prepare_tempfile_object(): new function, extracted from create_tempfile()
[git/git.git] / tempfile.h
CommitLineData
1a9d15db
MH
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
78struct 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 */
93extern 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 */
101extern FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode);
102
103static 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 */
112extern const char *get_tempfile_path(struct tempfile *tempfile);
113
114extern int get_tempfile_fd(struct tempfile *tempfile);
115extern 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 */
125extern 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 */
146extern 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 */
154extern 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 */
165extern int rename_tempfile(struct tempfile *tempfile, const char *path);
166
167#endif /* TEMPFILE_H */