How to output a list of block devices from /sys/block to the kernel log?

Question

I recently started learning how the Linux kernel works. and I wanted to implement my own iostat. To do this, I need to iterate over each block device and calculate the metrics, the problem is that I don't understand how to iterate over block devices. I take them from /sys/block.

I trying use structure dir_context and function iterate_dir.

static bool iterate_block_devices(struct dir_context *ctx, const char *name, int namelen,
                                 loff_t offset, u64 ino, unsigned int d_type) {
    pr_info("Block device: %.*s\n", namelen, name);
    return 0; // Continue iteration
}

int read_block_devices(void) {
   struct file *dir;
    struct dir_context ctx = {
        .actor = iterate_block_devices,
    };

    
    dir = filp_open("/sys/block", O_DIRECTORY | O_RDONLY, 0);
    if (IS_ERR(dir)) {
            pr_err("Error opening directory /sys/block\n");
            return -1;
    }

    iterate_dir(dir, &ctx);

    filp_close(dir, NULL);
    return 0;
}

but at the exit I get: "Block device: . " Please help me solve this problem. I don't understand well how iterate_dir and dir_context work.