1 /* NetBSD: dotlock.c,v 1.11 2009/10/21 01:07:46 snj Exp */ 2 3 /* 4 * Copyright (c) 1996 Christos Zoulas. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25 */ 26 #include "sh.h" 27 28 #include <stdio.h> 29 #ifndef O_SYNC 30 #define O_SYNC 0 31 #endif 32 33 #include "dotlock.h" 34 35 static int create_exclusive(const char *); 36 /* 37 * Create a unique file. O_EXCL does not really work over NFS so we follow 38 * the following trick: [Inspired by S.R. van den Berg] 39 * 40 * - make a mostly unique filename and try to create it. 41 * - link the unique filename to our target 42 * - get the link count of the target 43 * - unlink the mostly unique filename 44 * - if the link count was 2, then we are ok; else we've failed. 45 */ 46 static int 47 create_exclusive(const char *fname) 48 { 49 char path[MAXPATHLEN], hostname[MAXHOSTNAMELEN + 1]; 50 const char *ptr; 51 struct timeval tv; 52 pid_t pid; 53 size_t ntries, cookie; 54 int fd, serrno; 55 struct stat st; 56 57 (void)gettimeofday(&tv, NULL); 58 (void)gethostname(hostname, sizeof(hostname)); 59 hostname[sizeof(hostname) - 1] = '\0'; 60 pid = getpid(); 61 62 cookie = pid ^ tv.tv_usec; 63 64 /* 65 * We generate a semi-unique filename, from hostname.(pid ^ usec) 66 */ 67 if ((ptr = strrchr(fname, '/')) == NULL) 68 ptr = fname; 69 else 70 ptr++; 71 72 (void)snprintf(path, sizeof(path), "%.*s.%s.%lx", 73 (int)(ptr - fname), fname, hostname, (u_long)cookie); 74 75 /* 76 * We try to create the unique filename. 77 */ 78 for (ntries = 0; ntries < 5; ntries++) { 79 fd = open(path, O_WRONLY|O_CREAT|O_TRUNC|O_EXCL|O_SYNC, 0); 80 if (fd != -1) { 81 (void)close(fd); 82 break; 83 } 84 else if (errno == EEXIST) 85 continue; 86 else 87 return -1; 88 } 89 90 /* 91 * We link the path to the name 92 */ 93 if (link(path, fname) == -1) 94 goto bad; 95 96 /* 97 * Note that we stat our own exclusively created name, not the 98 * destination, since the destination can be affected by others. 99 */ 100 if (stat(path, &st) == -1) 101 goto bad; 102 103 (void)unlink(path); 104 105 /* 106 * If the number of links was two (one for the unique file and one 107 * for the lock), we've won the race 108 */ 109 if (st.st_nlink != 2) { 110 errno = EEXIST; 111 return -1; 112 } 113 return 0; 114 115 bad: 116 serrno = errno; 117 (void)unlink(path); 118 errno = serrno; 119 return -1; 120 } 121 122 /* 123 * fname -- Pathname to lock 124 * pollinterval -- Interval (miliseconds) to check for lock, -1 return 125 */ 126 int 127 dot_lock(const char *fname, int pollinterval) 128 { 129 char path[MAXPATHLEN]; 130 sigset_t nset, oset; 131 int retval; 132 133 (void)sigemptyset(&nset); 134 (void)sigaddset(&nset, SIGHUP); 135 (void)sigaddset(&nset, SIGINT); 136 (void)sigaddset(&nset, SIGQUIT); 137 (void)sigaddset(&nset, SIGTERM); 138 (void)sigaddset(&nset, SIGTTIN); 139 (void)sigaddset(&nset, SIGTTOU); 140 (void)sigaddset(&nset, SIGTSTP); 141 (void)sigaddset(&nset, SIGCHLD); 142 143 (void)snprintf(path, sizeof(path), "%s.lock", fname); 144 145 retval = -1; 146 for (;;) { 147 handle_pending_signals(); 148 (void)sigprocmask(SIG_BLOCK, &nset, &oset); 149 if (create_exclusive(path) != -1) { 150 (void)sigprocmask(SIG_SETMASK, &oset, NULL); 151 retval = 0; 152 break; 153 } 154 else 155 (void)sigprocmask(SIG_SETMASK, &oset, NULL); 156 157 if (errno != EEXIST) 158 break; 159 160 if (pollinterval) { 161 if (pollinterval == -1) { 162 errno = EEXIST; 163 break; 164 } 165 (void)usleep((unsigned int)pollinterval * 1000); 166 } 167 } 168 handle_pending_signals(); 169 return retval; 170 } 171 172 void 173 dot_unlock(const char *fname) 174 { 175 char path[MAXPATHLEN]; 176 177 (void)snprintf(path, sizeof(path), "%s.lock", fname); 178 (void)unlink(path); 179 } 180