#define _GNU_SOURCE
#define _XOPEN_SOURCE  600

#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static pid_t pid;
static int finished = 0;

static void child(char *buf, size_t size)
{
	char c = 'b';

	printf("child: Buf is %p\n", buf);
	while (1) {
		memset(buf, c, size);
		c++;
		sleep(1);
	}
}

void sig_handler(int sig)
{
	kill(pid, SIGINT);
	finished = 1;
	printf("Caught signal\n");
}

int main(int argc, char **argv)
{
	char *obuf, *ibuf;
	size_t size = 1024 * 1024 * 1;
	int err;
	int fd;
	int status;
	sighandler_t handler;

	err = posix_memalign((void **)&ibuf, 4096, size);
	if (err) {
		fprintf(stderr, "Error allocating buf: %d\n", err);
		return 1;
	}

	obuf = mmap(0, size, PROT_READ | PROT_WRITE,
		    MAP_ANONYMOUS | MAP_SHARED, -1, 0);
	if (obuf == MAP_FAILED) {
		free(obuf);
		fprintf(stderr, "Error allocating buf: %d\n", err);
		return 1;
	}

	pid = fork();
	if (pid < 0) {
		fprintf(stderr, "Problem forking: %d\n", errno);
		return 1;
	}

	if (pid == 0) {
		child(obuf, size);
		return 0;
	}

	handler = signal(SIGINT, sig_handler);

	fd = open("testfile", O_RDWR|O_CREAT|O_DIRECT, 0644);
	if (fd < 0) {
		fprintf(stderr, "Error opening file: %d\n", errno);
		err = 1;
		goto out;
	}

	printf("obuf is %p\n", obuf);

	while (!finished) {
		ssize_t copied;

		memset(obuf, 'a', size);
		lseek(fd, 0, SEEK_SET);
		copied = write(fd, obuf, size);
		if (copied < 0) {
			fprintf(stderr, "Error writing: %d\n", errno);
			err = 1;
			break;
		} else if (copied < size) {
			fprintf(stderr, "Weird, short write: %d\n", copied);
		}

		lseek(fd, 0, SEEK_SET);
		copied = read(fd, ibuf, copied);
		if (copied < 0) {
			fprintf(stderr, "Read failed: %d\n", copied);
			err = 1;
			break;
		}
	}

out:
	if (err)
		kill(pid, SIGINT);

	waitpid(pid, &status, 0);
	close(fd);
	munmap(obuf, 4096);
	free(ibuf);

	return err;
}