[dpdk-dev] [PATCH 03/11] ethdev: fix docs of functions getting xstats by IDs

[Andrew Rybchenko]

On 7/23/21 5:19 PM, Ferruh Yigit wrote:
> On 7/22/2021 10:12 AM, Andrew Rybchenko wrote:
>> On 7/20/21 7:25 PM, Ferruh Yigit wrote:
>>> On 6/4/2021 3:42 PM, Andrew Rybchenko wrote:
>>>> From: Ivan Ilchenko <ivan.ilchenko at oktetlabs.ru>
>>>>
>>>> Document valid combinations of input arguments in accordance with
>>>> current implementation in ethdev.
>>>>
>>>> Fixes: 79c913a42f0 ("ethdev: retrieve xstats by ID")
>>>> Cc: stable at dpdk.org
>>>>
>>>> Signed-off-by: Ivan Ilchenko <ivan.ilchenko at oktetlabs.ru>
>>>> Signed-off-by: Andrew Rybchenko <andrew.rybchenko at oktetlabs.ru>
>>>> Reviewed-by: Andy Moreton <amoreton at xilinx.com>
>>>> ---
>>>>    lib/ethdev/rte_ethdev.h | 23 ++++++++++++++---------
>>>>    1 file changed, 14 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
>>>> index faf3bd901d..1f63118544 100644
>>>> --- a/lib/ethdev/rte_ethdev.h
>>>> +++ b/lib/ethdev/rte_ethdev.h
>>>> @@ -2873,12 +2873,15 @@ int rte_eth_xstats_get(uint16_t port_id, struct
>>>> rte_eth_xstat *xstats,
>>>>     *   The port identifier of the Ethernet device.
>>>>     * @param xstats_names
>>>>     *   An rte_eth_xstat_name array of at least *size* elements to
>>>> - *   be filled. If set to NULL, the function returns the required number
>>>> - *   of elements.
>>>> + *   be filled. Must not be NULL if @p ids are specified (not NULL).
>>>
>>> Removed part is also valid. If both 'ids' & 'xstats_names' are NULL, API returns
>>> number of all elements.
>>
>> Yes, but it is an excessive information. The trigger to return number
>> of all elements is 'ids == NULL'. Here we are talking about
>> 'xstats_names' parameter. If the parameter is NULL, but ids is not
>> null, it does not trigger number of all elements return. It is an
>> invalid input parameters. That's what a new description says.
>>
> 
>     ids		xstats_names
> a) NULL		NULL		valid, return _number_ of all elements
> b) NULL		!NULL		valid, return all elements (if size big enough)
> c) !NULL	NULL		invalid
> 
> Above a) is a valid option, the previous comment tries to describe it via "If
> set to NULL, the function returns the required number of elements." and that
> part is removed.
> Since it is valid option I think we should keep it documented, location or
> wording is up to you.

OK, I see. IMHO, it looks better if it is mentioned in ids parameter
description.  See v4.

>>>
>>> Addition part looks good.
>>>
>>>>     * @param ids
>>>> - *   IDs array given by app to retrieve specific statistics
>>>> + *   IDs array given by app to retrieve specific statistics. May be NULL
>>>> + *   to retrieve all available statistics.
>>>
>>> ack
>>>
>>>>     * @param size
>>>> - *   The size of the xstats_names array (number of elements).
>>>> + *   If @p ids is not NULL, number of elements in the array with requested IDs
>>>> + *   and number of elements in @p xstats_names to put names in. If @p ids is
>>>> + *   NULL, number of elements in @p xstats_names to put all available
>>>> statistics
>>>> + *   names in.
>>>
>>> ack
>>>
>>>>     * @return
>>>>     *   - A positive value lower or equal to size: success. The return value
>>>>     *     is the number of entries filled in the stats table.
>>>> @@ -2886,7 +2889,7 @@ int rte_eth_xstats_get(uint16_t port_id, struct
>>>> rte_eth_xstat *xstats,
>>>>     *     is too small. The return value corresponds to the size that should
>>>>     *     be given to succeed. The entries in the table are not valid and
>>>>     *     shall not be used by the caller.
>>>> - *   - A negative value on error (invalid port id).
>>>> + *   - A negative value on error.
>>>
>>> ack
>>>
>>>
>>> The 'eth_dev_get_xstats_count()' API is flexible but it makes API unnecessarily
>>> complex, not for this patch but for future perhaps we can update the API and it
>>> can return error if either 'ids' or 'xstats_names' is NULL. Remove support to
>>> get all elements or getting number of elements support, these already supported
>>> by non _id version of API.
>>
>> I'm not sure that it is a right direction. The support allows
>> application to use less number of functions and depend on less
>> number of function prototypes.
>>
> 
> True, but makes API more complex, and creates multiple way to do same thing (get
> number of all entries), trade off.

