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1 | /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/ |
2 | ||
3 | /*** | |
4 | This file is part of systemd. | |
5 | ||
6 | Copyright 2010 Lennart Poettering | |
7 | ||
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. | |
12 | ||
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. | |
17 | ||
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/>. | |
20 | ***/ | |
21 | ||
22 | #include <stdlib.h> | |
23 | #include <stdbool.h> | |
24 | #include <errno.h> | |
25 | #include <string.h> | |
26 | #include <stdio.h> | |
27 | #include <limits.h> | |
28 | #include <sys/file.h> | |
29 | ||
30 | #include "util.h" | |
31 | #include "lockfile-util.h" | |
32 | #include "fileio.h" | |
33 | ||
34 | int make_lock_file(const char *p, int operation, LockFile *ret) { | |
35 | _cleanup_close_ int fd = -1; | |
36 | _cleanup_free_ char *t = NULL; | |
37 | int r; | |
38 | ||
39 | /* | |
40 | * We use UNPOSIX locks if they are available. They have nice | |
41 | * semantics, and are mostly compatible with NFS. However, | |
42 | * they are only available on new kernels. When we detect we | |
43 | * are running on an older kernel, then we fall back to good | |
44 | * old BSD locks. They also have nice semantics, but are | |
45 | * slightly problematic on NFS, where they are upgraded to | |
46 | * POSIX locks, even though locally they are orthogonal to | |
47 | * POSIX locks. | |
48 | */ | |
49 | ||
50 | t = strdup(p); | |
51 | if (!t) | |
52 | return -ENOMEM; | |
53 | ||
54 | for (;;) { | |
55 | struct flock fl = { | |
56 | .l_type = (operation & ~LOCK_NB) == LOCK_EX ? F_WRLCK : F_RDLCK, | |
57 | .l_whence = SEEK_SET, | |
58 | }; | |
59 | struct stat st; | |
60 | ||
61 | fd = open(p, O_CREAT|O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NOCTTY, 0600); | |
62 | if (fd < 0) | |
63 | return -errno; | |
64 | ||
65 | r = fcntl(fd, (operation & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW, &fl); | |
66 | if (r < 0) { | |
67 | ||
68 | /* If the kernel is too old, use good old BSD locks */ | |
69 | if (errno == EINVAL) | |
70 | r = flock(fd, operation); | |
71 | ||
72 | if (r < 0) | |
73 | return errno == EAGAIN ? -EBUSY : -errno; | |
74 | } | |
75 | ||
76 | /* If we acquired the lock, let's check if the file | |
77 | * still exists in the file system. If not, then the | |
78 | * previous exclusive owner removed it and then closed | |
79 | * it. In such a case our acquired lock is worthless, | |
80 | * hence try again. */ | |
81 | ||
82 | r = fstat(fd, &st); | |
83 | if (r < 0) | |
84 | return -errno; | |
85 | if (st.st_nlink > 0) | |
86 | break; | |
87 | ||
88 | fd = safe_close(fd); | |
89 | } | |
90 | ||
91 | ret->path = t; | |
92 | ret->fd = fd; | |
93 | ret->operation = operation; | |
94 | ||
95 | fd = -1; | |
96 | t = NULL; | |
97 | ||
98 | return r; | |
99 | } | |
100 | ||
101 | int make_lock_file_for(const char *p, int operation, LockFile *ret) { | |
102 | const char *fn; | |
103 | char *t; | |
104 | ||
105 | assert(p); | |
106 | assert(ret); | |
107 | ||
108 | fn = basename(p); | |
109 | if (!filename_is_valid(fn)) | |
110 | return -EINVAL; | |
111 | ||
112 | t = newa(char, strlen(p) + 2 + 4 + 1); | |
113 | stpcpy(stpcpy(stpcpy(mempcpy(t, p, fn - p), ".#"), fn), ".lck"); | |
114 | ||
115 | return make_lock_file(t, operation, ret); | |
116 | } | |
117 | ||
118 | void release_lock_file(LockFile *f) { | |
119 | int r; | |
120 | ||
121 | if (!f) | |
122 | return; | |
123 | ||
124 | if (f->path) { | |
125 | ||
126 | /* If we are the exclusive owner we can safely delete | |
127 | * the lock file itself. If we are not the exclusive | |
128 | * owner, we can try becoming it. */ | |
129 | ||
130 | if (f->fd >= 0 && | |
131 | (f->operation & ~LOCK_NB) == LOCK_SH) { | |
132 | static const struct flock fl = { | |
133 | .l_type = F_WRLCK, | |
134 | .l_whence = SEEK_SET, | |
135 | }; | |
136 | ||
137 | r = fcntl(f->fd, F_OFD_SETLK, &fl); | |
138 | if (r < 0 && errno == EINVAL) | |
139 | r = flock(f->fd, LOCK_EX|LOCK_NB); | |
140 | ||
141 | if (r >= 0) | |
142 | f->operation = LOCK_EX|LOCK_NB; | |
143 | } | |
144 | ||
145 | if ((f->operation & ~LOCK_NB) == LOCK_EX) | |
146 | unlink_noerrno(f->path); | |
147 | ||
6300502b | 148 | f->path = mfree(f->path); |
e3bff60a MP |
149 | } |
150 | ||
151 | f->fd = safe_close(f->fd); | |
152 | f->operation = 0; | |
153 | } |