You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: eventfd.rs
    path of file: ./repos/aero/src/aero_kernel/src/fs
    
    the code of the file until where you have to start completion: // Copyright (C) 2021-2024 The Aero Project Developers.
//
// This file is part of The Aero Project.
//
// Aero is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Aero is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; wi
    
    fn write_at(&self, _offset: usize, buffer: &[u8]) -> super::Result<usize> {
        let chunk_size = core::mem::size_of::<u64>();
        assert!(buffer.len() >= chunk_size);

        // TODO: use bytemuck to remove the unsafe.
        let target = unsafe { *(buffer.as_ptr() as *const u64) };

        if target == u64::MAX {
            return Err(FileSystemError::NotSupported);
        }

        let mut count = self.count.lock();

        if u64::MAX - *count > target {
            *count += target;
        } else if !self.is_nonblock() {
            unimplemented!()
        } else {
            return Ok(0);
        };

        self.wq.notify_all();
        Ok(chunk_size)
    }