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1/* Copyright (C) 1992-2019 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/* This file implements the `flock' function in terms of the POSIX.1 `fcntl'
19 locking mechanism. In 4BSD, these are two incompatible locking mechanisms,
20 perhaps with different semantics? */
21
22#include <errno.h>
23#include <unistd.h>
24#include <fcntl.h>
25#include <sys/file.h>
26
27/* Apply or remove an advisory lock, according to OPERATION,
28 on the file FD refers to. */
29int
30__flock (int fd, int operation)
31{
32 struct flock lbuf;
33
34 switch (operation & ~LOCK_NB)
35 {
36 case LOCK_SH:
37 lbuf.l_type = F_RDLCK;
38 break;
39 case LOCK_EX:
40 lbuf.l_type = F_WRLCK;
41 break;
42 case LOCK_UN:
43 lbuf.l_type = F_UNLCK;
44 break;
45 default:
46 __set_errno (EINVAL);
47 return -1;
48 }
49
50 lbuf.l_whence = SEEK_SET;
51 lbuf.l_start = lbuf.l_len = 0L; /* Lock the whole file. */
52
53 return __fcntl (fd, (operation & LOCK_NB) ? F_SETLK : F_SETLKW, &lbuf);
54}
55
56weak_alias (__flock, flock)
57

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