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53e1b683 | 1 | /* SPDX-License-Identifier: LGPL-2.1+ */ |
cd2eb9e9 CW |
2 | /*** |
3 | This file is part of systemd. | |
4 | ||
5 | Copyright 2010 Lennart Poettering | |
cd2eb9e9 CW |
6 | ***/ |
7 | ||
cd2eb9e9 | 8 | #include <errno.h> |
11c3a366 | 9 | #include <fcntl.h> |
cf0fbc49 | 10 | #include <stdio.h> |
cf0fbc49 | 11 | #include <string.h> |
cd2eb9e9 | 12 | #include <sys/file.h> |
11c3a366 | 13 | #include <sys/stat.h> |
cd2eb9e9 | 14 | |
b5efdb8a | 15 | #include "alloc-util.h" |
3ffd4af2 | 16 | #include "fd-util.h" |
f4f15635 | 17 | #include "fs-util.h" |
3ffd4af2 | 18 | #include "lockfile-util.h" |
11c3a366 | 19 | #include "macro.h" |
93cc7779 | 20 | #include "path-util.h" |
cd2eb9e9 CW |
21 | |
22 | int make_lock_file(const char *p, int operation, LockFile *ret) { | |
23 | _cleanup_close_ int fd = -1; | |
24 | _cleanup_free_ char *t = NULL; | |
25 | int r; | |
26 | ||
27 | /* | |
28 | * We use UNPOSIX locks if they are available. They have nice | |
29 | * semantics, and are mostly compatible with NFS. However, | |
30 | * they are only available on new kernels. When we detect we | |
31 | * are running on an older kernel, then we fall back to good | |
32 | * old BSD locks. They also have nice semantics, but are | |
33 | * slightly problematic on NFS, where they are upgraded to | |
34 | * POSIX locks, even though locally they are orthogonal to | |
35 | * POSIX locks. | |
36 | */ | |
37 | ||
38 | t = strdup(p); | |
39 | if (!t) | |
40 | return -ENOMEM; | |
41 | ||
42 | for (;;) { | |
43 | struct flock fl = { | |
44 | .l_type = (operation & ~LOCK_NB) == LOCK_EX ? F_WRLCK : F_RDLCK, | |
45 | .l_whence = SEEK_SET, | |
46 | }; | |
47 | struct stat st; | |
48 | ||
49 | fd = open(p, O_CREAT|O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NOCTTY, 0600); | |
50 | if (fd < 0) | |
51 | return -errno; | |
52 | ||
53 | r = fcntl(fd, (operation & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW, &fl); | |
54 | if (r < 0) { | |
55 | ||
56 | /* If the kernel is too old, use good old BSD locks */ | |
57 | if (errno == EINVAL) | |
58 | r = flock(fd, operation); | |
59 | ||
60 | if (r < 0) | |
61 | return errno == EAGAIN ? -EBUSY : -errno; | |
62 | } | |
63 | ||
64 | /* If we acquired the lock, let's check if the file | |
65 | * still exists in the file system. If not, then the | |
66 | * previous exclusive owner removed it and then closed | |
67 | * it. In such a case our acquired lock is worthless, | |
68 | * hence try again. */ | |
69 | ||
70 | r = fstat(fd, &st); | |
71 | if (r < 0) | |
72 | return -errno; | |
73 | if (st.st_nlink > 0) | |
74 | break; | |
75 | ||
76 | fd = safe_close(fd); | |
77 | } | |
78 | ||
79 | ret->path = t; | |
80 | ret->fd = fd; | |
81 | ret->operation = operation; | |
82 | ||
83 | fd = -1; | |
84 | t = NULL; | |
85 | ||
86 | return r; | |
87 | } | |
88 | ||
89 | int make_lock_file_for(const char *p, int operation, LockFile *ret) { | |
90 | const char *fn; | |
91 | char *t; | |
92 | ||
93 | assert(p); | |
94 | assert(ret); | |
95 | ||
96 | fn = basename(p); | |
97 | if (!filename_is_valid(fn)) | |
98 | return -EINVAL; | |
99 | ||
100 | t = newa(char, strlen(p) + 2 + 4 + 1); | |
101 | stpcpy(stpcpy(stpcpy(mempcpy(t, p, fn - p), ".#"), fn), ".lck"); | |
102 | ||
103 | return make_lock_file(t, operation, ret); | |
104 | } | |
105 | ||
106 | void release_lock_file(LockFile *f) { | |
107 | int r; | |
108 | ||
109 | if (!f) | |
110 | return; | |
111 | ||
112 | if (f->path) { | |
113 | ||
114 | /* If we are the exclusive owner we can safely delete | |
115 | * the lock file itself. If we are not the exclusive | |
116 | * owner, we can try becoming it. */ | |
117 | ||
118 | if (f->fd >= 0 && | |
119 | (f->operation & ~LOCK_NB) == LOCK_SH) { | |
120 | static const struct flock fl = { | |
121 | .l_type = F_WRLCK, | |
122 | .l_whence = SEEK_SET, | |
123 | }; | |
124 | ||
125 | r = fcntl(f->fd, F_OFD_SETLK, &fl); | |
126 | if (r < 0 && errno == EINVAL) | |
127 | r = flock(f->fd, LOCK_EX|LOCK_NB); | |
128 | ||
129 | if (r >= 0) | |
130 | f->operation = LOCK_EX|LOCK_NB; | |
131 | } | |
132 | ||
133 | if ((f->operation & ~LOCK_NB) == LOCK_EX) | |
134 | unlink_noerrno(f->path); | |
135 | ||
a1e58e8e | 136 | f->path = mfree(f->path); |
cd2eb9e9 CW |
137 | } |
138 | ||
139 | f->fd = safe_close(f->fd); | |
140 | f->operation = 0; | |
141 | } |