Re: [PATCHv3 1/1] io_uring: add support for IORING_SETUP_SQE_MIXED

[Jens Axboe <axboe@kernel.dk>]

On 9/24/25 9:12 AM, Keith Busch wrote:
> contiguous in the SQ ring, a 128b SQE cannot wrap the ring. For this
> case, a single NOP SQE should be posted with the SKIP_SUCCESS flag set.
> The kernel should simply ignore those.

I think this mirrors the CQE side too much - the kernel doesn't ignore
then, they get processed just like any other NOP that has SKIP_SUCCESS
set. They don't post a CQE, but that's not because they are ignored,
that's just the nature of a successful NOP w/SKIP_SUCCESS set.

> @@ -2179,6 +2179,14 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
>  	opcode = array_index_nospec(opcode, IORING_OP_LAST);
>  
>  	def = &io_issue_defs[opcode];
> +	if (def->is_128) {
> +		if (!(ctx->flags & IORING_SETUP_SQE_MIXED) || *left < 2 ||
> +		    (ctx->cached_sq_head & (ctx->sq_entries - 1)) == 0)
> +			return io_init_fail_req(req, -EINVAL);
> +		ctx->cached_sq_head++;
> +		(*left)--;
> +	}

This could do with a comment!

> @@ -582,9 +583,10 @@ static inline void io_req_queue_tw_complete(struct io_kiocb *req, s32 res)
>   * IORING_SETUP_SQE128 contexts allocate twice the normal SQE size for each
>   * slot.
>   */
> -static inline size_t uring_sqe_size(struct io_ring_ctx *ctx)
> +static inline size_t uring_sqe_size(struct io_kiocb *req)
>  {
> -	if (ctx->flags & IORING_SETUP_SQE128)
> +	if (req->ctx->flags & IORING_SETUP_SQE128 ||
> +	    req->opcode == IORING_OP_URING_CMD128)
>  		return 2 * sizeof(struct io_uring_sqe);
>  	return sizeof(struct io_uring_sqe);

This one really confused me, but then I grep'ed, and it's uring_cmd
specific. Should probably move this one to uring_cmd.c rather than have
it elsewhere.

> +int io_uring_cmd128_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
> +{
> +	if (!(req->ctx->flags & IORING_SETUP_SQE_MIXED))
> +		return -EINVAL;
> +	return io_uring_cmd_prep(req, sqe);
> +}

Why isn't this just allowed for SQE128 as well? There should be no
reason to disallow explicitly 128b sqe commands in SQE128 mode, they
should work for any mode that supports 128b SQEs which is either
SQE_MIXED or SQE128?

-- 
Jens Axboe