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
|
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/errno.h>
#include <errno.h> /* errno */
#if defined(_LP64)
/*
* The symbols _sys_errlist and _sys_nerr are not visible in the
* LP64 libc. Use strerror(3C) instead.
*/
#else /* #_LP64 */
extern char * sys_errlist[];
extern int sys_nerr;
#endif /* #_LP64 */
static void file_lock_error();
/*
* This code stolen from the NSE library and changed to not depend
* upon any NSE routines or header files.
*
* Simple file locking.
* Create a symlink to a file. The "test and set" will be
* atomic as creating the symlink provides both functions.
*
* The timeout value specifies how long to wait for stale locks
* to disappear. If the lock is more than 'timeout' seconds old
* then it is ok to blow it away. This part has a small window
* of vunerability as the operations of testing the time,
* removing the lock and creating a new one are not atomic.
* It would be possible for two processes to both decide to blow
* away the lock and then have process A remove the lock and establish
* its own, and then then have process B remove the lock which accidentily
* removes A's lock rather than the stale one.
*
* A further complication is with the NFS. If the file in question is
* being served by an NFS server, then its time is set by that server.
* We can not use the time on the client machine to check for a stale
* lock. Therefore, a temp file on the server is created to get
* the servers current time.
*
* Returns an error message. NULL return means the lock was obtained.
*
*/
char *
file_lock(char * name, char * lockname, int timeout)
{
int r;
int fd;
struct stat statb;
struct stat fs_statb;
char tmpname[MAXPATHLEN];
static char msg[MAXPATHLEN];
if (timeout <= 0) {
timeout = 15;
}
for (;;) {
r = symlink(name, lockname);
if (r == 0) {
return (NULL);
}
if (errno != EEXIST) {
file_lock_error(msg, name,
(const char *)"symlink(%s, %s)", name, lockname);
return (msg);
}
for (;;) {
(void) sleep(1);
r = lstat(lockname, &statb);
if (r == -1) {
/*
* The lock must have just gone away - try
* again.
*/
break;
}
/*
* With the NFS the time given a file is the time on
* the file server. This time may vary from the
* client's time. Therefore, we create a tmpfile in
* the same directory to establish the time on the
* server and use this time to see if the lock has
* expired.
*/
(void) sprintf(tmpname, "%s.XXXXXX", lockname);
(void) mktemp(tmpname);
fd = creat(tmpname, 0666);
if (fd != -1) {
(void) close(fd);
} else {
file_lock_error(msg, name,
(const char *)"creat(%s)", tmpname);
return (msg);
}
if (stat(tmpname, &fs_statb) == -1) {
file_lock_error(msg, name,
(const char *)"stat(%s)", tmpname);
return (msg);
}
(void) unlink(tmpname);
if (statb.st_mtime + timeout < fs_statb.st_mtime) {
/*
* The lock has expired - blow it away.
*/
(void) unlink(lockname);
break;
}
}
}
/* NOTREACHED */
}
/*
* Format a message telling why the lock could not be created.
*/
/* VARARGS4 */
static void
file_lock_error(char * msg, char * file, const char * str, char * arg1,
char * arg2)
{
int len;
(void) sprintf(msg, "Could not lock file `%s'; ", file);
len = strlen(msg);
(void) sprintf(&msg[len], str, arg1, arg2);
(void) strcat(msg, " failed - ");
#if defined(_LP64)
/* Needs to be changed to use strerror(3C) instead. */
len = strlen(msg);
(void) sprintf(&msg[len], "errno %d", errno);
#else /* #_LP64 */
if (errno < sys_nerr) {
(void) strcat(msg, sys_errlist[errno]);
} else {
len = strlen(msg);
(void) sprintf(&msg[len], "errno %d", errno);
}
#endif /* #_LP64 */
}
|
