xref: /illumos-gate/usr/src/cmd/make/lib/makestate/lock.c (revision 10d63b7d)
1*10d63b7dSRichard Lowe /*
2*10d63b7dSRichard Lowe  * CDDL HEADER START
3*10d63b7dSRichard Lowe  *
4*10d63b7dSRichard Lowe  * The contents of this file are subject to the terms of the
5*10d63b7dSRichard Lowe  * Common Development and Distribution License (the "License").
6*10d63b7dSRichard Lowe  * You may not use this file except in compliance with the License.
7*10d63b7dSRichard Lowe  *
8*10d63b7dSRichard Lowe  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9*10d63b7dSRichard Lowe  * or http://www.opensolaris.org/os/licensing.
10*10d63b7dSRichard Lowe  * See the License for the specific language governing permissions
11*10d63b7dSRichard Lowe  * and limitations under the License.
12*10d63b7dSRichard Lowe  *
13*10d63b7dSRichard Lowe  * When distributing Covered Code, include this CDDL HEADER in each
14*10d63b7dSRichard Lowe  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15*10d63b7dSRichard Lowe  * If applicable, add the following below this CDDL HEADER, with the
16*10d63b7dSRichard Lowe  * fields enclosed by brackets "[]" replaced with your own identifying
17*10d63b7dSRichard Lowe  * information: Portions Copyright [yyyy] [name of copyright owner]
18*10d63b7dSRichard Lowe  *
19*10d63b7dSRichard Lowe  * CDDL HEADER END
20*10d63b7dSRichard Lowe  */
21*10d63b7dSRichard Lowe /*
22*10d63b7dSRichard Lowe  * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
23*10d63b7dSRichard Lowe  * Use is subject to license terms.
24*10d63b7dSRichard Lowe  */
25*10d63b7dSRichard Lowe 
26*10d63b7dSRichard Lowe #include <stdio.h>
27*10d63b7dSRichard Lowe #include <stdlib.h>
28*10d63b7dSRichard Lowe #include <unistd.h>
29*10d63b7dSRichard Lowe #include <string.h>
30*10d63b7dSRichard Lowe #include <fcntl.h>
31*10d63b7dSRichard Lowe #include <sys/types.h>
32*10d63b7dSRichard Lowe #include <sys/param.h>
33*10d63b7dSRichard Lowe #include <sys/stat.h>
34*10d63b7dSRichard Lowe #include <sys/errno.h>
35*10d63b7dSRichard Lowe #include <errno.h>		/* errno */
36*10d63b7dSRichard Lowe 
37*10d63b7dSRichard Lowe #if defined(_LP64)
38*10d63b7dSRichard Lowe /*
39*10d63b7dSRichard Lowe  * The symbols _sys_errlist and _sys_nerr are not visible in the
40*10d63b7dSRichard Lowe  * LP64 libc.  Use strerror(3C) instead.
41*10d63b7dSRichard Lowe  */
42*10d63b7dSRichard Lowe #else  /* #_LP64 */
43*10d63b7dSRichard Lowe extern	char *		sys_errlist[];
44*10d63b7dSRichard Lowe extern	int		sys_nerr;
45*10d63b7dSRichard Lowe #endif /* #_LP64 */
46*10d63b7dSRichard Lowe 
47*10d63b7dSRichard Lowe static	void		file_lock_error();
48*10d63b7dSRichard Lowe 
49*10d63b7dSRichard Lowe /*
50*10d63b7dSRichard Lowe  * This code stolen from the NSE library and changed to not depend
51*10d63b7dSRichard Lowe  * upon any NSE routines or header files.
52*10d63b7dSRichard Lowe  *
53*10d63b7dSRichard Lowe  * Simple file locking.
54*10d63b7dSRichard Lowe  * Create a symlink to a file.  The "test and set" will be
55*10d63b7dSRichard Lowe  * atomic as creating the symlink provides both functions.
56*10d63b7dSRichard Lowe  *
57*10d63b7dSRichard Lowe  * The timeout value specifies how long to wait for stale locks
58*10d63b7dSRichard Lowe  * to disappear.  If the lock is more than 'timeout' seconds old
59*10d63b7dSRichard Lowe  * then it is ok to blow it away.  This part has a small window
60*10d63b7dSRichard Lowe  * of vunerability as the operations of testing the time,
61*10d63b7dSRichard Lowe  * removing the lock and creating a new one are not atomic.
