fcntl.c

glibc 库, 不仅可以学习使用库函数,还可以学习函数的具体实现,是提高功力的好资料

/* Copyright (C) 2000,2002,2003,2004,2006 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, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <assert.h>
#include <errno.h>
#include <sysdep-cancel.h>	/* Must come before <fcntl.h>.  */
#include <fcntl.h>
#include <stdarg.h>

#include <sys/syscall.h>
#include <kernel-features.h>

#if __ASSUME_FCNTL64 == 0
/* This variable is shared with all files that check for fcntl64.  */
int __have_no_fcntl64;
#endif

#if defined NO_CANCELLATION && __ASSUME_FCNTL64 == 0
# define __fcntl_nocancel  __libc_fcntl
#endif

#if !defined NO_CANCELLATION || __ASSUME_FCNTL64 == 0
int
__fcntl_nocancel (int fd, int cmd, ...)
{
  va_list ap;
  void *arg;

  va_start (ap, cmd);
  arg = va_arg (ap, void *);
  va_end (ap);

#if __ASSUME_FCNTL64 == 0
# ifdef __NR_fcntl64
  if (! __have_no_fcntl64)
    {
      int result = INLINE_SYSCALL (fcntl64, 3, fd, cmd, arg);
      if (result >= 0 || errno != ENOSYS)
	return result;

      __have_no_fcntl64 = 1;
    }
# endif
  switch (cmd)
    {
    case F_GETLK64:
      /* Convert arg from flock64 to flock and back.  */
      {
	struct flock fl;
	struct flock64 *fl64 = arg;
	int res;

	fl.l_start = (off_t)fl64->l_start;
	/* Check if we can represent the values with the smaller type.  */
	if ((off64_t) fl.l_start != fl64->l_start)
	  {
	  eoverflow:
	    __set_errno (EOVERFLOW);
	    return -1;
	  }
	fl.l_len = (off_t) fl64->l_len;
	/* Check if we can represent the values with the smaller type.  */
	if ((off64_t) fl.l_len != fl64->l_len)
	  goto eoverflow;

	fl.l_type = fl64->l_type;
	fl.l_whence = fl64->l_whence;
	fl.l_pid = fl64->l_pid;

	res = INLINE_SYSCALL (fcntl, 3, fd, F_GETLK, &fl);
	if (res  != 0)
	  return res;
	/* Everything ok, convert back.  */
	fl64->l_type = fl.l_type;
	fl64->l_whence = fl.l_whence;
	fl64->l_start = fl.l_start;
	fl64->l_len = fl.l_len;
	fl64->l_pid = fl.l_pid;

	return 0;
      }
    case F_SETLK64:
    case F_SETLKW64:
      /* Try to convert arg from flock64 to flock.  */
      {
	struct flock fl;
	struct flock64 *fl64 = arg;

	fl.l_start = (off_t) fl64->l_start;
	/* Check if we can represent the values with the smaller type.  */
	if ((off64_t) fl.l_start != fl64->l_start)
	  goto eoverflow;

	fl.l_len = (off_t)fl64->l_len;
	/* Check if we can represent the values with the smaller type.  */
	if ((off64_t) fl.l_len != fl64->l_len)
	  {
	    __set_errno (EOVERFLOW);
	    return -1;
	  }
	fl.l_type = fl64->l_type;
	fl.l_whence = fl64->l_whence;
	fl.l_pid = fl64->l_pid;
	assert (F_SETLK - F_SETLKW == F_SETLK64 - F_SETLKW64);
	return INLINE_SYSCALL (fcntl, 3, fd, cmd + F_SETLK - F_SETLK64, &fl);
      }
    default:
      return INLINE_SYSCALL (fcntl, 3, fd, cmd, arg);
    }
  return -1;
#else
  return INLINE_SYSCALL (fcntl64, 3, fd, cmd, arg);
#endif  /* !__ASSUME_FCNTL64  */
}
#endif /* NO_CANCELLATION || !__ASSUME_FCNTL64 */


#ifndef __fcntl_nocancel
int
__libc_fcntl (int fd, int cmd, ...)
{
  va_list ap;
  void *arg;

  va_start (ap, cmd);
  arg = va_arg (ap, void *);
  va_end (ap);

#if __ASSUME_FCNTL64 > 0
  if (SINGLE_THREAD_P || (cmd != F_SETLKW && cmd != F_SETLKW64))
    return INLINE_SYSCALL (fcntl64, 3, fd, cmd, arg);

  int oldtype = LIBC_CANCEL_ASYNC ();

  int result = INLINE_SYSCALL (fcntl64, 3, fd, cmd, arg);
#else
  if (SINGLE_THREAD_P || (cmd != F_SETLKW && cmd != F_SETLKW64))
    return __fcntl_nocancel (fd, cmd, arg);

  int oldtype = LIBC_CANCEL_ASYNC ();

  int result = __fcntl_nocancel (fd, cmd, arg);
#endif

  LIBC_CANCEL_RESET (oldtype);

  return result;
}
#endif
libc_hidden_def (__libc_fcntl)

weak_alias (__libc_fcntl, __fcntl)
libc_hidden_weak (__fcntl)
weak_alias (__libc_fcntl, fcntl)