Linux 0.11 unistd.h 源码文件

前言

这学期在学操作系统，一些实验内容主要是使用 Linux C，很多头文件不知所然，总觉得盲目去看别人的代码，连哪个函数需要使用哪个头文件都不知道，还写个锤儿的代码！首当其冲的就是这个 unistd.h，一怒之下，找到 Linux 0.11 版本的源码来看，这样至少知道我使用的库中的函数有哪些是 unistd.h 中声明的。

功能描述

标准符号常数和类型头文件。该文件定义了很多各种各样的常数和类型，以及一些函数声明。（如果在程序中定义了符号 __LIBRARY__，则还包括内核系统调用号和内嵌汇编 _syscall0()）（括号中的内容暂时不理解，暂时按下不表）

源代码

源码位置：linux/include/unistd.h

#ifndef _UNISTD_H
#define _UNISTD_H

/* ok, this may be a joke, but I'm working on it */
#define _POSIX_VERSION 198808L

#define _POSIX_CHOWN_RESTRICTED	/* only root can do a chown (I think..) */
#define _POSIX_NO_TRUNC		/* no pathname truncation (but see in kernel) */
#define _POSIX_VDISABLE '\0'	/* character to disable things like ^C */
/*#define _POSIX_SAVED_IDS */	/* we'll get to this yet */
/*#define _POSIX_JOB_CONTROL */	/* we aren't there quite yet. Soon hopefully */

#define STDIN_FILENO	0
#define STDOUT_FILENO	1
#define STDERR_FILENO	2

#ifndef NULL
#define NULL    ((void *)0)
#endif

/* access */
#define F_OK	0
#define X_OK	1
#define W_OK	2
#define R_OK	4

/* lseek */
#define SEEK_SET	0
#define SEEK_CUR	1
#define SEEK_END	2

/* _SC stands for System Configuration. We don't use them much */
#define _SC_ARG_MAX		1
#define _SC_CHILD_MAX		2
#define _SC_CLOCKS_PER_SEC	3
#define _SC_NGROUPS_MAX		4
#define _SC_OPEN_MAX		5
#define _SC_JOB_CONTROL		6
#define _SC_SAVED_IDS		7
#define _SC_VERSION		8

/* more (possibly) configurable things - now pathnames */
#define _PC_LINK_MAX		1
#define _PC_MAX_CANON		2
#define _PC_MAX_INPUT		3
#define _PC_NAME_MAX		4
#define _PC_PATH_MAX		5
#define _PC_PIPE_BUF		6
#define _PC_NO_TRUNC		7
#define _PC_VDISABLE		8
#define _PC_CHOWN_RESTRICTED	9

#include <sys/stat.h>
#include <sys/times.h>
#include <sys/utsname.h>
#include <utime.h>

#ifdef __LIBRARY__

#define __NR_setup	0	/* used only by init, to get system going */
#define __NR_exit	1
#define __NR_fork	2
#define __NR_read	3
#define __NR_write	4
#define __NR_open	5
#define __NR_close	6
#define __NR_waitpid	7
#define __NR_creat	8
#define __NR_link	9
#define __NR_unlink	10
#define __NR_execve	11
#define __NR_chdir	12
#define __NR_time	13
#define __NR_mknod	14
#define __NR_chmod	15
#define __NR_chown	16
#define __NR_break	17
#define __NR_stat	18
#define __NR_lseek	19
#define __NR_getpid	20
#define __NR_mount	21
#define __NR_umount	22
#define __NR_setuid	23
#define __NR_getuid	24
#define __NR_stime	25
#define __NR_ptrace	26
#define __NR_alarm	27
#define __NR_fstat	28
#define __NR_pause	29
#define __NR_utime	30
#define __NR_stty	31
#define __NR_gtty	32
#define __NR_access	33
#define __NR_nice	34
#define __NR_ftime	35
#define __NR_sync	36
#define __NR_kill	37
#define __NR_rename	38
#define __NR_mkdir	39
#define __NR_rmdir	40
#define __NR_dup	41
#define __NR_pipe	42
#define __NR_times	43
#define __NR_prof	44
#define __NR_brk	45
#define __NR_setgid	46
#define __NR_getgid	47
#define __NR_signal	48
#define __NR_geteuid	49
#define __NR_getegid	50
#define __NR_acct	51
#define __NR_phys	52
#define __NR_lock	53
#define __NR_ioctl	54
#define __NR_fcntl	55
#define __NR_mpx	56
#define __NR_setpgid	57
#define __NR_ulimit	58
#define __NR_uname	59
#define __NR_umask	60
#define __NR_chroot	61
#define __NR_ustat	62
#define __NR_dup2	63
#define __NR_getppid	64
#define __NR_getpgrp	65
#define __NR_setsid	66
#define __NR_sigaction	67
#define __NR_sgetmask	68
#define __NR_ssetmask	69
#define __NR_setreuid	70
#define __NR_setregid	71

