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 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 * 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