balloon: transitional device support

Virtio 1.0 cs02 doesn't include a modern balloon device.  At some
point we'll likely define an incompatible interface with a
different ID and different semantics.  But for now, it's not a
big effort to support a transitional balloon device: this has the
advantage of supporting existing drivers, transparently, as well
as transports that don't allow mixing virtio 0 and virtio 1
devices. And balloon is an easy device to test, so it's also
useful for people to test virtio core handling of transitional
devices.

Three issues with legacy hypervisors have been identified:
1. Actual value is actually used, and is necessary for management
   to work. Luckily 4 byte config space writes are now atomic.
   When using old guests, hypervisors can detect access to the last byte.
   When using old hypervisors, drivers can use atomic 4-byte accesses.
2. Hypervisors actually didn't ignore the stats from the first
   buffer supplied. This means the values there would be
   incorrect until hypervisor resends the request.
   Add a note suggesting hypervisors ignore the 1st buffer.
3. QEMU simply over-writes stats from each buffer it gets.
   Thus if driver supplies a different subset of stats
   on each request, stale values will be there.
   Require drivers to supply the same subset on each
   request. This also gives us a simple way to figure out
   which stats are supported.

VIRTIO-143

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

git-svn-id: https://tools.oasis-open.org/version-control/svn/virtio/branches/v1.0@526 0c8fb4dd-22a2-4bb5-bc14-6c75a5f43652

1 files changed, 23 insertions, 3 deletions

diff --git a/conformance.tex b/conformance.tex
index 80b333f..279b5cb 100644
--- a/conformance.tex
+++ b/conformance.tex
@@ -15,13 +15,13 @@ Conformance targets:
   \begin{itemize}
     \item Clause \ref{sec:Conformance / Driver Conformance},
     \item One of clauses \ref{sec:Conformance / Driver Conformance / PCI Driver Conformance}, \ref{sec:Conformance / Driver Conformance / MMIO Driver Conformance} or \ref{sec:Conformance / Driver Conformance / Channel I/O Driver Conformance}.
-    \item One of clauses \ref{sec:Conformance / Driver Conformance / Network Driver Conformance}, \ref{sec:Conformance / Driver Conformance / Block Driver Conformance}, \ref{sec:Conformance / Driver Conformance / Console Driver Conformance}, \ref{sec:Conformance / Driver Conformance / Entropy Driver Conformance} or \ref{sec:Conformance / Driver Conformance / SCSI Host Driver Conformance}.
+    \item One of clauses \ref{sec:Conformance / Driver Conformance / Network Driver Conformance}, \ref{sec:Conformance / Driver Conformance / Block Driver Conformance}, \ref{sec:Conformance / Driver Conformance / Console Driver Conformance}, \ref{sec:Conformance / Driver Conformance / Entropy Driver Conformance}, \ref{sec:Conformance / Driver Conformance / Traditional Memory Balloon Driver Conformance} or \ref{sec:Conformance / Driver Conformance / SCSI Host Driver Conformance}.
   \end{itemize}
 \item[Device] A device MUST conform to three conformance clauses:
   \begin{itemize}
     \item Clause \ref{sec:Conformance / Device Conformance},
     \item One of clauses \ref{sec:Conformance / Device Conformance / PCI Device Conformance}, \ref{sec:Conformance / Device Conformance / MMIO Device Conformance} or \ref{sec:Conformance / Device Conformance / Channel I/O Device Conformance}.
-    \item One of clauses \ref{sec:Conformance / Device Conformance / Network Device Conformance}, \ref{sec:Conformance / Device Conformance / Block Device Conformance}, \ref{sec:Conformance / Device Conformance / Console Device Conformance}, \ref{sec:Conformance / Device Conformance / Entropy Device Conformance} or \ref{sec:Conformance / Device Conformance / SCSI Host Device Conformance}.
+    \item One of clauses \ref{sec:Conformance / Device Conformance / Network Device Conformance}, \ref{sec:Conformance / Device Conformance / Block Device Conformance}, \ref{sec:Conformance / Device Conformance / Console Device Conformance}, \ref{sec:Conformance / Device Conformance / Entropy Device Conformance}, \ref{sec:Conformance / Device Conformance / Traditional Memory Balloon Device Conformance} or \ref{sec:Conformance / Device Conformance / SCSI Host Device Conformance}.
   \end{itemize}
 \end{description}
 
@@ -123,6 +123,16 @@ An entropy driver MUST conform to the following normative statements:
 \item \ref{drivernormative:Device Types / Entropy Device / Device Operation}
 \end{itemize}
 
+\subsection{Traditional Memory Balloon Driver Conformance}\label{sec:Conformance / Driver Conformance / Traditional Memory Balloon Driver Conformance}
+
+A traditional memory balloon driver MUST conform to the following normative statements:
+
+\begin{itemize}
+\item \ref{drivernormative:Device Types / Memory Balloon Device / Feature bits}
+\item \ref{drivernormative:Device Types / Memory Balloon Device / Device Operation}
+\item \ref{drivernormative:Device Types / Memory Balloon Device / Device Operation / Memory Statistics}
+\end{itemize}
+
 \subsection{SCSI Host Driver Conformance}\label{sec:Conformance / Driver Conformance / SCSI Host Driver Conformance}
 
 An SCSI host driver MUST conform to the following normative statements:
@@ -230,6 +240,16 @@ An entropy device MUST conform to the following normative statements:
 \item \ref{devicenormative:Device Types / Entropy Device / Device Operation}
 \end{itemize}
 
+\subsection{Traditional Memory Balloon Device Conformance}\label{sec:Conformance / Device Conformance / Traditional Memory Balloon Device Conformance}
+
+A traditional memory balloon device MUST conform to the following normative statements:
+
+\begin{itemize}
+\item \ref{devicenormative:Device Types / Memory Balloon Device / Feature bits}
+\item \ref{devicenormative:Device Types / Memory Balloon Device / Device Operation}
+\item \ref{devicenormative:Device Types / Memory Balloon Device / Device Operation / Memory Statistics}
+\end{itemize}
+
 \subsection{SCSI Host Device Conformance}\label{sec:Conformance / Device Conformance / SCSI Host Device Conformance}
 
 An SCSI host device MUST conform to the following normative statements:
@@ -292,7 +312,7 @@ Feature Bits / Legacy Interface: A Note on Feature Bits}
 \item Section \ref{sec:Device Types / Block Device / Device Operation / Legacy Interface: Device Operation}
 \item Section \ref{sec:Device Types / Console Device / Device configuration layout / Legacy Interface: Device configuration layout}
 \item Section \ref{sec:Device Types / Console Device / Device Operation / Legacy Interface: Device Operation}
-\item Section \ref{drivernormative:Device Types / Memory Balloon Device / Device Operation}
+\item Section \ref{sec:Device Types / Memory Balloon Device / Feature bits / Legacy Interface: Feature bits}
 \item Section \ref{sec:Device Types / Memory Balloon Device / Device Operation / Legacy Interface: Device Operation}
 \item Section \ref{sec:Device Types / Memory Balloon Device / Device Operation / Memory Statistics / Legacy Interface: Memory Statistics}
 \item Section \ref{sec:Device Types / SCSI Host Device / Device configuration layout / Legacy Interface: Device configuration layout}