t6026-merge-attr: child processes must not inherit index.lock handles
[git/git.git] / tempfile.c
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1/*
2 * State diagram and cleanup
3 * -------------------------
4 *
5 * If the program exits while a temporary file is active, we want to
6 * make sure that we remove it. This is done by remembering the active
7 * temporary files in a linked list, `tempfile_list`. An `atexit(3)`
8 * handler and a signal handler are registered, to clean up any active
9 * temporary files.
10 *
11 * Because the signal handler can run at any time, `tempfile_list` and
12 * the `tempfile` objects that comprise it must be kept in
13 * self-consistent states at all times.
14 *
15 * The possible states of a `tempfile` object are as follows:
16 *
17 * - Uninitialized. In this state the object's `on_list` field must be
18 * zero but the rest of its contents need not be initialized. As
19 * soon as the object is used in any way, it is irrevocably
20 * registered in `tempfile_list`, and `on_list` is set.
21 *
22 * - Active, file open (after `create_tempfile()` or
23 * `reopen_tempfile()`). In this state:
24 *
25 * - the temporary file exists
26 * - `active` is set
27 * - `filename` holds the filename of the temporary file
28 * - `fd` holds a file descriptor open for writing to it
29 * - `fp` holds a pointer to an open `FILE` object if and only if
30 * `fdopen_tempfile()` has been called on the object
31 * - `owner` holds the PID of the process that created the file
32 *
33 * - Active, file closed (after successful `close_tempfile()`). Same
34 * as the previous state, except that the temporary file is closed,
35 * `fd` is -1, and `fp` is `NULL`.
36 *
37 * - Inactive (after `delete_tempfile()`, `rename_tempfile()`, a
38 * failed attempt to create a temporary file, or a failed
39 * `close_tempfile()`). In this state:
40 *
41 * - `active` is unset
42 * - `filename` is empty (usually, though there are transitory
43 * states in which this condition doesn't hold). Client code should
44 * *not* rely on the filename being empty in this state.
45 * - `fd` is -1 and `fp` is `NULL`
46 * - the object is left registered in the `tempfile_list`, and
47 * `on_list` is set.
48 *
49 * A temporary file is owned by the process that created it. The
50 * `tempfile` has an `owner` field that records the owner's PID. This
51 * field is used to prevent a forked process from deleting a temporary
52 * file created by its parent.
53 */
54
55#include "cache.h"
56#include "tempfile.h"
57#include "sigchain.h"
58
59static struct tempfile *volatile tempfile_list;
60
61static void remove_tempfiles(int skip_fclose)
62{
63 pid_t me = getpid();
64
65 while (tempfile_list) {
66 if (tempfile_list->owner == me) {
67 /* fclose() is not safe to call in a signal handler */
68 if (skip_fclose)
69 tempfile_list->fp = NULL;
70 delete_tempfile(tempfile_list);
71 }
72 tempfile_list = tempfile_list->next;
73 }
74}
75
76static void remove_tempfiles_on_exit(void)
77{
78 remove_tempfiles(0);
79}
80
81static void remove_tempfiles_on_signal(int signo)
82{
83 remove_tempfiles(1);
84 sigchain_pop(signo);
85 raise(signo);
86}
87
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88/*
89 * Initialize *tempfile if necessary and add it to tempfile_list.
90 */
91static void prepare_tempfile_object(struct tempfile *tempfile)
1a9d15db 92{
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93 if (!tempfile_list) {
94 /* One-time initialization */
95 sigchain_push_common(remove_tempfiles_on_signal);
96 atexit(remove_tempfiles_on_exit);
97 }
98
99 if (tempfile->active)
7eba6ce5 100 die("BUG: prepare_tempfile_object called for active object");
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101 if (!tempfile->on_list) {
102 /* Initialize *tempfile and add it to tempfile_list: */
103 tempfile->fd = -1;
104 tempfile->fp = NULL;
105 tempfile->active = 0;
106 tempfile->owner = 0;
7eba6ce5 107 strbuf_init(&tempfile->filename, 0);
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108 tempfile->next = tempfile_list;
109 tempfile_list = tempfile;
110 tempfile->on_list = 1;
111 } else if (tempfile->filename.len) {
112 /* This shouldn't happen, but better safe than sorry. */
7eba6ce5 113 die("BUG: prepare_tempfile_object called for improperly-reset object");
1a9d15db 114 }
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115}
116
117/* Make sure errno contains a meaningful value on error */
118int create_tempfile(struct tempfile *tempfile, const char *path)
119{
120 prepare_tempfile_object(tempfile);
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121
122 strbuf_add_absolute_path(&tempfile->filename, path);
123 tempfile->fd = open(tempfile->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
