prepare_index(): declare return value to be (const char *)
[git/git.git] / lockfile.c
CommitLineData
021b6e45
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1/*
2 * Copyright (c) 2005, Junio C Hamano
3 */
021b6e45 4#include "cache.h"
4a16d072 5#include "sigchain.h"
021b6e45 6
0a06f148
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7/*
8 * File write-locks as used by Git.
9 *
10 * For an overview of how to use the lockfile API, please see
11 *
12 * Documentation/technical/api-lockfile.txt
13 *
14 * This module keeps track of all locked files in lock_file_list for
15 * use at cleanup. This list and the lock_file objects that comprise
16 * it must be kept in self-consistent states at all time, because the
17 * program can be interrupted any time by a signal, in which case the
18 * signal handler will walk through the list attempting to clean up
19 * any open lock files.
20 *
21 * A lockfile is owned by the process that created it. The lock_file
22 * object has an "owner" field that records its owner. This field is
23 * used to prevent a forked process from closing a lockfile created by
24 * its parent.
25 *
26 * A lock_file object can be in several states:
27 *
28 * - Uninitialized. In this state the object's on_list field must be
29 * zero but the rest of its contents need not be initialized. As
30 * soon as the object is used in any way, it is irrevocably
31 * registered in the lock_file_list, and on_list is set.
32 *
33 * - Locked, lockfile open (after hold_lock_file_for_update(),
34 * hold_lock_file_for_append(), or reopen_lock_file()). In this
35 * state, the lockfile exists, filename holds the filename of the
36 * lockfile, fd holds a file descriptor open for writing to the
37 * lockfile, and owner holds the PID of the process that locked the
38 * file.
39 *
40 * - Locked, lockfile closed (after close_lock_file()). Same as the
41 * previous state, except that the lockfile is closed and fd is -1.
42 *
43 * - Unlocked (after commit_lock_file(), rollback_lock_file(), or a
44 * failed attempt to lock). In this state, filename[0] == '\0' and
45 * fd is -1. The object is left registered in the lock_file_list,
46 * and on_list is set.
47 */
48
021b6e45
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49static struct lock_file *lock_file_list;
50
51static void remove_lock_file(void)
52{
5e635e39
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53 pid_t me = getpid();
54
021b6e45 55 while (lock_file_list) {
5e635e39 56 if (lock_file_list->owner == me &&
4723ee99 57 lock_file_list->filename[0]) {
d6cf61bf
BC
58 if (lock_file_list->fd >= 0)
59 close(lock_file_list->fd);
691f1a28 60 unlink_or_warn(lock_file_list->filename);
4723ee99 61 }
021b6e45
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62 lock_file_list = lock_file_list->next;
63 }
64}
65
66static void remove_lock_file_on_signal(int signo)
67{
68 remove_lock_file();
4a16d072 69 sigchain_pop(signo);
021b6e45
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70 raise(signo);
71}
72
5d5a7a67
BS
73/*
74 * p = absolute or relative path name
75 *
76 * Return a pointer into p showing the beginning of the last path name
77 * element. If p is empty or the root directory ("/"), just return p.
78 */
79static char *last_path_elm(char *p)
80{
81 /* r starts pointing to null at the end of the string */
82 char *r = strchr(p, '\0');
83
84 if (r == p)
85 return p; /* just return empty string */
86
87 r--; /* back up to last non-null character */
88
89 /* back up past trailing slashes, if any */
90 while (r > p && *r == '/')
91 r--;
92
93 /*
94 * then go backwards until I hit a slash, or the beginning of
95 * the string
96 */
97 while (r > p && *(r-1) != '/')
98 r--;
99 return r;
100}
101
102
103/* We allow "recursive" symbolic links. Only within reason, though */
104#define MAXDEPTH 5
105
106/*
107 * p = path that may be a symlink
108 * s = full size of p
109 *
110 * If p is a symlink, attempt to overwrite p with a path to the real
111 * file or directory (which may or may not exist), following a chain of
112 * symlinks if necessary. Otherwise, leave p unmodified.
113 *
114 * This is a best-effort routine. If an error occurs, p will either be
115 * left unmodified or will name a different symlink in a symlink chain
116 * that started with p's initial contents.
