test block size of FICLONERANGE

testalign.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <linux/fs.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <errno.h>

int setup_src(const char *path, size_t size)
{
	int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
	if (fd < 0)
		return fd;

	char *buf = malloc(size);
	if (!buf)
		return 1;

	if (write(fd, buf, size) != size)
		return 1;

	close(fd);

	return 0;
}

int main(int argc, char *argv[]) {
	if (argc != 3)
		return 1;

	struct file_clone_range fcr = {
		.src_length = sysconf(_SC_PAGESIZE),
	};
	int ret;

	if (setup_src(argv[1], 1024 * 1024))
		return 1;

	printf("page: %lluK\n", fcr.src_length / 1024);

	fcr.src_fd = open(argv[1], O_RDONLY);
	if (fcr.src_fd < 0)
		return 1;

	for (; fcr.src_length > 0; fcr.src_length /= 2) {
		int fd = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0644);
		if (fd < 0)
			return 1;

		printf("Trying block size %lluK.. ", fcr.src_length);
		ret = ioctl(fd, FICLONERANGE, &fcr);
		if (!ret) {
			puts("OK");
		} else {
			printf("errno = %d\n", errno);
			return 1;
		}

		close(fd);
	}

	return 0;
}

testall.sh

#!/bin/sh

mkdir fs
fallocate -l 512M xfs

try() {
	echo "Creating FS with block size of $1"
	mkfs.xfs -qf xfs -b size=$1	&&
	sudo mount -oloop xfs fs	&&
	sudo chmod 777 fs		&&
	./testalign fs/src fs/dst
	sudo umount xfs
}

size=65536

while [ $size -ge 512 ]; do
	try $size
	size=$((size/2))
done