daemon.h

/*
 * Copyright (C) 2021-2022 Skycharge GmbH
 * Author: Roman Penyaev <r.peniaev@gmail.com>
 *
 * 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.
 *
 * 3. Neither the name of the copyright holder nor the names of its
 * contributors may be used to endorse or promote products derived
 * from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "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
 * COPYRIGHT HOLDER OR CONTRIBUTORS 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.
 */

#ifndef DAEMON_H
#define DAEMON_H

#include "types.h"

static inline int sky_pidfile_create(const char *pidfile, int pid)
{
	int rc, fd, n;
	char buf[16];

	fd = open(pidfile, O_CREAT | O_EXCL | O_TRUNC | O_WRONLY, 0600);
	if (fd < 0) {
		sky_err("sky_pidfile_create: failed open(%s) errno=%d\n",
			pidfile, errno);

		return -1;
	}
	n = snprintf(buf, sizeof(buf), "%u\n", pid);
	rc = write(fd, buf, n);
	if (rc < 0) {
		sky_err("sky_pidfile_create: failed write(%s) errno=%d\n",
			pidfile, errno);
		close(fd);

		return -1;
	}
	close(fd);

	return 0;
}

/*
 * This routine is aimed to be used instead of standard call daemon(),
 * because we want to create pidfile from a parent process not to race
 * with a systemd PIDFile handler.
 */
static inline int sky_daemonize(const char *pidfile)
{
	int pid, rc;

	pid = fork();
	if (pid == -1) {
		sky_err("sky_daemonize: fork() failed, errno=%d\n", errno);
		return -1;
	}
	else if (pid != 0) {
		if (pidfile) {
			/*
			 * Yes, we write pid from a parent to avoid any races
			 * inside systemd PIDFile handlers.  In case of errors
			 * child is gracefully killed.
			 */

			rc = sky_pidfile_create(pidfile, pid);
			if (rc) {
				kill(pid, SIGTERM);

				return -1;
			}
		}
		/* Parent exits */
		exit(0);
	}
	if (setsid() == -1) {
		sky_err("sky_daemonize: setsid() failed, errno=%d\n", errno);
		return -1;
	}
	pid = chdir("/");
	(void)pid;

	return 0;
}

#endif /* DAEMON_H */