[dpdk-dev] [PATCH v3 1/6] ethdev: add capability to keep flow rules on restart

[Ferruh Yigit]

On 10/19/2021 1:37 PM, Dmitry Kozlyuk wrote:
> diff --git a/doc/guides/prog_guide/rte_flow.rst b/doc/guides/prog_guide/rte_flow.rst
> index 2b42d5ec8c..ff67b211e3 100644
> --- a/doc/guides/prog_guide/rte_flow.rst
> +++ b/doc/guides/prog_guide/rte_flow.rst
> @@ -87,6 +87,31 @@ To avoid resource leaks on the PMD side, handles must be explicitly
>   destroyed by the application before releasing associated resources such as
>   queues and ports.
>   
> +If ``RTE_ETH_DEV_CAPA_FLOW_RULE_KEEP`` is not advertised,
> +rules cannot be created until the device is started for the first time
> +and cannot be kept when the device is stopped.

So flag means two things:
1) rules cannot be created until the device is started for the first time
2) rules cannot be kept when the device is stopped

Can't be a case one is true but other is not? I was thinking flag is
only for (2).

> +However, PMD also does not flush them automatically on stop,
> +so the application must call ``rte_flow_flush()`` or ``rte_flow_destroy()``
> +before stopping the device to ensure no rules remain.
> +
> +If ``RTE_ETH_DEV_CAPA_FLOW_RULE_KEEP`` is advertised, this means
> +the PMD can keep at least some rules across the device stop and start.
> +However, ``rte_eth_dev_configure()`` may fail if any rules remain,
> +so the application must flush them before attempting a reconfiguration.

If there are any remaining rules, should we fail the ``rte_eth_dev_configure()``,
or is it allowed PMD to flush the rules itself?

As far as I know some Intel PMDs flush remaining rules in configure itself
without failing, @Qi can correct me if I am wrong.


> +Keeping may be unsupported for some types of rule items and actions,
> +as well as depending on the value of flow attributes transfer bit.
> +A combination of an item or action type and a value of the transfer bit
> +is called a rule feature.
> +To test if rules with a particular feature are kept, the application must try
> +to create a valid rule using this feature when the device is stopped
> +(after it has been configured or started previously).
> +If it fails with an error of type ``RTE_FLOW_ERROR_TYPE_STATE``,
> +rules using this feature are flushed when the device is stopped.
> +If it suceeds, such rules will be kept when the device is stopped,
> +provided they do not use other features that are not supported.
> +Rules that are created when the device is stopped, including the rules
> +created for the test, will be kept after the device is started.
> +

I understand the intention, but I don't know if this is true for all devices.
Can't there be a case that driver can't create rule when it is stopped,
but it can keep the rules after stop. Or other-way around, driver can
create rule when it is stopped, but can't keep rule after stop.

I am feeling we are missing comments from different vendors if this logic
works for them.