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

[Thomas Monjalon <thomas@monjalon.net>]

21/04/2020 12:04, Ferruh Yigit:
> On 4/20/2020 5:10 PM, Thomas Monjalon wrote:
> > 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
> > 
> 
> Same here, as far as I can see it is safe to get this change.
> 
> If any DPDK API returns this enum, either as return of the API or as output
> parameter, this still can be problem, because application may use that returned
> value, this was the concern in the QAT sample.
> 
> But here application registers an event and DPDK library process callback for
> it, so application callbacks won't be called for anything that application
> doesn't already know about, in that respect this should be safe for old
> applications.
> 
> Not sure if we can generalize above two conditions for all enum changes, but we
> can investigate them case by case as we get the warnings.
> 
> > 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.
> > 
> 
> OK to exception.

v3 was sent.
I hope we'll get a v4 with justification for the exception.