内核就可以在任何时间抢占任何任务。

    24.   内核抢占发生在:

    *当中断处理程序正在执行,返回内核空间之前;

    *内核代码再一次具有可抢占性时;

    *内核中的任务显示调用schedule()

    *内核任务阻塞。

    25.   Linux提供两种实时调度策略:SHED_FIFOSHED_RR(带有时间片的FIFO)。普通非实时调度策略为SHED_NORMAL。调度优先度SHED_NORMAL < SHED_FIFO < 较高优先级的SHED_FIFO < SHED_RR

    26.   Shed_yield()系统调用能够主动让出进程的处理器时间,把自己放入过期数组。但实时进程不会过期,因此只是被移到优先级队列最后面。

     

     

    第五章   系统调用

    1.       系统调用特点:所有系统调用函数声明都需要加asmlinkage限定词,通知编译器仅从栈中提取该函数的参数;系统调用内部命名规则sys_xxx();

    2.       每个syscalls都有系统调用号,一旦分配不能更变,一旦删除也不能被从新利用,而是用sys_ni_syscall()填充。

    3.       内核记录了系统调用表中的所有已注册过的系统调用的列表,储存在sys_call_table中。

    4.       应用程序通过软中断来通知内核,具体实现是引发一个异常使系统切换到内核态去执行异常处理程序。X86系统用int $0x80产生软中断。

    5.       X86系统中,系统调用号通过eax寄存器传递给内核。每个系统调用在系统调用表中占4字节,因此将在系统调用表中偏移eax *4就是系统调用函数的入口地址。

    6.       X86系统中,ebxecxedxesiedi按顺序存放系统调用前5个参数。给用户空间的返回值地址保存在eax寄存器中。

    7.       系统调用的参数验证:

    *指针指向的内存区域属于用户空间。

    *指针指向的内存区域中进程的地址空间。

    *如果是读,内存应标记为可读,如果是写,应标记为可写。

    8.       注册系统调用:

    *在系统调用表最后加入一项。

    *<asm/unistd.h>中定义系统调用号。

    *系统调用编译入内核镜像。

    9.       对系统调用的直接访问,通过宏_syscall1()_syscall6()16表示要传递的参数个数。

    例如对于long open(const char *filename, int flags, int mode);

    直接进行系统调用就可以写成_syscall3(long, open, const char *, filename, int, flags, int, mode).

     

    展开全文
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