Annotation of src/usr.bin/mail/dotlock.c, Revision 1.1
1.1 ! deraadt 1: /* $OpenBSD: dotlock.c,v 1.1 1996/06/08 19:48:19 christos Exp $ */
! 2: /* $NetBSD: dotlock.c,v 1.1 1996/06/08 19:48:19 christos Exp $ */
! 3:
! 4: /*
! 5: * Copyright (c) 1996 Christos Zoulas. All rights reserved.
! 6: *
! 7: * Redistribution and use in source and binary forms, with or without
! 8: * modification, are permitted provided that the following conditions
! 9: * are met:
! 10: * 1. Redistributions of source code must retain the above copyright
! 11: * notice, this list of conditions and the following disclaimer.
! 12: * 2. Redistributions in binary form must reproduce the above copyright
! 13: * notice, this list of conditions and the following disclaimer in the
! 14: * documentation and/or other materials provided with the distribution.
! 15: * 3. All advertising materials mentioning features or use of this software
! 16: * must display the following acknowledgement:
! 17: * This product includes software developed by Christos Zoulas.
! 18: * 4. The name of the author may not be used to endorse or promote products
! 19: * derived from this software without specific prior written permission.
! 20: *
! 21: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
! 22: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
! 23: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
! 24: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
! 25: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
! 26: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
! 27: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
! 28: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
! 29: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
! 30: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
! 31: */
! 32:
! 33: #ifndef lint
! 34: static char rcsid[] = "$OpenBSD: dotlock.c,v 1.1 1996/06/08 19:48:19 christos Exp $";
! 35: #endif
! 36:
! 37: #include <sys/types.h>
! 38: #include <sys/param.h>
! 39: #include <sys/stat.h>
! 40: #include <sys/time.h>
! 41:
! 42: #include <stdio.h>
! 43: #include <string.h>
! 44: #include <fcntl.h>
! 45: #include <stdlib.h>
! 46: #include <unistd.h>
! 47: #include <errno.h>
! 48: #include <signal.h>
! 49:
! 50: #include "extern.h"
! 51:
! 52: #ifndef O_SYNC
! 53: #define O_SYNC 0
! 54: #endif
! 55:
! 56: static int create_exclusive __P((const char *));
! 57: /*
! 58: * Create a unique file. O_EXCL does not really work over NFS so we follow
! 59: * the following trick: [Inspired by S.R. van den Berg]
! 60: *
! 61: * - make a mostly unique filename and try to create it.
! 62: * - link the unique filename to our target
! 63: * - get the link count of the target
! 64: * - unlink the mostly unique filename
! 65: * - if the link count was 2, then we are ok; else we've failed.
! 66: */
! 67: static int
! 68: create_exclusive(fname)
! 69: const char *fname;
! 70: {
! 71: char path[MAXPATHLEN], hostname[MAXHOSTNAMELEN];
! 72: const char *ptr;
! 73: struct timeval tv;
! 74: pid_t pid;
! 75: size_t ntries, cookie;
! 76: int fd, serrno;
! 77: struct stat st;
! 78:
! 79: (void) gettimeofday(&tv, NULL);
! 80: (void) gethostname(hostname, MAXHOSTNAMELEN);
! 81: pid = getpid();
! 82:
! 83: cookie = pid ^ tv.tv_usec;
! 84:
! 85: /*
! 86: * We generate a semi-unique filename, from hostname.(pid ^ usec)
! 87: */
! 88: if ((ptr = strrchr(fname, '/')) == NULL)
! 89: ptr = fname;
! 90: else
! 91: ptr++;
! 92:
! 93: (void) snprintf(path, sizeof(path), "%.*s.%s.%x",
! 94: ptr - fname, fname, hostname, cookie);
! 95:
! 96: /*
! 97: * We try to create the unique filename.
! 98: */
! 99: for (ntries = 0; ntries < 5; ntries++) {
! 100: fd = open(path, O_WRONLY|O_CREAT|O_TRUNC|O_EXCL|O_SYNC, 0);
! 101: if (fd != -1) {
! 102: (void) close(fd);
! 103: break;
! 104: }
! 105: else if (errno == EEXIST)
! 106: continue;
! 107: else
! 108: return -1;
! 109: }
! 110:
! 111: /*
! 112: * We link the path to the name
! 113: */
! 114: if (link(path, fname) == -1)
! 115: goto bad;
! 116:
! 117: /*
! 118: * Note that we stat our own exclusively created name, not the
! 119: * destination, since the destination can be affected by others.
! 120: */
! 121: if (stat(path, &st) == -1)
! 122: goto bad;
! 123:
! 124: (void) unlink(path);
! 125:
! 126: /*
! 127: * If the number of links was two (one for the unique file and one
! 128: * for the lock), we've won the race
! 129: */
! 130: if (st.st_nlink != 2) {
! 131: errno = EEXIST;
! 132: return -1;
! 133: }
! 134: return 0;
! 135:
! 136: bad:
! 137: serrno = errno;
! 138: (void) unlink(path);
! 139: errno = serrno;
! 140: return -1;
! 141: }
! 142:
! 143: int
! 144: dot_lock(fname, pollinterval, fp, msg)
! 145: const char *fname; /* Pathname to lock */
! 146: int pollinterval; /* Interval to check for lock, -1 return */
! 147: FILE *fp; /* File to print message */
! 148: const char *msg; /* Message to print */
! 149: {
! 150: char path[MAXPATHLEN];
! 151: sigset_t nset, oset;
! 152:
! 153: sigemptyset(&nset);
! 154: sigaddset(&nset, SIGHUP);
! 155: sigaddset(&nset, SIGINT);
! 156: sigaddset(&nset, SIGQUIT);
! 157: sigaddset(&nset, SIGTERM);
! 158: sigaddset(&nset, SIGTTIN);
! 159: sigaddset(&nset, SIGTTOU);
! 160: sigaddset(&nset, SIGTSTP);
! 161: sigaddset(&nset, SIGCHLD);
! 162:
! 163: (void) snprintf(path, sizeof(path), "%s.lock", fname);
! 164:
! 165: for (;;) {
! 166: (void) sigprocmask(SIG_BLOCK, &nset, &oset);
! 167: if (create_exclusive(path) != -1) {
! 168: (void) sigprocmask(SIG_SETMASK, &oset, NULL);
! 169: return 0;
! 170: }
! 171: else
! 172: (void) sigprocmask(SIG_SETMASK, &oset, NULL);
! 173:
! 174: if (errno != EEXIST)
! 175: return -1;
! 176:
! 177: if (fp && msg)
! 178: (void) fputs(msg, fp);
! 179:
! 180: if (pollinterval) {
! 181: if (pollinterval == -1) {
! 182: errno = EEXIST;
! 183: return -1;
! 184: }
! 185: sleep(pollinterval);
! 186: }
! 187: }
! 188: }
! 189:
! 190: void
! 191: dot_unlock(fname)
! 192: const char *fname;
! 193: {
! 194: char path[MAXPATHLEN];
! 195:
! 196: (void) snprintf(path, sizeof(path), "%s.lock", fname);
! 197: (void) unlink(path);
! 198: }
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