pread.c

Glibc 2.3.2源代码(解压后有100多M)

/* Copyright (C) 1997, 1998, 2000, 2002 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <[e-mail]>, 1997.

   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 <unistd.h>
#include <endian.h>

#include <sysdep-cancel.h>
#include <sys/syscall.h>
#include <bp-checks.h>

#include <kernel-features.h>

#ifdef __NR_pread64             /* Newer kernels renamed but it's the same.  */
# ifdef __NR_pread
#  error "__NR_pread and __NR_pread64 both defined???"
# endif
# define __NR_pread __NR_pread64
#endif

#if defined __NR_pread || __ASSUME_PREAD_SYSCALL > 0

# if __ASSUME_PREAD_SYSCALL == 0
static ssize_t __emulate_pread (int fd, void *buf, size_t count,
				off_t offset) internal_function;
# endif
extern ssize_t __syscall_pread (int fd, void *__unbounded buf, size_t count,
				int dummy, off_t offset_hi, off_t offset_lo);



ssize_t
__libc_pread (fd, buf, count, offset)
     int fd;
     void *buf;
     size_t count;
     off_t offset;
{
  ssize_t result;

  if (SINGLE_THREAD_P)
    {
     /* First try the syscall.  */
     assert (sizeof (offset) == 4);
     result = INLINE_SYSCALL (pread, 6, fd, CHECK_N (buf, count), count, 0,
			      __LONG_LONG_PAIR (offset >> 31, offset));
# if __ASSUME_PREAD_SYSCALL == 0
     if (result == -1 && errno == ENOSYS)
     /* No system call available.  Use the emulation.  */
     result = __emulate_pread (fd, buf, count, offset);
# endif
     return result;
    }

  int oldtype = LIBC_CANCEL_ASYNC ();

  /* First try the syscall.  */
  assert (sizeof (offset) == 4);
  result = INLINE_SYSCALL (pread, 6, fd, CHECK_N (buf, count), count, 0,
			   __LONG_LONG_PAIR (offset >> 31, offset));
# if __ASSUME_PREAD_SYSCALL == 0
  if (result == -1 && errno == ENOSYS)
    /* No system call available.  Use the emulation.  */
    result = __emulate_pread (fd, buf, count, offset);
# endif

  LIBC_CANCEL_RESET (oldtype);

  return result;
}

strong_alias (__libc_pread, __pread)
weak_alias (__libc_pread, pread)

# define __libc_pread(fd, buf, count, offset) \
     static internal_function __emulate_pread (fd, buf, count, offset)
#endif

#if __ASSUME_PREAD_SYSCALL == 0
# include <sysdeps/posix/pread.c>
#endif