1 /* $NetBSD: dotlock.c,v 1.6 2002/03/05 21:18:15 wiz 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 * 3. All advertising materials mentioning features or use of this software 15 * must display the following acknowledgement: 16 * This product includes software developed by Christos Zoulas. 17 * 4. The name of the author may not be used to endorse or promote products 18 * derived from this software without specific prior written permission. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 21 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 22 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 23 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 24 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 25 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 28 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 29 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 #include <sys/cdefs.h> 33 #ifndef lint 34 __RCSID("$NetBSD: dotlock.c,v 1.6 2002/03/05 21:18:15 wiz Exp $"); 35 #endif 36 37 #include "rcv.h" 38 #include "extern.h" 39 40 #ifndef O_SYNC 41 #define O_SYNC 0 42 #endif 43 44 static int create_exclusive(const char *); 45 /* 46 * Create a unique file. O_EXCL does not really work over NFS so we follow 47 * the following trick: [Inspired by S.R. van den Berg] 48 * 49 * - make a mostly unique filename and try to create it. 50 * - link the unique filename to our target 51 * - get the link count of the target 52 * - unlink the mostly unique filename 53 * - if the link count was 2, then we are ok; else we've failed. 54 */ 55 static int 56 create_exclusive(const char *fname) 57 { 58 char path[MAXPATHLEN], hostname[MAXHOSTNAMELEN + 1]; 59 const char *ptr; 60 struct timeval tv; 61 pid_t pid; 62 size_t ntries, cookie; 63 int fd, serrno; 64 struct stat st; 65 66 (void)gettimeofday(&tv, NULL); 67 (void)gethostname(hostname, sizeof hostname); 68 hostname[sizeof(hostname) - 1] = '\0'; 69 pid = getpid(); 70 71 cookie = pid ^ tv.tv_usec; 72 73 /* 74 * We generate a semi-unique filename, from hostname.(pid ^ usec) 75 */ 76 if ((ptr = strrchr(fname, '/')) == NULL) 77 ptr = fname; 78 else 79 ptr++; 80 81 (void)snprintf(path, sizeof(path), "%.*s.%s.%lx", 82 (int)(ptr - fname), fname, hostname, (u_long)cookie); 83 84 /* 85 * We try to create the unique filename. 86 */ 87 for (ntries = 0; ntries < 5; ntries++) { 88 fd = open(path, O_WRONLY|O_CREAT|O_TRUNC|O_EXCL|O_SYNC, 0); 89 if (fd != -1) { 90 (void)close(fd); 91 break; 92 } 93 else if (errno == EEXIST) 94 continue; 95 else 96 return -1; 97 } 98 99 /* 100 * We link the path to the name 101 */ 102 if (link(path, fname) == -1) 103 goto bad; 104 105 /* 106 * Note that we stat our own exclusively created name, not the 107 * destination, since the destination can be affected by others. 108 */ 109 if (stat(path, &st) == -1) 110 goto bad; 111 112 (void)unlink(path); 113 114 /* 115 * If the number of links was two (one for the unique file and one 116 * for the lock), we've won the race 117 */ 118 if (st.st_nlink != 2) { 119 errno = EEXIST; 120 return -1; 121 } 122 return 0; 123 124 bad: 125 serrno = errno; 126 (void)unlink(path); 127 errno = serrno; 128 return -1; 129 } 130 131 /* 132 * fname -- Pathname to lock 133 * pollinterval -- Interval to check for lock, -1 return 134 * fp -- File to print message 135 * msg -- Message to print 136 */ 137 int 138 dot_lock(const char *fname, int pollinterval, FILE *fp, const char *msg) 139 { 140 char path[MAXPATHLEN]; 141 sigset_t nset, oset; 142 143 sigemptyset(&nset); 144 sigaddset(&nset, SIGHUP); 145 sigaddset(&nset, SIGINT); 146 sigaddset(&nset, SIGQUIT); 147 sigaddset(&nset, SIGTERM); 148 sigaddset(&nset, SIGTTIN); 149 sigaddset(&nset, SIGTTOU); 150 sigaddset(&nset, SIGTSTP); 151 sigaddset(&nset, SIGCHLD); 152 153 (void)snprintf(path, sizeof(path), "%s.lock", fname); 154 155 for (;;) { 156 (void)sigprocmask(SIG_BLOCK, &nset, &oset); 157 if (create_exclusive(path) != -1) { 158 (void)sigprocmask(SIG_SETMASK, &oset, NULL); 159 return 0; 160 } 161 else 162 (void)sigprocmask(SIG_SETMASK, &oset, NULL); 163 164 if (errno != EEXIST) 165 return -1; 166 167 if (fp && msg) 168 (void)fputs(msg, fp); 169 170 if (pollinterval) { 171 if (pollinterval == -1) { 172 errno = EEXIST; 173 return -1; 174 } 175 sleep(pollinterval); 176 } 177 } 178 } 179 180 void 181 dot_unlock(const char *fname) 182 { 183 char path[MAXPATHLEN]; 184 185 (void)snprintf(path, sizeof(path), "%s.lock", fname); 186 (void)unlink(path); 187 } 188