1/* Copyright (C) 1994-2020 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#ifndef __OFF_T_MATCHES_OFF64_T
19
20#include <unistd.h>
21#include <fcntl.h>
22#include <errno.h>
23
24/* lockf is a simplified interface to fcntl's locking facilities. */
25int
26lockf (int fd, int cmd, off_t len)
27{
28 /* lockf is always relative to the current file position. */
29 struct flock fl = {
30 .l_type = F_WRLCK,
31 .l_whence = SEEK_CUR,
32 .l_len = len
33 };
34
35 /* lockf() is a cancellation point but so is fcntl() if F_SETLKW is
36 used. Therefore we don't have to care about cancellation here,
37 the fcntl() function will take care of it. */
38 switch (cmd)
39 {
40 case F_TEST:
41 /* Test the lock: return 0 if FD is unlocked or locked by this process;
42 return -1, set errno to EACCES, if another process holds the lock. */
43 fl.l_type = F_RDLCK;
44 if (__fcntl (fd, F_GETLK, &fl) < 0)
45 return -1;
46 if (fl.l_type == F_UNLCK || fl.l_pid == __getpid ())
47 return 0;
48 __set_errno (EACCES);
49 return -1;
50 case F_ULOCK:
51 fl.l_type = F_UNLCK;
52 return __fcntl (fd, F_SETLK, &fl);
53 case F_LOCK:
54 return __fcntl (fd, F_SETLKW, &fl);
55 case F_TLOCK:
56 return __fcntl (fd, F_SETLK, &fl);
57 }
58 __set_errno (EINVAL);
59 return -1;
60}
61#endif
62