prepare_index(): declare return value to be (const char *)
[git/mingw.git] / lockfile.c
blob23847fc9f2d0f678a34b343902d304a8d022840a
1 /*
2 * Copyright (c) 2005, Junio C Hamano
3 */
4 #include "cache.h"
5 #include "sigchain.h"
7 /*
8 * File write-locks as used by Git.
10 * For an overview of how to use the lockfile API, please see
12 * Documentation/technical/api-lockfile.txt
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.
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.
26 * A lock_file object can be in several states:
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.
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.
40 * - Locked, lockfile closed (after close_lock_file()). Same as the
41 * previous state, except that the lockfile is closed and fd is -1.
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.
49 static struct lock_file *lock_file_list;
51 static void remove_lock_file(void)
53 pid_t me = getpid();
55 while (lock_file_list) {
56 if (lock_file_list->owner == me &&
57 lock_file_list->filename[0]) {
58 if (lock_file_list->fd >= 0)
59 close(lock_file_list->fd);
60 unlink_or_warn(lock_file_list->filename);
62 lock_file_list = lock_file_list->next;
66 static void remove_lock_file_on_signal(int signo)
68 remove_lock_file();
69 sigchain_pop(signo);
70 raise(signo);
74 * p = absolute or relative path name
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.
79 static char *last_path_elm(char *p)
81 /* r starts pointing to null at the end of the string */
82 char *r = strchr(p, '\0');
84 if (r == p)
85 return p; /* just return empty string */
87 r--; /* back up to last non-null character */
89 /* back up past trailing slashes, if any */
90 while (r > p && *r == '/')
91 r--;
94 * then go backwards until I hit a slash, or the beginning of
95 * the string
97 while (r > p && *(r-1) != '/')
98 r--;
99 return r;
103 /* We allow "recursive" symbolic links. Only within reason, though */
104 #define MAXDEPTH 5
107 * p = path that may be a symlink
108 * s = full size of p
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.
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.
118 * Always returns p.
121 static char *resolve_symlink(char *p, size_t s)
123 int depth = MAXDEPTH;
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;
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;
140 if (is_absolute_path(link)) {
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;
148 } else {
150 * link is a relative path, so I must replace the
151 * last element of p with it.
153 char *r = (char *)last_path_elm(p);
154 if (r - p + link_len < s)
155 strcpy(r, link);
156 else {
157 warning("%s: symlink too long", p);
158 return p;
162 return p;
165 /* Make sure errno contains a meaningful value on error */
166 static int lock_file(struct lock_file *lk, const char *path, int flags)
169 * subtract LOCK_SUFFIX_LEN from size to make sure there's
170 * room for adding ".lock" for the lock file name:
172 static const size_t max_path_len = sizeof(lk->filename) -
173 LOCK_SUFFIX_LEN;
175 if (!lock_file_list) {
176 /* One-time initialization */
177 sigchain_push_common(remove_lock_file_on_signal);
178 atexit(remove_lock_file);
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;
191 if (strlen(path) >= max_path_len) {
192 errno = ENAMETOOLONG;
193 return -1;
195 strcpy(lk->filename, path);
196 if (!(flags & LOCK_NODEREF))
197 resolve_symlink(lk->filename, max_path_len);
198 strcat(lk->filename, LOCK_SUFFIX);
199 lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
200 if (0 <= lk->fd) {
201 lk->owner = getpid();
202 if (adjust_shared_perm(lk->filename)) {
203 int save_errno = errno;
204 error("cannot fix permission bits on %s",
205 lk->filename);
206 rollback_lock_file(lk);
207 errno = save_errno;
208 return -1;
211 else
212 lk->filename[0] = 0;
213 return lk->fd;
216 void unable_to_lock_message(const char *path, int err, struct strbuf *buf)
218 if (err == EEXIST) {
219 strbuf_addf(buf, "Unable to create '%s.lock': %s.\n\n"
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.",
223 absolute_path(path), strerror(err));
224 } else
225 strbuf_addf(buf, "Unable to create '%s.lock': %s",
226 absolute_path(path), strerror(err));
229 int unable_to_lock_error(const char *path, int err)
231 struct strbuf buf = STRBUF_INIT;
233 unable_to_lock_message(path, err, &buf);
234 error("%s", buf.buf);
235 strbuf_release(&buf);
236 return -1;
239 NORETURN void unable_to_lock_die(const char *path, int err)
241 struct strbuf buf = STRBUF_INIT;
243 unable_to_lock_message(path, err, &buf);
244 die("%s", buf.buf);
247 /* This should return a meaningful errno on failure */
248 int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
250 int fd = lock_file(lk, path, flags);
251 if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
252 unable_to_lock_die(path, errno);
253 return fd;
256 int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
258 int fd, orig_fd;
260 fd = lock_file(lk, path, flags);
261 if (fd < 0) {
262 if (flags & LOCK_DIE_ON_ERROR)
263 unable_to_lock_die(path, errno);
264 return fd;
267 orig_fd = open(path, O_RDONLY);
268 if (orig_fd < 0) {
269 if (errno != ENOENT) {
270 if (flags & LOCK_DIE_ON_ERROR)
271 die("cannot open '%s' for copying", path);
272 rollback_lock_file(lk);
273 return error("cannot open '%s' for copying", path);
275 } else if (copy_fd(orig_fd, fd)) {
276 if (flags & LOCK_DIE_ON_ERROR)
277 exit(128);
278 rollback_lock_file(lk);
279 return -1;
281 return fd;
284 int close_lock_file(struct lock_file *lk)
286 int fd = lk->fd;
288 if (fd < 0)
289 return 0;
291 lk->fd = -1;
292 return close(fd);
295 int reopen_lock_file(struct lock_file *lk)
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;
305 int commit_lock_file(struct lock_file *lk)
307 char result_file[PATH_MAX];
308 size_t i;
309 if (close_lock_file(lk))
310 return -1;
311 strcpy(result_file, lk->filename);
312 i = strlen(result_file) - LOCK_SUFFIX_LEN; /* .lock */
313 result_file[i] = 0;
314 if (rename(lk->filename, result_file))
315 return -1;
316 lk->filename[0] = 0;
317 return 0;
320 int hold_locked_index(struct lock_file *lk, int die_on_error)
322 return hold_lock_file_for_update(lk, get_index_file(),
323 die_on_error
324 ? LOCK_DIE_ON_ERROR
325 : 0);
328 void rollback_lock_file(struct lock_file *lk)
330 if (!lk->filename[0])
331 return;
333 close_lock_file(lk);
334 unlink_or_warn(lk->filename);
335 lk->filename[0] = 0;