Yes.

>>> And as a note for future, if we ever consider updating these _by_id APIs, we can
>>> consider making the parameter order same for both, currently it is:
>>> "rte_eth_xstats_get_names_by_id(port_id, values, size, ids)"
>>> "      rte_eth_xstats_get_by_id(port_id, ids, values, size)"
>>
>> +1, current difference is terribly bad
>>
>>>>     */
>>>>    int
>>>>    rte_eth_xstats_get_names_by_id(uint16_t port_id,
>>>> @@ -2900,13 +2903,15 @@ rte_eth_xstats_get_names_by_id(uint16_t port_id,
>>>>     *   The port identifier of the Ethernet device.
>>>>     * @param ids
>>>>     *   A pointer to an ids array passed by application. This tells which
>>>> - *   statistics values function should retrieve. This parameter
>>>> - *   can be set to NULL if size is 0. In this case function will retrieve
>>>> + *   statistics values function should retrieve. May be NULL to retrieve
>>>>     *   all available statistics.
>>>
>>> Update is good. But what do you think to make it exact same in the both APIs
>>> ('rte_eth_xstats_get_names_by_id()' & 'rte_eth_xstats_get_by_id()')? Since it is
>>> used for same purpose and exact same way in both APIs, no need to have slightly
>>> different description.
>>
>> I agree. I'll fix in v2.
>>
>>>>     * @param values
>>>>     *   A pointer to a table to be filled with device statistics values.
>>>> + *   Must not be NULL if ids are specified (not NULL).
>>>
>>> Same comment on making description similar in both APIs.
>>
>> OK
>>
>>> Also both 'ids' & 'values' being NULL returns number of all elements should be
>>> addressed.
>>
>> I think it is excessibe. It is sufficient to say so for ids==NULL which
>> is a trigger to get all elements.
>>
> 
> But these two are different things,
> one fills values with stats and return number of filled elements
> other doesn't fill any value, but only return number of all elements

I get it. See v4. Hopefully I'll address it in ids parameter
description.

>>>>     * @param size
>>>> - *   The size of the ids array (number of elements).
>>>> + *   If @p ids is not NULL, number of elements in the array with requested IDs
>>>> + *   and number of elements in values to put statistics in. If @p ids is NULL,
>>>> + *   number of elements in values to put all available statistics in.
>>>
>>> ack
>>>
>>>>     * @return
>>>>     *   - A positive value lower or equal to size: success. The return value
>>>>     *     is the number of entries filled in the stats table.
>>>> @@ -2914,7 +2919,7 @@ rte_eth_xstats_get_names_by_id(uint16_t port_id,
>>>>     *     is too small. The return value corresponds to the size that should
>>>>     *     be given to succeed. The entries in the table are not valid and
>>>>     *     shall not be used by the caller.
>>>> - *   - A negative value on error (invalid port id).
>>>> + *   - A negative value on error.
>>>
>>> ack
>>>
>>>>     */
>>>>    int rte_eth_xstats_get_by_id(uint16_t port_id, const uint64_t *ids,
>>>>                     uint64_t *values, unsigned int size);
>>>>
>>