The virtio documentation currently doesn't define any generic requirements that are applicable to all transports. They can be useful while adding support for a new transport.

This commit tries to define the same.

Reviewed-by: Alex Bennée alex.bennee@linaro.org Signed-off-by: Viresh Kumar viresh.kumar@linaro.org --- V4->V5: - s/The transport/A transport/ - s/MUST provide/provides/ - Added some text for transport requirements.

V3->V4: - Remove the normative sections and use direct speech. - Change wording at few places.

V2->V3: - Minor fixes. - Added Reviewed by from Alex.

V1->V2: - Lot of changes after discussions with Alex and Cornelia. - Almost a rewrite of the first commit. - Add Transport normative sections.

content.tex | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 80 insertions(+), 2 deletions(-)

diff --git a/content.tex b/content.tex index 0a62dce5f65f..e2a836327818 100644 --- a/content.tex +++ b/content.tex @@ -631,8 +631,86 @@ \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 contains sections describing the transport-agnostic parts +of virtio, and sections describing how individual transports implement +virtio. + +\section{Virtio Transport Requirements}\label{sec:Virtio Transport Options / Virtio Transport Requirements} + +There are some mechanisms that any transport is required to implement, +and some requirements that devices and drivers are required to follow. + +\subsection{Transport Requirements}\label{sec:Virtio Transport Options / Virtio Transport Requirements / Transport Requirements} + +A transport provides a mechanism for the driver to discover the device. + +A transport provides a mechanism for the driver to identify the device +type. + +A transport provides a mechanism for communicating virtqueue +configurations between the device and the driver. + +A transport allows multiple virtqueues per device. The number of +virtqueues for a pair of device-driver are governed by the individual +device protocol. + +A transport provides a mechanism that the device and the driver use to +access memory for implementing virtqueues. + +A transport provides a mechanism for the device to notify the driver and +a mechanism for the driver to notify the device, for example regarding +availability of a buffer on the virtqueue. + +A transport provides a mechanism for the driver to initiate a reset of +the virtqueues and device. + +A transport provides a mechanism for the driver to read the device +status. A transport provides a mechanism for the driver to change the +device status. + +A transport provides a mechanism to implement configuration space +between the device and the driver. + +\subsection{Device Requirements}\label{sec:Virtio Transport Options / Virtio Transport Requirements / Device Requirements} + +The device keeps any data associated with a device-initiated transaction +accessible to the driver until the driver acknowledges the transaction +to be complete. + +The device doesn't 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 doesn't access or modify buffers on a virtqueue after it has +notified the driver about their availability. + +The device resets itself and the virtqueues if requested by the driver, +in a transport defined way, if the transport provides such a method. + +\subsection{Driver Requirements}\label{sec:Virtio Transport Options / Virtio Transport Requirements / Driver Requirements} + +The driver acknowledges device notifications, as mandated by the +transport. + +The driver doesn't access virtqueue contents before the device notifies +about the readiness of the same. + +The driver accesses queued buffers after the device has processed them +and notified the driver of their availability. This mechanism is +transport defined. + +The driver asks the device to reset itself and the virtqueues if, for +example, the driver times out waiting for a notification from the device +for a previously queued request. +

\input{transport-pci.tex} \input{transport-mmio.tex}