#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <fcntl.h>

int main(int argc, char **argv)
{
	uint8_t *data;
	int fd;
	unsigned long long offset;
	pid_t pid;
	int status;
	int opt;
	bool opt_fork = false;

	while ((opt = getopt(argc, argv, "f")) != -1) {
		switch (opt) {
		case 'f':
			opt_fork = true;
			break;
		}
	}

	if (argc <= optind) {
		fprintf(stderr, "%s: [-f] address\n", argv[0]);
		fprintf(stderr, "\t-f specifices if we should fork with the mmap\n");
		exit(EXIT_FAILURE);
	}
	if (sscanf(argv[optind], "%lli", &offset) != 1) {
		fprintf(stderr, "Cannot determine mmap address from %s\n", argv[optind]);
		exit(EXIT_FAILURE);
	}

	if ((fd = open("/dev/mem", O_RDONLY)) < 0) {
		fprintf(stderr, "Cannot open /dev/mem\n");
		exit(EXIT_FAILURE);
	}

	printf("mmap: 0x%llx..0x%llx\n", offset, offset + 4095);

	if ((data = mmap(NULL, 4096, PROT_READ, MAP_PRIVATE, fd, (off_t)offset)) == MAP_FAILED) {
		fprintf(stderr, "Cannot mmap 0x%llx\n", offset);
		exit(EXIT_FAILURE);
	}

	close(fd);

	if (opt_fork) {
		pid = fork();
		if (pid == 0) {
			/* child */
			_exit(0);
		} else {
			/* parent */
			waitpid(pid, &status, 0);
		}
	}

	if (munmap(data, 4096) < 0) {
		fprintf(stderr, "Cannot munmap %p\n", data);
		exit(EXIT_FAILURE);
	}
	exit(EXIT_SUCCESS);
}