Re: [RFC 1/8] virtio: Define InOrderVQElement

[Eugenio Perez Martin <eperezma@redhat.com>]

On Thu, Mar 21, 2024 at 4:57 PM Jonah Palmer <jonah.palmer@oracle.com> wrote:
>
> Define the InOrderVQElement structure for the VIRTIO_F_IN_ORDER
> transport feature implementation.
>
> The InOrderVQElement structure is used to encapsulate out-of-order
> VirtQueueElement data that was processed by the host. This data
> includes:
>  - The processed VirtQueueElement (elem)
>  - Length of data (len)
>  - VirtQueueElement array index (idx)
>  - Number of processed VirtQueueElements (count)
>
> InOrderVQElements will be stored in a buffering mechanism until an
> order can be achieved.
>
> Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
> ---
>  include/hw/virtio/virtio.h | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index b3c74a1bca..c8aa435a5e 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -77,6 +77,13 @@ typedef struct VirtQueueElement
>      struct iovec *out_sg;
>  } VirtQueueElement;
>
> +typedef struct InOrderVQElement {
> +    const VirtQueueElement *elem;

Some subsystems allocate space for extra elements after
VirtQueueElement, like VirtIOBlockReq. You can request virtqueue_pop
to allocate this extra space by its second argument. Would it work for
this?

> +    unsigned int len;
> +    unsigned int idx;
> +    unsigned int count;

Now I don't get why these fields cannot be obtained from elem->(len,
index, ndescs) ?

> +} InOrderVQElement;
> +
>  #define VIRTIO_QUEUE_MAX 1024
>
>  #define VIRTIO_NO_VECTOR 0xffff
> --
> 2.39.3
>