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 */