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

[Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>]

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@oktetlabs.ru>
>>
>> Document valid combinations of input arguments in accordance with
>> current implementation in ethdev.
>>
>> Fixes: 79c913a42f0 ("ethdev: retrieve xstats by ID")
>> Cc: stable@dpdk.org
>>
>> Signed-off-by: Ivan Ilchenko <ivan.ilchenko@oktetlabs.ru>
>> Signed-off-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
>> Reviewed-by: Andy Moreton <amoreton@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.

> 
> 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.

> 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.

>>    * @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);
>>