On 8/14/2023 10:30 PM, Stefan Hajnoczi wrote:
On Tue, Aug 15, 2023 at 03:29:00AM +0800, Zhu Lingshan wrote:
This patch introudces 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 stablize the device states and virtqueue states.
Its main use case is live migration.
Signed-off-by: Jason Wang <jasow...@redhat.com>
Signed-off-by: Eugenio PÃrez <epere...@redhat.com>
There is an character encoding issue in Eugenio's surname.
Oh, I copied his SOB form his email, I will copy from git log to fix this,
thanks for point out it.
Signed-off-by: Zhu Lingshan <lingshan....@intel.com>
---
content.tex | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
This patch hints at the asynchronous nature of the SUSPEND bit (the
driver must re-read the Device Status Field) but doesn't explain the
rationale or any limits.
For example, is there a timeout or should the driver re-read the Device
Status Field forever?
It depends on the driver, normally we expect this operation can be done
successfully
like how the driver/device handles FEATURES_OK.
Once failed due to:
1) driver timeout, the driver can reset the device
2) device failure, the device can set NEEDS_RESET.
Does the driver need to re-read the Device Status Field after clearing
the SUSPEND bit?
I think the driver should re-read, I will add this in the next version.
diff --git a/content.tex b/content.tex
index 0a62dce..1bb4401 100644
--- a/content.tex
+++ b/content.tex
@@ -47,6 +47,9 @@ \section{\field{Device Status} Field}\label{sec:Basic
Facilities of a Virtio Dev
\item[DRIVER_OK (4)] Indicates that the driver is set up and ready to
drive the device.
+\item[SUSPEND (16)] When VIRTIO_F_SUSPEND is negotiated, indicates that the
+ device has been suspended by the driver.
+
\item[DEVICE_NEEDS_RESET (64)] Indicates that the device has experienced
an error from which it can't recover.
\end{description}
@@ -73,6 +76,10 @@ \section{\field{Device Status} Field}\label{sec:Basic
Facilities of a Virtio Dev
recover by issuing a reset.
\end{note}
+The driver MUST NOT set SUSPEND if FEATURES_OK is not set.
+
+When set SUSPEND, the driver MUST re-read \field{device status} to ensure the
SUSPEND bit is set.
"When setting SUSPEND, ..." would be grammatically correct. Another
option is "After setting the SUSPEND bit, ...".
Will fix in the next version.
+
\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 +89,13 @@ \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 deivce MUST ignore SUSPEND if VIRTIO_F_SUSPEND is not negotiated.
+
+If VIRTIO_F_SUSPEND is negotiated and SUSPEND is set, the device MUST clear
SUSPEND
+and resumes operation upon DRIVER_OK.
I can't parse this sentence. If the driver writes SUSPEND | DRIVER_OK |
... to the Device Status Field, then the device accepts DRIVER_OK and
clears SUSPEND?
Why?
I expect DRIVER_OK can clear SUSPEND, so that the device can resume running
in case of a failed live migration.
Maybe I should say: DRIVER_OK clears SUSPEND, and if DRIVER_OK is set to
a suspended device, the device should resume operation
Thanks
+
\section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device /
Feature Bits}
Each virtio device offers all the features it understands. During
@@ -872,6 +886,10 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature
Bits}
\ref{devicenormative:Basic Facilities of a Virtio Device / Feature
Bits} for
handling features reserved for future use.
+ \item[VIRTIO_F_SUSPEND(41)] 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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