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

int
main(int argc, char *argv[])
{
	int fd;
	void *addr;
	char buf[4096];

	if (argc != 2) {
		fprintf(stderr, "usage: %s filename\n", argv[0]);
		exit(1);
	}

	if ((fd = open(argv[1], O_CREAT|O_RDWR, 0666)) < 0) {
		perror(argv[1]);
		exit(1);
	}

	if (ftruncate(fd, 4096) < 0) {
		perror("ftruncate");
		exit(1);
	}

	if ((addr = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED,
					fd, 0)) == MAP_FAILED) {
		perror("mmap");
		exit(1);
	}

	close(fd);

	/* first read */
	memcpy(buf, addr, 4096);

	/* now write a bit */
	memcpy(addr, buf, 8);

	printf("%s: test passed.\n", argv[0]);
	exit(0);
}