1  /* Copyright (C) 1997-2023 Free Software Foundation, Inc.
       2     This file is part of the GNU C Library.
       3  
       4     The GNU C Library is free software; you can redistribute it and/or
       5     modify it under the terms of the GNU Lesser General Public
       6     License as published by the Free Software Foundation; either
       7     version 2.1 of the License, or (at your option) any later version.
       8  
       9     The GNU C Library is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      12     Lesser General Public License for more details.
      13  
      14     You should have received a copy of the GNU Lesser General Public
      15     License along with the GNU C Library; if not, see
      16     <https://www.gnu.org/licenses/>.  */
      17  
      18  #include <errno.h>
      19  #include <termios.h>
      20  #include <sys/ioctl.h>
      21  #include <sys/types.h>
      22  #include <unistd.h>
      23  
      24  /* Return the session ID of FD.  */
      25  pid_t
      26  tcgetsid (int fd)
      27  {
      28    pid_t pgrp;
      29    pid_t sid;
      30  #ifdef TIOCGSID
      31    static int tiocgsid_does_not_work;
      32  
      33    if (! tiocgsid_does_not_work)
      34      {
      35        int serrno = errno;
      36        int sid;
      37  
      38        if (__ioctl (fd, TIOCGSID, &sid) < 0)
      39  	{
      40  	  if (errno == EINVAL)
      41  	    {
      42  	      tiocgsid_does_not_work = 1;
      43  	      __set_errno (serrno);
      44  	    }
      45  	  else
      46  	    return (pid_t) -1;
      47  	}
      48        else
      49  	return (pid_t) sid;
      50      }
      51  #endif
      52  
      53    pgrp = tcgetpgrp (fd);
      54    if (pgrp == -1)
      55      return (pid_t) -1;
      56  
      57    sid = getsid (pgrp);
      58    if (sid == -1 && errno == ESRCH)
      59      __set_errno (ENOTTY);
      60  
      61    return sid;
      62  }