Re: [dpdk-dev] [PATCH 2/2] lpm: hide internal data

[Ruifeng Wang <Ruifeng.Wang@arm.com>]

> -----Original Message-----
> From: Kevin Traynor <ktraynor@redhat.com>
> Sent: Wednesday, September 30, 2020 4:46 PM
> To: Ruifeng Wang <Ruifeng.Wang@arm.com>; Medvedkin, Vladimir
> <vladimir.medvedkin@intel.com>; Bruce Richardson
> <bruce.richardson@intel.com>
> Cc: dev@dpdk.org; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; nd <nd@arm.com>
> Subject: Re: [dpdk-dev] [PATCH 2/2] lpm: hide internal data
> 
> On 16/09/2020 04:17, Ruifeng Wang wrote:
> >
> >> -----Original Message-----
> >> From: Medvedkin, Vladimir <vladimir.medvedkin@intel.com>
> >> Sent: Wednesday, September 16, 2020 12:28 AM
> >> To: Bruce Richardson <bruce.richardson@intel.com>; Ruifeng Wang
> >> <Ruifeng.Wang@arm.com>
> >> Cc: dev@dpdk.org; Honnappa Nagarahalli
> >> <Honnappa.Nagarahalli@arm.com>; nd <nd@arm.com>
> >> Subject: Re: [PATCH 2/2] lpm: hide internal data
> >>
> >> Hi Ruifeng,
> >>
> >> On 15/09/2020 17:02, Bruce Richardson wrote:
> >>> On Mon, Sep 07, 2020 at 04:15:17PM +0800, Ruifeng Wang wrote:
> >>>> Fields except tbl24 and tbl8 in rte_lpm structure have no need to
> >>>> be exposed to the user.
> >>>> Hide the unneeded exposure of structure fields for better ABI
> >>>> maintainability.
> >>>>
> >>>> Suggested-by: David Marchand <david.marchand@redhat.com>
> >>>> Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
> >>>> Reviewed-by: Phil Yang <phil.yang@arm.com>
> >>>> ---
> >>>>   lib/librte_lpm/rte_lpm.c | 152
> >>>> +++++++++++++++++++++++---------------
> >> -
> >>>>   lib/librte_lpm/rte_lpm.h |   7 --
> >>>>   2 files changed, 91 insertions(+), 68 deletions(-)
> >>>>
> >>> <snip>
> >>>> diff --git a/lib/librte_lpm/rte_lpm.h b/lib/librte_lpm/rte_lpm.h
> >>>> index 03da2d37e..112d96f37 100644
> >>>> --- a/lib/librte_lpm/rte_lpm.h
> >>>> +++ b/lib/librte_lpm/rte_lpm.h
> >>>> @@ -132,17 +132,10 @@ struct rte_lpm_rule_info {
> >>>>
> >>>>   /** @internal LPM structure. */
> >>>>   struct rte_lpm {
> >>>> -	/* LPM metadata. */
> >>>> -	char name[RTE_LPM_NAMESIZE];        /**< Name of the lpm. */
> >>>> -	uint32_t max_rules; /**< Max. balanced rules per lpm. */
> >>>> -	uint32_t number_tbl8s; /**< Number of tbl8s. */
> >>>> -	struct rte_lpm_rule_info rule_info[RTE_LPM_MAX_DEPTH]; /**<
> >> Rule info table. */
> >>>> -
> >>>>   	/* LPM Tables. */
> >>>>   	struct rte_lpm_tbl_entry tbl24[RTE_LPM_TBL24_NUM_ENTRIES]
> >>>>   			__rte_cache_aligned; /**< LPM tbl24 table. */
> >>>>   	struct rte_lpm_tbl_entry *tbl8; /**< LPM tbl8 table. */
> >>>> -	struct rte_lpm_rule *rules_tbl; /**< LPM rules. */
> >>>>   };
> >>>>
> >>>
> >>> Since this changes the ABI, does it not need advance notice?
> >>>
> >>> [Basically the return value point from rte_lpm_create() will be
> >>> different, and that return value could be used by rte_lpm_lookup()
> >>> which as a static inline function will be in the binary and using
> >>> the old structure offsets.]
> >>>
> >>
> >> Agree with Bruce, this patch breaks ABI, so it can't be accepted
> >> without prior notice.
> >>
> > So if the change wants to happen in 20.11, a deprecation notice should
> > have been added in 20.08.
> > I should have added a deprecation notice. This change will have to wait for
> next ABI update window.
> >
> 
> Do you plan to extend? or is this just speculative?
It is speculative.

> 
> A quick scan and there seems to be several projects using some of these
> members that you are proposing to hide. e.g. BESS, NFF-Go, DPVS,
> gatekeeper. I didn't look at the details to see if they are really needed.
> 
> Not sure how much notice they'd need or if they update DPDK much, but I
> think it's worth having a closer look as to how they use lpm and what the
> impact to them is.
Checked the projects listed above. BESS, NFF-Go and DPVS don't access the members to be hided.
They will not be impacted by this patch.
But Gatekeeper accesses the rte_lpm internal members that to be hided. Its compilation will be broken with this patch.

> 
> > Thanks.
> > Ruifeng
> >>>>   /** LPM RCU QSBR configuration structure. */
> >>>> --
> >>>> 2.17.1
> >>>>
> >>
> >> --
> >> Regards,
> >> Vladimir