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[git] / lockfile.c
1 /*
2  * Copyright (c) 2005, Junio C Hamano
3  */
4 #include "cache.h"
5
6 static struct lock_file *lock_file_list;
7 static const char *alternate_index_output;
8
9 static void remove_lock_file(void)
10 {
11         pid_t me = getpid();
12
13         while (lock_file_list) {
14                 if (lock_file_list->owner == me &&
15                     lock_file_list->filename[0]) {
16                         if (lock_file_list->fd >= 0)
17                                 close(lock_file_list->fd);
18                         unlink(lock_file_list->filename);
19                 }
20                 lock_file_list = lock_file_list->next;
21         }
22 }
23
24 static void remove_lock_file_on_signal(int signo)
25 {
26         remove_lock_file();
27         signal(signo, SIG_DFL);
28         raise(signo);
29 }
30
31 /*
32  * p = absolute or relative path name
33  *
34  * Return a pointer into p showing the beginning of the last path name
35  * element.  If p is empty or the root directory ("/"), just return p.
36  */
37 static char *last_path_elm(char *p)
38 {
39         /* r starts pointing to null at the end of the string */
40         char *r = strchr(p, '\0');
41
42         if (r == p)
43                 return p; /* just return empty string */
44
45         r--; /* back up to last non-null character */
46
47         /* back up past trailing slashes, if any */
48         while (r > p && *r == '/')
49                 r--;
50
51         /*
52          * then go backwards until I hit a slash, or the beginning of
53          * the string
54          */
55         while (r > p && *(r-1) != '/')
56                 r--;
57         return r;
58 }
59
60
61 /* We allow "recursive" symbolic links. Only within reason, though */
62 #define MAXDEPTH 5
63
64 /*
65  * p = path that may be a symlink
66  * s = full size of p
67  *
68  * If p is a symlink, attempt to overwrite p with a path to the real
69  * file or directory (which may or may not exist), following a chain of
70  * symlinks if necessary.  Otherwise, leave p unmodified.
71  *
72  * This is a best-effort routine.  If an error occurs, p will either be
73  * left unmodified or will name a different symlink in a symlink chain
74  * that started with p's initial contents.
75  *
76  * Always returns p.
77  */
78
79 static char *resolve_symlink(char *p, size_t s)
80 {
81         int depth = MAXDEPTH;
82
83         while (depth--) {
84                 char link[PATH_MAX];
85                 int link_len = readlink(p, link, sizeof(link));
86                 if (link_len < 0) {
87                         /* not a symlink anymore */
88                         return p;
89                 }
90                 else if (link_len < sizeof(link))
91                         /* readlink() never null-terminates */
92                         link[link_len] = '\0';
93                 else {
94                         warning("%s: symlink too long", p);
95                         return p;
96                 }
97
98                 if (is_absolute_path(link)) {
99                         /* absolute path simply replaces p */
100                         if (link_len < s)
101                                 strcpy(p, link);
102                         else {
103                                 warning("%s: symlink too long", p);
104                                 return p;
105                         }
106                 } else {
107                         /*
108                          * link is a relative path, so I must replace the
109                          * last element of p with it.
110                          */
111                         char *r = (char*)last_path_elm(p);
112                         if (r - p + link_len < s)
113                                 strcpy(r, link);
114                         else {
115                                 warning("%s: symlink too long", p);
116                                 return p;
117                         }
118                 }
119         }
120         return p;
121 }
122
123
124 static int lock_file(struct lock_file *lk, const char *path)
125 {
126         if (strlen(path) >= sizeof(lk->filename)) return -1;
127         strcpy(lk->filename, path);
128         /*
129          * subtract 5 from size to make sure there's room for adding
130          * ".lock" for the lock file name
131          */
132         resolve_symlink(lk->filename, sizeof(lk->filename)-5);
133         strcat(lk->filename, ".lock");
134         lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
135         if (0 <= lk->fd) {
136                 if (!lock_file_list) {
137                         signal(SIGINT, remove_lock_file_on_signal);
138                         signal(SIGHUP, remove_lock_file_on_signal);
139                         signal(SIGTERM, remove_lock_file_on_signal);
140                         signal(SIGQUIT, remove_lock_file_on_signal);
141                         atexit(remove_lock_file);
142                 }
143                 lk->owner = getpid();
144                 if (!lk->on_list) {
145                         lk->next = lock_file_list;
146                         lock_file_list = lk;
147                         lk->on_list = 1;
148                 }
149                 if (adjust_shared_perm(lk->filename))
150                         return error("cannot fix permission bits on %s",
151                                      lk->filename);
152         }
153         else
154                 lk->filename[0] = 0;
155         return lk->fd;
156 }
157
158 int hold_lock_file_for_update(struct lock_file *lk, const char *path, int die_on_error)
159 {
160         int fd = lock_file(lk, path);
161         if (fd < 0 && die_on_error)
162                 die("unable to create '%s.lock': %s", path, strerror(errno));
163         return fd;
164 }
165
166 int hold_lock_file_for_append(struct lock_file *lk, const char *path, int die_on_error)
167 {
168         int fd, orig_fd;
169
170         fd = lock_file(lk, path);
171         if (fd < 0) {
172                 if (die_on_error)
173                         die("unable to create '%s.lock': %s", path, strerror(errno));
174                 return fd;
175         }
176
177         orig_fd = open(path, O_RDONLY);
178         if (orig_fd < 0) {
179                 if (errno != ENOENT) {
180                         if (die_on_error)
181                                 die("cannot open '%s' for copying", path);
182                         close(fd);
183                         return error("cannot open '%s' for copying", path);
184                 }
185         } else if (copy_fd(orig_fd, fd)) {
186                 if (die_on_error)
187                         exit(128);
188                 close(fd);
189                 return -1;
190         }
191         return fd;
192 }
193
194 int close_lock_file(struct lock_file *lk)
195 {
196         int fd = lk->fd;
197         lk->fd = -1;
198         return close(fd);
199 }
200
201 int commit_lock_file(struct lock_file *lk)
202 {
203         char result_file[PATH_MAX];
204         size_t i;
205         if (lk->fd >= 0 && close_lock_file(lk))
206                 return -1;
207         strcpy(result_file, lk->filename);
208         i = strlen(result_file) - 5; /* .lock */
209         result_file[i] = 0;
210         if (rename(lk->filename, result_file))
211                 return -1;
212         lk->filename[0] = 0;
213         return 0;
214 }
215
216 int hold_locked_index(struct lock_file *lk, int die_on_error)
217 {
218         return hold_lock_file_for_update(lk, get_index_file(), die_on_error);
219 }
220
221 void set_alternate_index_output(const char *name)
222 {
223         alternate_index_output = name;
224 }
225
226 int commit_locked_index(struct lock_file *lk)
227 {
228         if (alternate_index_output) {
229                 if (lk->fd >= 0 && close_lock_file(lk))
230                         return -1;
231                 if (rename(lk->filename, alternate_index_output))
232                         return -1;
233                 lk->filename[0] = 0;
234                 return 0;
235         }
236         else
237                 return commit_lock_file(lk);
238 }
239
240 void rollback_lock_file(struct lock_file *lk)
241 {
242         if (lk->filename[0]) {
243                 if (lk->fd >= 0)
244                         close(lk->fd);
245                 unlink(lk->filename);
246         }
247         lk->filename[0] = 0;
248 }