1*7c478bd9Sstevel@tonic-gate /*
2*7c478bd9Sstevel@tonic-gate  * CDDL HEADER START
3*7c478bd9Sstevel@tonic-gate  *
4*7c478bd9Sstevel@tonic-gate  * The contents of this file are subject to the terms of the
5*7c478bd9Sstevel@tonic-gate  * Common Development and Distribution License, Version 1.0 only
6*7c478bd9Sstevel@tonic-gate  * (the "License").  You may not use this file except in compliance
7*7c478bd9Sstevel@tonic-gate  * with the License.
8*7c478bd9Sstevel@tonic-gate  *
9*7c478bd9Sstevel@tonic-gate  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
10*7c478bd9Sstevel@tonic-gate  * or http://www.opensolaris.org/os/licensing.
11*7c478bd9Sstevel@tonic-gate  * See the License for the specific language governing permissions
12*7c478bd9Sstevel@tonic-gate  * and limitations under the License.
13*7c478bd9Sstevel@tonic-gate  *
14*7c478bd9Sstevel@tonic-gate  * When distributing Covered Code, include this CDDL HEADER in each
15*7c478bd9Sstevel@tonic-gate  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
16*7c478bd9Sstevel@tonic-gate  * If applicable, add the following below this CDDL HEADER, with the
17*7c478bd9Sstevel@tonic-gate  * fields enclosed by brackets "[]" replaced with your own identifying
18*7c478bd9Sstevel@tonic-gate  * information: Portions Copyright [yyyy] [name of copyright owner]
19*7c478bd9Sstevel@tonic-gate  *
20*7c478bd9Sstevel@tonic-gate  * CDDL HEADER END
21*7c478bd9Sstevel@tonic-gate  */
22*7c478bd9Sstevel@tonic-gate /*
23*7c478bd9Sstevel@tonic-gate  * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.
24*7c478bd9Sstevel@tonic-gate  * Use is subject to license terms.
25*7c478bd9Sstevel@tonic-gate  */
26*7c478bd9Sstevel@tonic-gate #pragma ident	"%Z%%M%	%I%	%E% SMI"
27*7c478bd9Sstevel@tonic-gate 
28*7c478bd9Sstevel@tonic-gate #include <stdio.h>
29*7c478bd9Sstevel@tonic-gate #include <stdlib.h>
30*7c478bd9Sstevel@tonic-gate #include <unistd.h>
31*7c478bd9Sstevel@tonic-gate #include <string.h>
32*7c478bd9Sstevel@tonic-gate #include <fcntl.h>
33*7c478bd9Sstevel@tonic-gate #include <sys/types.h>
34*7c478bd9Sstevel@tonic-gate #include <sys/param.h>
35*7c478bd9Sstevel@tonic-gate #include <sys/stat.h>
36*7c478bd9Sstevel@tonic-gate #include <errno.h>
37*7c478bd9Sstevel@tonic-gate 
38*7c478bd9Sstevel@tonic-gate 
39*7c478bd9Sstevel@tonic-gate /*
40*7c478bd9Sstevel@tonic-gate  * Format a message telling why the lock could not be created.
41*7c478bd9Sstevel@tonic-gate  */
42*7c478bd9Sstevel@tonic-gate /* VARARGS5 */
43*7c478bd9Sstevel@tonic-gate static void
file_lock_error(char * msg,char * file,int err,const char * str,char * arg1,char * arg2,size_t mlen)44*7c478bd9Sstevel@tonic-gate file_lock_error(char *msg, char *file, int err, const char *str,
45*7c478bd9Sstevel@tonic-gate     char *arg1, char *arg2, size_t mlen)
46*7c478bd9Sstevel@tonic-gate {
47*7c478bd9Sstevel@tonic-gate 	size_t	len;
48*7c478bd9Sstevel@tonic-gate 	char	*errstr;
49*7c478bd9Sstevel@tonic-gate 
50*7c478bd9Sstevel@tonic-gate 	(void) snprintf(msg, mlen, "Could not lock file `%s'; ", file);
51*7c478bd9Sstevel@tonic-gate 	len = strlen(msg);
52*7c478bd9Sstevel@tonic-gate 	(void) snprintf(&msg[len], (mlen - len), str, arg1, arg2);
53*7c478bd9Sstevel@tonic-gate 	(void) strcat(msg, " failed - ");
54*7c478bd9Sstevel@tonic-gate 	if ((errstr = strerror(err)) != NULL) {
55*7c478bd9Sstevel@tonic-gate 		(void) strlcat(msg, errstr, mlen);
56*7c478bd9Sstevel@tonic-gate 	} else {
57*7c478bd9Sstevel@tonic-gate 		len = strlen(msg);
58*7c478bd9Sstevel@tonic-gate 		(void) sprintf(&msg[len], "errno %d", err);
59*7c478bd9Sstevel@tonic-gate 	}
60*7c478bd9Sstevel@tonic-gate }
61*7c478bd9Sstevel@tonic-gate 
62*7c478bd9Sstevel@tonic-gate /*
63*7c478bd9Sstevel@tonic-gate  * This code stolen from the NSE library and changed to not depend
64*7c478bd9Sstevel@tonic-gate  * upon any NSE routines or header files.