117 *
118 * Always returns p.
119 */
120
121static char *resolve_symlink(char *p, size_t s)
122{
123 int depth = MAXDEPTH;
124
125 while (depth--) {
126 char link[PATH_MAX];
127 int link_len = readlink(p, link, sizeof(link));
128 if (link_len < 0) {
129 /* not a symlink anymore */
130 return p;
131 }
132 else if (link_len < sizeof(link))
133 /* readlink() never null-terminates */
134 link[link_len] = '\0';
135 else {
136 warning("%s: symlink too long", p);
137 return p;
138 }
139
ecf4831d 140 if (is_absolute_path(link)) {
5d5a7a67
BS
141 /* absolute path simply replaces p */
142 if (link_len < s)
143 strcpy(p, link);
144 else {
145 warning("%s: symlink too long", p);
146 return p;
147 }
148 } else {
149 /*
150 * link is a relative path, so I must replace the
151 * last element of p with it.
152 */
4b25d091 153 char *r = (char *)last_path_elm(p);
5d5a7a67
BS
154 if (r - p + link_len < s)
155 strcpy(r, link);
156 else {
157 warning("%s: symlink too long", p);
158 return p;
159 }
160 }
161 }
162 return p;
163}
164
447ff1bf 165/* Make sure errno contains a meaningful value on error */
acd3b9ec 166static int lock_file(struct lock_file *lk, const char *path, int flags)
021b6e45 167{
5d5a7a67 168 /*
7108ad23
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169 * subtract LOCK_SUFFIX_LEN from size to make sure there's
170 * room for adding ".lock" for the lock file name:
5d5a7a67 171 */
7108ad23
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172 static const size_t max_path_len = sizeof(lk->filename) -
173 LOCK_SUFFIX_LEN;
2fbd4f92 174
04e57d4d
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175 if (!lock_file_list) {
176 /* One-time initialization */
177 sigchain_push_common(remove_lock_file_on_signal);
178 atexit(remove_lock_file);
179 }
180
181 if (!lk->on_list) {
182 /* Initialize *lk and add it to lock_file_list: */
183 lk->fd = -1;
184 lk->owner = 0;
185 lk->filename[0] = 0;
186 lk->next = lock_file_list;
187 lock_file_list = lk;
188 lk->on_list = 1;
189 }
190
447ff1bf
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191 if (strlen(path) >= max_path_len) {
192 errno = ENAMETOOLONG;
2fbd4f92 193 return -1;
447ff1bf 194 }
2fbd4f92 195 strcpy(lk->filename, path);
acd3b9ec 196 if (!(flags & LOCK_NODEREF))
2fbd4f92 197 resolve_symlink(lk->filename, max_path_len);
7108ad23 198 strcat(lk->filename, LOCK_SUFFIX);
4723ee99
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199 lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
200 if (0 <= lk->fd) {
5e635e39 201 lk->owner = getpid();
447ff1bf
RS
202 if (adjust_shared_perm(lk->filename)) {
203 int save_errno = errno;
204 error("cannot fix permission bits on %s",
205 lk->filename);
41dd4ffa 206 rollback_lock_file(lk);
447ff1bf
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207 errno = save_errno;
208 return -1;
209 }
021b6e45 210 }
1084b845
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211 else
212 lk->filename[0] = 0;
4723ee99 213 return lk->fd;
021b6e45
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214}
215
6af926e8 216void unable_to_lock_message(const char *path, int err, struct strbuf *buf)
e43a6fd3 217{
bdfd739d 218 if (err == EEXIST) {
6af926e8 219 strbuf_addf(buf, "Unable to create '%s.lock': %s.\n\n"
e43a6fd3
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220 "If no other git process is currently running, this probably means a\n"
221 "git process crashed in this repository earlier. Make sure no other git\n"
222 "process is running and remove the file manually to continue.",
