sysdeps/unix/sysv/linux/sysconf.c

   1 /* Get file-specific information about a file.  Linux version.
   2    Copyright (C) 2003, 2004, 2006, 2008 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <errno.h>
  21 #include <fcntl.h>
  22 #include <stdlib.h>
  23 #include <sysdep.h>
  24 #include <time.h>
  25 #include <unistd.h>
  26 #include <sys/resource.h>
  27 #include <not-cancel.h>
  28 #include <ldsodefs.h>
  29
  30 static long int posix_sysconf (int name);
  31
  32
  33 /* Get the value of the system variable NAME.  */
  34 long int
  35 __sysconf (int name)
  36 {
  37   const char *procfname = NULL;
  38
  39   switch (name)
  40     {
  41 #ifdef __NR_clock_getres
  42     case _SC_MONOTONIC_CLOCK:
  43       /* Check using the clock_getres system call.  */
  44       {
  45         struct timespec ts;
  46         INTERNAL_SYSCALL_DECL (err);
  47         int r;
  48         r = INTERNAL_SYSCALL (clock_getres, err, 2, CLOCK_MONOTONIC, &ts);
  49         return INTERNAL_SYSCALL_ERROR_P (r, err) ? -1 : _POSIX_VERSION;
  50       }
  51 #endif
  52
  53 #if defined __NR_clock_getres || HP_TIMING_AVAIL
  54     case _SC_CPUTIME:
  55     case _SC_THREAD_CPUTIME:
  56       {
  57         /* If we have HP_TIMING, we will fall back on that if the system
  58            call does not work, so we support it either way.  */
  59 # if !HP_TIMING_AVAIL
  60         /* Check using the clock_getres system call.  */
  61         struct timespec ts;
  62         INTERNAL_SYSCALL_DECL (err);
  63         int r = INTERNAL_SYSCALL (clock_getres, err, 2,
  64                                   (name == _SC_CPUTIME
  65                                    ? CLOCK_PROCESS_CPUTIME_ID
  66                                    : CLOCK_THREAD_CPUTIME_ID),
  67                                   &ts);
  68         if (INTERNAL_SYSCALL_ERROR_P (r, err))
  69           return -1;
  70 # endif
  71         return _POSIX_VERSION;
  72       }
  73 #endif
  74
  75     case _SC_ARG_MAX:
  76 #if __LINUX_KERNEL_VERSION < 0x020617
  77       /* Determine whether this is a kernel 2.6.23 or later.  Only
  78          then do we have an argument limit determined by the stack
  79          size.  */
  80       if (GLRO(dl_discover_osversion) () >= 0x020617)
  81 #endif
  82         {
  83           /* Use getrlimit to get the stack limit.  */
  84           struct rlimit rlimit;
  85           if (__getrlimit (RLIMIT_STACK, &rlimit) == 0)
  86             return MAX (ARG_MAX, rlimit.rlim_cur / 4);
  87         }
  88
  89       return ARG_MAX;
  90
  91     case _SC_NGROUPS_MAX:
  92       /* Try to read the information from the /proc/sys/kernel/ngroups_max
  93          file.  */
  94       procfname = "/proc/sys/kernel/ngroups_max";
  95       break;
  96
  97     case _SC_SIGQUEUE_MAX:
  98       /* The /proc/sys/kernel/rtsig-max file contains the answer.  */
  99       procfname = "/proc/sys/kernel/rtsig-max";
 100       break;
 101
 102     default:
 103       break;
 104     }
 105
 106   if (procfname != NULL)
 107     {
 108       int fd = open_not_cancel_2 (procfname, O_RDONLY);
 109       if (fd != -1)
 110         {
 111           /* This is more than enough, the file contains a single integer.  */
 112           char buf[32];
 113           ssize_t n;
 114           n = TEMP_FAILURE_RETRY (read_not_cancel (fd, buf, sizeof (buf) - 1));
 115           close_not_cancel_no_status (fd);
 116
 117           if (n > 0)
 118             {
 119               /* Terminate the string.  */
 120               buf[n] = '\0';
 121
 122               char *endp;
 123               long int res = strtol (buf, &endp, 10);
 124               if (endp != buf && (*endp == '\0' || *endp == '\n'))
 125                 return res;
 126             }
 127         }
 128     }
 129
 130   return posix_sysconf (name);
 131 }
 132
 133 /* Now the POSIX version.  */
 134 #undef __sysconf
 135 #define __sysconf static posix_sysconf
 136 #include <sysdeps/posix/sysconf.c>