#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int
main(int ac, char **av)
{
	struct stat sb;
	ssize_t bs;
	int fd;

	if (ac < 3) {
		fprintf(stderr, "usage: %s file-to-read block-size\n", av[0]);
		return (1);
	}

	if (stat(av[1], &sb) != 0) {
		perror("stat");
		return (2);
	}

	bs = atol(av[2]);
	if (!(bs > 0))
		bs = sb.st_blksize;
	printf("using i/o size %zd (optimal %d)\n", bs, sb.st_blksize);

	fd = open(av[1], O_RDONLY);
	if (fd == -1) {
		perror("open");
		return (3);
	}

	char buf[bs];

	for (int cnt = 0; ; cnt++) {
		ssize_t rb;

		rb = read(fd, buf, sizeof(buf));
		if (rb == -1) {
			perror("read");
			fprintf(stderr, "%d reads were successful\n", cnt);
			return (4);
		} else if (rb < sizeof(buf))
			break;
	}

	return (0);
}