[PATCHv11 03/10] io_uring: add write stream attribute

[Kanchan Joshi]

On 12/6/2024 7:23 AM, Keith Busch wrote:
> From: Keith Busch <kbusch at kernel.org>
> 
> Adds a new attribute type to specify a write stream per-IO.
> 
> Signed-off-by: Keith Busch <kbusch at kernel.org>
> ---
>   include/uapi/linux/io_uring.h |  9 ++++++++-
>   io_uring/rw.c                 | 28 +++++++++++++++++++++++++++-
>   2 files changed, 35 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index 5fa38467d6070..263cd57aae72d 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -123,7 +123,14 @@ struct io_uring_attr_pi {
>   	__u64	rsvd;
>   };
>   
> -#define IORING_RW_ATTR_FLAGS_SUPPORTED (IORING_RW_ATTR_FLAG_PI)
> +#define IORING_RW_ATTR_FLAG_WRITE_STREAM (1U << 1)
> +struct io_uring_write_stream {
> +	__u16	write_stream;
> +	__u8	rsvd[6];
> +};

So this needs 8 bytes. Maybe passing just 'u16 write_stream' is better? 
Or do you expect future additions here (to keep rsvd).

Optimization is possible (now or in future) if it's 4 bytes or smaller, 
as that can be placed in SQE along with a new RW attribute flag that 
says it's placed inline. Like this -

--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -92,6 +92,10 @@ struct io_uring_sqe {
                         __u16   addr_len;
                         __u16   __pad3[1];
                 };
+               struct {
+                       __u16   write_hint;
+                       __u16   __rsvd[1];
+               };
         };
         union {
                 struct {
@@ -113,6 +117,7 @@ struct io_uring_sqe {

  /* sqe->attr_type_mask flags */
  #define IORING_RW_ATTR_FLAG_PI (1U << 0)
+#define IORING_RW_ATTR_FLAG_WRITE_STREAM_INLINE        (1U << 1)