dotlock.c revision 1.10
1 /* $NetBSD: dotlock.c,v 1.10 2009/04/10 13:08:24 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 * 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 1.10 2009/04/10 13:08:24 christos Exp $"); 35 #endif 36 37 #include "rcv.h" 38 #include "extern.h" 39 #include "sig.h" 40 41 #ifndef O_SYNC 42 #define O_SYNC 0 43 #endif 44 45 static int create_exclusive(const char *); 46 /* 47 * Create a unique file. O_EXCL does not really work over NFS so we follow 48 * the following trick: [Inspired by S.R. van den Berg] 49 * 50 * - make a mostly unique filename and try to create it. 51 * - link the unique filename to our target 52 * - get the link count of the target 53 * - unlink the mostly unique filename 54 * - if the link count was 2, then we are ok; else we've failed. 55 */ 56 static int 57 create_exclusive(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 /* 133 * fname -- Pathname to lock 134 * pollinterval -- Interval to check for lock, -1 return 135 * fp -- File to print message 136 * msg -- Message to print 137 */ 138 PUBLIC int 139 dot_lock(const char *fname, int pollinterval, FILE *fp, const char *msg) 140 { 141 char path[MAXPATHLEN]; 142 sigset_t nset, oset; 143 int retval; 144 145 (void)sigemptyset(&nset); 146 (void)sigaddset(&nset, SIGHUP); 147 (void)sigaddset(&nset, SIGINT); 148 (void)sigaddset(&nset, SIGQUIT); 149 (void)sigaddset(&nset, SIGTERM); 150 (void)sigaddset(&nset, SIGTTIN); 151 (void)sigaddset(&nset, SIGTTOU); 152 (void)sigaddset(&nset, SIGTSTP); 153 (void)sigaddset(&nset, SIGCHLD); 154 155 (void)snprintf(path, sizeof(path), "%s.lock", fname); 156 157 retval = -1; 158 for (;;) { 159 sig_check(); 160 (void)sigprocmask(SIG_BLOCK, &nset, &oset); 161 if (create_exclusive(path) != -1) { 162 (void)sigprocmask(SIG_SETMASK, &oset, NULL); 163 retval = 0; 164 break; 165 } 166 else 167 (void)sigprocmask(SIG_SETMASK, &oset, NULL); 168 169 if (errno != EEXIST) 170 break; 171 172 if (fp && msg) 173 (void)fputs(msg, fp); 174 175 if (pollinterval) { 176 if (pollinterval == -1) { 177 errno = EEXIST; 178 break; 179 } 180 (void)sleep((unsigned int)pollinterval); 181 } 182 } 183 sig_check(); 184 return retval; 185 } 186 187 PUBLIC void 188 dot_unlock(const char *fname) 189 { 190 char path[MAXPATHLEN]; 191 192 (void)snprintf(path, sizeof(path), "%s.lock", fname); 193 (void)unlink(path); 194 } 195
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