termios/tcgetsid.c

   1 /* Copyright (C) 1997, 1999 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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <errno.h>
  20 #include <termios.h>
  21 #include <sys/ioctl.h>
  22 #include <sys/types.h>
  23 #include <unistd.h>
  24
  25 /* Return the session ID of FD.  */
  26 pid_t
  27 tcgetsid (fd)
  28      int fd;
  29 {
  30   pid_t pgrp;
  31   pid_t sid;
  32 #ifdef TIOCGSID
  33   static int tiocgsid_does_not_work;
  34
  35   if (! tiocgsid_does_not_work)
  36     {
  37       int serrno = errno;
  38       int sid;
  39
  40       if (__ioctl (fd, TIOCGSID, &sid) < 0)
  41         {
  42           if (errno == EINVAL)
  43             {
  44               tiocgsid_does_not_work = 1;
  45               __set_errno (serrno);
  46             }
  47           else
  48             return (pid_t) -1;
  49         }
  50       else
  51         return (pid_t) sid;
  52     }
  53 #endif
  54
  55   pgrp = tcgetpgrp (fd);
  56   if (pgrp == -1)
  57     return (pid_t) -1;
  58
  59   sid = getsid (pgrp);
  60   if (sid == -1 && errno == ESRCH)
  61     __set_errno (ENOTTY);
  62
  63   return sid;
  64 }