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