Re: [RFC PATCH 4/5] virtqueue: constraints for virtqueue state

[Jason Wang <jasowang@redhat.com>]

On Mon, Aug 14, 2023 at 7:29âPM Zhu Lingshan <lingshan.zhu@intel.com> wrote:
>
> This commit specifies the constraints of the virtqueue state,
> and the actions should be taken by the device when SUSPEND
> and DRIVER_OK is set
>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> ---
>  content.tex | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
>
> diff --git a/content.tex b/content.tex
> index 43bd5de..f6ac581 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -587,6 +587,37 @@ \subsection{\field{Used State} Field}
>
>  See also \ref{sec:Packed Virtqueues / Driver and Device Ring Wrap Counters}.
>
> +\drivernormative{\subsection}{Virtqueue State}{Basic Facilities of a Virtio Device / Virtqueue State}
> +
> +If VIRTIO_F_QUEUE_STATE has been negotiated, the driver MUST set SUSPEND in \field{device status}
> +first before getting or setting Virtqueue State of any virtqueues.

I don't get why this is a must. It could be useful for debugging.

> +
> +If VIRTIO_F_QUEUE_STATE has been negotiaged but VIRTIO_RING_F_PACKED not been negotiated,

typo

> +the driver MUST NOT access \field{Used State} of any virtqueues, it should use the
> +used index in the used ring.
> +
> +\devicenormative{\subsection}{Virtqueue State}{Basic Facilities of a Virtio Device / Virtqueue State}
> +
> +If VIRTIO_F_QUEUE_STATE has been negotiated but SUSPEND is not set in \field{device status},
> +the device MUST ignore any accesses against Virtqueue State of any virtqueues.

Btw, do we need to clarify the behavior of ring reset after suspending?

> +
> +When VIRTIO_F_QUEUE_STATE has been negotiated but VIRTIO_RING_F_PACKED is not,
> +the device MUST ignore any accesses against \field{Used State}.
> +
> +If VIRTIO_F_QUEUE_STATE has been negotiaged, the device MUST reset
> +the Virtqueue State of every virtqueue upon a reset.

Need to define the meaning of "reset" this is important for packed virtqueue.

> +
> +If VIRTIO_F_QUEUE_STATE and VIRTIO_RING_F_PACKED have been negotiaged, when SUSPEND is set,
> +the device MUST record the Virtqueue State of every enabled virtqueue
> +in \field{Available State} and \field{Used State} respectively,
> +and correspondingly restore the Virtqueue State of every enabled virtqueue
> +from \field{Avaiable State} and \field{Used State} when DRIVER_OK is set.

We can just let the device report those states in any case then we
don't need to care about those details, or did you see any blockers?

Thanks

> +
> +If VIRTIO_F_QUEUE_STATE has been negotiated but VIRTIO_RING_F_PACKED has been not, when SUSPEND is set,
> +the device MUST record the available state of every enabled virtqueue in \field{Available State},
> +and restore the available state of every enabled virtqueue from \field{Avaiable State}
> +when DRIVER_OK is set.
> +
>  \input{admin.tex}
>
>  \chapter{General Initialization And Device Operation}\label{sec:General Initialization And Device Operation}
> --
> 2.35.3
>