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