1 /* $NetBSD: dotlock.c,v 1.4 1998/07/06 06:51:55 mrg 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 1.4 1998/07/06 06:51:55 mrg 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 __P((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(fname) 57 const char *fname; 58 { 59 char path[MAXPATHLEN], hostname[MAXHOSTNAMELEN + 1]; 60 const char *ptr; 61 struct timeval tv; 62 pid_t pid; 63 size_t ntries, cookie; 64 int fd, serrno; 65 struct stat st; 66 67 (void)gettimeofday(&tv, NULL); 68 (void)gethostname(hostname, sizeof hostname); 69 hostname[sizeof(hostname) - 1] = '\0'; 70 pid = getpid(); 71 72 cookie = pid ^ tv.tv_usec; 73 74 /* 75 * We generate a semi-unique filename, from hostname.(pid ^ usec) 76 */ 77 if ((ptr = strrchr(fname, '/')) == NULL) 78 ptr = fname; 79 else 80 ptr++; 81 82 (void) snprintf(path, sizeof(path), "%.*s.%s.%lx", 83 (int)(ptr - fname), fname, hostname, (u_long)cookie); 84 85 /* 86 * We try to create the unique filename. 87 */ 88 for (ntries = 0; ntries < 5; ntries++) { 89 fd = open(path, O_WRONLY|O_CREAT|O_TRUNC|O_EXCL|O_SYNC, 0); 90 if (fd != -1) { 91 (void) close(fd); 92 break; 93 } 94 else if (errno == EEXIST) 95 continue; 96 else 97 return -1; 98 } 99 100 /* 101 * We link the path to the name 102 */ 103 if (link(path, fname) == -1) 104 goto bad; 105 106 /* 107 * Note that we stat our own exclusively created name, not the 108 * destination, since the destination can be affected by others. 109 */ 110 if (stat(path, &st) == -1) 111 goto bad; 112 113 (void) unlink(path); 114 115 /* 116 * If the number of links was two (one for the unique file and one 117 * for the lock), we've won the race 118 */ 119 if (st.st_nlink != 2) { 120 errno = EEXIST; 121 return -1; 122 } 123 return 0; 124 125 bad: 126 serrno = errno; 127 (void) unlink(path); 128 errno = serrno; 129 return -1; 130 } 131 132 int 133 dot_lock(fname, pollinterval, fp, msg) 134 const char *fname; /* Pathname to lock */ 135 int pollinterval; /* Interval to check for lock, -1 return */ 136 FILE *fp; /* File to print message */ 137 const char *msg; /* Message to print */ 138 { 139 char path[MAXPATHLEN]; 140 sigset_t nset, oset; 141 142 sigemptyset(&nset); 143 sigaddset(&nset, SIGHUP); 144 sigaddset(&nset, SIGINT); 145 sigaddset(&nset, SIGQUIT); 146 sigaddset(&nset, SIGTERM); 147 sigaddset(&nset, SIGTTIN); 148 sigaddset(&nset, SIGTTOU); 149 sigaddset(&nset, SIGTSTP); 150 sigaddset(&nset, SIGCHLD); 151 152 (void) snprintf(path, sizeof(path), "%s.lock", fname); 153 154 for (;;) { 155 (void) sigprocmask(SIG_BLOCK, &nset, &oset); 156 if (create_exclusive(path) != -1) { 157 (void) sigprocmask(SIG_SETMASK, &oset, NULL); 158 return 0; 159 } 160 else 161 (void) sigprocmask(SIG_SETMASK, &oset, NULL); 162 163 if (errno != EEXIST) 164 return -1; 165 166 if (fp && msg) 167 (void) fputs(msg, fp); 168 169 if (pollinterval) { 170 if (pollinterval == -1) { 171 errno = EEXIST; 172 return -1; 173 } 174 sleep(pollinterval); 175 } 176 } 177 } 178 179 void 180 dot_unlock(fname) 181 const char *fname; 182 { 183 char path[MAXPATHLEN]; 184 185 (void) snprintf(path, sizeof(path), "%s.lock", fname); 186 (void) unlink(path); 187 } 188