62*10d63b7dSRichard Lowe  * It would be possible for two processes to both decide to blow
63*10d63b7dSRichard Lowe  * away the lock and then have process A remove the lock and establish
64*10d63b7dSRichard Lowe  * its own, and then then have process B remove the lock which accidentily
65*10d63b7dSRichard Lowe  * removes A's lock rather than the stale one.
66*10d63b7dSRichard Lowe  *
67*10d63b7dSRichard Lowe  * A further complication is with the NFS.  If the file in question is
68*10d63b7dSRichard Lowe  * being served by an NFS server, then its time is set by that server.
69*10d63b7dSRichard Lowe  * We can not use the time on the client machine to check for a stale
70*10d63b7dSRichard Lowe  * lock.  Therefore, a temp file on the server is created to get
71*10d63b7dSRichard Lowe  * the servers current time.
72*10d63b7dSRichard Lowe  *
73*10d63b7dSRichard Lowe  * Returns an error message.  NULL return means the lock was obtained.
74*10d63b7dSRichard Lowe  *
75*10d63b7dSRichard Lowe  */
76*10d63b7dSRichard Lowe char *
file_lock(char * name,char * lockname,int timeout)77*10d63b7dSRichard Lowe file_lock(char * name, char * lockname, int timeout)
78*10d63b7dSRichard Lowe {
79*10d63b7dSRichard Lowe 	int		r;
80*10d63b7dSRichard Lowe 	int		fd;
81*10d63b7dSRichard Lowe 	struct	stat	statb;
82*10d63b7dSRichard Lowe 	struct	stat	fs_statb;
83*10d63b7dSRichard Lowe 	char		tmpname[MAXPATHLEN];
84*10d63b7dSRichard Lowe 	static	char	msg[MAXPATHLEN];
85*10d63b7dSRichard Lowe 
86*10d63b7dSRichard Lowe 	if (timeout <= 0) {
87*10d63b7dSRichard Lowe 		timeout = 15;
88*10d63b7dSRichard Lowe 	}
89*10d63b7dSRichard Lowe 	for (;;) {
90*10d63b7dSRichard Lowe 		r = symlink(name, lockname);
91*10d63b7dSRichard Lowe 		if (r == 0) {
92*10d63b7dSRichard Lowe 			return (NULL);
93*10d63b7dSRichard Lowe 		}
94*10d63b7dSRichard Lowe 		if (errno != EEXIST) {
95*10d63b7dSRichard Lowe 			file_lock_error(msg, name,
96*10d63b7dSRichard Lowe 			    (const char *)"symlink(%s, %s)", name, lockname);
97*10d63b7dSRichard Lowe 			return (msg);
98*10d63b7dSRichard Lowe 		}
99*10d63b7dSRichard Lowe 		for (;;) {
100*10d63b7dSRichard Lowe 			(void) sleep(1);
101*10d63b7dSRichard Lowe 			r = lstat(lockname, &statb);
102*10d63b7dSRichard Lowe 			if (r == -1) {
103*10d63b7dSRichard Lowe 				/*
104*10d63b7dSRichard Lowe 				 * The lock must have just gone away - try
105*10d63b7dSRichard Lowe 				 * again.
106*10d63b7dSRichard Lowe 				 */
107*10d63b7dSRichard Lowe 				break;
108*10d63b7dSRichard Lowe 			}
109*10d63b7dSRichard Lowe 
110*10d63b7dSRichard Lowe 			/*
111*10d63b7dSRichard Lowe 			 * With the NFS the time given a file is the time on
112*10d63b7dSRichard Lowe 			 * the file server.  This time may vary from the
113*10d63b7dSRichard Lowe 			 * client's time.  Therefore, we create a tmpfile in
114*10d63b7dSRichard Lowe 			 * the same directory to establish the time on the
115*10d63b7dSRichard Lowe 			 * server and use this time to see if the lock has
116*10d63b7dSRichard Lowe 			 * expired.
