Re: [PATCH v11 06/10] io_uring: introduce attributes for read/write and PI support

[Keith Busch <kbusch@kernel.org>]

On Thu, Nov 28, 2024 at 04:52:36PM +0530, Anuj Gupta wrote:
> Add the ability to pass additional attributes along with read/write.
> Application can prepare attibute specific information and pass its
> address using the SQE field:
> 	__u64	attr_ptr;
> 
> Along with setting a mask indicating attributes being passed:
> 	__u64	attr_type_mask;
> 
> Overall 64 attributes are allowed and currently one attribute
> 'IORING_RW_ATTR_FLAG_PI' is supported.
> 
> With PI attribute, userspace can pass following information:
> - flags: integrity check flags IO_INTEGRITY_CHK_{GUARD/APPTAG/REFTAG}
> - len: length of PI/metadata buffer
> - addr: address of metadata buffer
> - seed: seed value for reftag remapping
> - app_tag: application defined 16b value
> 
> Process this information to prepare uio_meta_descriptor and pass it down
> using kiocb->private.
> 
> PI attribute is supported only for direct IO.
> 
> Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> ---
>  include/uapi/linux/io_uring.h | 16 +++++++
>  io_uring/io_uring.c           |  2 +
>  io_uring/rw.c                 | 83 ++++++++++++++++++++++++++++++++++-
>  io_uring/rw.h                 | 14 +++++-
>  4 files changed, 112 insertions(+), 3 deletions(-)
> 
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index aac9a4f8fa9a..38f0d6b10eaf 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -98,6 +98,10 @@ struct io_uring_sqe {
>  			__u64	addr3;
>  			__u64	__pad2[1];
>  		};
> +		struct {
> +			__u64	attr_ptr; /* pointer to attribute information */
> +			__u64	attr_type_mask; /* bit mask of attributes */
> +		};

I can't say I'm a fan of how this turned out. I'm merging up the write
hint stuff, and these new fields occupy where that 16-bit value was
initially going. Okay, so I guess I need to just add a new attribute
flag? That might work if I am only appending exactly one extra attribute
per SQE, but what if I need both PI and Write Hint? Do the attributes
need to appear in a strict order?