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| -rw-r--r-- | content.tex | 38 |
1 files changed, 35 insertions, 3 deletions
diff --git a/content.tex b/content.tex index 973a2e7..7ec8bf7 100644 --- a/content.tex +++ b/content.tex @@ -359,9 +359,11 @@ addition, the specification for virtio_blk SCSI commands required intuiting field lengths from frame boundaries (see \ref{sec:Device Types / Block Device / Device Operation / Legacy Interface: Device Operation}~\nameref{sec:Device Types / Block Device / Device Operation / Legacy Interface: Device Operation}) -It is thus RECOMMENDED that when using legacy interfaces, transitional -drivers be conservative in their assumptions, unless the -VIRTIO_F_ANY_LAYOUT feature is accepted. +Thus when using the legacy interface, the VIRTIO_F_ANY_LAYOUT +feature indicates to both the device and the driver that no +assumptions were made about framing. Requirements for +transitional drivers when this is not negotiated are included in +each device section. \subsection{The Virtqueue Descriptor Table}\label{sec:Basic Facilities of a Virtio Device / Virtqueues / The Virtqueue Descriptor Table} @@ -3496,6 +3498,36 @@ according to the native endian of the guest rather than (necessarily when not using the legacy interface) little-endian. +\subsubsection{Legacy Interface: Virtqueue}\label{sec:Device +Types / Network Device / Legacy Interface: Framing Requirements} + +When using legacy interfaces, transitional drivers which have not +negotiated VIRTIO_F_ANY_LAYOUT MUST use a single descriptor for the +struct virtio_net_hdr on both transmit and receive, with the +network data in the following descriptors. See \ref{sec:Basic +Facilities of a Virtio Device / Virtqueues / Message Framing}. +Further, when using the control virtqueue (see \ref{sec:Device +Types / Network Device / Device Operation / Control Virtqueue}) +, transitional drivers which have not +negotiated VIRTIO_F_ANY_LAYOUT MUST: +\begin{itemize} +\item for all commands, use a single 2-byte descriptor including the first two +fields: \field{class} and \field{command} +\item for all commands except VIRTIO_NET_CTRL_MAC_TABLE_SET +use a single descriptor including command-specific-data +with no padding. +\item for the VIRTIO_NET_CTRL_MAC_TABLE_SET command use exactly +two descriptors including command-specific-data with no padding: +the first of these descriptors MUST include the +virtio_net_ctrl_mac table structure for the unicast addresses with no padding, +the second of these descriptors MUST include the +virtio_net_ctrl_mac table structure for the multicast addresses +with no padding. +\item for all commands, use a single 1-byte descriptor for the +\field{ack} field +\end{itemize} + + \section{Block Device}\label{sec:Device Types / Block Device} The virtio block device is a simple virtual block device (ie. |