Re: [virtio-comment] [PATCH requirements 7/7] net-features: Add header data split requirements

[David Edmondson <david.edmondson@oracle.com>]

On Monday, 2023-07-24 at 06:34:21 +03, Parav Pandit wrote:
> Add header data split requirements for the receive packets.
>
> Signed-off-by: Parav Pandit <parav@nvidia.com>
> ---
>  net-workstream/features-1.4.md | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/net-workstream/features-1.4.md b/net-workstream/features-1.4.md
> index 37820b6..a64e356 100644
> --- a/net-workstream/features-1.4.md
> +++ b/net-workstream/features-1.4.md
> @@ -11,6 +11,7 @@ together is desired while updating the virtio net interface.
>  3. Virtqueue notification coalescing re-arming support
>  4  Virtqueue receive flow filters (RFF)
>  5. Device timestamp for tx and rx packets
> +6. Header data split for the receive virtqueue
>  
>  # 3. Requirements
>  ## 3.1 Device counters
> @@ -306,3 +307,15 @@ struct virtio_net_rff_delete {
>     point of reception from the network.
>  3. The device should provide a receive packet timestamp in a single DMA
>     transaction along with the rest of the receive completion fields.
> +
> +## 3.6 Header data split for the receive virtqueue
> +1. The device should be able to DMA the packet header and data to two different
> +   memory locations, this enables driver and networking stack to perform zero
> +   copy to application buffer(s).
> +2. The driver should be able to configure maximum header buffer size per
> +   virtqueue.
> +3. The header buffer to be in a physically contiguous memory per virtqueue
> +4. The device should be able to indicate header data split in the receive
> +   completion.
> +5. The device should be able to zero pad the header buffer when the received
> +   header is shorter than cpu cache line size.

What's the use case for this (item 5)?
-- 
And now I know what every step is for.