io_file_get_fixed
req->file = io_file_get_fixed(req, cancel->fd,
req->file = io_file_get_fixed(req, req->cqe.fd, issue_flags);
struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
req->file = io_file_get_fixed(req, nop->fd, issue_flags);