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glibc  2.9
pread.c
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00001 /* Copyright (C) 1997-2000,2002,2003,2004,2006 Free Software Foundation, Inc.
00002    This file is part of the GNU C Library.
00003    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
00004 
00005    The GNU C Library is free software; you can redistribute it and/or
00006    modify it under the terms of the GNU Lesser General Public
00007    License as published by the Free Software Foundation; either
00008    version 2.1 of the License, or (at your option) any later version.
00009 
00010    The GNU C Library is distributed in the hope that it will be useful,
00011    but WITHOUT ANY WARRANTY; without even the implied warranty of
00012    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00013    Lesser General Public License for more details.
00014 
00015    You should have received a copy of the GNU Lesser General Public
00016    License along with the GNU C Library; if not, write to the Free
00017    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00018    02111-1307 USA.  */
00019 
00020 #include <assert.h>
00021 #include <errno.h>
00022 #include <endian.h>
00023 #include <unistd.h>
00024 
00025 #include <sysdep-cancel.h>
00026 #include <sys/syscall.h>
00027 #include <bp-checks.h>
00028 
00029 #include <kernel-features.h>
00030 
00031 #ifdef __NR_pread64         /* Newer kernels renamed but it's the same.  */
00032 # ifdef __NR_pread
00033 #  error "__NR_pread and __NR_pread64 both defined???"
00034 # endif
00035 # define __NR_pread __NR_pread64
00036 #endif
00037 
00038 #if defined __NR_pread || __ASSUME_PREAD_SYSCALL > 0
00039 
00040 # if __ASSUME_PREAD_SYSCALL == 0
00041 static ssize_t __emulate_pread (int fd, void *buf, size_t count,
00042                             off_t offset) internal_function;
00043 # endif
00044 
00045 
00046 static ssize_t
00047 #ifdef NO_CANCELLATION
00048 inline __attribute ((always_inline))
00049 #endif
00050 do_pread (int fd, void *buf, size_t count, off_t offset)
00051 {
00052   ssize_t result;
00053 
00054   /* First try the syscall.  */
00055   assert (sizeof (offset) == 4);
00056   result = INLINE_SYSCALL (pread, 5, fd, CHECK_N (buf, count), count,
00057                         __LONG_LONG_PAIR (offset >> 31, offset));
00058 # if __ASSUME_PREAD_SYSCALL == 0
00059   if (result == -1 && errno == ENOSYS)
00060     /* No system call available.  Use the emulation.  */
00061     result = __emulate_pread (fd, buf, count, offset);
00062 # endif
00063 
00064   return result;
00065 }
00066 
00067 
00068 ssize_t
00069 __libc_pread (fd, buf, count, offset)
00070      int fd;
00071      void *buf;
00072      size_t count;
00073      off_t offset;
00074 {
00075   if (SINGLE_THREAD_P)
00076     return do_pread (fd, buf, count, offset);
00077 
00078   int oldtype = LIBC_CANCEL_ASYNC ();
00079 
00080   ssize_t result = do_pread (fd, buf, count, offset);
00081 
00082   LIBC_CANCEL_RESET (oldtype);
00083 
00084   return result;
00085 }
00086 
00087 strong_alias (__libc_pread, __pread)
00088 weak_alias (__libc_pread, pread)
00089 
00090 # define __libc_pread(fd, buf, count, offset) \
00091      static internal_function __emulate_pread (fd, buf, count, offset)
00092 #endif
00093 
00094 #if __ASSUME_PREAD_SYSCALL == 0
00095 # include <sysdeps/posix/pread.c>
00096 #endif