On Thu, Aug 25, 2022 at 10:34:11AM +0100, Pavel Begunkov wrote:

On 8/22/22 12:33, Kanchan Joshi wrote:

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On Mon, Aug 22, 2022 at 11:58:24AM +0100, Pavel Begunkov wrote:

[...]

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diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 1463cfecb56b..80ea35d1ed5c 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h

@@ -203,6 +203,7 @@ enum io_uring_op {

    IORING_OP_SOCKET,
    IORING_OP_URING_CMD,
    IORING_OP_SENDZC_NOTIF,
+    IORING_OP_URING_CMD_FIXED,

I don't think it should be another opcode, is there any
control flags we can fit it in?

using sqe->rw_flags could be another way.

We also use ->ioprio for io_uring opcode specific flags,
e.g. like in io_sendmsg_prep() for IORING_RECVSEND_POLL_FIRST,
might be even better better.

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But I think that may create bit of disharmony in user-space.
Current choice (IORING_OP_URING_CMD_FIXED) is along the same lines as
IORING_OP_READ/WRITE_FIXED.

And I still believe it was a bad choice, I don't like this encoding
of independent options/features by linearising toggles into opcodes.
A consistent way to add vectored fixed bufs would be to have a 4th
opcode, e.g. READV_FIXED, which is not great.

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User-space uses new opcode, and sends the
buffer by filling sqe->buf_index. So must we take a different way?

I do think so

I see. Will change this in next iteration.