sysdeps/unix/sysv/linux/sysconf.c

   1 /* Get file-specific information about a file.  Linux version.
   2    Copyright (C) 2003-2014 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, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <fcntl.h>
  21 #include <stdlib.h>
  22 #include <sysdep.h>
  23 #include <time.h>
  24 #include <unistd.h>
  25 #include <sys/resource.h>
  26 #include <not-cancel.h>
  27 #include <ldsodefs.h>
  28
  29 /* Legacy value of ARG_MAX.  The macro is now not defined since the
  30    actual value varies based on the stack size.  */
  31 #define legacy_ARG_MAX 131072
  32
  33
  34 static long int posix_sysconf (int name);
  35
  36
  37 #ifndef HAS_CPUCLOCK
  38 static long int
  39 has_cpuclock (int name)
  40 {
  41 # if defined __NR_clock_getres || HP_TIMING_AVAIL
  42   /* If we have HP_TIMING, we will fall back on that if the system
  43      call does not work, so we support it either way.  */
  44 #  if !HP_TIMING_AVAIL
  45   /* Check using the clock_getres system call.  */
  46   struct timespec ts;
  47   INTERNAL_SYSCALL_DECL (err);
  48   int r = INTERNAL_SYSCALL (clock_getres, err, 2,
  49                             (name == _SC_CPUTIME
  50                              ? CLOCK_PROCESS_CPUTIME_ID
  51                              : CLOCK_THREAD_CPUTIME_ID),
  52                             &ts);
  53   if (INTERNAL_SYSCALL_ERROR_P (r, err))
  54     return -1;
  55 #  endif
  56   return _POSIX_VERSION;
  57 # else
  58   return -1;
  59 # endif
  60 }
  61 # define HAS_CPUCLOCK(name) has_cpuclock (name)
  62 #endif
  63
  64
  65 /* Get the value of the system variable NAME.  */
  66 long int
  67 __sysconf (int name)
  68 {
  69   const char *procfname = NULL;
  70
  71   switch (name)
  72     {
  73       struct rlimit rlimit;
  74 #ifdef __NR_clock_getres
  75     case _SC_MONOTONIC_CLOCK:
  76       /* Check using the clock_getres system call.  */
  77       {
  78         struct timespec ts;
  79         INTERNAL_SYSCALL_DECL (err);
  80         int r;
  81         r = INTERNAL_SYSCALL (clock_getres, err, 2, CLOCK_MONOTONIC, &ts);
  82         return INTERNAL_SYSCALL_ERROR_P (r, err) ? -1 : _POSIX_VERSION;
  83       }
  84 #endif
  85
  86     case _SC_CPUTIME:
  87     case _SC_THREAD_CPUTIME:
  88       return HAS_CPUCLOCK (name);
  89
  90     case _SC_ARG_MAX:
  91 #if !__ASSUME_ARG_MAX_STACK_BASED
  92       /* Determine whether this is a kernel with an argument limit
  93          determined by the stack size.  */
  94       if (GLRO(dl_discover_osversion) ()
  95           >= __LINUX_ARG_MAX_STACK_BASED_MIN_KERNEL)
  96 #endif
  97         /* Use getrlimit to get the stack limit.  */
  98         if (__getrlimit (RLIMIT_STACK, &rlimit) == 0)
  99           return MAX (legacy_ARG_MAX, rlimit.rlim_cur / 4);
 100
 101       return legacy_ARG_MAX;
 102
 103     case _SC_NGROUPS_MAX:
 104       /* Try to read the information from the /proc/sys/kernel/ngroups_max
 105          file.  */
 106       procfname = "/proc/sys/kernel/ngroups_max";
 107       break;
 108
 109     case _SC_SIGQUEUE_MAX:
 110       if (__getrlimit (RLIMIT_SIGPENDING, &rlimit) == 0)
 111         return rlimit.rlim_cur;
 112
 113       /* The /proc/sys/kernel/rtsig-max file contains the answer.  */
 114       procfname = "/proc/sys/kernel/rtsig-max";
 115       break;
 116
 117     default:
 118       break;
 119     }
 120
 121   if (procfname != NULL)
 122     {
 123       int fd = open_not_cancel_2 (procfname, O_RDONLY);
 124       if (fd != -1)
 125         {
 126           /* This is more than enough, the file contains a single integer.  */
 127           char buf[32];
 128           ssize_t n;
 129           n = TEMP_FAILURE_RETRY (read_not_cancel (fd, buf, sizeof (buf) - 1));
 130           close_not_cancel_no_status (fd);
 131
 132           if (n > 0)
 133             {
 134               /* Terminate the string.  */
 135               buf[n] = '\0';
 136
 137               char *endp;
 138               long int res = strtol (buf, &endp, 10);
 139               if (endp != buf && (*endp == '\0' || *endp == '\n'))
 140                 return res;
 141             }
 142         }
 143     }
 144
 145   return posix_sysconf (name);
 146 }
 147
 148 /* Now the POSIX version.  */
 149 #undef __sysconf
 150 #define __sysconf static posix_sysconf
 151 #include <sysdeps/posix/sysconf.c>