Why is my callback not called?

Question

I'm trying to implement the fuse hello example (https://lastlog.de/misc/fuse-doc/doc/html/hello_8c.html) in C++ (with g++ compiler). I had to change it a little bit to do so.

#define FUSE_USE_VERSION 30

#include <cstdlib>
#include <iostream>

#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>

static const char *hello_str = "Hello World!\n";

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 | 0777;
        stbuf->st_nlink = 2;
    }
    else if (strcmp(path, "/hello") == 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", NULL, 0);

    return 0;
};

static int hello_open(const char *path, struct fuse_file_info *fi)
{
    if (strcmp(path, "/hello") != 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") != 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 int hello_opendir(const char *path, struct fuse_file_info *fi)
{
    return 0;
};

struct hello_fuse_operations : fuse_operations
{
    hello_fuse_operations()
    {
        this->getattr = hello_getattr;
        this->open = hello_open;
        this->read = hello_read;
        this->opendir = hello_opendir;
        this->readdir = hello_readdir;
    }
};

static struct hello_fuse_operations hello_oper;

int main(int argc, char** argv)
{
    return fuse_main_real(argc, argv, &hello_oper, sizeof(&hello_oper), NULL);
}

My problem is, fuse says read and readdir are not implemented and doesn't call them, even though they clearly are implemented.

unique: 13, opcode: READDIR (28), nodeid: 1, insize: 80, pid: 16153
   unique: 13, error: -38 (Function not implemented), outsize: 16

It almost seems like I'm doing something basic wrong, but I can't figure out what. (I'm also not very experienced with C++)

How do I get the example to work?

Answer 1

sizeof(&hello_oper) looks like a mistake - this is the size of a pointer, not the size of a struct.

sizeof(fuse_operations) might be what you want. sizeof hello_oper would be the same in this case, but if you later add data members to hello_fuse_operations then it would become wrong.