RE: [virtio] [PATCH requirements 6/7] net-features: Add packet timestamp requirements

[Parav Pandit <parav@nvidia.com>]

> From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Sent: Wednesday, August 9, 2023 2:06 PM
>  struct vring_used_elem {
>  	/* Index of start of used descriptor chain. */
>  	__virtio32 id;
>  	/* Total length of the descriptor chain which was used (written to) */
>  	__virtio32 len;
> 
> +	__virtio64 timestamp;
>  };
> 
> 
> Then, the existing devices can support this easily. If we introduce this by the
> new desc structure, we can foresee that this function will not be implemented
> by many existing machines. But this function is useful. So we want support this
> by a simple way.

This only works for split q.
Packed q needs yet another format.
And even after that we still have to live with other limitations listed in other requirements.

Therefore its better to do the new desc definition one time which enables to optionally support timestamp, using single descriptor format.