/* Copyright (C) 1997-2018 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

   <http://www.gnu.org/licenses/>.  */

#include <errno.h>

#include <termios.h>

#include <sys/ioctl.h>

#include <sys/types.h>

#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;

}