termios/tcgetsid.c

   1 /* Copyright (C) 1997-2015 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    <http://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 (fd)
  27      int fd;
  28 {
  29   pid_t pgrp;
  30   pid_t sid;
  31 #ifdef TIOCGSID
  32   static int tiocgsid_does_not_work;
  33
  34   if (! tiocgsid_does_not_work)
  35     {
  36       int serrno = errno;
  37       int sid;
  38
  39       if (__ioctl (fd, TIOCGSID, &sid) < 0)
  40         {
  41           if (errno == EINVAL)
  42             {
  43               tiocgsid_does_not_work = 1;
  44               __set_errno (serrno);
  45             }
  46           else
  47             return (pid_t) -1;
  48         }
  49       else
  50         return (pid_t) sid;
  51     }
  52 #endif
  53
  54   pgrp = tcgetpgrp (fd);
  55   if (pgrp == -1)
  56     return (pid_t) -1;
  57
  58   sid = getsid (pgrp);
  59   if (sid == -1 && errno == ESRCH)
  60     __set_errno (ENOTTY);
  61
  62   return sid;
  63 }