signals.c

/* 
 * dhcpcd - DHCP client daemon
 * Copyright (c) 2006-2009 Roy Marples <roy@marples.name>
 * 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 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 AUTHOR 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.
 */

#include <sys/types.h>
#include <sys/socket.h>

#include <errno.h>
#include <signal.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>

#include "common.h"
#include "signals.h"

static int signal_pipe[2];

static const int handle_sigs[] = {
	SIGALRM,
	SIGHUP,
	SIGINT,
	SIGPIPE,
	SIGTERM,
	SIGUSR1,
};

static void
signal_handler(int sig)
{
	int serrno = errno;

	if (write(signal_pipe[1], &sig, sizeof(sig)) != sizeof(sig))
		syslog(LOG_ERR, "failed to write signal %d: %m", sig);
	/* Restore errno */
	errno = serrno;
}

/* Read a signal from the signal pipe. Returns 0 if there is
 * no signal, -1 on error (and sets errno appropriately), and
 * your signal on success */
int
signal_read(void)
{
	int sig = -1;
	char buf[16];
	ssize_t bytes;

	memset(buf, 0, sizeof(buf));
	bytes = read(signal_pipe[0], buf, sizeof(buf));
	if (bytes >= 0 && (size_t)bytes >= sizeof(sig))
		memcpy(&sig, buf, sizeof(sig));
	return sig;
}

/* Call this before doing anything else. Sets up the socket pair
 * and installs the signal handler */
int
signal_init(void)
{
	if (pipe(signal_pipe) == -1)
		return -1;
	/* Don't block on read */
	if (set_nonblock(signal_pipe[0]) == -1)
		return -1;
	/* Stop any scripts from inheriting us */
	if (set_cloexec(signal_pipe[0]) == -1)
		return -1;
	if (set_cloexec(signal_pipe[1]) == -1)
		return -1;
	return signal_pipe[0];
}

static int
signal_handle(void (*func)(int))
{
	unsigned int i;
	struct sigaction sa;

	memset(&sa, 0, sizeof(sa));
	sa.sa_handler = func;
	sigemptyset(&sa.sa_mask);

	for (i = 0; i < sizeof(handle_sigs) / sizeof(handle_sigs[0]); i++)
		if (sigaction(handle_sigs[i], &sa, NULL) == -1)
			return -1;
	return 0;
}

int
signal_setup(void)
{
	return signal_handle(signal_handler);
}

int
signal_reset(void)
{
	return signal_handle(SIG_DFL);
}