prepare_tempfile_object(): new function, extracted from create_tempfile()
[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
140FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode)
141{
142 if (!tempfile->active)
143 die("BUG: fdopen_tempfile() called for inactive object");
144 if (tempfile->fp)
145 die("BUG: fdopen_tempfile() called for open object");
146
147 tempfile->fp = fdopen(tempfile->fd, mode);
148 return tempfile->fp;
149}
150
151const char *get_tempfile_path(struct tempfile *tempfile)
152{
153 if (!tempfile->active)
154 die("BUG: get_tempfile_path() called for inactive object");
155 return tempfile->filename.buf;
156}
157
158int get_tempfile_fd(struct tempfile *tempfile)
159{
160 if (!tempfile->active)
161 die("BUG: get_tempfile_fd() called for inactive object");
162 return tempfile->fd;
163}
164
165FILE *get_tempfile_fp(struct tempfile *tempfile)
166{
167 if (!tempfile->active)
168 die("BUG: get_tempfile_fp() called for inactive object");
169 return tempfile->fp;
170}
171
172int close_tempfile(struct tempfile *tempfile)
173{
174 int fd = tempfile->fd;
175 FILE *fp = tempfile->fp;
176 int err;
177
178 if (fd < 0)
179 return 0;
180
181 tempfile->fd = -1;
182 if (fp) {
183 tempfile->fp = NULL;
184
185 /*
186 * Note: no short-circuiting here; we want to fclose()
187 * in any case!
188 */
189 err = ferror(fp) | fclose(fp);
190 } else {
191 err = close(fd);
192 }
193
194 if (err) {
195 int save_errno = errno;
196 delete_tempfile(tempfile);
197 errno = save_errno;
198 return -1;
199 }
200
201 return 0;
202}
203
204int reopen_tempfile(struct tempfile *tempfile)
205{
206 if (0 <= tempfile->fd)
207 die("BUG: reopen_tempfile called for an open object");
208 if (!tempfile->active)
209 die("BUG: reopen_tempfile called for an inactive object");
210 tempfile->fd = open(tempfile->filename.buf, O_WRONLY);
211 return tempfile->fd;
212}
213
214int rename_tempfile(struct tempfile *tempfile, const char *path)
215{
216 if (!tempfile->active)
217 die("BUG: rename_tempfile called for inactive object");
218
219 if (close_tempfile(tempfile))
220 return -1;
221
222 if (rename(tempfile->filename.buf, path)) {
223 int save_errno = errno;
224 delete_tempfile(tempfile);
225 errno = save_errno;
226 return -1;
227 }
228
229 tempfile->active = 0;
230 strbuf_reset(&tempfile->filename);
231 return 0;
232}
233
234void delete_tempfile(struct tempfile *tempfile)
235{
236 if (!tempfile->active)
237 return;
238
239 if (!close_tempfile(tempfile)) {
240 unlink_or_warn(tempfile->filename.buf);
241 tempfile->active = 0;
242 strbuf_reset(&tempfile->filename);
243 }
244}