117*10d63b7dSRichard Lowe 			 */
118*10d63b7dSRichard Lowe 			(void) sprintf(tmpname, "%s.XXXXXX", lockname);
119*10d63b7dSRichard Lowe 			(void) mktemp(tmpname);
120*10d63b7dSRichard Lowe 			fd = creat(tmpname, 0666);
121*10d63b7dSRichard Lowe 			if (fd != -1) {
122*10d63b7dSRichard Lowe 				(void) close(fd);
123*10d63b7dSRichard Lowe 			} else {
124*10d63b7dSRichard Lowe 				file_lock_error(msg, name,
125*10d63b7dSRichard Lowe 				    (const char *)"creat(%s)", tmpname);
126*10d63b7dSRichard Lowe 				return (msg);
127*10d63b7dSRichard Lowe 			}
128*10d63b7dSRichard Lowe 			if (stat(tmpname, &fs_statb) == -1) {
129*10d63b7dSRichard Lowe 				file_lock_error(msg, name,
130*10d63b7dSRichard Lowe 				    (const char *)"stat(%s)", tmpname);
131*10d63b7dSRichard Lowe 				return (msg);
132*10d63b7dSRichard Lowe 			}
133*10d63b7dSRichard Lowe 			(void) unlink(tmpname);
134*10d63b7dSRichard Lowe 			if (statb.st_mtime + timeout < fs_statb.st_mtime) {
135*10d63b7dSRichard Lowe 				/*
136*10d63b7dSRichard Lowe 				 * The lock has expired - blow it away.
137*10d63b7dSRichard Lowe 				 */
138*10d63b7dSRichard Lowe 				(void) unlink(lockname);
139*10d63b7dSRichard Lowe 				break;
140*10d63b7dSRichard Lowe 			}
141*10d63b7dSRichard Lowe 		}
142*10d63b7dSRichard Lowe 	}
143*10d63b7dSRichard Lowe 	/* NOTREACHED */
144*10d63b7dSRichard Lowe }
145*10d63b7dSRichard Lowe 
146*10d63b7dSRichard Lowe /*
147*10d63b7dSRichard Lowe  * Format a message telling why the lock could not be created.
148*10d63b7dSRichard Lowe  */
149*10d63b7dSRichard Lowe /* VARARGS4 */
150*10d63b7dSRichard Lowe static	void
file_lock_error(char * msg,char * file,const char * str,char * arg1,char * arg2)151*10d63b7dSRichard Lowe file_lock_error(char * msg, char * file, const char * str, char * arg1,
152*10d63b7dSRichard Lowe 	char * arg2)
153*10d63b7dSRichard Lowe {
154*10d63b7dSRichard Lowe 	int	len;
155*10d63b7dSRichard Lowe 
156*10d63b7dSRichard Lowe 	(void) sprintf(msg, "Could not lock file `%s'; ", file);
157*10d63b7dSRichard Lowe 	len = strlen(msg);
158*10d63b7dSRichard Lowe 	(void) sprintf(&msg[len], str, arg1, arg2);
159*10d63b7dSRichard Lowe 	(void) strcat(msg, " failed - ");
160*10d63b7dSRichard Lowe #if defined(_LP64)
161*10d63b7dSRichard Lowe 	/* Needs to be changed to use strerror(3C) instead. */
162*10d63b7dSRichard Lowe 	len = strlen(msg);
163*10d63b7dSRichard Lowe 	(void) sprintf(&msg[len], "errno %d", errno);
164*10d63b7dSRichard Lowe #else  /* #_LP64 */
165*10d63b7dSRichard Lowe 	if (errno < sys_nerr) {
166*10d63b7dSRichard Lowe 		(void) strcat(msg, sys_errlist[errno]);
167*10d63b7dSRichard Lowe 	} else {
168*10d63b7dSRichard Lowe 		len = strlen(msg);
169*10d63b7dSRichard Lowe 		(void) sprintf(&msg[len], "errno %d", errno);
170*10d63b7dSRichard Lowe 	}
171*10d63b7dSRichard Lowe #endif /* #_LP64 */
172*10d63b7dSRichard Lowe }