#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <limits.h>
#include <inttypes.h>
#include <errno.h>
#include <err.h>

static void
usage(void)
{

	fprintf(stderr, "usage: %s dev offset size\n", getprogname());
	exit(EXIT_FAILURE);
}

int
main(int argc, char *argv[])
{
	char *path, *buf;
	off_t offset;
	size_t size;
	ssize_t done;
	int fd;

	if (argc != 4)
		usage();
	path = argv[1];
	errno = 0;
	offset = (off_t)strtoumax(argv[2], NULL, 0);
	if (errno != 0)
		err(EXIT_FAILURE, "Invalid offset");
	errno = 0;
	size = strtoul(argv[3], NULL, 0);
	if (errno != 0)
		err(EXIT_FAILURE, "Invalid size");
	buf = malloc(size);
	if (buf == NULL)
		errx(EXIT_FAILURE, "Cannot allocate memory.");
	fd = open(path, O_WRONLY);
	if (fd == -1)
		err(EXIT_FAILURE, "Cannot open %s", path);
	done = pwrite(fd, buf, size, offset);
	if (done == -1)
		err(EXIT_FAILURE, "Cannot write");
	printf("write(%jd, %zu) = %zd\n", (intmax_t)offset, size, done);
	exit(EXIT_SUCCESS);
}