rem: new_fd(struct io_context *ioctx, struct file_descriptor *f)
add: new_fd(struct io_context *context, struct file_descriptor *descriptor)
context: new_fd(struct io_context *ioctx, struct file_descriptor *f){	int fd = -1;	int i;	mutex_lock(&ioctx->io_mutex);	for (i = 0; i < ioctx->table_size; i++) {		if (!ioctx->fds[i]) {			fd = i;			break;		}	}	if (fd < 0) {		fd = EMFILE;		goto err;	}	ioctx->fds[fd] = f;	ioctx->num_used_fds++;err:	mutex_unlock(&ioctx->io_mutex);	return fd;}