sha1_file: avoid bogus "file exists" error message
[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, int flags)
125 {
126         if (strlen(path) >= sizeof(lk->filename))
127                 return -1;
128         strcpy(lk->filename, path);
129         /*
130          * subtract 5 from size to make sure there's room for adding
131          * ".lock" for the lock file name
132          */
133         if (!(flags & LOCK_NODEREF))
134                 resolve_symlink(lk->filename, sizeof(lk->filename)-5);
135         strcat(lk->filename, ".lock");
136         lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
137         if (0 <= lk->fd) {
138                 if (!lock_file_list) {
139                         signal(SIGINT, remove_lock_file_on_signal);
140                         signal(SIGHUP, remove_lock_file_on_signal);
141                         signal(SIGTERM, remove_lock_file_on_signal);
142                         signal(SIGQUIT, remove_lock_file_on_signal);
143                         atexit(remove_lock_file);
144                 }
145                 lk->owner = getpid();
146                 if (!lk->on_list) {
147                         lk->next = lock_file_list;
148                         lock_file_list = lk;
149                         lk->on_list = 1;
150                 }
151                 if (adjust_shared_perm(lk->filename))
152                         return error("cannot fix permission bits on %s",
153                                      lk->filename);
154         }
155         else
156                 lk->filename[0] = 0;
157         return lk->fd;
158 }
159
160 int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
161 {
162         int fd = lock_file(lk, path, flags);
163         if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
164                 die("unable to create '%s.lock': %s", path, strerror(errno));
165         return fd;
166 }
167
168 int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
169 {
170         int fd, orig_fd;
171
172         fd = lock_file(lk, path, flags);
173         if (fd < 0) {
174                 if (flags & LOCK_DIE_ON_ERROR)
175                         die("unable to create '%s.lock': %s", path, strerror(errno));
176                 return fd;
177         }
178
179         orig_fd = open(path, O_RDONLY);
180         if (orig_fd < 0) {
181                 if (errno != ENOENT) {
182                         if (flags & LOCK_DIE_ON_ERROR)
183                                 die("cannot open '%s' for copying", path);
184                         close(fd);
185                         return error("cannot open '%s' for copying", path);
186                 }
187         } else if (copy_fd(orig_fd, fd)) {
188                 if (flags & LOCK_DIE_ON_ERROR)
189                         exit(128);
190                 close(fd);
191                 return -1;
192         }
193         return fd;
194 }
195
196 int close_lock_file(struct lock_file *lk)
197 {
198         int fd = lk->fd;
199         lk->fd = -1;
200         return close(fd);
201 }
202
203 int commit_lock_file(struct lock_file *lk)
204 {
205         char result_file[PATH_MAX];
206         size_t i;
207         if (lk->fd >= 0 && close_lock_file(lk))
208                 return -1;
209         strcpy(result_file, lk->filename);
210         i = strlen(result_file) - 5; /* .lock */
211         result_file[i] = 0;
212         if (rename(lk->filename, result_file))
213                 return -1;
214         lk->filename[0] = 0;
215         return 0;
216 }
217
218 int hold_locked_index(struct lock_file *lk, int die_on_error)
219 {
220         return hold_lock_file_for_update(lk, get_index_file(),
221                                          die_on_error
222                                          ? LOCK_DIE_ON_ERROR
223                                          : 0);
224 }
225
226 void set_alternate_index_output(const char *name)
227 {
228         alternate_index_output = name;
229 }
230
231 int commit_locked_index(struct lock_file *lk)
232 {
233         if (alternate_index_output) {
234                 if (lk->fd >= 0 && close_lock_file(lk))
235                         return -1;
236                 if (rename(lk->filename, alternate_index_output))
237                         return -1;
238                 lk->filename[0] = 0;
239                 return 0;
240         }
241         else
242                 return commit_lock_file(lk);
243 }
244
245 void rollback_lock_file(struct lock_file *lk)
246 {
247         if (lk->filename[0]) {
248                 if (lk->fd >= 0)
249                         close(lk->fd);
250                 unlink(lk->filename);
251         }
252         lk->filename[0] = 0;
253 }