Re: [PATCH V2 3/3] selftests: ublk: add ublk zero copy test

On Wed, Feb 26, 2025 at 11:58:38PM +0800, Ming Lei wrote:

+	struct io_uring_sqe *reg;
+	struct io_uring_sqe *rw;
+	struct io_uring_sqe *ureg;
+
+	if (!zc) {
+		rw = ublk_queue_alloc_sqe(q);
+		if (!rw)
+			return -ENOMEM;
+
+		io_uring_prep_rw(op, rw, 1 /*fds[1]*/,
+				(void *)iod->addr,
+				iod->nr_sectors << 9,
+				iod->start_sector << 9);
+		io_uring_sqe_set_flags(rw, IOSQE_FIXED_FILE);
+		q->io_inflight++;
+		/* bit63 marks us as tgt io */
+		rw->user_data = build_user_data(tag, op, UBLK_IO_TGT_NORMAL, 1);
+		return 0;
+	}
+
+	ublk_queue_alloc_sqe3(q, &reg, &rw, &ureg);
+
+	io_uring_prep_buf_register(reg, 0, tag, q->q_id, tag);
+	reg->user_data = build_user_data(tag, 0xfe, 1, 1);
+	reg->flags |= IOSQE_CQE_SKIP_SUCCESS;
+	reg->flags |= IOSQE_IO_LINK;
+
+	io_uring_prep_rw(op, rw, 1 /*fds[1]*/, 0,
+		iod->nr_sectors << 9,
+		iod->start_sector << 9);
+	rw->buf_index = tag;
+	rw->flags |= IOSQE_FIXED_FILE;
+	rw->flags |= IOSQE_IO_LINK;
+	rw->user_data = build_user_data(tag, op, UBLK_IO_TGT_ZC_OP, 1);
+	q->io_inflight++;
+
+	io_uring_prep_buf_unregister(ureg, 0, tag, q->q_id, tag);
+	ureg->user_data = build_user_data(tag, 0xff, UBLK_IO_TGT_ZC_BUF, 1);

You don't have anything handling the unregister command's completion so
I think you want the IOSQE_CQE_SKIP_SUCCESS flag on it otherwise you get
an unexpected CQE for it.