65*7c478bd9Sstevel@tonic-gate  *
66*7c478bd9Sstevel@tonic-gate  * Simple file locking.
67*7c478bd9Sstevel@tonic-gate  * Create a symlink to a file.  The "test and set" will be
68*7c478bd9Sstevel@tonic-gate  * atomic as creating the symlink provides both functions.
69*7c478bd9Sstevel@tonic-gate  *
70*7c478bd9Sstevel@tonic-gate  * The timeout value specifies how long to wait for stale locks
71*7c478bd9Sstevel@tonic-gate  * to disappear.  If the lock is more than 'timeout' seconds old
72*7c478bd9Sstevel@tonic-gate  * then it is ok to blow it away.  This part has a small window
73*7c478bd9Sstevel@tonic-gate  * of vunerability as the operations of testing the time,
74*7c478bd9Sstevel@tonic-gate  * removing the lock and creating a new one are not atomic.
75*7c478bd9Sstevel@tonic-gate  * It would be possible for two processes to both decide to blow
76*7c478bd9Sstevel@tonic-gate  * away the lock and then have process A remove the lock and establish
77*7c478bd9Sstevel@tonic-gate  * its own, and then then have process B remove the lock which accidentily
78*7c478bd9Sstevel@tonic-gate  * removes A's lock rather than the stale one.
79*7c478bd9Sstevel@tonic-gate  *
80*7c478bd9Sstevel@tonic-gate  * A further complication is with the NFS.  If the file in question is
81*7c478bd9Sstevel@tonic-gate  * being served by an NFS server, then its time is set by that server.
82*7c478bd9Sstevel@tonic-gate  * We can not use the time on the client machine to check for a stale
83*7c478bd9Sstevel@tonic-gate  * lock.  Therefore, a temp file on the server is created to get
84*7c478bd9Sstevel@tonic-gate  * the servers current time.
85*7c478bd9Sstevel@tonic-gate  *
86*7c478bd9Sstevel@tonic-gate  * Returns an error message.  NULL return means the lock was obtained.
87*7c478bd9Sstevel@tonic-gate  *
88*7c478bd9Sstevel@tonic-gate  */
89*7c478bd9Sstevel@tonic-gate char *
file_lock(char * name,char * lockname,int timeout)90*7c478bd9Sstevel@tonic-gate file_lock(char *name, char *lockname, int timeout)
91*7c478bd9Sstevel@tonic-gate {
92*7c478bd9Sstevel@tonic-gate 	int		r;
93*7c478bd9Sstevel@tonic-gate 	int		fd;
94*7c478bd9Sstevel@tonic-gate 	struct	stat	statb;
95*7c478bd9Sstevel@tonic-gate 	struct	stat	fs_statb;
96*7c478bd9Sstevel@tonic-gate 	char		tmpname[MAXPATHLEN];
97*7c478bd9Sstevel@tonic-gate 	static	char	msg[MAXPATHLEN];
98*7c478bd9Sstevel@tonic-gate 
99*7c478bd9Sstevel@tonic-gate 	if (timeout <= 0) {
100*7c478bd9Sstevel@tonic-gate 		timeout = 15;
101*7c478bd9Sstevel@tonic-gate 	}
102*7c478bd9Sstevel@tonic-gate 	for (;;) {
103*7c478bd9Sstevel@tonic-gate 		r = symlink(name, lockname);
104*7c478bd9Sstevel@tonic-gate 		if (r == 0) {
105*7c478bd9Sstevel@tonic-gate 			return (NULL);
106*7c478bd9Sstevel@tonic-gate 		}
107*7c478bd9Sstevel@tonic-gate 		if (errno != EEXIST) {
108*7c478bd9Sstevel@tonic-gate 			file_lock_error(msg, name, errno,
109*7c478bd9Sstevel@tonic-gate 			    (const char *)"symlink(%s, %s)", name, lockname,
110*7c478bd9Sstevel@tonic-gate 			    sizeof (msg));
111*7c478bd9Sstevel@tonic-gate 			return (msg);
112*7c478bd9Sstevel@tonic-gate 		}
113*7c478bd9Sstevel@tonic-gate 		for (;;) {
114*7c478bd9Sstevel@tonic-gate 			(void) sleep(1);
115*7c478bd9Sstevel@tonic-gate 			r = lstat(lockname, &statb);
116*7c478bd9Sstevel@tonic-gate 			if (r == -1) {
117*7c478bd9Sstevel@tonic-gate 				/*
118*7c478bd9Sstevel@tonic-gate 				 * The lock must have just gone away - try
119*7c478bd9Sstevel@tonic-gate 				 * again.
