There will be hardware virtio devices in the future, which
require drivers to use the barriers suitable for I/O devices,
compared with software virtio devices which just require
drivers to use the barriers suitable for CPU cores.
To fix the ordering issue for hardware virtio devices, add
a new feature: VIRTIO_F_IO_BARRIER. When negotiated, driver
will use the barriers suitable for I/O devices.
Signed-off-by: Tiwei Bie <>
---
RFC -> v1:
- Use plural (Stefan);
- Add more details (Stefan);
content.tex | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/content.tex b/content.tex
index ae5fa4c..a1c09c4 100644
--- a/content.tex
+++ b/content.tex
@@ -5445,6 +5445,13 @@ Descriptors} and \ref{sec:Packed Virtqueues / Indirect Flag: Scatter-Gather Supp
that drivers pass extra data (besides identifying the Virtqueue)
in their device notifications.
See \ref{sec:Virtqueues / Driver notifications}~\nameref{sec:Virtqueues / Driver notifications}.
+ \item[VIRTIO_F_IO_BARRIER(37)] 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}
@@ -5460,6 +5467,10 @@ 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
@@ -5473,6 +5484,9 @@ 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:
--
2.11.0
