On Sun, Oct 03, 2021 at 07:00:30AM +0200, Halil Pasic wrote: > On Sat, 2 Oct 2021 14:20:47 -0400 > "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > > > > >From my perspective the problem is that the version of the device > > > remains in limbo as long as the features have not yet been finalized, > > > which means that the endianness of the config space remains in limbo as > > > well. Both device and driver might come to different conclusions. > > > > Version === legacy versus modern? > > It is true that feature negotiation can not be used by device to decide that > > question simply because it happens too late. > > So let's not use it for that then ;) > > > > Yes we have VERSION_1 which looks like it should allow this, but > > unfortunately it only helps with that for the driver, not the device. > > > > In practice legacy versus modern has to be determined by > > transport specific versioning, luckily we have that for all > > specified transports (can't say what happens with rproc). > > So if we look at ccw, you say that the revision negotiation already > determines whether VERSION_1 is negotiated or not, and the > feature bit VERSION_1 is superfluous? > > That would also imply, that > 1) if revision > 0 was negotiated then the device must offer VERSION_1 > 2) if revision > 0 was negotiated and the driver cleared VERSION_1 > the device must refuse to operate. > 3) if revision > 0 was negotiated then the driver should reject > to drive a device if it does not offer VERSION_1 > 4) if revision > 0 was negotiated the driver must accept VERSION_1 > 5) if revision > 0 was *not* negotiated then the device should not offer > VERSION_1 because at this point it is already certain that the device > can not act in accordance to the virtio 1.0 or higher interface. > > Does that sound about right? To me, it does. > IMHO we should also change > https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-160003 > and the definition of VERSION_1 because both sides have to know what is > going on before features are fully negotiated. Or? > > Regards, > Halil > I guess so. And I guess we need transport-specific sections describing this behaviour for each transport. So something like this, for starters? diff --git a/content.tex b/content.tex index 1398390..c526dd3 100644 --- a/content.tex +++ b/content.tex @@ -140,10 +140,13 @@ \subsection{Legacy Interface: A Note on Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature Bits / Legacy Interface: A Note on Feature Bits} -Transitional Drivers MUST detect Legacy Devices by detecting that -the feature bit VIRTIO_F_VERSION_1 is not offered. -Transitional devices MUST detect Legacy drivers by detecting that -VIRTIO_F_VERSION_1 has not been acknowledged by the driver. +Transitional drivers MAY support operating legacy devices. +Transitional devices MAY support operation by legacy drivers. + +Transitional drivers MUST detect legacy devices in a way that is +transport specific. +Transitional devices MUST detect legacy drivers in a way that +is transport specific. In this case device is used through the legacy interface. @@ -160,6 +163,25 @@ \subsection{Legacy Interface: A Note on Feature Specification text within these sections generally does not apply to non-transitional devices. +\begin{note} +The device offers different features when used through +the legacy interface and when operated in accordance with this +specification. +\end{note} + +Transitional drivers MUST use Devices only through the legacy interface +if the feature bit VIRTIO_F_VERSION_1 is not offered. +Transitional devices MUST NOT offer VIRTIO_F_VERSION_1 when used through +the legacy interface. + +When the driver uses a device through the legacy interface, then it +MUST only accept the features the device offered through the +legacy interface. + +When used through the legacy interface, the device SHOULD +validate that the driver only accepted the features it +offered through the legacy interface. + \section{Notifications}\label{sec:Basic Facilities of a Virtio Device / Notifications}
