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glibc  2.9
has_cpuclock.c
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00001 /* Copyright (C) 2000, 2001, 2003, 2004, 2005 Free Software Foundation, Inc.
00002    This file is part of the GNU C Library.
00003 
00004    The GNU C Library is free software; you can redistribute it and/or
00005    modify it under the terms of the GNU Lesser General Public
00006    License as published by the Free Software Foundation; either
00007    version 2.1 of the License, or (at your option) any later version.
00008 
00009    The GNU C Library is distributed in the hope that it will be useful,
00010    but WITHOUT ANY WARRANTY; without even the implied warranty of
00011    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00012    Lesser General Public License for more details.
00013 
00014    You should have received a copy of the GNU Lesser General Public
00015    License along with the GNU C Library; if not, write to the Free
00016    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00017    02111-1307 USA.  */
00018 
00019 #include <errno.h>
00020 #include <fcntl.h>
00021 #include <unistd.h>
00022 #include <sys/stat.h>
00023 #include <sys/types.h>
00024 #include <not-cancel.h>
00025 
00026 static int itc_usable;
00027 
00028 static int
00029 has_cpuclock (void)
00030 {
00031   if (__builtin_expect (itc_usable == 0, 0))
00032     {
00033       int newval = 1;
00034       int fd = open_not_cancel_2 ("/proc/sal/itc_drift", O_RDONLY);
00035       if (__builtin_expect (fd != -1, 1))
00036        {
00037          char buf[16];
00038          /* We expect the file to contain a single digit followed by
00039             a newline.  If the format changes we better not rely on
00040             the file content.  */
00041          if (read_not_cancel (fd, buf, sizeof buf) != 2
00042              || buf[0] != '0' || buf[1] != '\n')
00043            newval = -1;
00044 
00045          close_not_cancel_no_status (fd);
00046        }
00047 
00048       itc_usable = newval;
00049     }
00050 
00051   return itc_usable;
00052 }