[PATCH v6 1/3] virtio: introduce virtqueue reset as basic facility

This patch allows the driver to reset a queue individually.

This is very common on general network equipment. By disabling a queue,
you can quickly reclaim the buffer currently on the queue. If necessary,
we can reinitialize the queue separately.

For example, when virtio-net implements support for AF_XDP, we need to
disable a queue to release all the original buffers when AF_XDP setup.
And quickly release all the AF_XDP buffers that have been placed in the
queue when AF_XDP exits.

Signed-off-by: Xuan Zhuo <>
---
 content.tex | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/content.tex b/content.tex
index 37c45d3..dd095f4 100644
--- a/content.tex
+++ b/content.tex
@@ -350,6 +350,48 @@ \section{Virtqueues}\label{sec:Basic Facilities of a Virtio Device / Virtqueues}
 Every driver and device supports either the Packed or the Split
 Virtqueue format, or both.
 
+\subsection{Virtqueue Reset}\label{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}
+
+When VIRTIO_F_RING_RESET is negotiated, the driver can reset a virtqueue
+individually. The way to reset the virtqueue is transport specific.
+
+Virtqueue reset is divided into two parts. The driver first resets a queue and
+can afterwards optionally re-enable it.
+
+\subsubsection{Virtqueue Reset}\label{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset / Virtqueue Reset}
+
+\devicenormative{\paragraph}{Virtqueue Reset}{Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset / Virtqueue Reset}
+
+After a queue has been reset by the driver, the device MUST NOT execute
+any requests from that virtqueue, or notify the driver for it.
+
+The device MUST reset any state of a virtqueue to be reset to the default state,
+including the available state and the used state.
+
+\drivernormative{\paragraph}{Virtqueue Reset}{Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset / Virtqueue Reset}
+
+After the driver tells the device to reset a queue, the driver MUST verify that
+the queue has actually been reset.
+
+After the queue has been successfully reset, the driver MAY release any
+resource associated with that virtqueue.
+
+\subsubsection{Virtqueue Re-enable}\label{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset / Virtqueue Re-enable}
+
+This process is the same as the initialization process of a single queue during
+the initialization of the entire device.
+
+\devicenormative{\paragraph}{Virtqueue Re-enable}{Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset / Virtqueue Re-enable}
+
+The device MUST observe any queue configuration that may have been
+changed by the driver, like the maximum queue size.
+
+\drivernormative{\paragraph}{Virtqueue Re-enable}{Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset / Virtqueue Re-enable}
+
+When re-enabling a queue, the driver MUST configure the queue resources
+as during initial virtqueue discovery, but optionally with different
+parameters.
+
 \input{split-ring.tex}
 
 \input{packed-ring.tex}
@@ -6673,6 +6715,10 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
   transport specific.
   For more details about driver notifications over PCI see \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Available Buffer Notifications}.
 
+  \item[VIRTIO_F_RING_RESET(40)] This feature indicates
+  that the driver can reset a queue individually.
+  See \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}.
+
 \end{description}
 
 \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
-- 
2.31.0