Re: [PATCH V2 4/6] virtio-pci: implement VIRTIO_F_QUEUE_STATE

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Nov 03, 2023 at 06:34:35PM +0800, Zhu Lingshan wrote:
> This patch adds two new le16 fields to common configuration structure
> to support VIRTIO_F_QUEUE_STATE in PCI transport layer.
> 
> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> ---
>  transport-pci.tex | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/transport-pci.tex b/transport-pci.tex
> index a5c6719..3161519 100644
> --- a/transport-pci.tex
> +++ b/transport-pci.tex
> @@ -325,6 +325,10 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>          /* About the administration virtqueue. */
>          le16 admin_queue_index;         /* read-only for driver */
>          le16 admin_queue_num;         /* read-only for driver */
> +
> +	/* Virtqueue state */
> +        le16 queue_avail_state;         /* read-write */
> +        le16 queue_used_state;          /* read-write */
>  };
>  \end{lstlisting}
>  
> @@ -428,6 +432,17 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>  	The value 0 indicates no supported administration virtqueues.
>  	This field is valid only if VIRTIO_F_ADMIN_VQ has been
>  	negotiated.
> +
> +\item[\field{queue_avail_state}]
> +        This field is valid only if VIRTIO_F_QUEUE_STATE has been
> +        negotiated. The driver sets and gets the available state of
> +        the virtqueue here (see \ref{sec:Virtqueues / Virtqueue State}).
> +
> +\item[\field{queue_used_state}]
> +        This field is valid only if VIRTIO_F_QUEUE_STATE has been
> +        negotiated. The driver sets and gets the used state of the
> +        virtqueue here (see \ref{sec:Virtqueues / Virtqueue State}).
> +
>  \end{description}
>  
>  \devicenormative{\paragraph}{Common configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Common configuration structure layout}


Two fields are pointless in the general case.  Fix this to at least
support out of order buffer use, then there's something to talk about.
I suspect we'll be back to yet another bespoke mailbox and a bitmap for
this.


> @@ -488,6 +503,9 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>  present either a value of 0 or a power of 2 in
>  \field{queue_size}.
>  
> +If VIRTIO_F_QUEUE_STATE has not been negotiated, the device MUST ignore
> +any accesses to \field{queue_avail_state} and \field{queue_used_state}.
> +
>  If VIRTIO_F_ADMIN_VQ has been negotiated, the value
>  \field{admin_queue_index} MUST be equal to, or bigger than
>  \field{num_queues}; also, \field{admin_queue_num} MUST be
> -- 
> 2.35.3