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git.ipfire.org Git - thirdparty/systemd.git/blob - src/basic/lockfile-util.c
1 /* SPDX-License-Identifier: LGPL-2.1+ */
3 This file is part of systemd.
5 Copyright 2010 Lennart Poettering
7 systemd is free software; you can redistribute it and/or modify it
8 under the terms of the GNU Lesser General Public License as published by
9 the Free Software Foundation; either version 2.1 of the License, or
10 (at your option) any later version.
12 systemd is distributed in the hope that it will be useful, but
13 WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Lesser General Public License for more details.
17 You should have received a copy of the GNU Lesser General Public License
18 along with systemd; If not, see <http://www.gnu.org/licenses/>.
28 #include "alloc-util.h"
31 #include "lockfile-util.h"
33 #include "path-util.h"
35 int make_lock_file(const char *p
, int operation
, LockFile
*ret
) {
36 _cleanup_close_
int fd
= -1;
37 _cleanup_free_
char *t
= NULL
;
41 * We use UNPOSIX locks if they are available. They have nice
42 * semantics, and are mostly compatible with NFS. However,
43 * they are only available on new kernels. When we detect we
44 * are running on an older kernel, then we fall back to good
45 * old BSD locks. They also have nice semantics, but are
46 * slightly problematic on NFS, where they are upgraded to
47 * POSIX locks, even though locally they are orthogonal to
57 .l_type
= (operation
& ~LOCK_NB
) == LOCK_EX
? F_WRLCK
: F_RDLCK
,
62 fd
= open(p
, O_CREAT
|O_RDWR
|O_NOFOLLOW
|O_CLOEXEC
|O_NOCTTY
, 0600);
66 r
= fcntl(fd
, (operation
& LOCK_NB
) ? F_OFD_SETLK
: F_OFD_SETLKW
, &fl
);
69 /* If the kernel is too old, use good old BSD locks */
71 r
= flock(fd
, operation
);
74 return errno
== EAGAIN
? -EBUSY
: -errno
;
77 /* If we acquired the lock, let's check if the file
78 * still exists in the file system. If not, then the
79 * previous exclusive owner removed it and then closed
80 * it. In such a case our acquired lock is worthless,
94 ret
->operation
= operation
;
102 int make_lock_file_for(const char *p
, int operation
, LockFile
*ret
) {
110 if (!filename_is_valid(fn
))
113 t
= newa(char, strlen(p
) + 2 + 4 + 1);
114 stpcpy(stpcpy(stpcpy(mempcpy(t
, p
, fn
- p
), ".#"), fn
), ".lck");
116 return make_lock_file(t
, operation
, ret
);
119 void release_lock_file(LockFile
*f
) {
127 /* If we are the exclusive owner we can safely delete
128 * the lock file itself. If we are not the exclusive
129 * owner, we can try becoming it. */
132 (f
->operation
& ~LOCK_NB
) == LOCK_SH
) {
133 static const struct flock fl
= {
135 .l_whence
= SEEK_SET
,
138 r
= fcntl(f
->fd
, F_OFD_SETLK
, &fl
);
139 if (r
< 0 && errno
== EINVAL
)
140 r
= flock(f
->fd
, LOCK_EX
|LOCK_NB
);
143 f
->operation
= LOCK_EX
|LOCK_NB
;
146 if ((f
->operation
& ~LOCK_NB
) == LOCK_EX
)
147 unlink_noerrno(f
->path
);
149 f
->path
= mfree(f
->path
);
152 f
->fd
= safe_close(f
->fd
);