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

[Keith Busch]

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.