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| -rw-r--r-- | content.tex | 20 |
1 files changed, 18 insertions, 2 deletions
diff --git a/content.tex b/content.tex index 110ab70..c4b3b5c 100644 --- a/content.tex +++ b/content.tex @@ -95,10 +95,10 @@ Feature bits are allocated as follows: \begin{description} \item[0 to 23] Feature bits for the specific device type -\item[24 to 33] Feature bits reserved for extensions to the queue and +\item[24 to 36] Feature bits reserved for extensions to the queue and feature negotiation mechanisms -\item[34 and above] Feature bits reserved for future extensions. +\item[37 and above] Feature bits reserved for future extensions. \end{description} \begin{note} @@ -5356,6 +5356,15 @@ Descriptors} and \ref{sec:Packed Virtqueues / Indirect Flag: Scatter-Gather Supp \item[VIRTIO_F_IN_ORDER(35)] This feature indicates that all buffers are used by the device in the same order in which they have been made available. + \item[VIRTIO_F_IO_BARRIER(36)] This feature indicates + that the device needs the driver to use the barriers + suitable for hardware devices. Some transports require + barriers to ensure devices have a consistent view of + memory. When devices are implemented in software a + weaker form of barrier may be sufficient and yield + better performance. This feature indicates whether + a stronger form of barrier suitable for hardware + devices is necessary. \end{description} \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits} @@ -5371,6 +5380,10 @@ addresses to the device. A driver SHOULD accept VIRTIO_F_RING_PACKED if it is offered. +A driver SHOULD accept VIRTIO_F_IO_BARRIER if it is offered. +If VIRTIO_F_IO_BARRIER has been negotiated, a driver MUST use +the barriers suitable for hardware devices. + \devicenormative{\section}{Reserved Feature Bits}{Reserved Feature Bits} A device MUST offer VIRTIO_F_VERSION_1. A device MAY fail to operate further @@ -5384,6 +5397,9 @@ accepted. If VIRTIO_F_IN_ORDER has been negotiated, a device MUST use buffers in the same order in which they have been available. +A device MAY fail to operate further if VIRTIO_F_IO_BARRIER +is not accepted. + \section{Legacy Interface: Reserved Feature Bits}\label{sec:Reserved Feature Bits / Legacy Interface: Reserved Feature Bits} Transitional devices MAY offer the following: |