1 /* $NetBSD: dotlock.c,v 1.3 1997/10/19 14:12:30 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 1.3 1997/10/19 14:12:30 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]; 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, MAXHOSTNAMELEN); 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 int 132 dot_lock(fname, pollinterval, fp, msg) 133 const char *fname; /* Pathname to lock */ 134 int pollinterval; /* Interval to check for lock, -1 return */ 135 FILE *fp; /* File to print message */ 136 const char *msg; /* Message to print */ 137 { 138 char path[MAXPATHLEN]; 139 sigset_t nset, oset; 140 141 sigemptyset(&nset); 142 sigaddset(&nset, SIGHUP); 143 sigaddset(&nset, SIGINT); 144 sigaddset(&nset, SIGQUIT); 145 sigaddset(&nset, SIGTERM); 146 sigaddset(&nset, SIGTTIN); 147 sigaddset(&nset, SIGTTOU); 148 sigaddset(&nset, SIGTSTP); 149 sigaddset(&nset, SIGCHLD); 150 151 (void) snprintf(path, sizeof(path), "%s.lock", fname); 152 153 for (;;) { 154 (void) sigprocmask(SIG_BLOCK, &nset, &oset); 155 if (create_exclusive(path) != -1) { 156 (void) sigprocmask(SIG_SETMASK, &oset, NULL); 157 return 0; 158 } 159 else 160 (void) sigprocmask(SIG_SETMASK, &oset, NULL); 161 162 if (errno != EEXIST) 163 return -1; 164 165 if (fp && msg) 166 (void) fputs(msg, fp); 167 168 if (pollinterval) { 169 if (pollinterval == -1) { 170 errno = EEXIST; 171 return -1; 172 } 173 sleep(pollinterval); 174 } 175 } 176 } 177 178 void 179 dot_unlock(fname) 180 const char *fname; 181 { 182 char path[MAXPATHLEN]; 183 184 (void) snprintf(path, sizeof(path), "%s.lock", fname); 185 (void) unlink(path); 186 } 187