sysdeps/unix/sysv/linux/pread.c

   1 /* Copyright (C) 1997-2000,2002,2003,2004,2006 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <endian.h>
  22 #include <unistd.h>
  23
  24 #include <sysdep-cancel.h>
  25 #include <sys/syscall.h>
  26 #include <bp-checks.h>
  27
  28 #include <kernel-features.h>
  29
  30 #ifdef __NR_pread64             /* Newer kernels renamed but it's the same.  */
  31 # ifdef __NR_pread
  32 #  error "__NR_pread and __NR_pread64 both defined???"
  33 # endif
  34 # define __NR_pread __NR_pread64
  35 #endif
  36
  37 #if defined __NR_pread || __ASSUME_PREAD_SYSCALL > 0
  38
  39 # if __ASSUME_PREAD_SYSCALL == 0
  40 static ssize_t __emulate_pread (int fd, void *buf, size_t count,
  41                                 off_t offset) internal_function;
  42 # endif
  43
  44
  45 static ssize_t
  46 #ifdef NO_CANCELLATION
  47 inline __attribute ((always_inline))
  48 #endif
  49 do_pread (int fd, void *buf, size_t count, off_t offset)
  50 {
  51   ssize_t result;
  52
  53   /* First try the syscall.  */
  54   assert (sizeof (offset) == 4);
  55   result = INLINE_SYSCALL (pread, 5, fd, CHECK_N (buf, count), count,
  56                            __LONG_LONG_PAIR (offset >> 31, offset));
  57 # if __ASSUME_PREAD_SYSCALL == 0
  58   if (result == -1 && errno == ENOSYS)
  59     /* No system call available.  Use the emulation.  */
  60     result = __emulate_pread (fd, buf, count, offset);
  61 # endif
  62
  63   return result;
  64 }
  65
  66
  67 ssize_t
  68 __libc_pread (fd, buf, count, offset)
  69      int fd;
  70      void *buf;
  71      size_t count;
  72      off_t offset;
  73 {
  74   if (SINGLE_THREAD_P)
  75     return do_pread (fd, buf, count, offset);
  76
  77   int oldtype = LIBC_CANCEL_ASYNC ();
  78
  79   ssize_t result = do_pread (fd, buf, count, offset);
  80
  81   LIBC_CANCEL_RESET (oldtype);
  82
  83   return result;
  84 }
  85
  86 strong_alias (__libc_pread, __pread)
  87 weak_alias (__libc_pread, pread)
  88
  89 # define __libc_pread(fd, buf, count, offset) \
  90      static internal_function __emulate_pread (fd, buf, count, offset)
  91 #endif
  92
  93 #if __ASSUME_PREAD_SYSCALL == 0
  94 # include <sysdeps/posix/pread.c>
  95 #endif