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git.ipfire.org Git - thirdparty/systemd.git/blob - src/basic/lockfile-util.c
1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
4 This file is part of systemd.
6 Copyright 2010 Lennart Poettering
8 systemd is free software; you can redistribute it and/or modify it
9 under the terms of the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 2.1 of the License, or
11 (at your option) any later version.
13 systemd is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 Lesser General Public License for more details.
18 You should have received a copy of the GNU Lesser General Public License
19 along with systemd; If not, see <http://www.gnu.org/licenses/>.
29 #include "alloc-util.h"
32 #include "lockfile-util.h"
34 #include "path-util.h"
36 int make_lock_file(const char *p
, int operation
, LockFile
*ret
) {
37 _cleanup_close_
int fd
= -1;
38 _cleanup_free_
char *t
= NULL
;
42 * We use UNPOSIX locks if they are available. They have nice
43 * semantics, and are mostly compatible with NFS. However,
44 * they are only available on new kernels. When we detect we
45 * are running on an older kernel, then we fall back to good
46 * old BSD locks. They also have nice semantics, but are
47 * slightly problematic on NFS, where they are upgraded to
48 * POSIX locks, even though locally they are orthogonal to
58 .l_type
= (operation
& ~LOCK_NB
) == LOCK_EX
? F_WRLCK
: F_RDLCK
,
63 fd
= open(p
, O_CREAT
|O_RDWR
|O_NOFOLLOW
|O_CLOEXEC
|O_NOCTTY
, 0600);
67 r
= fcntl(fd
, (operation
& LOCK_NB
) ? F_OFD_SETLK
: F_OFD_SETLKW
, &fl
);
70 /* If the kernel is too old, use good old BSD locks */
72 r
= flock(fd
, operation
);
75 return errno
== EAGAIN
? -EBUSY
: -errno
;
78 /* If we acquired the lock, let's check if the file
79 * still exists in the file system. If not, then the
80 * previous exclusive owner removed it and then closed
81 * it. In such a case our acquired lock is worthless,
95 ret
->operation
= operation
;
103 int make_lock_file_for(const char *p
, int operation
, LockFile
*ret
) {
111 if (!filename_is_valid(fn
))
114 t
= newa(char, strlen(p
) + 2 + 4 + 1);
115 stpcpy(stpcpy(stpcpy(mempcpy(t
, p
, fn
- p
), ".#"), fn
), ".lck");
117 return make_lock_file(t
, operation
, ret
);
120 void release_lock_file(LockFile
*f
) {
128 /* If we are the exclusive owner we can safely delete
129 * the lock file itself. If we are not the exclusive
130 * owner, we can try becoming it. */
133 (f
->operation
& ~LOCK_NB
) == LOCK_SH
) {
134 static const struct flock fl
= {
136 .l_whence
= SEEK_SET
,
139 r
= fcntl(f
->fd
, F_OFD_SETLK
, &fl
);
140 if (r
< 0 && errno
== EINVAL
)
141 r
= flock(f
->fd
, LOCK_EX
|LOCK_NB
);
144 f
->operation
= LOCK_EX
|LOCK_NB
;
147 if ((f
->operation
& ~LOCK_NB
) == LOCK_EX
)
148 unlink_noerrno(f
->path
);
150 f
->path
= mfree(f
->path
);
153 f
->fd
= safe_close(f
->fd
);