RE: [PATCH v3 0/2] Support enabling virtqueue after DRIVER_OK

[Parav Pandit <parav@nvidia.com>]

Hi Michael, Cornelia,


> From: Parav Pandit <parav@nvidia.com>
> Sent: Monday, October 2, 2023 10:46 AM
> 
> Summary:
> ========
> This patch enables driver to create virtqueues after DRIVER_OK status bit is set.
> 
> This patch take the inspiration from the thread [2] with credits to Eugenio PÃrez.
> 
> Details:
> ========
> Currently, a virtqueue must be enabled before driver has set the DRIVER_OK
> status bit.
> 
> spec citation to section "Driver Requirements: Device Initialization"
> 
> "Perform device-specific setup, including discovery of virtqueues for the device,
> optional per-bus setup, reading and possibly writing the deviceâs virtio
> configuration space, and population of virtqueues."
> 
> This implies that a virtqueue must be enabled before reaching the DRIVER_OK
> stage. There was no explicit mention about ability to enable the virtqueue after
> DRIVER_OK stage.
> 
> In following usecases, creating a virtqueue after DRIVER_OK phase is desired.
> 
> Use cases:
> =========
> 1. Dynamically create aq when administrative commands to be used.
> ate the net device tx/rxq when device is
>    opened when deploying for a container.
>    In a container, number of virtqueues to be used may be <= max queues.
> 3. Dynamically create flow filter queues of netdevice when
>    ARFS or ethtool filters are enabled as listed in [1].
> 4. Dynamically create rtc functionality related read virtqueue only
>    when net device when timestamping to be used.
> 5. When XDP program is set, one can create additional XDP specific
>    queues without affecting existing queues.
> 
> Hence, This patch introduces an existing queue enable and disable (aka reset)
> facility and a new feature bit to explicitly indicate such support by the device.
> 
> With this feature, drivers can skip optional queues creation during driver init
> time. For example, a Linux net device driver can create/destroy the transmit and
> receive queues when net device's
> ndo_open() and ndo_stop() callbacks are invoked respectively.
> 
> [1] https://lists.oasis-open.org/archives/virtio-
> comment/202308/msg00263.html
> [2] https://lists.oasis-open.org/archives/virtio-
> comment/202306/msg00097.html
> 
> Patch summary:
> ==============
> patch-1 fixes to add virtqueue reset conformance references
> patch-2 adds VIRTIO_F_RING_DYNAMIC feature bit, requirements
> 
> Please review.
> 
> Fixes: https://github.com/oasis-tcs/virtio-spec/issues/177
> 
> ---
> changelog:
> v2->v3:
> - github issue link updated
> v1->v2:
> - fixed comments from Michael
> - reduced device and driver normatives (simplified)
> - replace 'a virtqueue' to 'the virtqueues'
> - reworded to remove 'interested'
> - avoided repeated 'device initialization text', replaced with
>   DRIVER_OK status bit language
> - avoided confusing text around 'MAY' in the requirements
> - replaced 'the queue' to 'specific virtqueues'
> - replaced queue to virtqueue
> - simplified commit log to talk about msix
> v0->v1:
> - fixed comments from Xuan
> - removed blank lines
> - fixed wrong requirement link to device in driver section
> 

I have updated v3 to link to the github issue.
Now that this small feature was up for few weeks, can you please create the ballot review?