aboutsummaryrefslogtreecommitdiff
path: root/lockfile.c
blob: 4f16ee78ce3dbc263a762a8800dfe9ddfcfaecd5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
/*
 * Copyright (c) 2005, Junio C Hamano
 */
#include "cache.h"
#include "lockfile.h"
#include "sigchain.h"

static struct lock_file *volatile lock_file_list;

static void remove_lock_files(int skip_fclose)
{
	pid_t me = getpid();

	while (lock_file_list) {
		if (lock_file_list->owner == me) {
			/* fclose() is not safe to call in a signal handler */
			if (skip_fclose)
				lock_file_list->fp = NULL;
			rollback_lock_file(lock_file_list);
		}
		lock_file_list = lock_file_list->next;
	}
}

static void remove_lock_files_on_exit(void)
{
	remove_lock_files(0);
}

static void remove_lock_files_on_signal(int signo)
{
	remove_lock_files(1);
	sigchain_pop(signo);
	raise(signo);
}

/*
 * path = absolute or relative path name
 *
 * Remove the last path name element from path (leaving the preceding
 * "/", if any).  If path is empty or the root directory ("/"), set
 * path to the empty string.
 */
static void trim_last_path_component(struct strbuf *path)
{
	int i = path->len;

	/* back up past trailing slashes, if any */
	while (i && path->buf[i - 1] == '/')
		i--;

	/*
	 * then go backwards until a slash, or the beginning of the
	 * string
	 */
	while (i && path->buf[i - 1] != '/')
		i--;

	strbuf_setlen(path, i);
}


/* We allow "recursive" symbolic links. Only within reason, though */
#define MAXDEPTH 5

/*
 * path contains a path that might be a symlink.
 *
 * If path is a symlink, attempt to overwrite it with a path to the
 * real file or directory (which may or may not exist), following a
 * chain of symlinks if necessary.  Otherwise, leave path unmodified.
 *
 * This is a best-effort routine.  If an error occurs, path will
 * either be left unmodified or will name a different symlink in a
 * symlink chain that started with the original path.
 */
static void resolve_symlink(struct strbuf *path)
{
	int depth = MAXDEPTH;
	static struct strbuf link = STRBUF_INIT;

	while (depth--) {
		if (strbuf_readlink(&link, path->buf, path->len) < 0)
			break;

		if (is_absolute_path(link.buf))
			/* absolute path simply replaces p */
			strbuf_reset(path);
		else
			/*
			 * link is a relative path, so replace the
			 * last element of p with it.
			 */
			trim_last_path_component(path);

		strbuf_addbuf(path, &link);
	}
	strbuf_reset(&link);
}

/* Make sure errno contains a meaningful value on error */
static int lock_file(struct lock_file *lk, const char *path, int flags)
{
	size_t pathlen = strlen(path);

	if (!lock_file_list) {
		/* One-time initialization */
		sigchain_push_common(remove_lock_files_on_signal);
		atexit(remove_lock_files_on_exit);
	}

	if (lk->active)
		die("BUG: cannot lock_file(\"%s\") using active struct lock_file",
		    path);
	if (!lk->on_list) {
		/* Initialize *lk and add it to lock_file_list: */
		lk->fd = -1;
		lk->fp = NULL;
		lk->active = 0;
		lk->owner = 0;
		strbuf_init(&lk->filename, pathlen + LOCK_SUFFIX_LEN);
		lk->next = lock_file_list;
		lock_file_list = lk;
		lk->on_list = 1;
	} else if (lk->filename.len) {
		/* This shouldn't happen, but better safe than sorry. */
		die("BUG: lock_file(\"%s\") called with improperly-reset lock_file object",
		    path);
	}

	strbuf_add(&lk->filename, path, pathlen);
	if (!(flags & LOCK_NO_DEREF))
		resolve_symlink(&lk->filename);
	strbuf_addstr(&lk->filename, LOCK_SUFFIX);
	lk->fd = open(lk->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
	if (lk->fd < 0) {
		strbuf_reset(&lk->filename);
		return -1;
	}
	lk->owner = getpid();
	lk->active = 1;
	if (adjust_shared_perm(lk->filename.buf)) {
		int save_errno = errno;
		error("cannot fix permission bits on %s", lk->filename.buf);
		rollback_lock_file(lk);
		errno = save_errno;
		return -1;
	}
	return lk->fd;
}

void unable_to_lock_message(const char *path, int err, struct strbuf *buf)
{
	if (err == EEXIST) {
		strbuf_addf(buf, "Unable to create '%s.lock': %s.\n\n"
		    "If no other git process is currently running, this probably means a\n"
		    "git process crashed in this repository earlier. Make sure no other git\n"
		    "process is running and remove the file manually to continue.",
			    absolute_path(path), strerror(err));
	} else
		strbuf_addf(buf, "Unable to create '%s.lock': %s",
			    absolute_path(path), strerror(err));
}

