#include <sys/signalfd.h>
#include <assert.h>
#include <errno.h>
#include <mqueue.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static int handler_run;
static const union sigval my_sigval = { .sival_int = 42, };

static const char msgbuf[] = "hello";

#define bail(msg) \
	do { perror(msg); exit(EXIT_FAILURE); } while (0);

static void handler(int sig, siginfo_t *si, void *notused)
{
	assert(si->si_code == SI_MESGQ);
	assert(si->si_ptr == my_sigval.sival_ptr); /* Succeeds */
	assert(si->si_int == my_sigval.sival_int); /* Succeeds */

	/* This should run only once */
	assert(handler_run == 0);
	handler_run++;
}

int main(int argc, char *argv[])
{
	struct signalfd_siginfo fdsi;
	struct sigaction newact;
	struct sigevent sev;
	struct mq_attr attr;
	sigset_t mask;
	size_t msglen;
	char *rcvbuf;
	mqd_t mqdes;
	ssize_t s;
	int sfd;

	if (argc != 2) {
		fprintf(stderr, "Usage: %s <mq-name>\n", argv[0]);
		exit(EXIT_FAILURE);
	}

	newact.sa_flags = SA_SIGINFO | SA_RESETHAND;
	newact.sa_sigaction = handler;
	sigemptyset(&newact.sa_mask);

	if (sigaction(SIGRTMIN, &newact, NULL) == -1)
		bail("sigaction");

	mqdes = mq_unlink(argv[1]);
	if (mqdes == -1 && errno != ENOENT)
		bail("mq_unlink");

	mqdes = mq_open(argv[1], (O_RDWR | O_CREAT), 0600, NULL);
	if (mqdes == (mqd_t) -1)
		bail("mq_open");

	memset(&sev, 0, sizeof(sev));
	sev.sigev_notify = SIGEV_SIGNAL;
	sev.sigev_signo = SIGRTMIN;
	sev.sigev_value = my_sigval;

	if (mq_notify(mqdes, &sev) == -1)
		bail("mq_notify");

	if (mq_send(mqdes, msgbuf, sizeof(msgbuf), 0) == -1)
		bail("mq_send");

	while (!handler_run)
		usleep(100000);

	if (mq_getattr(mqdes, &attr) == -1)
		bail("mq_getattr");

	msglen = attr.mq_msgsize;

	rcvbuf = malloc(msglen);
	if (!rcvbuf)
		bail("malloc");

	/* Empty the queue */
	if (mq_receive(mqdes, rcvbuf, msglen, NULL) != sizeof(msgbuf))
		bail("mq_receive");

	/* Inhibit default SIGRTMIN handling */
	sigemptyset(&mask);
	sigaddset(&mask, SIGRTMIN);
	if (sigprocmask(SIG_BLOCK, &mask, NULL) == -1)
		bail("sigprocmask");

	/* Reregister the notifier and post another message */
	if (mq_notify(mqdes, &sev) == -1)
		bail("mq_notify");

	if (mq_send(mqdes, msgbuf, sizeof(msgbuf), 0) == -1)
		bail("mq_send");

	sfd = signalfd(-1, &mask, 0);
	if (sfd == -1)
		bail("signalfd");

	/* Handle the signal */
	s = read(sfd, &fdsi, sizeof(struct signalfd_siginfo));
	if (s != sizeof(struct signalfd_siginfo))
		bail("read");

	assert(fdsi.ssi_code == SI_MESGQ);
	assert(fdsi.ssi_ptr ==
	       (unsigned long)my_sigval.sival_ptr); /* Succeeds */
	assert(fdsi.ssi_int == my_sigval.sival_int); /* Fails */

	exit(EXIT_SUCCESS);
}