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/* Get file-specific information about a file. Linux version.
Copyright (C) 2003-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sysdep.h>
#include <time.h>
#include <unistd.h>
#include <sys/resource.h>
#include <sys/param.h>
#include <not-cancel.h>
#include <ldsodefs.h>
#include <sysconf-sigstksz.h>
/* Legacy value of ARG_MAX. The macro is now not defined since the
actual value varies based on the stack size. */
#define legacy_ARG_MAX 131072
/* Newer kernels (4.13) limit the maximum command line arguments lengths to
6MiB. */
#define maximum_ARG_MAX (6 * 1024 * 1024)
static long int posix_sysconf (int name);
/* Get the value of the system variable NAME. */
long int
__sysconf (int name)
{
const char *procfname = NULL;
switch (name)
{
case _SC_MONOTONIC_CLOCK:
case _SC_CPUTIME:
case _SC_THREAD_CPUTIME:
return _POSIX_VERSION;
case _SC_ARG_MAX:
{
struct rlimit rlimit;
/* Use getrlimit to get the stack limit. */
if (__getrlimit (RLIMIT_STACK, &rlimit) == 0)
{
const long int limit = MAX (legacy_ARG_MAX, rlimit.rlim_cur / 4);
return MIN (limit, maximum_ARG_MAX);
}
return legacy_ARG_MAX;
}
case _SC_NGROUPS_MAX:
/* Try to read the information from the /proc/sys/kernel/ngroups_max
file. */
procfname = "/proc/sys/kernel/ngroups_max";
break;
case _SC_SIGQUEUE_MAX:
{
struct rlimit rlimit;
if (__getrlimit (RLIMIT_SIGPENDING, &rlimit) == 0)
return rlimit.rlim_cur;
/* The /proc/sys/kernel/rtsig-max file contains the answer. */
procfname = "/proc/sys/kernel/rtsig-max";
}
break;
case _SC_MINSIGSTKSZ:
assert (GLRO(dl_minsigstacksize) != 0);
return GLRO(dl_minsigstacksize);
case _SC_SIGSTKSZ:
return sysconf_sigstksz ();
default:
break;
}
if (procfname != NULL)
{
int fd = __open_nocancel (procfname, O_RDONLY | O_CLOEXEC);
if (fd != -1)
{
/* This is more than enough, the file contains a single integer. */
char buf[32];
ssize_t n;
n = TEMP_FAILURE_RETRY (__read_nocancel (fd, buf, sizeof (buf) - 1));
__close_nocancel_nostatus (fd);
if (n > 0)
{
/* Terminate the string. */
buf[n] = '\0';
char *endp;
long int res = strtol (buf, &endp, 10);
if (endp != buf && (*endp == '\0' || *endp == '\n'))
return res;
}
}
}
return posix_sysconf (name);
}
/* Now the POSIX version. */
#undef __sysconf
#define __sysconf static posix_sysconf
#include <sysdeps/posix/sysconf.c>
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