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| -rw-r--r-- | content.tex | 34 |
1 files changed, 19 insertions, 15 deletions
diff --git a/content.tex b/content.tex index 1d09eb0..fdfec91 100644 --- a/content.tex +++ b/content.tex @@ -4695,7 +4695,7 @@ native endian of the guest rather than (necessarily) little-endian. \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits} -Currently there are four device-independent feature bits defined: +Currently there are three device-independent feature bits defined: \begin{description} \item[VIRTIO_F_RING_INDIRECT_DESC (28)] Negotiating this feature indicates @@ -4703,21 +4703,22 @@ Currently there are four device-independent feature bits defined: flag set, as described in \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / The Virtqueue Descriptor Table / Indirect Descriptors}~\nameref{sec:Basic Facilities of a Virtio Device / Virtqueues / The Virtqueue Descriptor Table / Indirect Descriptors}. \item[VIRTIO_F_RING_EVENT_IDX(29)] This feature enables the \field{used_event} - and the \field{avail_event} fields. If set, it indicates that the - device should ignore \field{flags} in the available ring - structure. Instead, \field{used_event} in this structure is - used by driver to suppress device interrupts. Further, the - driver should ignore the \field{flags} field in the used ring - structure. Instead, \field{avail_event} in this structure is - used by the device to suppress notifications. If unset, the - driver should ignore \field{used_event}; the device should - ignore \field{avail_event} and the \field{flags} fields should be used, - - \item[VIRTIO_F_VERSION_1(32)] This feature must be offered by any device - compliant with this specification, and acknowledged by all device - drivers. + and the \field{avail_event} fields as described in \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Interrupt Suppression} and \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / The Virtqueue Used Ring}. + + \item[VIRTIO_F_VERSION_1(32)] This indicates compliance with this + specification, giving a simple way to detect legacy devices or drivers. \end{description} +\drivernormative{Reserved Feature Bits} + +A driver MUST accept VIRTIO_F_VERSION_1 if it is offered. A driver +MAY fail to operate further if VIRTIO_F_VERSION_1 is not offered. + +\devicenormative{Reserved Feature Bits} + +A device MUST offer VIRTIO_F_VERSION_1. A device MAY fail to operate further +if VIRTIO_F_VERSION_1 is not accepted. + \section{Legacy Interface: Reserved Feature Bits}\label{sec:Reserved Feature Bits / Legacy Interface: Reserved Feature Bits} Legacy or transitional devices may offer the following: @@ -4727,12 +4728,15 @@ Legacy or transitional devices may offer the following: indicates that the driver wants an interrupt if the device runs out of available descriptors on a virtqueue, even though interrupts are suppressed using the VRING_AVAIL_F_NO_INTERRUPT - flag or the \field{used_event} field. An example of this is the + flag or the \field{used_event} field. +\begin{note} + An example of this is the networking driver: it doesn't need to know every time a packet is transmitted, but it does need to free the transmitted packets a finite time after they are transmitted. It can avoid using a timer if the device interrupts it when all the packets are transmitted. +\end{note} \item[VIRTIO_F_ANY_LAYOUT (27)] This feature indicates that the device accepts arbitrary descriptor layouts, as described in Section |