async_write.rs

    pub fn write_async<F>(&self,
                          file_handle: *mut Struct_glfs_fd,
                          buffer: &[u8],
                          flags: i32,
                          callback: F,
                          data: &mut ::libc::c_void)
                          -> Result<(), GlusterError>
        where F: Fn(*mut Struct_glfs_fd, isize, *mut ::libc::c_void)
    {
        let closure = Closure3::new(&callback);
        let callback_ptr = closure.code_ptr();
        unsafe {
            let ret_code = glfs_write_async(file_handle,
                                            buffer.as_ptr() as *const c_void,
                                            buffer.len(),
                                            flags,
                                            Some(*callback_ptr),
                                            data);
            if ret_code < 0 {
                return Err(GlusterError::new(get_error()));
            }
        }
        Ok(())
    }