commit_lock_file(): die() if called for unlocked lockfile object
[git/git.git] / lockfile.c
CommitLineData
021b6e45
JH
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
JH
53 pid_t me = getpid();
54
021b6e45 55 while (lock_file_list) {
a1754bcc
MH
56 if (lock_file_list->owner == me)
57 rollback_lock_file(lock_file_list);
021b6e45
JH
58 lock_file_list = lock_file_list->next;
59 }
60}
61
62static void remove_lock_file_on_signal(int signo)
63{
64 remove_lock_file();
4a16d072 65 sigchain_pop(signo);
021b6e45
JH
66 raise(signo);
67}
68
5d5a7a67
BS
69/*
70 * p = absolute or relative path name
71 *
72 * Return a pointer into p showing the beginning of the last path name
73 * element. If p is empty or the root directory ("/"), just return p.
74 */
75static char *last_path_elm(char *p)
76{
77 /* r starts pointing to null at the end of the string */
78 char *r = strchr(p, '\0');
79
80 if (r == p)
81 return p; /* just return empty string */
82
83 r--; /* back up to last non-null character */
84
85 /* back up past trailing slashes, if any */
86 while (r > p && *r == '/')
87 r--;
88
89 /*
90 * then go backwards until I hit a slash, or the beginning of
91 * the string
92 */
93 while (r > p && *(r-1) != '/')
94 r--;
95 return r;
96}
97
98
99/* We allow "recursive" symbolic links. Only within reason, though */
100#define MAXDEPTH 5
101
102/*
103 * p = path that may be a symlink
104 * s = full size of p
105 *
106 * If p is a symlink, attempt to overwrite p with a path to the real
107 * file or directory (which may or may not exist), following a chain of
108 * symlinks if necessary. Otherwise, leave p unmodified.
109 *
110 * This is a best-effort routine. If an error occurs, p will either be
111 * left unmodified or will name a different symlink in a symlink chain
112 * that started with p's initial contents.
113 *
114 * Always returns p.
115 */
116
117static char *resolve_symlink(char *p, size_t s)
118{
119 int depth = MAXDEPTH;
120
121 while (depth--) {
122 char link[PATH_MAX];
123 int link_len = readlink(p, link, sizeof(link));
124 if (link_len < 0) {
125 /* not a symlink anymore */
126 return p;
127 }
128 else if (link_len < sizeof(link))
129 /* readlink() never null-terminates */
130 link[link_len] = '\0';
131 else {
132 warning("%s: symlink too long", p);
133 return p;
134 }
135
ecf4831d 136 if (is_absolute_path(link)) {
5d5a7a67
BS
137 /* absolute path simply replaces p */
138 if (link_len < s)
139 strcpy(p, link);
140 else {
141 warning("%s: symlink too long", p);
142 return p;
143 }
144 } else {
145 /*
146 * link is a relative path, so I must replace the
147 * last element of p with it.
148 */
4b25d091 149 char *r = (char *)last_path_elm(p);
5d5a7a67
BS
150 if (r - p + link_len < s)
151 strcpy(r, link);
152 else {
153 warning("%s: symlink too long", p);
154 return p;
155 }
156 }
157 }
158 return p;
159}
160
447ff1bf 161/* Make sure errno contains a meaningful value on error */
acd3b9ec 162static int lock_file(struct lock_file *lk, const char *path, int flags)
021b6e45 163{
5d5a7a67 164 /*
7108ad23
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165 * subtract LOCK_SUFFIX_LEN from size to make sure there's
166 * room for adding ".lock" for the lock file name:
5d5a7a67 167 */
7108ad23
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168 static const size_t max_path_len = sizeof(lk->filename) -
169 LOCK_SUFFIX_LEN;
2fbd4f92 170
04e57d4d
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171 if (!lock_file_list) {
172 /* One-time initialization */
173 sigchain_push_common(remove_lock_file_on_signal);
174 atexit(remove_lock_file);
175 }
176
177 if (!lk->on_list) {
178 /* Initialize *lk and add it to lock_file_list: */
179 lk->fd = -1;
180 lk->owner = 0;
181 lk->filename[0] = 0;
182 lk->next = lock_file_list;
183 lock_file_list = lk;
184 lk->on_list = 1;
185 }
186
447ff1bf
RS
187 if (strlen(path) >= max_path_len) {
188 errno = ENAMETOOLONG;
2fbd4f92 189 return -1;
447ff1bf 190 }
2fbd4f92 191 strcpy(lk->filename, path);
