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/* Copyright (C) 1997, 1999 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 Library General Public License as
   published by the Free Software Foundation; either version 2 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
   Library General Public License for more details.
 
   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */
 
#include <errno.h>
#include <termios.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#define __USE_XOPEN_EXTENDED
#include <unistd.h>
 
 
/* Return the session ID of FD.  */
pid_t tcgetsid (int fd)
{
    pid_t pgrp;
    pid_t sid;
#ifdef TIOCGSID
    static int tiocgsid_does_not_work;
 
    if (! tiocgsid_does_not_work)
    {
	int serrno = errno;
	int sid;
 
	if (ioctl (fd, TIOCGSID, &sid) < 0)
	{
	    if (errno == EINVAL)
	    {
		tiocgsid_does_not_work = 1;
		__set_errno(serrno);
	    }
	    else
		return (pid_t) -1;
	}
	else
	    return (pid_t) sid;
    }
#endif
 
    pgrp = tcgetpgrp (fd);
    if (pgrp == -1)
	return (pid_t) -1;
 
    sid = getsid (pgrp);
    if (sid == -1 && errno == ESRCH)
	__set_errno(ENOTTY);
 
    return sid;
}