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[git.git] / tempfile.h
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1 #ifndef TEMPFILE_H
2 #define TEMPFILE_H
4 #include "list.h"
6 /*
7 * Handle temporary files.
9 * The tempfile API allows temporary files to be created, deleted, and
10 * atomically renamed. Temporary files that are still active when the
11 * program ends are cleaned up automatically. Lockfiles (see
12 * "lockfile.h") are built on top of this API.
15 * Calling sequence
16 * ----------------
18 * The caller:
20 * * Attempts to create a temporary file by calling
21 * `create_tempfile()`. The resources used for the temporary file are
22 * managed by the tempfile API.
24 * * Writes new content to the file by either:
26 * * writing to the `tempfile->fd` file descriptor
28 * * calling `fdopen_tempfile()` to get a `FILE` pointer for the
29 * open file and writing to the file using stdio.
31 * Note that the file descriptor created by create_tempfile()
32 * is marked O_CLOEXEC, so the new contents must be written by
33 * the current process, not any spawned one.
35 * When finished writing, the caller can:
37 * * Close the file descriptor and remove the temporary file by
38 * calling `delete_tempfile()`.
40 * * Close the temporary file and rename it atomically to a specified
41 * filename by calling `rename_tempfile()`. This relinquishes
42 * control of the file.
44 * * Close the file descriptor without removing or renaming the
45 * temporary file by calling `close_tempfile_gently()`, and later call
46 * `delete_tempfile()` or `rename_tempfile()`.
48 * After the temporary file is renamed or deleted, the `tempfile`
49 * object is no longer valid and should not be reused.
51 * If the program exits before `rename_tempfile()` or
52 * `delete_tempfile()` is called, an `atexit(3)` handler will close
53 * and remove the temporary file.
55 * If you need to close the file descriptor yourself, do so by calling
56 * `close_tempfile_gently()`. You should never call `close(2)` or `fclose(3)`
57 * yourself, otherwise the `struct tempfile` structure would still
58 * think that the file descriptor needs to be closed, and a later
59 * cleanup would result in duplicate calls to `close(2)`. Worse yet,
60 * if you close and then later open another file descriptor for a
61 * completely different purpose, then the unrelated file descriptor
62 * might get closed.
65 * Error handling
66 * --------------
68 * `create_tempfile()` returns an allocated tempfile on success or NULL
69 * on failure. On errors, `errno` describes the reason for failure.
71 * `delete_tempfile()`, `rename_tempfile()`, and `close_tempfile_gently()`
72 * return 0 on success. On failure they set `errno` appropriately and return
73 * -1. `delete` and `rename` (but not `close`) do their best to delete the
74 * temporary file before returning.
77 struct tempfile {
78 volatile struct volatile_list_head list;
79 volatile sig_atomic_t active;
80 volatile int fd;
81 FILE *volatile fp;
82 volatile pid_t owner;
83 struct strbuf filename;
87 * Attempt to create a temporary file at the specified `path`. Return
88 * a tempfile (whose "fd" member can be used for writing to it), or
89 * NULL on error. It is an error if a file already exists at that path.
91 extern struct tempfile *create_tempfile(const char *path);
94 * Register an existing file as a tempfile, meaning that it will be
95 * deleted when the program exits. The tempfile is considered closed,
96 * but it can be worked with like any other closed tempfile (for
97 * example, it can be opened using reopen_tempfile()).
99 extern struct tempfile *register_tempfile(const char *path);
103 * mks_tempfile functions
105 * The following functions attempt to create and open temporary files
106 * with names derived automatically from a template, in the manner of
107 * mkstemps(), and arrange for them to be deleted if the program ends
108 * before they are deleted explicitly. There is a whole family of such
109 * functions, named according to the following pattern:
111 * x?mks_tempfile_t?s?m?()
113 * The optional letters have the following meanings:
115 * x - die if the temporary file cannot be created.
117 * t - create the temporary file under $TMPDIR (as opposed to
118 * relative to the current directory). When these variants are
119 * used, template should be the pattern for the filename alone,
120 * without a path.
122 * s - template includes a suffix that is suffixlen characters long.
124 * m - the temporary file should be created with the specified mode
125 * (otherwise, the mode is set to 0600).
127 * None of these functions modify template. If the caller wants to
128 * know the (absolute) path of the file that was created, it can be
129 * read from tempfile->filename.
131 * On success, the functions return a tempfile whose "fd" member is open
132 * for writing the temporary file. On errors, they return NULL and set
133 * errno appropriately (except for the "x" variants, which die() on
134 * errors).
