Re: [PATCH V3 Resend] virtio-transport: Clarify requirements

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

On Tue, May 21, 2024 at 04:27:06PM +0530, Viresh Kumar wrote:
> On 20-05-24, 09:27, Michael S. Tsirkin wrote:
> > On Mon, May 20, 2024 at 02:59:40PM +0530, Viresh Kumar wrote:
> > > diff --git a/content.tex b/content.tex
> > > index 0a62dce5f65f..a79993b5ed69 100644
> > > --- a/content.tex
> > > +++ b/content.tex
> > > @@ -631,8 +631,82 @@ \section{Device Cleanup}\label{sec:General Initialization And Device Operation /
> > >  
> > >  \chapter{Virtio Transport Options}\label{sec:Virtio Transport Options}
> > >  
> > > -Virtio can use various different buses, thus the standard is split
> > > -into virtio general and bus-specific sections.
> 
> > > +Devices and drivers can use different transport methods to enable
> > > +interaction, for example PCI, MMIO, or Channel I/O. The transport
> > > +methods define various aspects of the communication between the device
> > > +and the driver, like device discovery, exchanging capabilities,
> > > +interrupt handling, data transfer, etc. For example, in a host/guest
> > > +architecture, the host might expose a device to the guest on a PCI bus,
> > > +and the guest will use a PCI-specific driver to interact with it.
> > > +
> > > +The standard is split into sections describing general virtio
> > > +implementation and transport-specific sections.
> > > +
> > 
> > This makes it seem like trasport is distinct from both
> > device and driver. Makes no sense to me.
> 
> Yeah, looks wrongly worded. I think we can just retain the earlier
> statement here:
> 
> Virtio can use various different buses, thus the standard is split
> into virtio general and bus-specific sections.
> 
> > > +\devicenormative{\subsection}{Virtio Transport Requirements}{Virtio Transport Options / Virtio Transport Requirements}
> > > +
> > > +The device MUST keep any data associated with a device-initiated
> > > +transaction accessible to the driver until the driver acknowledges the
> > > +transaction to be complete.
> > > +
> > > +The device MUST NOT access the contents of a virtqueue before the
> > > +driver notifies, in a transport defined way, the device that the
> > > +virtqueue is ready to be accessed.
> > > +
> > > +The device MUST NOT access or modify buffers on a virtqueue after it has
> > > +notified the driver about their availability.
> > > +
> > > +The device MUST reset the virtqueues if requested by the driver, in a
> > > +transport defined way, if the transport provides such a method.
> > > +
> > > +\drivernormative{\subsection}{Virtio Transport Requirements}{Virtio Transport Options / Virtio Transport Requirements}
> > > +
> > > +The driver MUST acknowledge device notifications, as mandated by the
> > > +transport.
> > > +
> > > +The driver MUST NOT access virtqueue contents before the device notifies
> > > +about the readiness of the same.
> > > +
> > > +The driver MUST NOT access buffers, after it has added them to the
> > > +virtqueue and notified the device about their availability. The driver
> > > +MAY access them after the device has processed them and notified the
> > > +driver of their availability, in a transport defined way.
> > > +
> > > +The driver MAY ask the device to reset the virtqueues if, for example,
> > > +the driver times out waiting for a notification from the device for a
> > > +previously queued request.
> > >  
> > 
> > This makes no sense in a normative section.
> 
> I am okay with wherever you and Cornelia decide to put this.
> 
> > Normative statements are for implementations not spec writers.
> 
> Hmm.
> 
> > If you think of defining lots of new transports
> > (questionable)
> 
> There is just one in discussion at the moment on the ARM side,
> virtio-msg (for communication between the VMs), but nothing is
> finalized yet.


I feel a non-normative section is enough for this.
Just convert should/must to direct speech.

> > I think a new non-normative section
> > along the lines of newdevice.tex will make sense.
> 
> -- 
> viresh