Re: [RFC 1/2] io_uring/notif: change notif CQE uapi format

[Stefan Metzmacher <metze@samba.org>]

Am 16.08.22 um 09:42 schrieb Pavel Begunkov:
> Change the notification CQE layout while we can, put the seq number into
> cqe->res so we can cqe->flags to mark notification CQEs with
> IORING_CQE_F_NOTIF and add other flags in the future if needed. This
> will be needed to distinguish notifications from send completions when
> they use the same user_data.
> 
> Also, limit the sequence number to u16 and reserve upper 16 bits for the
> future. We also want it to mask out the sign bit for userspace
> convenience as it's easier to test for (cqe->res < 0).
> 
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>   include/uapi/linux/io_uring.h | 6 ++++++
>   io_uring/notif.c              | 4 ++--
>   2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index 1463cfecb56b..20368394870e 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -286,6 +286,9 @@ enum io_uring_op {
>   #define IORING_RECVSEND_FIXED_BUF	(1U << 2)
>   #define IORING_RECVSEND_NOTIF_FLUSH	(1U << 3)
>   
> +/* cqe->res mask for extracting the notification sequence number */
> +#define IORING_NOTIF_SEQ_MASK		0xFFFFU
> +
>   /*
>    * accept flags stored in sqe->ioprio
>    */
> @@ -337,10 +340,13 @@ struct io_uring_cqe {
>    * IORING_CQE_F_BUFFER	If set, the upper 16 bits are the buffer ID
>    * IORING_CQE_F_MORE	If set, parent SQE will generate more CQE entries
>    * IORING_CQE_F_SOCK_NONEMPTY	If set, more data to read after socket recv
> + * IORING_CQE_F_NOTIF	Set for notification CQEs. Can be used to distinct
> + *			them from sends.
>    */
>   #define IORING_CQE_F_BUFFER		(1U << 0)
>   #define IORING_CQE_F_MORE		(1U << 1)
>   #define IORING_CQE_F_SOCK_NONEMPTY	(1U << 2)
> +#define IORING_CQE_F_NOTIF		(1U << 3)
>   
>   enum {
>   	IORING_CQE_BUFFER_SHIFT		= 16,
> diff --git a/io_uring/notif.c b/io_uring/notif.c
> index 714715678817..6e17d1ae5a0d 100644
> --- a/io_uring/notif.c
> +++ b/io_uring/notif.c
> @@ -60,8 +60,8 @@ struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx,
>   	notif->rsrc_node = NULL;
>   	io_req_set_rsrc_node(notif, ctx, 0);
>   	notif->cqe.user_data = slot->tag;
> -	notif->cqe.flags = slot->seq++;
> -	notif->cqe.res = 0;
> +	notif->cqe.flags = IORING_CQE_F_NOTIF;
> +	notif->cqe.res = slot->seq++ & IORING_NOTIF_SEQ_MASK;
>   
>   	nd = io_notif_to_data(notif);
>   	nd->account_pages = 0;

This looks good.

metze