#define _syscall0(type,name) \
type name(void) \
{ \
long __res; \
__asm__ volatile ("int $0x80" \
	: "=a" (__res) \
	: "0" (__NR_##name)); \
if (__res >= 0) \
	return (type) __res; \
errno = -__res; \
return -1; \
}

#define _syscall1(type,name,atype,a) \
type name(atype a) \
{ \
long __res; \
__asm__ volatile ("int $0x80" \
	: "=a" (__res) \
	: "0" (__NR_##name),"b" ((long)(a))); \
if (__res >= 0) \
	return (type) __res; \
errno = -__res; \
return -1; \
}

#define _syscall2(type,name,atype,a,btype,b) \
type name(atype a,btype b) \
{ \
long __res; \
__asm__ volatile ("int $0x80" \
	: "=a" (__res) \
	: "0" (__NR_##name),"b" ((long)(a)),"c" ((long)(b))); \
if (__res >= 0) \
	return (type) __res; \
errno = -__res; \
return -1; \
}

#define _syscall3(type,name,atype,a,btype,b,ctype,c) \
type name(atype a,btype b,ctype c) \
{ \
long __res; \
__asm__ volatile ("int $0x80" \
	: "=a" (__res) \
	: "0" (__NR_##name),"b" ((long)(a)),"c" ((long)(b)),"d" ((long)(c))); \
if (__res>=0) \
	return (type) __res; \
errno=-__res; \
return -1; \
}

#endif /* __LIBRARY__ */

extern int errno;

int access(const char * filename, mode_t mode);
int acct(const char * filename);
int alarm(int sec);
int brk(void * end_data_segment);
void * sbrk(ptrdiff_t increment);
int chdir(const char * filename);
int chmod(const char * filename, mode_t mode);
int chown(const char * filename, uid_t owner, gid_t group);
int chroot(const char * filename);
int close(int fildes);
int creat(const char * filename, mode_t mode);
int dup(int fildes);
int execve(const char * filename, char ** argv, char ** envp);
int execv(const char * pathname, char ** argv);
int execvp(const char * file, char ** argv);
int execl(const char * pathname, char * arg0, ...);
int execlp(const char * file, char * arg0, ...);
int execle(const char * pathname, char * arg0, ...);
volatile void exit(int status);
volatile void _exit(int status);
int fcntl(int fildes, int cmd, ...);
int fork(void);
int getpid(void);
int getuid(void);
int geteuid(void);
int getgid(void);
int getegid(void);
int ioctl(int fildes, int cmd, ...);
int kill(pid_t pid, int signal);
int link(const char * filename1, const char * filename2);
int lseek(int fildes, off_t offset, int origin);
int mknod(const char * filename, mode_t mode, dev_t dev);
int mount(const char * specialfile, const char * dir, int rwflag);
int nice(int val);
int open(const char * filename, int flag, ...);
int pause(void);
int pipe(int * fildes);
int read(int fildes, char * buf, off_t count);
int setpgrp(void);
int setpgid(pid_t pid,pid_t pgid);
int setuid(uid_t uid);
int setgid(gid_t gid);
void (*signal(int sig, void (*fn)(int)))(int);
int stat(const char * filename, struct stat * stat_buf);
int fstat(int fildes, struct stat * stat_buf);
int stime(time_t * tptr);
int sync(void);
time_t time(time_t * tloc);
time_t times(struct tms * tbuf);
int ulimit(int cmd, long limit);
mode_t umask(mode_t mask);
int umount(const char * specialfile);
int uname(struct utsname * name);
int unlink(const char * filename);
int ustat(dev_t dev, struct ustat * ubuf);
int utime(const char * filename, struct utimbuf * times);
pid_t waitpid(pid_t pid,int * wait_stat,int options);
pid_t wait(int * wait_stat);
int write(int fildes, const char * buf, off_t count);
int dup2(int oldfd, int newfd);
int getppid(void);
pid_t getpgrp(void);
pid_t setsid(void);

#endif

上面的是 0.11 内核的代码，下面贴一个 5.7 版本的代码。代码位置 /usr/include/unistd.h

/* 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

/* Encryption is present.  */
#define	_XOPEN_CRYPT	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 */


/* XPG4.2 specifies that prototypes for the encryption functions must
   be defined here.  */
#ifdef	__USE_XOPEN
/* Encrypt at most 8 characters from KEY using salt to perturb DES.  */
extern char *crypt (const char *__key, const char *__salt)
     __THROW __nonnull ((1, 2));

/* Encrypt data in BLOCK in place if EDFLAG is zero; otherwise decrypt
   block in place.  */
extern void encrypt (char *__glibc_block, int __edflag)
     __THROW __nonnull ((1));


/* 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  */

参考：《Linux 内核完全剖析（0.11）》github 仓库（源码）