diff options
Diffstat (limited to 'dotlock.c')
| -rw-r--r-- | dotlock.c | 180 |
1 files changed, 180 insertions, 0 deletions
diff --git a/dotlock.c b/dotlock.c new file mode 100644 index 000000000000..d7a49eb545c7 --- /dev/null +++ b/dotlock.c @@ -0,0 +1,180 @@ +/* $NetBSD: dotlock.c,v 1.11 2009/10/21 01:07:46 snj Exp $ */ + +/* + * Copyright (c) 1996 Christos Zoulas. All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR + * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES + * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. + * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT + * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF + * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + */ +#include "sh.h" +RCSID("$tcsh: dotlock.c,v 3.4 2015/11/03 21:04:13 christos Exp $") + +#include <stdio.h> +#ifndef O_SYNC +#define O_SYNC 0 +#endif + +#include "dotlock.h" + +static int create_exclusive(const char *); +/* + * Create a unique file. O_EXCL does not really work over NFS so we follow + * the following trick: [Inspired by S.R. van den Berg] + * + * - make a mostly unique filename and try to create it. + * - link the unique filename to our target + * - get the link count of the target + * - unlink the mostly unique filename + * - if the link count was 2, then we are ok; else we've failed. + */ +static int +create_exclusive(const char *fname) +{ + char path[MAXPATHLEN], hostname[MAXHOSTNAMELEN + 1]; + const char *ptr; + struct timeval tv; + pid_t pid; + size_t ntries, cookie; + int fd, serrno; + struct stat st; + + (void)gettimeofday(&tv, NULL); + (void)gethostname(hostname, sizeof(hostname)); + hostname[sizeof(hostname) - 1] = '\0'; + pid = getpid(); + + cookie = pid ^ tv.tv_usec; + + /* + * We generate a semi-unique filename, from hostname.(pid ^ usec) + */ + if ((ptr = strrchr(fname, '/')) == NULL) + ptr = fname; + else + ptr++; + + (void)snprintf(path, sizeof(path), "%.*s.%s.%lx", + (int)(ptr - fname), fname, hostname, (u_long)cookie); + + /* + * We try to create the unique filename. + */ + for (ntries = 0; ntries < 5; ntries++) { + fd = open(path, O_WRONLY|O_CREAT|O_TRUNC|O_EXCL|O_SYNC, 0); + if (fd != -1) { + (void)close(fd); + break; + } + else if (errno == EEXIST) + continue; + else + return -1; + } + + /* + * We link the path to the name + */ + if (link(path, fname) == -1) + goto bad; + + /* + * Note that we stat our own exclusively created name, not the + * destination, since the destination can be affected by others. + */ + if (stat(path, &st) == -1) + goto bad; + + (void)unlink(path); + + /* + * If the number of links was two (one for the unique file and one + * for the lock), we've won the race + */ + if (st.st_nlink != 2) { + errno = EEXIST; + return -1; + } + return 0; + +bad: + serrno = errno; + (void)unlink(path); + errno = serrno; + return -1; +} + +/* + * fname -- Pathname to lock + * pollinterval -- Interval (miliseconds) to check for lock, -1 return + */ +int +dot_lock(const char *fname, int pollinterval) +{ + char path[MAXPATHLEN]; + sigset_t nset, oset; + int retval; + + (void)sigemptyset(&nset); + (void)sigaddset(&nset, SIGHUP); + (void)sigaddset(&nset, SIGINT); + (void)sigaddset(&nset, SIGQUIT); + (void)sigaddset(&nset, SIGTERM); + (void)sigaddset(&nset, SIGTTIN); + (void)sigaddset(&nset, SIGTTOU); + (void)sigaddset(&nset, SIGTSTP); + (void)sigaddset(&nset, SIGCHLD); + + (void)snprintf(path, sizeof(path), "%s.lock", fname); + + retval = -1; + for (;;) { + handle_pending_signals(); + (void)sigprocmask(SIG_BLOCK, &nset, &oset); + if (create_exclusive(path) != -1) { + (void)sigprocmask(SIG_SETMASK, &oset, NULL); + retval = 0; + break; + } + else + (void)sigprocmask(SIG_SETMASK, &oset, NULL); + + if (errno != EEXIST) + break; + + if (pollinterval) { + if (pollinterval == -1) { + errno = EEXIST; + break; + } + (void)usleep((unsigned int)pollinterval * 1000); + } + } + handle_pending_signals(); + return retval; +} + +void +dot_unlock(const char *fname) +{ + char path[MAXPATHLEN]; + + (void)snprintf(path, sizeof(path), "%s.lock", fname); + (void)unlink(path); +} |