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1 | #ifndef TEMPFILE_H |
2 | #define TEMPFILE_H | |
3 | ||
4 | /* | |
5 | * Handle temporary files. | |
6 | * | |
7 | * The tempfile API allows temporary files to be created, deleted, and | |
8 | * atomically renamed. Temporary files that are still active when the | |
9 | * program ends are cleaned up automatically. Lockfiles (see | |
10 | * "lockfile.h") are built on top of this API. | |
11 | * | |
12 | * | |
13 | * Calling sequence | |
14 | * ---------------- | |
15 | * | |
16 | * The caller: | |
17 | * | |
18 | * * Allocates a `struct tempfile` either as a static variable or on | |
19 | * the heap, initialized to zeros. Once you use the structure to | |
20 | * call `create_tempfile()`, it belongs to the tempfile subsystem | |
21 | * and its storage must remain valid throughout the life of the | |
22 | * program (i.e. you cannot use an on-stack variable to hold this | |
23 | * structure). | |
24 | * | |
25 | * * Attempts to create a temporary file by calling | |
26 | * `create_tempfile()`. | |
27 | * | |
28 | * * Writes new content to the file by either: | |
29 | * | |
30 | * * writing to the file descriptor returned by `create_tempfile()` | |
31 | * (also available via `tempfile->fd`). | |
32 | * | |
33 | * * calling `fdopen_tempfile()` to get a `FILE` pointer for the | |
34 | * open file and writing to the file using stdio. | |
35 | * | |
36 | * When finished writing, the caller can: | |
37 | * | |
38 | * * Close the file descriptor and remove the temporary file by | |
39 | * calling `delete_tempfile()`. | |
40 | * | |
41 | * * Close the temporary file and rename it atomically to a specified | |
42 | * filename by calling `rename_tempfile()`. This relinquishes | |
43 | * control of the file. | |
44 | * | |
45 | * * Close the file descriptor without removing or renaming the | |
46 | * temporary file by calling `close_tempfile()`, and later call | |
47 | * `delete_tempfile()` or `rename_tempfile()`. | |
48 | * | |
49 | * Even after the temporary file is renamed or deleted, the `tempfile` | |
50 | * object must not be freed or altered by the caller. However, it may | |
51 | * be reused; just pass it to another call of `create_tempfile()`. | |
52 | * | |
53 | * If the program exits before `rename_tempfile()` or | |
54 | * `delete_tempfile()` is called, an `atexit(3)` handler will close | |
55 | * and remove the temporary file. | |
56 | * | |
57 | * If you need to close the file descriptor yourself, do so by calling | |
58 | * `close_tempfile()`. You should never call `close(2)` or `fclose(3)` | |
59 | * yourself, otherwise the `struct tempfile` structure would still | |
60 | * think that the file descriptor needs to be closed, and a later | |
61 | * cleanup would result in duplicate calls to `close(2)`. Worse yet, | |
62 | * if you close and then later open another file descriptor for a | |
63 | * completely different purpose, then the unrelated file descriptor | |
64 | * might get closed. | |
65 | * | |
66 | * | |
67 | * Error handling | |
68 | * -------------- | |
69 | * | |
70 | * `create_tempfile()` returns a file descriptor on success or -1 on | |
71 | * failure. On errors, `errno` describes the reason for failure. | |
72 | * | |
73 | * `delete_tempfile()`, `rename_tempfile()`, and `close_tempfile()` | |
74 | * return 0 on success. On failure they set `errno` appropriately, do | |
75 | * their best to delete the temporary file, and return -1. | |
76 | */ | |
77 | ||
78 | struct tempfile { | |
79 | struct tempfile *volatile next; | |
80 | volatile sig_atomic_t active; | |
81 | volatile int fd; | |
82 | FILE *volatile fp; | |
83 | volatile pid_t owner; | |
84 | char on_list; | |
85 | struct strbuf filename; | |
86 | }; | |
87 | ||
88 | /* | |
89 | * Attempt to create a temporary file at the specified `path`. Return | |
90 | * a file descriptor for writing to it, or -1 on error. It is an error | |
91 | * if a file already exists at that path. | |
92 | */ | |
93 | extern int create_tempfile(struct tempfile *tempfile, const char *path); | |
94 | ||
95 | /* | |
96 | * Associate a stdio stream with the temporary file (which must still | |
97 | * be open). Return `NULL` (*without* deleting the file) on error. The | |
98 | * stream is closed automatically when `close_tempfile()` is called or | |
99 | * when the file is deleted or renamed. | |
100 | */ | |
101 | extern FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode); | |
102 | ||
103 | static inline int is_tempfile_active(struct tempfile *tempfile) | |
104 | { | |
105 | return tempfile->active; | |
106 | } | |
107 | ||
108 | /* | |
109 | * Return the path of the lockfile. The return value is a pointer to a | |
110 | * field within the lock_file object and should not be freed. | |
111 | */ | |
112 | extern const char *get_tempfile_path(struct tempfile *tempfile); | |
113 | ||
114 | extern int get_tempfile_fd(struct tempfile *tempfile); | |
115 | extern FILE *get_tempfile_fp(struct tempfile *tempfile); | |
116 | ||
117 | /* | |
118 | * If the temporary file is still open, close it (and the file pointer | |
119 | * too, if it has been opened using `fdopen_tempfile()`) without | |
120 | * deleting the file. Return 0 upon success. On failure to `close(2)`, | |
121 | * return a negative value and delete the file. Usually | |
122 | * `delete_tempfile()` or `rename_tempfile()` should eventually be | |
123 | * called if `close_tempfile()` succeeds. | |
124 | */ | |
125 | extern int close_tempfile(struct tempfile *tempfile); | |
126 | ||
127 | /* | |
128 | * Re-open a temporary file that has been closed using | |
129 | * `close_tempfile()` but not yet deleted or renamed. This can be used | |
130 | * to implement a sequence of operations like the following: | |
131 | * | |
132 | * * Create temporary file. | |
133 | * | |
134 | * * Write new contents to file, then `close_tempfile()` to cause the | |
135 | * contents to be written to disk. | |
136 | * | |
137 | * * Pass the name of the temporary file to another program to allow | |
138 | * it (and nobody else) to inspect or even modify the file's | |
139 | * contents. | |
140 | * | |
141 | * * `reopen_tempfile()` to reopen the temporary file. Make further | |
142 | * updates to the contents. | |
143 | * | |
144 | * * `rename_tempfile()` to move the file to its permanent location. | |
145 | */ | |
146 | extern int reopen_tempfile(struct tempfile *tempfile); | |
147 | ||
148 | /* | |
149 | * Close the file descriptor and/or file pointer and remove the | |
150 | * temporary file associated with `tempfile`. It is a NOOP to call | |
151 | * `delete_tempfile()` for a `tempfile` object that has already been | |
152 | * deleted or renamed. | |
153 | */ | |
154 | extern void delete_tempfile(struct tempfile *tempfile); | |
155 | ||
156 | /* | |
157 | * Close the file descriptor and/or file pointer if they are still | |
158 | * open, and atomically rename the temporary file to `path`. `path` | |
159 | * must be on the same filesystem as the lock file. Return 0 on | |
160 | * success. On failure, delete the temporary file and return -1, with | |
161 | * `errno` set to the value from the failing call to `close(2)` or | |
162 | * `rename(2)`. It is a bug to call `rename_tempfile()` for a | |
163 | * `tempfile` object that is not currently active. | |
164 | */ | |
165 | extern int rename_tempfile(struct tempfile *tempfile, const char *path); | |
166 | ||
167 | #endif /* TEMPFILE_H */ |