1 /*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21 /*
22 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
23 * Use is subject to license terms.
24 */
25
26 #include <stdio.h>
27 #include <stdlib.h>
28 #include <unistd.h>
29 #include <string.h>
30 #include <fcntl.h>
31 #include <sys/types.h>
32 #include <sys/param.h>
33 #include <sys/stat.h>
34 #include <sys/errno.h>
35 #include <errno.h> /* errno */
36
37 #if defined(_LP64)
38 /*
39 * The symbols _sys_errlist and _sys_nerr are not visible in the
40 * LP64 libc. Use strerror(3C) instead.
41 */
42 #else /* #_LP64 */
43 extern char * sys_errlist[];
44 extern int sys_nerr;
45 #endif /* #_LP64 */
46
47 static void file_lock_error();
48
49 /*
50 * This code stolen from the NSE library and changed to not depend
51 * upon any NSE routines or header files.
52 *
53 * Simple file locking.
54 * Create a symlink to a file. The "test and set" will be
55 * atomic as creating the symlink provides both functions.
56 *
57 * The timeout value specifies how long to wait for stale locks
58 * to disappear. If the lock is more than 'timeout' seconds old
59 * then it is ok to blow it away. This part has a small window
60 * of vunerability as the operations of testing the time,
61 * removing the lock and creating a new one are not atomic.
62 * It would be possible for two processes to both decide to blow
63 * away the lock and then have process A remove the lock and establish
64 * its own, and then then have process B remove the lock which accidentily
65 * removes A's lock rather than the stale one.
66 *
67 * A further complication is with the NFS. If the file in question is
68 * being served by an NFS server, then its time is set by that server.
69 * We can not use the time on the client machine to check for a stale
70 * lock. Therefore, a temp file on the server is created to get
71 * the servers current time.
72 *
73 * Returns an error message. NULL return means the lock was obtained.
74 *
75 */
76 char *
file_lock(char * name,char * lockname,int timeout)77 file_lock(char * name, char * lockname, int timeout)
78 {
79 int r;
80 int fd;
81 struct stat statb;
82 struct stat fs_statb;
83 char tmpname[MAXPATHLEN];
84 static char msg[MAXPATHLEN];
85
86 if (timeout <= 0) {
87 timeout = 15;
88 }
89 for (;;) {
90 r = symlink(name, lockname);
91 if (r == 0) {
92 return (NULL);
93 }
94 if (errno != EEXIST) {
95 file_lock_error(msg, name,
96 (const char *)"symlink(%s, %s)", name, lockname);
97 return (msg);
98 }
99 for (;;) {
100 (void) sleep(1);
101 r = lstat(lockname, &statb);
102 if (r == -1) {
103 /*
104 * The lock must have just gone away - try
105 * again.
106 */
107 break;
108 }
109
110 /*
111 * With the NFS the time given a file is the time on
112 * the file server. This time may vary from the
113 * client's time. Therefore, we create a tmpfile in
114 * the same directory to establish the time on the
115 * server and use this time to see if the lock has
116 * expired.
117 */
118 (void) sprintf(tmpname, "%s.XXXXXX", lockname);
119 (void) mktemp(tmpname);
120 fd = creat(tmpname, 0666);
121 if (fd != -1) {
122 (void) close(fd);
123 } else {
124 file_lock_error(msg, name,
125 (const char *)"creat(%s)", tmpname);
126 return (msg);
127 }
128 if (stat(tmpname, &fs_statb) == -1) {
129 file_lock_error(msg, name,
130 (const char *)"stat(%s)", tmpname);
131 return (msg);
132 }
133 (void) unlink(tmpname);
134 if (statb.st_mtime + timeout < fs_statb.st_mtime) {
135 /*
136 * The lock has expired - blow it away.
137 */
138 (void) unlink(lockname);
139 break;
140 }
141 }
142 }
143 /* NOTREACHED */
144 }
145
146 /*
147 * Format a message telling why the lock could not be created.
148 */
149 /* VARARGS4 */
150 static void
file_lock_error(char * msg,char * file,const char * str,char * arg1,char * arg2)151 file_lock_error(char * msg, char * file, const char * str, char * arg1,
152 char * arg2)
153 {
154 int len;
155
156 (void) sprintf(msg, "Could not lock file `%s'; ", file);
157 len = strlen(msg);
158 (void) sprintf(&msg[len], str, arg1, arg2);
159 (void) strcat(msg, " failed - ");
160 #if defined(_LP64)
161 /* Needs to be changed to use strerror(3C) instead. */
162 len = strlen(msg);
163 (void) sprintf(&msg[len], "errno %d", errno);
164 #else /* #_LP64 */
165 if (errno < sys_nerr) {
166 (void) strcat(msg, sys_errlist[errno]);
167 } else {
168 len = strlen(msg);
169 (void) sprintf(&msg[len], "errno %d", errno);
170 }
171 #endif /* #_LP64 */
172 }
173