sysdeps/unix/sysv/linux/ia64/has_cpuclock.c

   1 /* Copyright (C) 2000-2019 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <fcntl.h>
  20 #include <unistd.h>
  21 #include <sys/stat.h>
  22 #include <sys/types.h>
  23 #include <not-cancel.h>
  24
  25 static int itc_usable;
  26
  27 static int
  28 has_cpuclock (void)
  29 {
  30   if (__builtin_expect (itc_usable == 0, 0))
  31     {
  32       int newval = 1;
  33       int fd = __open_nocancel ("/proc/sal/itc_drift", O_RDONLY);
  34       if (__builtin_expect (fd != -1, 1))
  35         {
  36           char buf[16];
  37           /* We expect the file to contain a single digit followed by
  38              a newline.  If the format changes we better not rely on
  39              the file content.  */
  40           if (__read_nocancel (fd, buf, sizeof buf) != 2
  41               || buf[0] != '0' || buf[1] != '\n')
  42             newval = -1;
  43
  44           __close_nocancel_nostatus (fd);
  45         }
  46
  47       itc_usable = newval;
  48     }
  49
  50   return itc_usable;
  51 }