Re: [dpdk-dev] [PATCH v7 1/4] ethdev: support device reset and recovery events

[Thomas Monjalon <thomas@monjalon.net>]

14/02/2022 11:16, Ray Kinsella:
> Ray Kinsella <mdr@ashroe.eu> writes:
> > Thomas Monjalon <thomas@monjalon.net> writes:
> >> 02/02/2022 12:44, Ray Kinsella:
> >>> Ferruh Yigit <ferruh.yigit@intel.com> writes:
> >>> > On 1/28/2022 12:48 PM, Kalesh A P wrote:
> >>> >> --- a/lib/ethdev/rte_ethdev.h
> >>> >> +++ b/lib/ethdev/rte_ethdev.h
> >>> >> @@ -3818,6 +3818,24 @@ enum rte_eth_event_type {
> >>> >>   	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_ERR_RECOVERING,
> >>> >> +			/**< port recovering from an error
> >>> >> +			 *
> >>> >> +			 * PMD detected a FW reset or error condition.
> >>> >> +			 * PMD will try to recover from the error.
> >>> >> +			 * Data path may be quiesced and Control path operations
> >>> >> +			 * may fail at this time.
> >>> >> +			 */
> >>> >> +	RTE_ETH_EVENT_RECOVERED,
> >>> >> +			/**< port recovered from an error
> >>> >> +			 *
> >>> >> +			 * PMD has recovered from the error condition.
> >>> >> +			 * Control path and Data path are up now.
> >>> >> +			 * PMD re-configures the port to the state prior to the error.
> >>> >> +			 * Since the device has undergone a reset, flow rules
> >>> >> +			 * offloaded prior to reset may be lost and
> >>> >> +			 * the application should recreate the rules again.
> >>> >> +			 */
> >>> >>   	RTE_ETH_EVENT_MAX       /**< max value of this enum */
> >>> >
> >>> >
> >>> > Also ABI check complains about 'RTE_ETH_EVENT_MAX' value check, cc'ed more people
> >>> > to evaluate if it is a false positive:
> >>> >
> >>> >
> >>> > 1 function with some indirect sub-type change:
> >>> >   [C] 'function int rte_eth_dev_callback_register(uint16_t, rte_eth_event_type, rte_eth_dev_cb_fn, void*)' at rte_ethdev.c:4637:1 has some indirect sub-type changes:
> >>> >     parameter 3 of type 'typedef rte_eth_dev_cb_fn' has sub-type changes:
> >>> >       underlying type 'int (typedef uint16_t, enum rte_eth_event_type, void*, void*)*' changed:
> >>> >         in pointed to type 'function type int (typedef uint16_t, enum rte_eth_event_type, void*, void*)':
> >>> >           parameter 2 of type 'enum rte_eth_event_type' has sub-type changes:
> >>> >             type size hasn't changed
> >>> >             2 enumerator insertions:
> >>> >               'rte_eth_event_type::RTE_ETH_EVENT_ERR_RECOVERING' value '11'
> >>> >               'rte_eth_event_type::RTE_ETH_EVENT_RECOVERED' value '12'
> >>> >             1 enumerator change:
> >>> >               'rte_eth_event_type::RTE_ETH_EVENT_MAX' from value '11' to '13' at rte_ethdev.h:3807:1
> >>> 
> >>> I don't immediately see the problem that this would cause.
> >>> There are no array sizes etc dependent on the value of MAX for instance.
> >>> 
> >>> Looks safe?
> >>
> >> We never know how this enum will be used by the application.
> >> The max value may be used for the size of an event array.
> >> It looks a real ABI issue unfortunately.
> >
> > Right - but we only really care about it when an array size based on MAX
> > is likely to be passed to DPDK, which doesn't apply in this case.

I don't completely agree.
A developer may assume an event will never exceed MAX value.
However, after an upgrade of DPDK without app rebuild,
a higher event value may be received in the app,
breaking the assumption.
Should we consider this case as an ABI breakage?

> > I noted that some Linux folks explicitly mark similar MAX values as not
> > part of the ABI.
> >
> > /usr/include/linux/perf_event.h
> > 37:     PERF_TYPE_MAX,                          /* non-ABI */
> > 60:     PERF_COUNT_HW_MAX,                      /* non-ABI */
> > 79:     PERF_COUNT_HW_CACHE_MAX,                /* non-ABI */
> > 87:     PERF_COUNT_HW_CACHE_OP_MAX,             /* non-ABI */
> > 94:     PERF_COUNT_HW_CACHE_RESULT_MAX,         /* non-ABI */
> > 116:    PERF_COUNT_SW_MAX,                      /* non-ABI */
> > 149:    PERF_SAMPLE_MAX = 1U << 24,             /* non-ABI */
> > 151:    __PERF_SAMPLE_CALLCHAIN_EARLY           = 1ULL << 63, /*
> > non-ABI; internal use */
> > 189:    PERF_SAMPLE_BRANCH_MAX_SHIFT            /* non-ABI */
> > 267:    PERF_TXN_MAX            = (1 << 8), /* non-ABI */
> > 301:    PERF_FORMAT_MAX = 1U << 4,              /* non-ABI */
> > 1067:   PERF_RECORD_MAX,                        /* non-ABI */
> > 1078:   PERF_RECORD_KSYMBOL_TYPE_MAX            /* non-ABI */
> > 1087:   PERF_BPF_EVENT_MAX,             /* non-ABI */
> 
> Any thoughts on similarly annotating all our _MAX enums in the same way?
> We could also add a section in the ABI Policy to make it explicit _MAX
> enum values are not part of the ABI - what do folks think?

Interesting. I am not sure it is always ABI-safe though.