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 /* Legacy value of ARG_MAX.  The macro is now not defined since the
  31    actual value varies based on the stack size.  */
  32 #define legacy_ARG_MAX 131072
  33
  34
  35 static long int posix_sysconf (int name);
  36
  37
  38 /* Get the value of the system variable NAME.  */
  39 long int
  40 __sysconf (int name)
  41 {
  42   const char *procfname = NULL;
  43
  44   switch (name)
  45     {
  46 #ifdef __NR_clock_getres
  47     case _SC_MONOTONIC_CLOCK:
  48       /* Check using the clock_getres system call.  */
  49       {
  50         struct timespec ts;
  51         INTERNAL_SYSCALL_DECL (err);
  52         int r;
  53         r = INTERNAL_SYSCALL (clock_getres, err, 2, CLOCK_MONOTONIC, &ts);
  54         return INTERNAL_SYSCALL_ERROR_P (r, err) ? -1 : _POSIX_VERSION;
  55       }
  56 #endif
  57
  58 #if defined __NR_clock_getres || HP_TIMING_AVAIL
  59     case _SC_CPUTIME:
  60     case _SC_THREAD_CPUTIME:
  61       {
  62         /* If we have HP_TIMING, we will fall back on that if the system
  63            call does not work, so we support it either way.  */
  64 # if !HP_TIMING_AVAIL
  65         /* Check using the clock_getres system call.  */
  66         struct timespec ts;
  67         INTERNAL_SYSCALL_DECL (err);
  68         int r = INTERNAL_SYSCALL (clock_getres, err, 2,
  69                                   (name == _SC_CPUTIME
  70                                    ? CLOCK_PROCESS_CPUTIME_ID
  71                                    : CLOCK_THREAD_CPUTIME_ID),
  72                                   &ts);
  73         if (INTERNAL_SYSCALL_ERROR_P (r, err))
  74           return -1;
  75 # endif
  76         return _POSIX_VERSION;
  77       }
  78 #endif
  79
  80     case _SC_ARG_MAX:
  81 #if __LINUX_KERNEL_VERSION < 0x020617
  82       /* Determine whether this is a kernel 2.6.23 or later.  Only
  83          then do we have an argument limit determined by the stack
  84          size.  */
  85       if (GLRO(dl_discover_osversion) () >= 0x020617)
  86 #endif
  87         {
  88           /* Use getrlimit to get the stack limit.  */
  89           struct rlimit rlimit;
  90           if (__getrlimit (RLIMIT_STACK, &rlimit) == 0)
  91             return MAX (legacy_ARG_MAX, rlimit.rlim_cur / 4);
  92         }
  93
  94       return legacy_ARG_MAX;
  95
  96     case _SC_NGROUPS_MAX:
  97       /* Try to read the information from the /proc/sys/kernel/ngroups_max
  98          file.  */
  99       procfname = "/proc/sys/kernel/ngroups_max";
 100       break;
 101
 102     case _SC_SIGQUEUE_MAX:
 103       /* The /proc/sys/kernel/rtsig-max file contains the answer.  */
 104       procfname = "/proc/sys/kernel/rtsig-max";
 105       break;
 106
 107     default:
 108       break;
 109     }
 110
 111   if (procfname != NULL)
 112     {
 113       int fd = open_not_cancel_2 (procfname, O_RDONLY);
 114       if (fd != -1)
 115         {
 116           /* This is more than enough, the file contains a single integer.  */
 117           char buf[32];
 118           ssize_t n;
 119           n = TEMP_FAILURE_RETRY (read_not_cancel (fd, buf, sizeof (buf) - 1));
 120           close_not_cancel_no_status (fd);
 121
 122           if (n > 0)
 123             {
 124               /* Terminate the string.  */
 125               buf[n] = '\0';
 126
 127               char *endp;
 128               long int res = strtol (buf, &endp, 10);
 129               if (endp != buf && (*endp == '\0' || *endp == '\n'))
 130                 return res;
 131             }
 132         }
 133     }
 134
 135   return posix_sysconf (name);
 136 }
 137
 138 /* Now the POSIX version.  */
 139 #undef __sysconf
 140 #define __sysconf static posix_sysconf
 141 #include <sysdeps/posix/sysconf.c>