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. */
25pid_t
26tcgetsid (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}
63