137 /* See "mks_tempfile functions" above. */
138 extern struct tempfile *mks_tempfile_sm(const char *template,
139 int suffixlen, int mode);
141 /* See "mks_tempfile functions" above. */
142 static inline struct tempfile *mks_tempfile_s(const char *template,
143 int suffixlen)
145 return mks_tempfile_sm(template, suffixlen, 0600);
148 /* See "mks_tempfile functions" above. */
149 static inline struct tempfile *mks_tempfile_m(const char *template, int mode)
151 return mks_tempfile_sm(template, 0, mode);
154 /* See "mks_tempfile functions" above. */
155 static inline struct tempfile *mks_tempfile(const char *template)
157 return mks_tempfile_sm(template, 0, 0600);
160 /* See "mks_tempfile functions" above. */
161 extern struct tempfile *mks_tempfile_tsm(const char *template,
162 int suffixlen, int mode);
164 /* See "mks_tempfile functions" above. */
165 static inline struct tempfile *mks_tempfile_ts(const char *template,
166 int suffixlen)
168 return mks_tempfile_tsm(template, suffixlen, 0600);
171 /* See "mks_tempfile functions" above. */
172 static inline struct tempfile *mks_tempfile_tm(const char *template, int mode)
174 return mks_tempfile_tsm(template, 0, mode);
177 /* See "mks_tempfile functions" above. */
178 static inline struct tempfile *mks_tempfile_t(const char *template)
180 return mks_tempfile_tsm(template, 0, 0600);
183 /* See "mks_tempfile functions" above. */
184 extern struct tempfile *xmks_tempfile_m(const char *template, int mode);
186 /* See "mks_tempfile functions" above. */
187 static inline struct tempfile *xmks_tempfile(const char *template)
189 return xmks_tempfile_m(template, 0600);
193 * Associate a stdio stream with the temporary file (which must still
194 * be open). Return `NULL` (*without* deleting the file) on error. The
195 * stream is closed automatically when `close_tempfile_gently()` is called or
196 * when the file is deleted or renamed.
198 extern FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode);
200 static inline int is_tempfile_active(struct tempfile *tempfile)
202 return tempfile && tempfile->active;
206 * Return the path of the lockfile. The return value is a pointer to a
207 * field within the lock_file object and should not be freed.
209 extern const char *get_tempfile_path(struct tempfile *tempfile);
211 extern int get_tempfile_fd(struct tempfile *tempfile);
212 extern FILE *get_tempfile_fp(struct tempfile *tempfile);
215 * If the temporary file is still open, close it (and the file pointer
216 * too, if it has been opened using `fdopen_tempfile()`) without
217 * deleting the file. Return 0 upon success. On failure to `close(2)`,
218 * return a negative value. Usually `delete_tempfile()` or `rename_tempfile()`
219 * should eventually be called regardless of whether `close_tempfile_gently()`
220 * succeeds.
222 extern int close_tempfile_gently(struct tempfile *tempfile);
225 * Re-open a temporary file that has been closed using
226 * `close_tempfile_gently()` but not yet deleted or renamed. This can be used
227 * to implement a sequence of operations like the following:
229 * * Create temporary file.
231 * * Write new contents to file, then `close_tempfile_gently()` to cause the
232 * contents to be written to disk.
234 * * Pass the name of the temporary file to another program to allow
235 * it (and nobody else) to inspect or even modify the file's
236 * contents.
238 * * `reopen_tempfile()` to reopen the temporary file. Make further
239 * updates to the contents.
241 * * `rename_tempfile()` to move the file to its permanent location.
243 extern int reopen_tempfile(struct tempfile *tempfile);
246 * Close the file descriptor and/or file pointer and remove the
247 * temporary file associated with `tempfile`. It is a NOOP to call
248 * `delete_tempfile()` for a `tempfile` object that has already been
249 * deleted or renamed.
251 extern void delete_tempfile(struct tempfile **tempfile_p);
254 * Close the file descriptor and/or file pointer if they are still
255 * open, and atomically rename the temporary file to `path`. `path`
256 * must be on the same filesystem as the lock file. Return 0 on
257 * success. On failure, delete the temporary file and return -1, with
258 * `errno` set to the value from the failing call to `close(2)` or
259 * `rename(2)`. It is a bug to call `rename_tempfile()` for a
260 * `tempfile` object that is not currently active.
262 extern int rename_tempfile(struct tempfile **tempfile_p, const char *path);
264 #endif /* TEMPFILE_H */