Re: [PATCH] io_uring: support to inject result for NOP

[Jens Axboe <axboe@kernel.dk>]

On 5/9/24 7:14 PM, Ming Lei wrote:
> Support to inject result for NOP so that we can inject failure from
> userspace. It is very helpful for covering failure handling code in
> io_uring core change.
> 
> With nop flags, it could be possible to add more test feature for NOP in
> future, but the NOP behavior of direct completion has to be kept.
> 
> Cleared NOP SQE is required, look both liburing and Rust io-uring crate
> clears SQE, and it shouldn't be one big deal for raw, especially it is
> just NOP.

I think this implementation looks fine, but probably would be best if
you first had a prep patch that adds nop_flags to io_uring_sqe, and
checks it in io_nop_prep() and fails if it's non-zero. Then we can mark
that for stable, rather than need to do the whole thing.

Then patch 2 adds the actual meat of this patch, and now adds the proper
check in io_nop_prep() for whether any unknown flags are set.

> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index 922f29b07ccc..5db3a209b302 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -48,7 +48,10 @@ struct io_uring_sqe {
>  			__u32	optname;
>  		};
>  	};
> -	__u32	len;		/* buffer size or number of iovecs */
> +	union {
> +		__u32	len;		/* buffer size or number of iovecs */
> +		__s32	result;		/* for NOP to inject result only */
> +	};
>  	union {

And I'd drop that, just use 'len' throughout.

Rest of the patch looks fine as-is.

-- 
Jens Axboe