Re: [dpdk-dev] [PATCH v2] ethdev: support flow aging

[Thomas Monjalon <thomas@monjalon.net>]

20/04/2020 16:06, Ferruh Yigit:
> On 4/18/2020 10:44 AM, Thomas Monjalon wrote:
> > 18/04/2020 07:04, Bill Zhou:
> >> From: Ferruh Yigit <ferruh.yigit@intel.com>
> >>> On 4/14/2020 9:32 AM, Dong Zhou wrote:
> >>>> --- a/lib/librte_ethdev/rte_ethdev.h
> >>>> +++ b/lib/librte_ethdev/rte_ethdev.h
> >>>> @@ -3015,6 +3015,7 @@ enum rte_eth_event_type {
> >>>>  	RTE_ETH_EVENT_NEW,      /**< port is probed */
> >>>>  	RTE_ETH_EVENT_DESTROY,  /**< port is released */
> >>>>  	RTE_ETH_EVENT_IPSEC,    /**< IPsec offload related event */
> >>>> +	RTE_ETH_EVENT_FLOW_AGED,/**< New aged-out flows is detected
> >>> */
> >>>>  	RTE_ETH_EVENT_MAX       /**< max value of this enum */
> >>>>  };
> >>>
> >>>
> >>> Just recognized that this is failing in ABI check [1], as far as last time for a
> >>> similar enum warning a QAT patch has been dropped, should this need to
> >>> wait for
> >>> 20.11 too?
> >>
> >> This patch is commonly used for flow aging, there are 2 other patches have 
> >> implement flow aging in mlx5 driver reply to this patch.
[...]
> > These MAX values in enums are a pain.
> > We can try to think what can be done, waiting 20.11.
> > Not sure there is a solution, except hijacking an existing value
> > not used in the PMD, waiting the definitive value in 20.11...
> 
> Dropping from the tree as of now, to not cause more merge conflicts, we can add
> it later when issue is resolved.

Thanks for dropping, that's the right thing to do
when a patch is breaking ABI check.

After some thoughts, I think it is acceptable to make a v3
which ignore this specific enum change. I explain my thought below:

An enum can accept a new value at 2 conditions:
	- added as last value (not changing old values)
	- new value not used by existing API

The value RTE_ETH_EVENT_FLOW_AGED meet the above 2 conditions:
	- only RTE_ETH_EVENT_MAX is changed, which is consistent
	- new value sent to the app only if the app registered for it

So, except if I miss something, I suggest we add this exception:
Allow new value in rte_eth_event_type if added just before RTE_ETH_EVENT_MAX.
In other words, allow changing the value of RTE_ETH_EVENT_MAX.
The file to add such exception is devtools/libabigail.abignore.