Re: [dpdk-dev] [PATCH v4 1/2] ethdev: fix docs of functions getting xstats by IDs

[Olivier Matz <olivier.matz@6wind.com>]

Hi Andrew,

Some comments below.

On Sat, Jul 24, 2021 at 03:33:13PM +0300, 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 | 32 +++++++++++++++++++-------------
>  1 file changed, 19 insertions(+), 13 deletions(-)
> 
> diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
> index d2b27c351f..b14067fe7e 100644
> --- a/lib/ethdev/rte_ethdev.h
> +++ b/lib/ethdev/rte_ethdev.h
> @@ -2872,13 +2872,17 @@ int rte_eth_xstats_get(uint16_t port_id, struct rte_eth_xstat *xstats,
>   * @param port_id
>   *   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.
> + *   Array to be filled in with names of requested device statistics.
> + *   Must not be NULL if @p ids are specified (not NULL).
>   * @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 names of all available statistics or, if @p xstats_names is
> + *   NULL as well,  just a number of available statistics.

double spaces before "just"

"a number" -> "the number"?

>   * @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.

Just a suggestion here, I feel the following description would be clearer:

  Number of elements in @p xstats_names array (if not NULL) and
  in @p ids array (if not NULL).

Shouldn't we say that it has to be 0 if both arrays are NULL?


Also, the order of arguments is not the same in comment and in
the function. I think it can make sense to align the comment
to the prototype.


>   * @return
>   *   - A positive value lower or equal to size: success. The return value
>   *     is the number of entries filled in the stats table.

Not seen in the patch, but right after this line, there is:

 *   - A positive value higher than size: error, the given statistics table
 *     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.

I wonder if it shouldn't be slighly reworded to remove 'error'. After
all, passing NULL arrays (and size == 0) is a valid, so the return is
not an error.


> @@ -2886,7 +2890,7 @@ 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.
>   */
>  int
>  rte_eth_xstats_get_names_by_id(uint16_t port_id,
> @@ -2899,14 +2903,16 @@ rte_eth_xstats_get_names_by_id(uint16_t port_id,
>   * @param 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
> - *   all available statistics.
> + *   IDs array given by app to retrieve specific statistics. May be NULL to
> + *   retrieve all available statistics or, if @p values is NULL as well,
> + *   just a number of available statistics.
>   * @param values
> - *   A pointer to a table to be filled with device statistics values.
> + *   Array to be filled in with requested device statistics.
> + *   Must not be NULL if ids are specified (not NULL).
>   * @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 @p values to put statistics in. If @p ids is NULL,
> + *   number of elements in @p values to put all available statistics in.
>   * @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 +2920,7 @@ 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.
>   */

Some of the comments above also apply here.

>  int rte_eth_xstats_get_by_id(uint16_t port_id, const uint64_t *ids,
>  			     uint64_t *values, unsigned int size);
> -- 
> 2.30.2
>