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5649afd028
The problem with fcntl(2) locks is that they are not inherited by child processes. This breaks pidfile(3), where the common idiom is to open and lock the PID file before daemonizing.
106 lines
2.8 KiB
C
106 lines
2.8 KiB
C
/*-
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* Copyright (c) 2007 Dag-Erling Coïdan Smørgrav
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer
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* in this position and unchanged.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/file.h>
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#include <sys/stat.h>
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#include <errno.h>
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#include <stdarg.h>
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#include <unistd.h>
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#include <libutil.h>
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int
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flopen(const char *path, int flags, ...)
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{
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int fd, operation, serrno, trunc;
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struct stat sb, fsb;
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mode_t mode;
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#ifdef O_EXLOCK
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flags &= ~O_EXLOCK;
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#endif
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mode = 0;
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if (flags & O_CREAT) {
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va_list ap;
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va_start(ap, flags);
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mode = (mode_t)va_arg(ap, int); /* mode_t promoted to int */
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va_end(ap);
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}
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operation = LOCK_EX;
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if (flags & O_NONBLOCK)
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operation |= LOCK_NB;
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trunc = (flags & O_TRUNC);
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flags &= ~O_TRUNC;
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for (;;) {
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if ((fd = open(path, flags, mode)) == -1)
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/* non-existent or no access */
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return (-1);
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if (flock(fd, operation) == -1) {
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/* unsupported or interrupted */
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serrno = errno;
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(void)close(fd);
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errno = serrno;
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return (-1);
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}
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if (stat(path, &sb) == -1) {
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/* disappeared from under our feet */
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(void)close(fd);
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continue;
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}
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if (fstat(fd, &fsb) == -1) {
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/* can't happen [tm] */
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serrno = errno;
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(void)close(fd);
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errno = serrno;
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return (-1);
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}
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if (sb.st_dev != fsb.st_dev ||
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sb.st_ino != fsb.st_ino) {
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/* changed under our feet */
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(void)close(fd);
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continue;
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}
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if (trunc && ftruncate(fd, 0) != 0) {
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/* can't happen [tm] */
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serrno = errno;
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(void)close(fd);
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errno = serrno;
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return (-1);
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}
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return (fd);
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}
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}
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