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

[Michel Machado]

Hi Kevin,

    We do need fields max_rules and number_tbl8s of struct rte_lpm, so 
the removal would force us to have another patch to our local copy of 
DPDK. We'd rather avoid this new local patch because we wish to 
eventually be in sync with the stock DPDK.

    Those fields are needed in Gatekeeper because we found a condition 
in an ongoing deployment in which the entries of some LPM tables may 
suddenly change a lot to reflect policy changes. To avoid getting into a 
state in which the LPM table is inconsistent because it cannot fit all 
the new entries, we compute the needed parameters to support the new 
entries, and compare with the current parameters. If the current table 
doesn't fit everything, we have to replace it with a new LPM table.

    If there were a way to obtain the struct rte_lpm_config of a given 
LPM table, it would cleanly address our need. We have the same need in 
IPv6 and have a local patch to work around it (see 
https://github.com/cjdoucette/dpdk/commit/3eaf124a781349b8ec8cd880db26a78115cb8c8f). 
Thus, an IPv4 and IPv6 solution would be best.

    PS: I've added Qiaobin Fu, another Gatekeeper maintainer, to this 
disscussion.

[ ]'s
Michel Machado

On 10/13/20 9:53 AM, Kevin Traynor wrote:
> Hi Gatekeeper maintainers (I think),
> 
> fyi - there is a proposal to remove some members of a struct in DPDK LPM
> API that Gatekeeper is using [1]. It would be only from DPDK 20.11 but
> as it's an LTS I guess it would probably hit Debian in a few months.
> 
> The full thread is here:
> http://inbox.dpdk.org/dev/20200907081518.46350-1-ruifeng.wang@arm.com/
> 
> Maybe you can take a look and tell us if they are needed in Gatekeeper
> or you can workaround it?
> 
> thanks,
> Kevin.
> 
> [1]
> https://github.com/AltraMayor/gatekeeper/blob/master/gt/lua_lpm.c#L235-L248
> 
> On 09/10/2020 07:54, Ruifeng Wang wrote:
>>
>>> -----Original Message-----
>>> From: Kevin Traynor <ktraynor at redhat.com>
>>> Sent: Wednesday, September 30, 2020 4:46 PM
>>> To: Ruifeng Wang <Ruifeng.Wang at arm.com>; Medvedkin, Vladimir
>>> <vladimir.medvedkin at intel.com>; Bruce Richardson
>>> <bruce.richardson at intel.com>
>>> Cc: dev at dpdk.org; Honnappa Nagarahalli
>>> <Honnappa.Nagarahalli at arm.com>; nd <nd at 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 at intel.com>
>>>>> Sent: Wednesday, September 16, 2020 12:28 AM
>>>>> To: Bruce Richardson <bruce.richardson at intel.com>; Ruifeng Wang
>>>>> <Ruifeng.Wang at arm.com>
>>>>> Cc: dev at dpdk.org; Honnappa Nagarahalli
>>>>> <Honnappa.Nagarahalli at arm.com>; nd <nd at 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 at redhat.com>
>>>>>>> Signed-off-by: Ruifeng Wang <ruifeng.wang at arm.com>
>>>>>>> Reviewed-by: Phil Yang <phil.yang at 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
>>
>