OASIS Mailing List ArchivesView the OASIS mailing list archive below
or browse/search using MarkMail.


Help: OASIS Mailing Lists Help | MarkMail Help

virtio-comment message

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]

Subject: Re: [virtio-comment] [RFC PATCH 1/5] virtio: introduce SUSPEND bit in device status

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 <jasowang@redhat.com>
Signed-off-by: Eugenio PÃrez <eperezma@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.zhu@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.
@@ -73,6 +76,10 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
  recover by issuing a reset.
+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?

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


  \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}.
\drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}

This publicly archived list offers a means to provide input to the
OASIS Virtual I/O Device (VIRTIO) TC.

In order to verify user consent to the Feedback License terms and
to minimize spam in the list archive, subscription is required
before posting.

Subscribe: virtio-comment-subscribe@lists.oasis-open.org
Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org
List help: virtio-comment-help@lists.oasis-open.org
List archive: https://lists.oasis-open.org/archives/virtio-comment/
Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf
List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists
Committee: https://www.oasis-open.org/committees/virtio/
Join OASIS: https://www.oasis-open.org/join/

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]