sysdeps/unix/sysv/linux/sysconf.c

   1 /* Get file-specific information about a file.  Linux version.
   2    Copyright (C) 2003, 2004, 2006, 2008, 2009 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       struct rlimit rlimit;
  47 #ifdef __NR_clock_getres
  48     case _SC_MONOTONIC_CLOCK:
  49       /* Check using the clock_getres system call.  */
  50       {
  51         struct timespec ts;
  52         INTERNAL_SYSCALL_DECL (err);
  53         int r;
  54         r = INTERNAL_SYSCALL (clock_getres, err, 2, CLOCK_MONOTONIC, &ts);
  55         return INTERNAL_SYSCALL_ERROR_P (r, err) ? -1 : _POSIX_VERSION;
  56       }
  57 #endif
  58
  59 #if defined __NR_clock_getres || HP_TIMING_AVAIL
  60     case _SC_CPUTIME:
  61     case _SC_THREAD_CPUTIME:
  62       {
  63         /* If we have HP_TIMING, we will fall back on that if the system
  64            call does not work, so we support it either way.  */
  65 # if !HP_TIMING_AVAIL
  66         /* Check using the clock_getres system call.  */
  67         struct timespec ts;
  68         INTERNAL_SYSCALL_DECL (err);
  69         int r = INTERNAL_SYSCALL (clock_getres, err, 2,
  70                                   (name == _SC_CPUTIME
  71                                    ? CLOCK_PROCESS_CPUTIME_ID
  72                                    : CLOCK_THREAD_CPUTIME_ID),
  73                                   &ts);
  74         if (INTERNAL_SYSCALL_ERROR_P (r, err))
  75           return -1;
  76 # endif
  77         return _POSIX_VERSION;
  78       }
  79 #endif
  80
  81     case _SC_ARG_MAX:
  82 #if __LINUX_KERNEL_VERSION < 0x020617
  83       /* Determine whether this is a kernel 2.6.23 or later.  Only
  84          then do we have an argument limit determined by the stack
  85          size.  */
  86       if (GLRO(dl_discover_osversion) () >= 0x020617)
  87 #endif
  88         /* Use getrlimit to get the stack limit.  */
  89         if (__getrlimit (RLIMIT_STACK, &rlimit) == 0)
  90           return MAX (legacy_ARG_MAX, rlimit.rlim_cur / 4);
  91
  92       return legacy_ARG_MAX;
  93
  94     case _SC_NGROUPS_MAX:
  95       /* Try to read the information from the /proc/sys/kernel/ngroups_max
  96          file.  */
  97       procfname = "/proc/sys/kernel/ngroups_max";
  98       break;
  99
 100     case _SC_SIGQUEUE_MAX:
 101       if (__getrlimit (RLIMIT_SIGPENDING, &rlimit) == 0)
 102         return rlimit.rlim_cur;
 103
 104       /* The /proc/sys/kernel/rtsig-max file contains the answer.  */
 105       procfname = "/proc/sys/kernel/rtsig-max";
 106       break;
 107
 108     default:
 109       break;
 110     }
 111
 112   if (procfname != NULL)
 113     {
 114       int fd = open_not_cancel_2 (procfname, O_RDONLY);
 115       if (fd != -1)
 116         {
 117           /* This is more than enough, the file contains a single integer.  */
 118           char buf[32];
 119           ssize_t n;
 120           n = TEMP_FAILURE_RETRY (read_not_cancel (fd, buf, sizeof (buf) - 1));
 121           close_not_cancel_no_status (fd);
 122
 123           if (n > 0)
 124             {
 125               /* Terminate the string.  */
 126               buf[n] = '\0';
 127
 128               char *endp;
 129               long int res = strtol (buf, &endp, 10);
 130               if (endp != buf && (*endp == '\0' || *endp == '\n'))
 131                 return res;
 132             }
 133         }
 134     }
 135
 136   return posix_sysconf (name);
 137 }
 138
 139 /* Now the POSIX version.  */
 140 #undef __sysconf
 141 #define __sysconf static posix_sysconf
 142 #include <sysdeps/posix/sysconf.c>