#define _GNU_SOURCE
#define _LARGEFILE64_SOURCE
#define _XOPEN_SOURCE 600
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

int main(void)
{
	int ret;
	int fd = open("test.txt", O_CREAT | O_DIRECT | O_RDWR | O_TRUNC, 0777);
	if (fd < 0) {
		perror("open()");
		exit(1);
	}

	const size_t pagesize = getpagesize();
	printf("PAGE_SIZE: %d\n", pagesize);

	size_t buffsize = pagesize * 2;
	char *buf;

	ret = posix_memalign((void**)&buf, pagesize, buffsize);
	if (ret) {
		fprintf(stderr, "posix_memalign: %s\n", strerror(ret));
		exit(1);
	}

	/* check file offset boundary */
	off_t fboundary = pagesize;
	while (pwrite(fd, buf, buffsize, fboundary/2) == buffsize) {
		fboundary /= 2;
	}
	printf("O_DIRECT file offset boundary: %llu\n",
			(unsigned long long)fboundary);

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

	/* check block size boundary */
	size_t sboundary = pagesize;
	while (sboundary && pwrite(fd, buf, sboundary/2, 0) == sboundary/2) {
		sboundary /= 2;
	}
	printf("O_DIRECT block size boundary: %d\n", sboundary);

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

	/* check buffer address boundary */
	off_t aboundary = pagesize;
	if (sboundary == 0)
		sboundary = 512;
	while (pwrite(fd, buf + aboundary/2, sboundary, 0) == sboundary) {
		aboundary /= 2;
	}
	printf("O_DIRECT buffer address boundary: %llu\n",
			(unsigned long long)aboundary);

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

	free(buf);

	/* test */
	ret = posix_memalign((void**)&buf, aboundary, sboundary);
	if (ret) {
		fprintf(stderr, "posix_memalign: %s\n", strerror(ret));
		exit(1);
	}
	if ((unsigned long)buf % aboundary) {
		fputs("not aligned mem\n", stderr);
		exit(1);
	}

	ssize_t written;
	written = pwrite(fd, buf, sboundary, fboundary * 3);
	if (written < 0) {
		perror("pwrite()");
		exit(1);
	}

	free(buf);
	close(fd);

	struct stat st;
	ret = stat("test.txt", &st);
	if (ret < 0) {
		perror("stat()");
		exit(1);
	}
	
	if (st.st_size != sboundary + fboundary * 3) {
		fputs("wrong size\n", stderr);
		exit(1);
	}

	puts("offset,size test OK");

	unlink("test.txt");

	return 0;
}