e2a57aac 223 absolute_path(path), strerror(err));
1b018fd9 224 } else
6af926e8 225 strbuf_addf(buf, "Unable to create '%s.lock': %s",
e2a57aac 226 absolute_path(path), strerror(err));
1b018fd9
MV
227}
228
229int unable_to_lock_error(const char *path, int err)
230{
6af926e8
RS
231 struct strbuf buf = STRBUF_INIT;
232
233 unable_to_lock_message(path, err, &buf);
234 error("%s", buf.buf);
235 strbuf_release(&buf);
1b018fd9
MV
236 return -1;
237}
238
e197c218 239NORETURN void unable_to_lock_die(const char *path, int err)
1b018fd9 240{
6af926e8
RS
241 struct strbuf buf = STRBUF_INIT;
242
243 unable_to_lock_message(path, err, &buf);
244 die("%s", buf.buf);
e43a6fd3
MM
245}
246
447ff1bf 247/* This should return a meaningful errno on failure */
acd3b9ec 248int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
40aaae88 249{
acd3b9ec
JH
250 int fd = lock_file(lk, path, flags);
251 if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
e197c218 252 unable_to_lock_die(path, errno);
40aaae88
JH
253 return fd;
254}
255
acd3b9ec 256int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
ea3cd5c7
DB
257{
258 int fd, orig_fd;
259
acd3b9ec 260 fd = lock_file(lk, path, flags);
ea3cd5c7 261 if (fd < 0) {
acd3b9ec 262 if (flags & LOCK_DIE_ON_ERROR)
e197c218 263 unable_to_lock_die(path, errno);
ea3cd5c7
DB
264 return fd;
265 }
266
267 orig_fd = open(path, O_RDONLY);
268 if (orig_fd < 0) {
269 if (errno != ENOENT) {
acd3b9ec 270 if (flags & LOCK_DIE_ON_ERROR)
ea3cd5c7 271 die("cannot open '%s' for copying", path);
ebb8e380 272 rollback_lock_file(lk);
ea3cd5c7
DB
273 return error("cannot open '%s' for copying", path);
274 }
275 } else if (copy_fd(orig_fd, fd)) {
acd3b9ec 276 if (flags & LOCK_DIE_ON_ERROR)
ea3cd5c7 277 exit(128);
ebb8e380 278 rollback_lock_file(lk);
ea3cd5c7
DB
279 return -1;
280 }
281 return fd;
282}
283
d6cf61bf
BC
284int close_lock_file(struct lock_file *lk)
285{
286 int fd = lk->fd;
419f0c0f
MH
287
288 if (fd < 0)
289 return 0;
290
d6cf61bf
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291 lk->fd = -1;
292 return close(fd);
293}
294
93dcaea2
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295int reopen_lock_file(struct lock_file *lk)
296{
297 if (0 <= lk->fd)
298 die(_("BUG: reopen a lockfile that is still open"));
299 if (!lk->filename[0])
300 die(_("BUG: reopen a lockfile that has been committed"));
301 lk->fd = open(lk->filename, O_WRONLY);
302 return lk->fd;
303}
304
021b6e45
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305int commit_lock_file(struct lock_file *lk)
306{
307 char result_file[PATH_MAX];
d6cf61bf 308 size_t i;
419f0c0f 309 if (close_lock_file(lk))
d6cf61bf 310 return -1;
021b6e45 311 strcpy(result_file, lk->filename);
7108ad23 312 i = strlen(result_file) - LOCK_SUFFIX_LEN; /* .lock */
021b6e45 313 result_file[i] = 0;
d6cf61bf
BC
314 if (rename(lk->filename, result_file))
315 return -1;
021b6e45 316 lk->filename[0] = 0;
d6cf61bf 317 return 0;
021b6e45
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318}
319
30ca07a2
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320int hold_locked_index(struct lock_file *lk, int die_on_error)
321{
acd3b9ec
JH
322 return hold_lock_file_for_update(lk, get_index_file(),
323 die_on_error
324 ? LOCK_DIE_ON_ERROR
325 : 0);
30ca07a2
JH
326}
327
021b6e45
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328void rollback_lock_file(struct lock_file *lk)
329{
9085f8e2
MH
330 if (!lk->filename[0])
331 return;
332
26f5d3b6 333 close_lock_file(lk);
9085f8e2
MH
334 unlink_or_warn(lk->filename);
335 lk->filename[0] = 0;
021b6e45 336}