sysdeps/unix/sysv/linux/sysconf.c

   1 /* Get file-specific information about a file.  Linux version.
   2    Copyright (C) 2003-2024 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    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  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 <sys/param.h>
  28 #include <not-cancel.h>
  29 #include <ldsodefs.h>
  30 #include <sysconf-sigstksz.h>
  31
  32 /* Legacy value of ARG_MAX.  The macro is now not defined since the
  33    actual value varies based on the stack size.  */
  34 #define legacy_ARG_MAX 131072
  35
  36 /* Newer kernels (4.13) limit the maximum command line arguments lengths to
  37    6MiB.  */
  38 #define maximum_ARG_MAX (6 * 1024 * 1024)
  39
  40 static long int posix_sysconf (int name);
  41
  42
  43 /* Get the value of the system variable NAME.  */
  44 long int
  45 __sysconf (int name)
  46 {
  47   const char *procfname = NULL;
  48
  49   switch (name)
  50     {
  51     case _SC_MONOTONIC_CLOCK:
  52     case _SC_CPUTIME:
  53     case _SC_THREAD_CPUTIME:
  54       return _POSIX_VERSION;
  55
  56     case _SC_ARG_MAX:
  57       {
  58         struct rlimit rlimit;
  59         /* Use getrlimit to get the stack limit.  */
  60         if (__getrlimit (RLIMIT_STACK, &rlimit) == 0)
  61           {
  62             const long int limit = MAX (legacy_ARG_MAX, rlimit.rlim_cur / 4);
  63             return MIN (limit, maximum_ARG_MAX);
  64           }
  65
  66         return legacy_ARG_MAX;
  67       }
  68
  69     case _SC_NGROUPS_MAX:
  70       /* Try to read the information from the /proc/sys/kernel/ngroups_max
  71          file.  */
  72       procfname = "/proc/sys/kernel/ngroups_max";
  73       break;
  74
  75     case _SC_SIGQUEUE_MAX:
  76       {
  77         struct rlimit rlimit;
  78         if (__getrlimit (RLIMIT_SIGPENDING, &rlimit) == 0)
  79           return rlimit.rlim_cur;
  80
  81         /* The /proc/sys/kernel/rtsig-max file contains the answer.  */
  82         procfname = "/proc/sys/kernel/rtsig-max";
  83       }
  84       break;
  85
  86     case _SC_MINSIGSTKSZ:
  87       assert (GLRO(dl_minsigstacksize) != 0);
  88       return GLRO(dl_minsigstacksize);
  89
  90     case _SC_SIGSTKSZ:
  91       return sysconf_sigstksz ();
  92
  93     default:
  94       break;
  95     }
  96
  97   if (procfname != NULL)
  98     {
  99       int fd = __open_nocancel (procfname, O_RDONLY | O_CLOEXEC);
 100       if (fd != -1)
 101         {
 102           /* This is more than enough, the file contains a single integer.  */
 103           char buf[32];
 104           ssize_t n;
 105           n = TEMP_FAILURE_RETRY (__read_nocancel (fd, buf, sizeof (buf) - 1));
 106           __close_nocancel_nostatus (fd);
 107
 108           if (n > 0)
 109             {
 110               /* Terminate the string.  */
 111               buf[n] = '\0';
 112
 113               char *endp;
 114               long int res = strtol (buf, &endp, 10);
 115               if (endp != buf && (*endp == '\0' || *endp == '\n'))
 116                 return res;
 117             }
 118         }
 119     }
 120
 121   return posix_sysconf (name);
 122 }
 123
 124 /* Now the POSIX version.  */
 125 #undef __sysconf
 126 #define __sysconf static posix_sysconf
 127 #include <sysdeps/posix/sysconf.c>