Re: [PATCH v6 06/10] io_uring/rw: add support to send metadata along with read/write

[Keith Busch <kbusch@kernel.org>]

On Wed, Oct 30, 2024 at 11:31:08PM +0530, Kanchan Joshi wrote:
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index 024745283783..48dcca125db3 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -105,6 +105,22 @@ struct io_uring_sqe {
>  		 */
>  		__u8	cmd[0];
>  	};
> +	/*
> +	 * If the ring is initialized with IORING_SETUP_SQE128, then
> +	 * this field is starting offset for 64 bytes of data. For meta io
> +	 * this contains 'struct io_uring_meta_pi'
> +	 */
> +	__u8	big_sqe[0];
> +};
> +
> +/* this is placed in SQE128 */
> +struct io_uring_meta_pi {
> +	__u16		pi_flags;
> +	__u16		app_tag;
> +	__u32		len;
> +	__u64		addr;
> +	__u64		seed;
> +	__u64		rsvd[2];
>  };

On the previous version, I was more questioning if it aligns with what
Pavel was trying to do here. I didn't quite get it, so I was more
confused than saying it should be this way now.

But I personally think this path makes sense. I would set it up just a
little differently for extended sqe's so that the PI overlays a more
generic struct that other opcodes might find a way to use later.
Something like:

struct io_uring_sqe_ext {
	union {
		__u32	rsvd0[8];
		struct {
			__u16		pi_flags;
			__u16		app_tag;
			__u32		len;
			__u64		addr;
			__u64		seed;
		} rw_pi;
	};
	__u32	rsvd1[8];
};
  
> @@ -3902,6 +3903,9 @@ static int __init io_uring_init(void)
>  	/* top 8bits are for internal use */
>  	BUILD_BUG_ON((IORING_URING_CMD_MASK & 0xff000000) != 0);
>  
> +	BUILD_BUG_ON(sizeof(struct io_uring_meta_pi) >
> +		     sizeof(struct io_uring_sqe));

Then this check would become:

	BUILD_BUG_ON(sizeof(struct io_uring_sqe_ext) != sizeof(struct io_uring_sqe));