Re: [virtio-dev] [PATCH 4/4] ccw: allow WRITE_STATUS to fail

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

On Fri, Oct 31, 2014 at 03:26:19PM +0100, Cornelia Huck wrote:
> We want to be able to reject a status (e.g. FEATURES_OK if the device
> can't work with the features negotiated).

I guess the reason it's needed is because ccw doesn't have
READ_STATUS?


> The easiest way to do that
> is to allow the device to fail the WRITE_STATUS command.
> 
> VIRTIO-116
> 
> Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> ---
>  conformance.tex |    2 ++
>  content.tex     |   15 +++++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/conformance.tex b/conformance.tex
> index b10ce96..aff92f1 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -79,6 +79,7 @@ A Channel I/O driver MUST conform to the following normative statements:
>  \begin{itemize}
>  \item \ref{drivernormative:Virtio Transport Options / Virtio over channel I/O / Basic Concepts}
>  \item \ref{drivernormative:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Setting the Virtio Revision}
> +\item \ref{drivernormative:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Communicating Status Information}
>  \item \ref{drivernormative:Virtio Transport Options / Virtio over channel I/O / Device Operation / Host->Guest Notification / Notification via Adapter I/O Interrupts}
>  \item \ref{drivernormative:Virtio Transport Options / Virtio over channel I/O / Device Operation / Guest->Host Notification}
>  \end{itemize}
> @@ -182,6 +183,7 @@ A Channel I/O device MUST conform to the following normative statements:
>  \item \ref{devicenormative:Virtio Transport Options / Virtio over channel I/O / Basic Concepts}
>  \item \ref{devicenormative:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Setting the Virtio Revision}
>  \item \ref{devicenormative:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Configuring a Virtqueue}
> +\item \ref{devicenormative:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Communicating Status Information}
>  \item \ref{devicenormative:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Handling Device Features}
>  \item \ref{devicenormative:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Setting Up Indicators / Setting Up Two-Stage Queue Indicators}
>  \item \ref{devicenormative:Virtio Transport Options / Virtio over channel I/O / Device Operation / Host->Guest Notification / Notification via Adapter I/O Interrupts}
> diff --git a/content.tex b/content.tex
> index 38ae49e..490823e 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -2627,6 +2627,21 @@ The driver changes the status of a device via the
>  CCW_CMD_WRITE_STATUS command, which transmits an 8 bit status
>  value.
>  
> +The device is allowed to reject a status: For example, it might fail to accept
> +the FEATURES_OK status bit during device initialization.

I kind of dislike it that we are adding this new concept of
"rejecting a status". The generic spec says:

	The device SHOULD accept any valid subset
	of features the driver accepts, otherwise it MUST fail to set the
	FEATURES_OK \field{device status} bit when the driver writes it.

so devices accept features, not status, I think applying concept of
accept/reject to status is confusing.
Let's say that device fails to set status to requested value.
For example:



	As described in <cross reference> devices sometimes fail to set
	the \field{device status} to value written by the driver.

> +
> +\drivernormative{\paragraph}{Communicating Status Information}{Virtio Transport Options / Virtio over channel I/O / Device Initialization / Communicating Status Information}
> +
> +If the device posts a unit check with command reject in response to the
> +CCW_CMD_WRITE_STATUS command, the driver MUST assume that

add:         setting device failed to set the status and that

> +the status
> +field
> +retained its previous value.
> +
> +\devicenormative{\paragraph}{Communicating Status Information}{Virtio Transport Options / Virtio over channel I/O / Device Initialization / Communicating Status Information}
> +

> +If the driver attempts to set a status that the device does not accept, 

instead:
	If the device fails to set the \field{device status} field
	to the value written by driver


> + the
> +device MUST leave the status field unchanged and MUST post a unit check
> +with command reject.
> +
>  \subsubsection{Handling Device Features}\label{sec:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Handling Device Features}
>  
>  Feature bits are arranged in an array of 32 bit values, making
> -- 
> 1.7.9.5
> 
> 
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