NORETURN void unable_to_lock_die(const char *path, int err)
{
	struct strbuf buf = STRBUF_INIT;

	unable_to_lock_message(path, err, &buf);
	die("%s", buf.buf);
}

/* This should return a meaningful errno on failure */
int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
{
	int fd = lock_file(lk, path, flags);
	if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
		unable_to_lock_die(path, errno);
	return fd;
}

int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
{
	int fd, orig_fd;

	fd = lock_file(lk, path, flags);
	if (fd < 0) {
		if (flags & LOCK_DIE_ON_ERROR)
			unable_to_lock_die(path, errno);
		return fd;
	}

	orig_fd = open(path, O_RDONLY);
	if (orig_fd < 0) {
		if (errno != ENOENT) {
			int save_errno = errno;

			if (flags & LOCK_DIE_ON_ERROR)
				die("cannot open '%s' for copying", path);
			rollback_lock_file(lk);
			error("cannot open '%s' for copying", path);
			errno = save_errno;
			return -1;
		}
	} else if (copy_fd(orig_fd, fd)) {
		int save_errno = errno;

		if (flags & LOCK_DIE_ON_ERROR)
			exit(128);
		close(orig_fd);
		rollback_lock_file(lk);
		errno = save_errno;
		return -1;
	} else {
		close(orig_fd);
	}
	return fd;
}

FILE *fdopen_lock_file(struct lock_file *lk, const char *mode)
{
	if (!lk->active)
		die("BUG: fdopen_lock_file() called for unlocked object");
	if (lk->fp)
		die("BUG: fdopen_lock_file() called twice for file '%s'", lk->filename.buf);

	lk->fp = fdopen(lk->fd, mode);
	return lk->fp;
}

char *get_locked_file_path(struct lock_file *lk)
{
	if (!lk->active)
		die("BUG: get_locked_file_path() called for unlocked object");
	if (lk->filename.len <= LOCK_SUFFIX_LEN)
		die("BUG: get_locked_file_path() called for malformed lock object");
	return xmemdupz(lk->filename.buf, lk->filename.len - LOCK_SUFFIX_LEN);
}

int close_lock_file(struct lock_file *lk)
{
	int fd = lk->fd;
	FILE *fp = lk->fp;
	int err;

	if (fd < 0)
		return 0;

	lk->fd = -1;
	if (fp) {
		lk->fp = NULL;

		/*
		 * Note: no short-circuiting here; we want to fclose()
		 * in any case!
		 */
		err = ferror(fp) | fclose(fp);
	} else {
		err = close(fd);
	}

	if (err) {
		int save_errno = errno;
		rollback_lock_file(lk);
		errno = save_errno;
		return -1;
	}

	return 0;
}

int reopen_lock_file(struct lock_file *lk)
{
	if (0 <= lk->fd)
		die(_("BUG: reopen a lockfile that is still open"));
	if (!lk->active)
		die(_("BUG: reopen a lockfile that has been committed"));
	lk->fd = open(lk->filename.buf, O_WRONLY);
	return lk->fd;
}

int commit_lock_file_to(struct lock_file *lk, const char *path)
{
	if (!lk->active)
		die("BUG: attempt to commit unlocked object to \"%s\"", path);

	if (close_lock_file(lk))
		return -1;

	if (rename(lk->filename.buf, path)) {
		int save_errno = errno;
		rollback_lock_file(lk);
		errno = save_errno;
		return -1;
	}

	lk->active = 0;
	strbuf_reset(&lk->filename);
	return 0;
}

int commit_lock_file(struct lock_file *lk)
{
	static struct strbuf result_file = STRBUF_INIT;
	int err;

	if (!lk->active)
		die("BUG: attempt to commit unlocked object");

	if (lk->filename.len <= LOCK_SUFFIX_LEN ||
	    strcmp(lk->filename.buf + lk->filename.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX))
		die("BUG: lockfile filename corrupt");

	/* remove ".lock": */
	strbuf_add(&result_file, lk->filename.buf,
		   lk->filename.len - LOCK_SUFFIX_LEN);
	err = commit_lock_file_to(lk, result_file.buf);
	strbuf_reset(&result_file);
	return err;
}

void rollback_lock_file(struct lock_file *lk)
{
	if (!lk->active)
		return;

	if (!close_lock_file(lk)) {
		unlink_or_warn(lk->filename.buf);
		lk->active = 0;
		strbuf_reset(&lk->filename);
	}
}