FUSE 샘플 코드가 이해가 안되서 질문합니다.

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2007  Miklos Szeredi <miklos@szeredi.hu>
 
  This program can be distributed under the terms of the GNU GPL.
  See the file COPYING.
 
  gcc -Wall `pkg-config fuse --cflags --libs` hello.c -o hello
*/
 
#define FUSE_USE_VERSION 26
 
#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
 
static const char *hello_str = "Hello World!\n";
static const char *hello_path = "/hello";
 
static int hello_getattr(const char *path, struct stat *stbuf)
{
	int res = 0;
 
	memset(stbuf, 0, sizeof(struct stat));
	if (strcmp(path, "/") == 0) {
		stbuf->st_mode = S_IFDIR | 0755;
		stbuf->st_nlink = 2;
	} else if (strcmp(path, hello_path) == 0) {
		stbuf->st_mode = S_IFREG | 0444;
		stbuf->st_nlink = 1;
		stbuf->st_size = strlen(hello_str);
	} else
		res = -ENOENT;
 
	return res;
}
 
static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
			 off_t offset, struct fuse_file_info *fi)
{
	(void) offset;
	(void) fi;
 
	if (strcmp(path, "/") != 0)
		return -ENOENT;
 
	filler(buf, ".", NULL, 0);
	filler(buf, "..", NULL, 0);
	filler(buf, hello_path + 1, NULL, 0);
 
	return 0;
}
 
static int hello_open(const char *path, struct fuse_file_info *fi)
{
	if (strcmp(path, hello_path) != 0)
		return -ENOENT;
 
	if ((fi->flags & 3) != O_RDONLY)
		return -EACCES;
 
	return 0;
}
 
static int hello_read(const char *path, char *buf, size_t size, off_t offset,
		      struct fuse_file_info *fi)
{
	size_t len;
	(void) fi;
	if(strcmp(path, hello_path) != 0)
		return -ENOENT;
 
	len = strlen(hello_str);
	if (offset < len) {
		if (offset + size > len)
			size = len - offset;
		memcpy(buf, hello_str + offset, size);
	} else
		size = 0;
 
	return size;
}
 
static struct fuse_operations hello_oper = {
	.getattr	= hello_getattr,
	.readdir	= hello_readdir,
	.open	= hello_open,
	.read	= hello_read,
};
 
int main(int argc, char *argv[])
{
	return fuse_main(argc, argv, &hello_oper, NULL);
}