#include <signal.h>
#include <stdio.h>
#include <string.h>

static void
handler1(int signum)
{
}

static void
handler2(int signum)
{
}

int main()
{
	struct sigaction sa;
	struct sigaction old_sa;
	int ret;

	sa.sa_handler = handler1; /* 1st */
	sigemptyset(&sa.sa_mask);
	sa.sa_flags = 0;
	ret = sigaction(SIGHUP, &sa, &old_sa);
	if (ret == -1) {
		perror("sigaction");
		return (1);
	}

	if (old_sa.sa_handler != SIG_DFL) {
		fprintf(stderr, "expected previous handler to be SIG_DFL\n");
		return (1);
	}

	/* Just in case. */
	memset(&old_sa, 0, sizeof(old_sa));

	sa.sa_handler = handler2; /* 2nd */
	sigemptyset(&sa.sa_mask);
	sa.sa_flags = 0;
	ret = sigaction(SIGHUP, &sa, &old_sa);
	if (ret == -1) {
		perror("sigaction");
		return (1);
	}

	if (old_sa.sa_handler != handler1) {
		fprintf(stderr, "expected previous handler to be handler1\n");
		if (old_sa.sa_handler == handler2) 
			fprintf(stderr,
			    "previous handler is reported to be handler2\n");
		else
			fprintf(stderr,
			    "previous handler is reported to be %p\n",
			    old_sa.sa_handler);
		return (1);
	}

	printf("OK\n");
	return (0);
}