termios/tcgetsid.c

   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 }