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

["Zhu, Lingshan" <lingshan.zhu@intel.com>]

On 11/9/2023 1:56 AM, Michael S. Tsirkin wrote:
> 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.
For split virtqueue, it has available ring, used ring and descriptor table,
means the device can always tell which descriptor/buffer is in-flight
or not processed even when out_of_order.

For packed virtqueue, because the descriptors may be overwritten, so when
out_out_order, the descriptors behind last_avial_idx should be considered
as in-flight and should be processed at the destination side.

Does this work for you?
> > @@ -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