1 /* $NetBSD: dotlock.c,v 1.14 2021/02/17 21:09:39 christos 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 27 #include <sys/cdefs.h> 28 #ifndef lint 29 __RCSID("$NetBSD: dotlock.c,v 1.14 2021/02/17 21:09:39 christos Exp $"); 30 #endif 31 32 #include "rcv.h" 33 #include "extern.h" 34 #include "sig.h" 35 36 #ifndef O_SYNC 37 #define O_SYNC 0 38 #endif 39 40 static int create_exclusive(const char *); 41 /* 42 * Create a unique file. O_EXCL does not really work over NFS so we follow 43 * the following trick: [Inspired by S.R. van den Berg] 44 * 45 * - make a mostly unique filename and try to create it. 46 * - link the unique filename to our target 47 * - get the link count of the target 48 * - unlink the mostly unique filename 49 * - if the link count was 2, then we are ok; else we've failed. 50 */ 51 static int 52 create_exclusive(const char *fname) 53 { 54 char path[MAXPATHLEN], hostname[MAXHOSTNAMELEN + 1]; 55 const char *ptr; 56 struct timeval tv; 57 pid_t pid; 58 size_t ntries, cookie; 59 int fd, serrno; 60 struct stat st; 61 62 (void)gettimeofday(&tv, NULL); 63 (void)gethostname(hostname, sizeof(hostname)); 64 hostname[sizeof(hostname) - 1] = '\0'; 65 pid = getpid(); 66 67 cookie = pid ^ tv.tv_usec; 68 69 /* 70 * We generate a semi-unique filename, from hostname.(pid ^ usec) 71 */ 72 if ((ptr = strrchr(fname, '/')) == NULL) 73 ptr = fname; 74 else 75 ptr++; 76 77 (void)snprintf(path, sizeof(path), "%.*s.%s.%lx", 78 (int)(ptr - fname), fname, hostname, (u_long)cookie); 79 80 /* 81 * We try to create the unique filename. 82 */ 83 for (ntries = 0; ; ntries++) { 84 fd = open(path, 85 O_WRONLY|O_CREAT|O_TRUNC|O_EXCL|O_SYNC|O_CLOEXEC, 0); 86 if (fd != -1) { 87 (void)close(fd); 88 break; 89 } 90 else if (errno == EEXIST && ntries < 5) 91 continue; 92 else 93 return -1; 94 } 95 96 /* 97 * We link the path to the name 98 */ 99 if (link(path, fname) == -1) 100 goto bad; 101 102 /* 103 * Note that we stat our own exclusively created name, not the 104 * destination, since the destination can be affected by others. 105 */ 106 if (stat(path, &st) == -1) 107 goto bad; 108 109 (void)unlink(path); 110 111 /* 112 * If the number of links was two (one for the unique file and one 113 * for the lock), we've won the race 114 */ 115 if (st.st_nlink != 2) { 116 errno = EEXIST; 117 return -1; 118 } 119 return 0; 120 121 bad: 122 serrno = errno; 123 (void)unlink(path); 124 errno = serrno; 125 return -1; 126 } 127 128 /* 129 * fname -- Pathname to lock 130 * pollinterval -- Interval to check for lock, -1 return 131 * fp -- File to print message 132 * msg -- Message to print 133 */ 134 PUBLIC int 135 dot_lock(const char *fname, int pollinterval, FILE *fp, const char *msg) 136 { 137 char path[MAXPATHLEN]; 138 sigset_t nset, oset; 139 int retval; 140 141 (void)sigemptyset(&nset); 142 (void)sigaddset(&nset, SIGHUP); 143 (void)sigaddset(&nset, SIGINT); 144 (void)sigaddset(&nset, SIGQUIT); 145 (void)sigaddset(&nset, SIGTERM); 146 (void)sigaddset(&nset, SIGTTIN); 147 (void)sigaddset(&nset, SIGTTOU); 148 (void)sigaddset(&nset, SIGTSTP); 149 (void)sigaddset(&nset, SIGCHLD); 150 151 (void)snprintf(path, sizeof(path), "%s.lock", fname); 152 153 retval = -1; 154 for (;;) { 155 sig_check(); 156 (void)sigprocmask(SIG_BLOCK, &nset, &oset); 157 if (create_exclusive(path) != -1) { 158 (void)sigprocmask(SIG_SETMASK, &oset, NULL); 159 retval = 0; 160 break; 161 } 162 else 163 (void)sigprocmask(SIG_SETMASK, &oset, NULL); 164 165 if (errno != EEXIST) 166 break; 167 168 if (fp && msg) 169 (void)fputs(msg, fp); 170 171 if (pollinterval) { 172 if (pollinterval == -1) { 173 errno = EEXIST; 174 break; 175 } 176 (void)sleep((unsigned int)pollinterval); 177 } 178 } 179 sig_check(); 180 return retval; 181 } 182 183 PUBLIC void 184 dot_unlock(const char *fname) 185 { 186 char path[MAXPATHLEN]; 187 188 (void)snprintf(path, sizeof(path), "%s.lock", fname); 189 (void)unlink(path); 190 } 191
Indexes created Mon Sep 22 21:09:42 GMT 2025