120*7c478bd9Sstevel@tonic-gate 				 */
121*7c478bd9Sstevel@tonic-gate 				break;
122*7c478bd9Sstevel@tonic-gate 			}
123*7c478bd9Sstevel@tonic-gate 
124*7c478bd9Sstevel@tonic-gate 			/*
125*7c478bd9Sstevel@tonic-gate 			 * With the NFS the time given a file is the time on
126*7c478bd9Sstevel@tonic-gate 			 * the file server.  This time may vary from the
127*7c478bd9Sstevel@tonic-gate 			 * client's time.  Therefore, we create a tmpfile in
128*7c478bd9Sstevel@tonic-gate 			 * the same directory to establish the time on the
129*7c478bd9Sstevel@tonic-gate 			 * server and use this time to see if the lock has
130*7c478bd9Sstevel@tonic-gate 			 * expired.
131*7c478bd9Sstevel@tonic-gate 			 */
132*7c478bd9Sstevel@tonic-gate 			(void) snprintf(tmpname, MAXPATHLEN, "%s.XXXXXX",
133*7c478bd9Sstevel@tonic-gate 			    lockname);
134*7c478bd9Sstevel@tonic-gate 			(void) mktemp(tmpname);
135*7c478bd9Sstevel@tonic-gate 			fd = creat(tmpname, 0666);
136*7c478bd9Sstevel@tonic-gate 			if (fd != -1) {
137*7c478bd9Sstevel@tonic-gate 				(void) close(fd);
138*7c478bd9Sstevel@tonic-gate 			} else {
139*7c478bd9Sstevel@tonic-gate 				file_lock_error(msg, name, errno,
140*7c478bd9Sstevel@tonic-gate 				    (const char *)"creat(%s)", tmpname, 0,
141*7c478bd9Sstevel@tonic-gate 				    sizeof (msg));
142*7c478bd9Sstevel@tonic-gate 				return (msg);
143*7c478bd9Sstevel@tonic-gate 			}
144*7c478bd9Sstevel@tonic-gate 			if (stat(tmpname, &fs_statb) == -1) {
145*7c478bd9Sstevel@tonic-gate 				file_lock_error(msg, name, errno,
146*7c478bd9Sstevel@tonic-gate 				    (const char *)"stat(%s)", tmpname, 0,
147*7c478bd9Sstevel@tonic-gate 				    sizeof (msg));
148*7c478bd9Sstevel@tonic-gate 				return (msg);
149*7c478bd9Sstevel@tonic-gate 			}
150*7c478bd9Sstevel@tonic-gate 			(void) unlink(tmpname);
151*7c478bd9Sstevel@tonic-gate 			if (statb.st_mtime + timeout < fs_statb.st_mtime) {
152*7c478bd9Sstevel@tonic-gate 				/*
153*7c478bd9Sstevel@tonic-gate 				 * The lock has expired - blow it away.
154*7c478bd9Sstevel@tonic-gate 				 */
155*7c478bd9Sstevel@tonic-gate 				(void) unlink(lockname);
156*7c478bd9Sstevel@tonic-gate 				break;
157*7c478bd9Sstevel@tonic-gate 			}
158*7c478bd9Sstevel@tonic-gate 		}
159*7c478bd9Sstevel@tonic-gate 	}
160*7c478bd9Sstevel@tonic-gate 	/* NOTREACHED */
161*7c478bd9Sstevel@tonic-gate }
162