posix_fadvise64.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) 2003, 2004 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 <errno.h>
#include <fcntl.h>
#include <sysdep.h>
#include <kernel-features.h>

int __posix_fadvise64_l64 (int fd, off64_t offset, off64_t len, int advise);
int __posix_fadvise64_l32 (int fd, off64_t offset, size_t len, int advise);

/* Advice the system about the expected behaviour of the application with
   respect to the file associated with FD.  */

struct fadvise64_64_layout
{
  int fd;
  off64_t offset;
  off64_t len;
  int advise;
};

int
__posix_fadvise64_l64 (int fd, off64_t offset, off64_t len, int advise)
{
#ifdef __NR_fadvise64_64
  struct fadvise64_64_layout parameters;
  INTERNAL_SYSCALL_DECL (err);
  
  parameters.fd = fd;
  parameters.offset = offset;
  parameters.len = len;
  parameters.advise = advise;
  int ret = INTERNAL_SYSCALL (fadvise64_64, err, 1, &parameters);
  if (!INTERNAL_SYSCALL_ERROR_P (ret, err))
    return 0;
# ifndef __ASSUME_FADVISE64_64_SYSCALL
  if (INTERNAL_SYSCALL_ERRNO (ret, err) != ENOSYS)
# endif
   return INTERNAL_SYSCALL_ERRNO (ret, err);
#endif
#ifndef __ASSUME_FADVISE64_64_SYSCALL
# ifdef __NR_fadvise64
  if (len != (off_t) len)
    return EOVERFLOW;

  INTERNAL_SYSCALL_DECL (err2);
  int ret2 = INTERNAL_SYSCALL (fadvise64, err2, 5, fd,
			       __LONG_LONG_PAIR ((long) (offset >> 32),
						 (long) offset),
			       (off_t) len, advise);
  if (!INTERNAL_SYSCALL_ERROR_P (ret2, err2))
    return 0;
  return INTERNAL_SYSCALL_ERRNO (ret2, err2);
# else
  return ENOSYS;
# endif
#endif
}

#include <shlib-compat.h>

#if SHLIB_COMPAT(libc, GLIBC_2_2, GLIBC_2_3_3)

int
attribute_compat_text_section
__posix_fadvise64_l32 (int fd, off64_t offset, size_t len, int advise)
{
  return __posix_fadvise64_l64 (fd, offset, len, advise);
}

versioned_symbol (libc, __posix_fadvise64_l64, posix_fadvise64, GLIBC_2_3_3);
compat_symbol (libc, __posix_fadvise64_l32, posix_fadvise64, GLIBC_2_2);
#else
strong_alias (__posix_fadvise64_l64, posix_fadvise64);
#endif