glibc/sysdeps/unix/sysv/linux/sysconf.c

/* Get file-specific information about a file.  Linux version.
   Copyright (C) 2003, 2004 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, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <fcntl.h>
#include <stdlib.h>
#include <sysdep.h>
#include <time.h>
#include <unistd.h>
#include <not-cancel.h>

static long int posix_sysconf (int name);

/* Define this first, so it can be inlined.  */
#define __sysconf static posix_sysconf
#include <sysdeps/posix/sysconf.c>


/* Get the value of the system variable NAME.  */
long int
__sysconf (int name)
{
  switch (name)
    {
#ifdef __NR_clock_getres
    case _SC_MONOTONIC_CLOCK:
      /* Check using the clock_getres system call.  */
      {
	struct timespec ts;
	INTERNAL_SYSCALL_DECL (err);
	int r;
	r = INTERNAL_SYSCALL (clock_getres, err, 2, CLOCK_MONOTONIC, &ts);
	return INTERNAL_SYSCALL_ERROR_P (r, err) ? -1 : 1;
      }
#endif

    case _SC_NGROUPS_MAX:
      {
	/* Try to read the information from the /proc/sys/kernel/ngroups_max
	   file.  */
	int fd = open_not_cancel_2 ("/proc/sys/kernel/ngroups_max", O_RDONLY);
	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_not_cancel (fd, buf,
						     sizeof (buf) - 1));
	    close_not_cancel_no_status (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;
	      }
	  }
      }
      break;

    default:
      break;
    }
  return posix_sysconf (name);
}