#include <sys/time.h>
#include <sys/types.h>
#include <sys/event.h>
#include <sys/wait.h>
#include <errno.h>
#include <err.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>

int kqsock;

#define	WATCH_PPROC(proc, data)	 watch(EVFILT_PROC, proc, data, NOTE_EXIT|NOTE_TRACK, 1)
#define	WATCH_PROC(proc, data)	 watch(EVFILT_PROC, proc, data, NOTE_EXIT, 1)
#define	WATCH_SIG(sig, data)	watch(EVFILT_SIGNAL, sig, data, 0, 1)

void
watch(filter, ident, data, fflags, addrm)
	short filter;
	uintptr_t ident;
	void *data;
	u_int fflags;
	int addrm;
{
	struct kevent kev;
	struct kevent *kptr;
	int i;

	kptr = &kev;

	kev.ident = ident;
	kev.filter = filter;
	kev.flags = addrm ? EV_ADD|EV_ENABLE : EV_DELETE|EV_DISABLE;
	kev.fflags = fflags;
	kev.udata = data;

	i = kevent(kqsock, 1, &kptr, 0, NULL, NULL);

	if (i == -1)
		warn("kevent");
	
	warnx("kqueue, ident: %d, addrm: %d, ret: %d, data: %p, errno: %s", ident, addrm, i, data, strerror(errno));
}

void
printch()
{
	printf("got SIGCHLD\n");
	fflush(stdout);
}

int
main(int argc, char *argv[])
{
	struct kevent kqevlist[16];
	pid_t pid;
	int status;
	int i;
	int j;
	int n;
	char *data;
	void (*fun)();

	if (argc != 2)
		errx(1, "usage: %s <0|1>", argv[0]);

	i = atoi(argv[1]);

	if ((kqsock = kqueue()) == -1)
		err(1, "kqueue");

	WATCH_PPROC(getpid(), getpid());
	WATCH_SIG(SIGCHLD, printch);

	printf("parent: %d\n", getpid());
	fflush(stdout);

	switch((pid = fork())) {
	case 0:
		printf("child: %d\n", getpid());
		fflush(stdout);
		exit(0);
		break;
	case -1:
		err(1, "fork");
		break;
	default:
		break;
	}

	/* parent */
	if (i)
		sleep(1);

	WATCH_PROC(pid, "this is a string");

	if ((n = kevent(kqsock, 0, NULL, sizeof kqevlist / sizeof *kqevlist,
	    kqevlist, (struct timespec *)0)) <= 0) {
		if (n == -1 && errno != EINTR) {
			err(1, "kevent");
		}
	}

	for (j = 0; j < n; j++) {
		if (kqevlist[j].filter == EVFILT_PROC) {
			data = kqevlist[j].udata;
			pid = wait4(kqevlist[j].ident, &status, WNOHANG, NULL);
			if (pid == 0)
				warnx("pid is zero");
			printf("[%d]: exit status 0x%x\n", pid, status);
			printf("returned: %p: %s\n", data, data);
			fflush(stdout);
		} else if (kqevlist[j].filter == EVFILT_SIGNAL) {
			fun = kqevlist[j].udata;
			fun();
		} else
			warn("unknown filter: %x", kqevlist[j].filter);
	}

	return 0;
}