124 if (tempfile->fd < 0) {
125 strbuf_reset(&tempfile->filename);
126 return -1;
127 }
128 tempfile->owner = getpid();
129 tempfile->active = 1;
130 if (adjust_shared_perm(tempfile->filename.buf)) {
131 int save_errno = errno;
132 error("cannot fix permission bits on %s", tempfile->filename.buf);
133 delete_tempfile(tempfile);
134 errno = save_errno;
135 return -1;
136 }
137 return tempfile->fd;
138}
139
99397152
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140void register_tempfile(struct tempfile *tempfile, const char *path)
141{
142 prepare_tempfile_object(tempfile);
143 strbuf_add_absolute_path(&tempfile->filename, path);
144 tempfile->owner = getpid();
145 tempfile->active = 1;
146}
147
354ab112
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148int mks_tempfile_sm(struct tempfile *tempfile,
149 const char *template, int suffixlen, int mode)
150{
151 prepare_tempfile_object(tempfile);
152
153 strbuf_add_absolute_path(&tempfile->filename, template);
154 tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
155 if (tempfile->fd < 0) {
156 strbuf_reset(&tempfile->filename);
157 return -1;
158 }
159 tempfile->owner = getpid();
160 tempfile->active = 1;
161 return tempfile->fd;
162}
163
164int mks_tempfile_tsm(struct tempfile *tempfile,
165 const char *template, int suffixlen, int mode)
166{
167 const char *tmpdir;
168
169 prepare_tempfile_object(tempfile);
170
171 tmpdir = getenv("TMPDIR");
172 if (!tmpdir)
173 tmpdir = "/tmp";
174
175 strbuf_addf(&tempfile->filename, "%s/%s", tmpdir, template);
176 tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
177 if (tempfile->fd < 0) {
178 strbuf_reset(&tempfile->filename);
179 return -1;
180 }
181 tempfile->owner = getpid();
182 tempfile->active = 1;
183 return tempfile->fd;
184}
185
186int xmks_tempfile_m(struct tempfile *tempfile, const char *template, int mode)
187{
188 int fd;
189 struct strbuf full_template = STRBUF_INIT;
190
191 strbuf_add_absolute_path(&full_template, template);
192 fd = mks_tempfile_m(tempfile, full_template.buf, mode);
193 if (fd < 0)
194 die_errno("Unable to create temporary file '%s'",
195 full_template.buf);
196
197 strbuf_release(&full_template);
198 return fd;
199}
200
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201FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode)
202{
203 if (!tempfile->active)
204 die("BUG: fdopen_tempfile() called for inactive object");
205 if (tempfile->fp)
206 die("BUG: fdopen_tempfile() called for open object");
207
208 tempfile->fp = fdopen(tempfile->fd, mode);
209 return tempfile->fp;
210}
211
212const char *get_tempfile_path(struct tempfile *tempfile)
213{
214 if (!tempfile->active)
215 die("BUG: get_tempfile_path() called for inactive object");
216 return tempfile->filename.buf;
217}
218
219int get_tempfile_fd(struct tempfile *tempfile)
220{
221 if (!tempfile->active)
222 die("BUG: get_tempfile_fd() called for inactive object");
223 return tempfile->fd;
224}
225
226FILE *get_tempfile_fp(struct tempfile *tempfile)
227{
228 if (!tempfile->active)
229 die("BUG: get_tempfile_fp() called for inactive object");
230 return tempfile->fp;
231}
232
233int close_tempfile(struct tempfile *tempfile)
234{
235 int fd = tempfile->fd;
236 FILE *fp = tempfile->fp;
237 int err;
238
239 if (fd < 0)
240 return 0;
241
242 tempfile->fd = -1;
243 if (fp) {
244 tempfile->fp = NULL;
245
246 /*
247 * Note: no short-circuiting here; we want to fclose()
248 * in any case!
249 */
250 err = ferror(fp) | fclose(fp);
251 } else {
252 err = close(fd);
253 }
254
255 if (err) {
256 int save_errno = errno;
257 delete_tempfile(tempfile);
258 errno = save_errno;
259 return -1;
260 }
261
262 return 0;
263}
264
265int reopen_tempfile(struct tempfile *tempfile)
266{
267 if (0 <= tempfile->fd)
268 die("BUG: reopen_tempfile called for an open object");
269 if (!tempfile->active)
270 die("BUG: reopen_tempfile called for an inactive object");
271 tempfile->fd = open(tempfile->filename.buf, O_WRONLY);
272 return tempfile->fd;
273}
274
275int rename_tempfile(struct tempfile *tempfile, const char *path)
276{
277 if (!tempfile->active)
278 die("BUG: rename_tempfile called for inactive object");
279
280 if (close_tempfile(tempfile))
281 return -1;
282
283 if (rename(tempfile->filename.buf, path)) {
284 int save_errno = errno;
285 delete_tempfile(tempfile);
286 errno = save_errno;
287 return -1;
288 }
289
290 tempfile->active = 0;
291 strbuf_reset(&tempfile->filename);
292 return 0;
293}
294
295void delete_tempfile(struct tempfile *tempfile)
296{
297 if (!tempfile->active)
298 return;
299
300 if (!close_tempfile(tempfile)) {
301 unlink_or_warn(tempfile->filename.buf);
302 tempfile->active = 0;
303 strbuf_reset(&tempfile->filename);
304 }
305}