sysdeps/unix/sysv/linux/sysconf.c

   1 /* Get file-specific information about a file.  Linux version.
   2    Copyright (C) 2003-2015 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 <sys/param.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 #ifndef HAS_CPUCLOCK
  39 static long int
  40 has_cpuclock (int name)
  41 {
  42 # if defined __NR_clock_getres || HP_TIMING_AVAIL
  43   /* If we have HP_TIMING, we will fall back on that if the system
  44      call does not work, so we support it either way.  */
  45 #  if !HP_TIMING_AVAIL
  46   /* Check using the clock_getres system call.  */
  47   struct timespec ts;
  48   INTERNAL_SYSCALL_DECL (err);
  49   int r = INTERNAL_SYSCALL (clock_getres, err, 2,
  50                             (name == _SC_CPUTIME
  51                              ? CLOCK_PROCESS_CPUTIME_ID
  52                              : CLOCK_THREAD_CPUTIME_ID),
  53                             &ts);
  54   if (INTERNAL_SYSCALL_ERROR_P (r, err))
  55     return -1;
  56 #  endif
  57   return _POSIX_VERSION;
  58 # else
  59   return -1;
  60 # endif
  61 }
  62 # define HAS_CPUCLOCK(name) has_cpuclock (name)
  63 #endif
  64
  65
  66 /* Get the value of the system variable NAME.  */
  67 long int
  68 __sysconf (int name)
  69 {
  70   const char *procfname = NULL;
  71
  72   switch (name)
  73     {
  74       struct rlimit rlimit;
  75 #ifdef __NR_clock_getres
  76     case _SC_MONOTONIC_CLOCK:
  77       /* Check using the clock_getres system call.  */
  78       {
  79         struct timespec ts;
  80         INTERNAL_SYSCALL_DECL (err);
  81         int r;
  82         r = INTERNAL_SYSCALL (clock_getres, err, 2, CLOCK_MONOTONIC, &ts);
  83         return INTERNAL_SYSCALL_ERROR_P (r, err) ? -1 : _POSIX_VERSION;
  84       }
  85 #endif
  86
  87     case _SC_CPUTIME:
  88     case _SC_THREAD_CPUTIME:
  89       return HAS_CPUCLOCK (name);
  90
  91     case _SC_ARG_MAX:
  92       /* Use getrlimit to get the stack limit.  */
  93       if (__getrlimit (RLIMIT_STACK, &rlimit) == 0)
  94         return MAX (legacy_ARG_MAX, rlimit.rlim_cur / 4);
  95
  96       return legacy_ARG_MAX;
  97
  98     case _SC_NGROUPS_MAX:
  99       /* Try to read the information from the /proc/sys/kernel/ngroups_max
 100          file.  */
 101       procfname = "/proc/sys/kernel/ngroups_max";
 102       break;
 103
 104     case _SC_SIGQUEUE_MAX:
 105       if (__getrlimit (RLIMIT_SIGPENDING, &rlimit) == 0)
 106         return rlimit.rlim_cur;
 107
 108       /* The /proc/sys/kernel/rtsig-max file contains the answer.  */
 109       procfname = "/proc/sys/kernel/rtsig-max";
 110       break;
 111
 112     default:
 113       break;
 114     }
 115
 116   if (procfname != NULL)
 117     {
 118       int fd = open_not_cancel_2 (procfname, O_RDONLY);
 119       if (fd != -1)
 120         {
 121           /* This is more than enough, the file contains a single integer.  */
 122           char buf[32];
 123           ssize_t n;
 124           n = TEMP_FAILURE_RETRY (read_not_cancel (fd, buf, sizeof (buf) - 1));
 125           close_not_cancel_no_status (fd);
 126
 127           if (n > 0)
 128             {
 129               /* Terminate the string.  */
 130               buf[n] = '\0';
 131
 132               char *endp;
 133               long int res = strtol (buf, &endp, 10);
 134               if (endp != buf && (*endp == '\0' || *endp == '\n'))
 135                 return res;
 136             }
 137         }
 138     }
 139
 140   return posix_sysconf (name);
 141 }
 142
 143 /* Now the POSIX version.  */
 144 #undef __sysconf
 145 #define __sysconf static posix_sysconf
 146 #include <sysdeps/posix/sysconf.c>