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Subject: [PATCH V2 2/6] virtio: introduce SUSPEND bit in device status
This patch introduces a new status bit in the device status: SUSPEND. This SUSPEND bit can be used by the driver to suspend a device, in order to stabilize the device states and virtqueue states. Its main use case is live migration. Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com> Signed-off-by: Jason Wang <jasowang@redhat.com> Signed-off-by: Eugenio PÃrez <eperezma@redhat.com> --- content.tex | 36 ++++++++++++++++++++++++++++++++++-- 1 file changed, 34 insertions(+), 2 deletions(-) diff --git a/content.tex b/content.tex index 76813b5..bcc9d4b 100644 --- a/content.tex +++ b/content.tex @@ -49,6 +49,10 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev \item[DEVICE_NEEDS_RESET (64)] Indicates that the device has experienced an error from which it can't recover. + +\item[SUSPEND (16)] When VIRTIO_F_SUSPEND is negotiated, indicates that the + device has been suspended by the driver. + \end{description} The \field{device status} field starts out as 0, and is reinitialized to 0 by @@ -73,6 +77,10 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev recover by issuing a reset. \end{note} +The driver SHOULD NOT set SUSPEND if FEATURES_OK is not set. + +When setting SUSPEND, the driver MUST re-read \field{device status} to ensure the SUSPEND bit is set. + \devicenormative{\subsection}{Device Status Field}{Basic Facilities of a Virtio Device / Device Status Field} The device MUST NOT consume buffers or send any used buffer @@ -82,6 +90,26 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev that a reset is needed. If DRIVER_OK is set, after it sets DEVICE_NEEDS_RESET, the device MUST send a device configuration change notification to the driver. +The device MUST ignore SUSPEND if FEATURES_OK is not set. + +The device MUST ignore SUSPEND if VIRTIO_F_SUSPEND is not negotiated. + +The device SHOULD allow settings to \field{device status} even when SUSPEND is set. + +If VIRTIO_F_SUSPEND is negotiated and SUSPEND is set, the device SHOULD clear SUSPEND +and resumes operation upon DRIVER_OK. + +If VIRTIO_F_SUSPEND is negotiated, when the driver sets SUSPEND, +the device SHOULD perform the following actions before presenting SUSPEND bit in the \field{device status}: + +\begin{itemize} +\item Stop consuming buffers of any virtqueues and mark all finished descritors as used. +\item Wait until all descriptors that being processed to finish and mark them as used. +\item Flush all used buffer and send used buffer notifications to the driver. +\item Record Virtqueue State of each enabled virtqueue, see section \ref{sec:Virtqueues / Virtqueue State} +\item Pause its operation except \field{device status} and preserve configurations in its Device Configuration Space, see \ref{sec:Basic Facilities of a Virtio Device / Device Configuration Space} +\end{itemize} + \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature Bits} Each virtio device offers all the features it understands. During @@ -99,10 +127,10 @@ \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature B \begin{description} \item[0 to 23, and 50 to 127] Feature bits for the specific device type -\item[24 to 42] Feature bits reserved for extensions to the queue and +\item[24 to 43] Feature bits reserved for extensions to the queue and feature negotiation mechanisms -\item[43 to 49, and 128 and above] Feature bits reserved for future extensions. +\item[44 to 49, and 128 and above] Feature bits reserved for future extensions. \end{description} \begin{note} @@ -875,6 +903,10 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits} \item[VIRTIO_F_QUEUE_STATE(42)] This feature indicates that the device allows the driver to access its internal virtqueue state. + \item[VIRTIO_F_SUSPEND(43)] This feature indicates that the driver can + SUSPEND the device. + See \ref{sec:Basic Facilities of a Virtio Device / Device Status Field}. + \end{description} \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits} -- 2.35.3
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