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53e1b683 | 1 | /* SPDX-License-Identifier: LGPL-2.1+ */ |
cd2eb9e9 | 2 | |
cd2eb9e9 | 3 | #include <errno.h> |
11c3a366 | 4 | #include <fcntl.h> |
cf0fbc49 | 5 | #include <stdio.h> |
cf0fbc49 | 6 | #include <string.h> |
cd2eb9e9 | 7 | #include <sys/file.h> |
11c3a366 | 8 | #include <sys/stat.h> |
cd2eb9e9 | 9 | |
b5efdb8a | 10 | #include "alloc-util.h" |
3ffd4af2 | 11 | #include "fd-util.h" |
f4f15635 | 12 | #include "fs-util.h" |
3ffd4af2 | 13 | #include "lockfile-util.h" |
11c3a366 | 14 | #include "macro.h" |
5269db45 | 15 | #include "missing_fcntl.h" |
93cc7779 | 16 | #include "path-util.h" |
cd2eb9e9 CW |
17 | |
18 | int make_lock_file(const char *p, int operation, LockFile *ret) { | |
19 | _cleanup_close_ int fd = -1; | |
20 | _cleanup_free_ char *t = NULL; | |
21 | int r; | |
22 | ||
23 | /* | |
24 | * We use UNPOSIX locks if they are available. They have nice | |
25 | * semantics, and are mostly compatible with NFS. However, | |
26 | * they are only available on new kernels. When we detect we | |
27 | * are running on an older kernel, then we fall back to good | |
28 | * old BSD locks. They also have nice semantics, but are | |
29 | * slightly problematic on NFS, where they are upgraded to | |
30 | * POSIX locks, even though locally they are orthogonal to | |
31 | * POSIX locks. | |
32 | */ | |
33 | ||
34 | t = strdup(p); | |
35 | if (!t) | |
36 | return -ENOMEM; | |
37 | ||
38 | for (;;) { | |
39 | struct flock fl = { | |
40 | .l_type = (operation & ~LOCK_NB) == LOCK_EX ? F_WRLCK : F_RDLCK, | |
41 | .l_whence = SEEK_SET, | |
42 | }; | |
43 | struct stat st; | |
44 | ||
45 | fd = open(p, O_CREAT|O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NOCTTY, 0600); | |
46 | if (fd < 0) | |
47 | return -errno; | |
48 | ||
49 | r = fcntl(fd, (operation & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW, &fl); | |
50 | if (r < 0) { | |
51 | ||
52 | /* If the kernel is too old, use good old BSD locks */ | |
53 | if (errno == EINVAL) | |
54 | r = flock(fd, operation); | |
55 | ||
56 | if (r < 0) | |
57 | return errno == EAGAIN ? -EBUSY : -errno; | |
58 | } | |
59 | ||
60 | /* If we acquired the lock, let's check if the file | |
61 | * still exists in the file system. If not, then the | |
62 | * previous exclusive owner removed it and then closed | |
63 | * it. In such a case our acquired lock is worthless, | |
64 | * hence try again. */ | |
65 | ||
66 | r = fstat(fd, &st); | |
67 | if (r < 0) | |
68 | return -errno; | |
69 | if (st.st_nlink > 0) | |
70 | break; | |
71 | ||
72 | fd = safe_close(fd); | |
73 | } | |
74 | ||
75 | ret->path = t; | |
76 | ret->fd = fd; | |
77 | ret->operation = operation; | |
78 | ||
79 | fd = -1; | |
80 | t = NULL; | |
81 | ||
82 | return r; | |
83 | } | |
84 | ||
85 | int make_lock_file_for(const char *p, int operation, LockFile *ret) { | |
86 | const char *fn; | |
87 | char *t; | |
88 | ||
89 | assert(p); | |
90 | assert(ret); | |
91 | ||
92 | fn = basename(p); | |
93 | if (!filename_is_valid(fn)) | |
94 | return -EINVAL; | |
95 | ||
96 | t = newa(char, strlen(p) + 2 + 4 + 1); | |
97 | stpcpy(stpcpy(stpcpy(mempcpy(t, p, fn - p), ".#"), fn), ".lck"); | |
98 | ||
99 | return make_lock_file(t, operation, ret); | |
100 | } | |
101 | ||
102 | void release_lock_file(LockFile *f) { | |
103 | int r; | |
104 | ||
105 | if (!f) | |
106 | return; | |
107 | ||
108 | if (f->path) { | |
109 | ||
110 | /* If we are the exclusive owner we can safely delete | |
111 | * the lock file itself. If we are not the exclusive | |
112 | * owner, we can try becoming it. */ | |
113 | ||
114 | if (f->fd >= 0 && | |
115 | (f->operation & ~LOCK_NB) == LOCK_SH) { | |
116 | static const struct flock fl = { | |
117 | .l_type = F_WRLCK, | |
118 | .l_whence = SEEK_SET, | |
119 | }; | |
120 | ||
121 | r = fcntl(f->fd, F_OFD_SETLK, &fl); | |
122 | if (r < 0 && errno == EINVAL) | |
123 | r = flock(f->fd, LOCK_EX|LOCK_NB); | |
124 | ||
125 | if (r >= 0) | |
126 | f->operation = LOCK_EX|LOCK_NB; | |
127 | } | |
128 | ||
129 | if ((f->operation & ~LOCK_NB) == LOCK_EX) | |
130 | unlink_noerrno(f->path); | |
131 | ||
a1e58e8e | 132 | f->path = mfree(f->path); |
cd2eb9e9 CW |
133 | } |
134 | ||
135 | f->fd = safe_close(f->fd); | |
136 | f->operation = 0; | |
137 | } |