Re: [virtio-comment] Re: [PATCH 3/5] virtqueue: constraints for virtqueue state

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

On 9/19/2023 1:30 AM, Michael S. Tsirkin wrote:
> On Mon, Sep 18, 2023 at 11:02:18AM +0800, Zhu, Lingshan wrote:
> > On 9/15/2023 7:16 PM, Michael S. Tsirkin wrote:
> > > On Fri, Sep 15, 2023 at 10:59:29AM +0800, Zhu, Lingshan wrote:
> > > > On 9/14/2023 7:30 PM, Michael S. Tsirkin wrote:
> > > > > On Wed, Sep 06, 2023 at 04:16:35PM +0800, Zhu Lingshan 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: Zhu Lingshan <lingshan.zhu@intel.com>
> > > > > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > > > > Signed-off-by: Eugenio PÃrez <eperezma@redhat.com>
> > > > > > ---
> > > > > >     content.tex | 19 +++++++++++++++++++
> > > > > >     1 file changed, 19 insertions(+)
> > > > > >
> > > > > > diff --git a/content.tex b/content.tex
> > > > > > index 0fab537..9d727ce 100644
> > > > > > --- a/content.tex
> > > > > > +++ b/content.tex
> > > > > > @@ -594,6 +594,25 @@ \subsection{\field{Used State} Field}
> > > > > >     When VIRTIO_RING_F_PACKED is not negotiated, the 16-bit value of \field{used_idx}
> > > > > >     is always 0
> > > > > > +\drivernormative{\subsection}{Virtqueue State}{Basic Facilities of a Virtio Device / Virtqueue State}
> > > > > > +
> > > > > > +If VIRTIO_F_QUEUE_STATE has been negotiated but VIRTIO_RING_F_PACKED not been negotiated,
> > > > > > +the driver SHOULD 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, the device SHOULD only accept setting
> > > > > > +Virtqueue State of any virtqueues when DRIVER_OK is not set in \field{device status},
> > > > > > +or both of DRIVER_OK and SUSPEND are set in \field{device status}.
> > > > > > +Otherwise the device MUST ignore any writes to Virtqueue State of any virtqueues.
> > > > > > +
> > > > > > +If VIRTIO_F_QUEUE_STATE have been negotiated, when SUSPEND is set,
> > > > > > +the device MUST record the Virtqueue State of every enabled virtqueue
> > > > > > +in \field{Available State} and \field{Used State} respectively,
> > > > > record how?
> > > > This is transport specific, for PCI they are recorded in the common config
> > > > space,
> > > > two new fields of them are introduced in patch 5.
> > > that is not enough space to record state for every enabled vq.
> > They can work with queue_select like many other vq configurations.
> queue select is under driver control.
queue_select works for other fields like queue_size which is also RW.

It looks no difference between queue_size and vq_state.
> > I will mention this in the comment.
> > > > > > +and correspondingly restore the Virtqueue State of every enabled virtqueue
> > > > > > +from \field{Available State} and \field{Used State} when DRIVER_OK is set.
> > > > > when is that?
> > > > When the DRIVER sets DRIVER_OK and done before the device presents
> > > > DRIVER_OK.
> > > I don't really understand the flow here. does SUSPEND clear DRIVER_OK
> > > then?
> > SUSPEND does not clear DRIVER, I think this is not a must.
> then I don't get what does "when DRIVER_OK is set" mean - it stays
> set all the time.
That means the driver sets DRIVER_OK.

I am not a native speaker, but This wording can be found throughout the 
spec, e.g.:

2.1.2 Device Requirements: Device Status Field

If DRIVER_OK is set, after it sets DEVICE_NEEDS_RESET, the device MUST 
send a device configuration
change notification to the driver.
> > > > > > +
> > > > > >     \input{admin.tex}
> > > > > >     \chapter{General Initialization And Device Operation}\label{sec:General Initialization And Device Operation}
> > > > > > --
> > > > > > 2.35.3
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