1/* Reentrant function to return the current login name. Unix version.
2 Copyright (C) 1991-2024 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <errno.h>
20#include <unistd.h>
21#include <string.h>
22#include <stdio.h>
23#include <limits.h>
24#include <fcntl.h>
25
26#include <utmp.h>
27#include "../login/utmp-private.h"
28
29/* Return at most NAME_LEN characters of the login name of the user in NAME.
30 If it cannot be determined or some other error occurred, return the error
31 code. Otherwise return 0. */
32
33#ifdef STATIC
34STATIC
35#endif
36int
37__getlogin_r (char *name, size_t name_len)
38{
39 char tty_pathname[2 + 2 * NAME_MAX];
40 char *real_tty_path = tty_pathname;
41 int result;
42 struct utmp *ut, line, buffer;
43
44 /* Get name of tty connected to fd 0. Return if not a tty or
45 if fd 0 isn't open. Note that a lot of documentation says that
46 getlogin() is based on the controlling terminal---what they
47 really mean is "the terminal connected to standard input". The
48 getlogin() implementation of DEC Unix, SunOS, Solaris, HP-UX all
49 return NULL if fd 0 has been closed, so this is the compatible
50 thing to do. Note that ttyname(open("/dev/tty")) on those
51 systems returns /dev/tty, so that is not a possible solution for
52 getlogin(). */
53
54 result = __ttyname_r (0, real_tty_path, sizeof (tty_pathname));
55
56 if (result != 0)
57 return result;
58
59 real_tty_path += 5; /* Remove "/dev/". */
60 strncpy (line.ut_line, real_tty_path, sizeof line.ut_line);
61
62 /* We don't use the normal entry points __setutent et al, because we
63 want setutent + getutline_r + endutent all to happen with the lock
64 held so that our search is thread-safe. */
65
66 __libc_lock_lock (__libc_utmp_lock);
67 __libc_setutent ();
68 result = __libc_getutline_r (&line, &buffer, &ut);
69 if (result < 0)
70 {
71 if (errno == ESRCH)
72 /* The caller expects ENOENT if nothing is found. */
73 result = ENOENT;
74 else
75 result = errno;
76 }
77 __libc_endutent ();
78 __libc_lock_unlock (__libc_utmp_lock);
79
80 if (result == 0)
81 {
82 size_t needed = __strnlen (ut->ut_user, UT_NAMESIZE) + 1;
83
84 if (needed > name_len)
85 {
86 __set_errno (ERANGE);
87 result = ERANGE;
88 }
89 else
90 {
91 memcpy (name, ut->ut_user, needed - 1);
92 name[needed - 1] = 0;
93 result = 0;
94 }
95 }
96
97 return result;
98}
99#ifndef STATIC
100libc_hidden_def (__getlogin_r)
101weak_alias (__getlogin_r, getlogin_r)
102libc_hidden_weak (getlogin_r)
103#endif
104

source code of glibc/sysdeps/unix/getlogin_r.c