summaryrefslogtreecommitdiff
path: root/lockfile.c
blob: 258fb3f5ef8636e7ff144f551689da3090518a0e (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
/*
 * Copyright (c) 2005, Junio C Hamano
 */
#include "cache.h"
 
static struct lock_file *lock_file_list;
static const char *alternate_index_output;
 
static void remove_lock_file(void)
{
	pid_t me = getpid();
 
	while (lock_file_list) {
		if (lock_file_list->owner == me &&
		    lock_file_list->filename[0]) {
			close(lock_file_list->fd);
			unlink(lock_file_list->filename);
		}
		lock_file_list = lock_file_list->next;
	}
}
 
static void remove_lock_file_on_signal(int signo)
{
	remove_lock_file();
	signal(SIGINT, SIG_DFL);
	raise(signo);
}
 
/*
 * p = absolute or relative path name
 *
 * Return a pointer into p showing the beginning of the last path name
 * element.  If p is empty or the root directory ("/"), just return p.
 */
static char *last_path_elm(char *p)
{
	/* r starts pointing to null at the end of the string */
	char *r = strchr(p, '\0');
 
	if (r == p)
		return p; /* just return empty string */
 
	r--; /* back up to last non-null character */
 
	/* back up past trailing slashes, if any */
	while (r > p && *r == '/')
		r--;
 
	/*
	 * then go backwards until I hit a slash, or the beginning of
	 * the string
	 */
	while (r > p && *(r-1) != '/')
		r--;
	return r;
}
 
 
/* We allow "recursive" symbolic links. Only within reason, though */
#define MAXDEPTH 5
 
/*
 * p = path that may be a symlink
 * s = full size of p
 *
 * If p is a symlink, attempt to overwrite p with a path to the real
 * file or directory (which may or may not exist), following a chain of
 * symlinks if necessary.  Otherwise, leave p unmodified.
 *
 * This is a best-effort routine.  If an error occurs, p will either be
 * left unmodified or will name a different symlink in a symlink chain
 * that started with p's initial contents.
 *
 * Always returns p.
 */
 
static char *resolve_symlink(char *p, size_t s)
{
	int depth = MAXDEPTH;
 
	while (depth--) {
		char link[PATH_MAX];
		int link_len = readlink(p, link, sizeof(link));
		if (link_len < 0) {
			/* not a symlink anymore */
			return p;
		}
		else if (link_len < sizeof(link))
			/* readlink() never null-terminates */
			link[link_len] = '\0';
		else {
			warning("%s: symlink too long", p);
			return p;
		}
 
		if (link[0] == '/') {
			/* absolute path simply replaces p */
			if (link_len < s)
				strcpy(p, link);
			else {
				warning("%s: symlink too long", p);
				return p;
			}
		} else {
			/*
			 * link is a relative path, so I must replace the
			 * last element of p with it.
			 */
			char *r = (char*)last_path_elm(p);
			if (r - p + link_len < s)
				strcpy(r, link);
			else {
				warning("%s: symlink too long", p);
				return p;
			}
		}
	}
	return p;
}
 
 
static int lock_file(struct lock_file *lk, const char *path)
{
	if (strlen(path) >= sizeof(lk->filename)) return -1;
	strcpy(lk->filename, path);
	/*
	 * subtract 5 from size to make sure there's room for adding
	 * ".lock" for the lock file name
	 */
	resolve_symlink(lk->filename, sizeof(lk->filename)-5);
	strcat(lk->filename, ".lock");
	lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
	if (0 <= lk->fd) {
		if (!lock_file_list) {
			signal(SIGINT, remove_lock_file_on_signal);
			atexit(remove_lock_file);
		}
		lk->owner = getpid();
		if (!lk->on_list) {
			lk->next = lock_file_list;
			lock_file_list = lk;
			lk->on_list = 1;
		}
		if (adjust_shared_perm(lk->filename))
			return error("cannot fix permission bits on %s",
				     lk->filename);
	}
	else
		lk->filename[0] = 0;
	return lk->fd;
}
 
int hold_lock_file_for_update(struct lock_file *lk, const char *path, int die_on_error)
{
	int fd = lock_file(lk, path);
	if (fd < 0 && die_on_error)
		die("unable to create '%s.lock': %s", path, strerror(errno));
	return fd;
}
 
int commit_lock_file(struct lock_file *lk)
{
	char result_file[PATH_MAX];
	int i;
	close(lk->fd);
	strcpy(result_file, lk->filename);
	i = strlen(result_file) - 5; /* .lock */
	result_file[i] = 0;
	i = rename(lk->filename, result_file);
	lk->filename[0] = 0;
	return i;
}
 
int hold_locked_index(struct lock_file *lk, int die_on_error)
{
	return hold_lock_file_for_update(lk, get_index_file(), die_on_error);
}
 
void set_alternate_index_output(const char *name)
{
	alternate_index_output = name;
}
 
int commit_locked_index(struct lock_file *lk)
{
	if (alternate_index_output) {
		int result = rename(lk->filename, alternate_index_output);
		lk->filename[0] = 0;
		return result;
	}
	else
		return commit_lock_file(lk);
}
 
void rollback_lock_file(struct lock_file *lk)
{
	if (lk->filename[0]) {
		close(lk->fd);
		unlink(lk->filename);
	}
	lk->filename[0] = 0;
}