Re: [RFC 2/2] ethdev: add API to set process to primary or secondary

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 1 Dec 2022 10:20:05 +0200
Rongwei Liu <rongweil@nvidia.com> wrote:

> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice
> + *
> + * Set the rte_eth process to the primary or secondary role which affects
> + * the flow rules offloading. It doesn't allow multiple processes to be the
> + * same role unless no offload rules are set.
> + * The primary process's flow rules are effective immediately while the secondary
> + * process's rules will be queued in hardware until it becomes primary or no
> + * primary process is alive.
> + * The primary application will always receive traffic while the secondary
> + * application will receive traffic when no matching rules are present from
> + * the primary application.
> + *
> + * The application is primary by default if this API is not called.
> + *
> + * When a process transforms from a secondary to a primary role, all preceding
> + * flow rules which are queued by hardware will be effective immediately.
> + * Before role transition, all the rules set by the primary process should be
> + * flushed first.
> + *
> + * When role flag "RTE_ETH_PROCESS_NIC_DUP_WITH_SECONDARY" is set, NIC domain
> + * flow rules are effective immediately even if a process is secondary.
> + *
> + * @param active
> + *   Process primary (role) or not (secondary).
> + * @param flag
> + *   The role flag.
> + * @return
> + *   - (>=0) Number of rte devices which have been switched successfully.
> + *   - (-EINVAL) if bad parameter.
> + */
> +__rte_experimental
> +int rte_eth_process_set_primary(bool primary, uint32_t flag);

The state of the devices and the system is really unstable if
this fails. There is no rollback here.

I think this should have a PMD capability flag so that application
can check that device supports doing this. And it would have to
be opt-in so that existing devices would always fail.