acd3b9ec 192 if (!(flags & LOCK_NODEREF))
2fbd4f92 193 resolve_symlink(lk->filename, max_path_len);
7108ad23 194 strcat(lk->filename, LOCK_SUFFIX);
4723ee99 195 lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
e31e949b 196 if (lk->fd < 0) {
1084b845 197 lk->filename[0] = 0;
e31e949b
MH
198 return -1;
199 }
200 lk->owner = getpid();
201 if (adjust_shared_perm(lk->filename)) {
202 int save_errno = errno;
203 error("cannot fix permission bits on %s", lk->filename);
204 rollback_lock_file(lk);
205 errno = save_errno;
206 return -1;
207 }
4723ee99 208 return lk->fd;
021b6e45
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209}
210
6af926e8 211void unable_to_lock_message(const char *path, int err, struct strbuf *buf)
e43a6fd3 212{
bdfd739d 213 if (err == EEXIST) {
6af926e8 214 strbuf_addf(buf, "Unable to create '%s.lock': %s.\n\n"
e43a6fd3
MM
215 "If no other git process is currently running, this probably means a\n"
216 "git process crashed in this repository earlier. Make sure no other git\n"
217 "process is running and remove the file manually to continue.",
e2a57aac 218 absolute_path(path), strerror(err));
1b018fd9 219 } else
6af926e8 220 strbuf_addf(buf, "Unable to create '%s.lock': %s",
e2a57aac 221 absolute_path(path), strerror(err));
1b018fd9
MV
222}
223
224int unable_to_lock_error(const char *path, int err)
225{
6af926e8
RS
226 struct strbuf buf = STRBUF_INIT;
227
228 unable_to_lock_message(path, err, &buf);
229 error("%s", buf.buf);
230 strbuf_release(&buf);
1b018fd9
MV
231 return -1;
232}
233
e197c218 234NORETURN void unable_to_lock_die(const char *path, int err)
1b018fd9 235{
6af926e8
RS
236 struct strbuf buf = STRBUF_INIT;
237
238 unable_to_lock_message(path, err, &buf);
239 die("%s", buf.buf);
e43a6fd3
MM
240}
241
447ff1bf 242/* This should return a meaningful errno on failure */
acd3b9ec 243int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
40aaae88 244{
acd3b9ec
JH
245 int fd = lock_file(lk, path, flags);
246 if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
e197c218 247 unable_to_lock_die(path, errno);
40aaae88
JH
248 return fd;
249}
250
acd3b9ec 251int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
ea3cd5c7
DB
252{
253 int fd, orig_fd;
254
acd3b9ec 255 fd = lock_file(lk, path, flags);
ea3cd5c7 256 if (fd < 0) {
acd3b9ec 257 if (flags & LOCK_DIE_ON_ERROR)
e197c218 258 unable_to_lock_die(path, errno);
ea3cd5c7
DB
259 return fd;
260 }
261
262 orig_fd = open(path, O_RDONLY);
263 if (orig_fd < 0) {
264 if (errno != ENOENT) {
acd3b9ec 265 if (flags & LOCK_DIE_ON_ERROR)
ea3cd5c7 266 die("cannot open '%s' for copying", path);
ebb8e380 267 rollback_lock_file(lk);
ea3cd5c7
DB
268 return error("cannot open '%s' for copying", path);
269 }
270 } else if (copy_fd(orig_fd, fd)) {
acd3b9ec 271 if (flags & LOCK_DIE_ON_ERROR)
ea3cd5c7 272 exit(128);
ebb8e380 273 rollback_lock_file(lk);
ea3cd5c7
DB
274 return -1;
275 }
276 return fd;
277}
278
d6cf61bf
BC
279int close_lock_file(struct lock_file *lk)
280{
281 int fd = lk->fd;
419f0c0f
MH
282
283 if (fd < 0)
284 return 0;
285
d6cf61bf
BC
286 lk->fd = -1;
287 return close(fd);
288}
289
93dcaea2
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290int reopen_lock_file(struct lock_file *lk)
291{
292 if (0 <= lk->fd)
293 die(_("BUG: reopen a lockfile that is still open"));
294 if (!lk->filename[0])
295 die(_("BUG: reopen a lockfile that has been committed"));
296 lk->fd = open(lk->filename, O_WRONLY);
297 return lk->fd;
298}
299
021b6e45
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300int commit_lock_file(struct lock_file *lk)
301{
302 char result_file[PATH_MAX];
4f4713df 303
8a1c7533
MH
304 if (!lk->filename[0])
305 die("BUG: attempt to commit unlocked object");
306
419f0c0f 307 if (close_lock_file(lk))
d6cf61bf 308 return -1;
4f4713df 309
021b6e45 310 strcpy(result_file, lk->filename);
4f4713df
MH
311 /* remove ".lock": */
312 result_file[strlen(result_file) - LOCK_SUFFIX_LEN] = 0;
313
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}