[PATCH v2 1/2] doc/contributing: provide coding details for dynamic logging

[David Marchand]

On Tue, Jun 20, 2023 at 7:08 PM Bruce Richardson
<bruce.richardson at intel.com> wrote:
>
> While the section on dynamic logging in the contributors guide covered
> the details of the logging naming scheme, it failed to cover exactly how
> the component developer, i.e. the contributor, could actually use
> dynamic logging in their component.
>
> Fix this by splitting the details of the naming scheme into a separate
> subsection, and adding to the introduction on logging, a recommendation
> (and example) to use RTE_LOG_REGISTER_DEFAULT.
>
> Similarly, when discussing specialization, include a reference to the
> RTE_LOG_REGISTER_SUFFIX macro.
>
> Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
> ---
>  doc/guides/contributing/coding_style.rst | 17 +++++++++++++++++
>  lib/cfgfile/rte_cfgfile.c                |  2 ++
>  2 files changed, 19 insertions(+)
>
> diff --git a/doc/guides/contributing/coding_style.rst b/doc/guides/contributing/coding_style.rst
> index 89db6260cf..307c7deb9a 100644
> --- a/doc/guides/contributing/coding_style.rst
> +++ b/doc/guides/contributing/coding_style.rst
> @@ -803,6 +803,21 @@ logging of a particular topic, the ``--log-level`` parameter can be provided
>  to EAL, which will change the log level. DPDK code can register topics,
>  which allows the user to adjust the log verbosity for that specific topic.
>
> +To register a library or driver for dynamic logging,

Nit: no need for a line break here, it can be fixed when applying.


> +using the standardized naming scheme described below,
> +use ``RTE_LOG_REGISTER_DEFAULT`` macro to define a log-type variable inside your component's main C file.
> +Thereafter, it is usual to define a macro or macros inside your component to make logging more convenient.
> +
> +For example, the ``rte_cfgfile`` library defines:
> +
> +.. literalinclude:: ../../../lib/cfgfile/rte_cfgfile.c
> +    :language: c
> +    :start-after: Setting up dynamic logging 8<
> +    :end-before: >8 End of setting up dynamic logging
> +
> +Dynamic Logging Naming Scheme
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
>  In general, the naming scheme is as follows: ``type.section.name``
>
>   * Type is the type of component, where ``lib``, ``pmd``, ``bus`` and ``user``
> @@ -837,6 +852,8 @@ A specialization looks like this:
>   * Initialization output: ``type.section.name.init``
>   * PF/VF mailbox output: ``type.section.name.mbox``
>
> +These specializations are created using the ``RTE_LOG_REGISTER_SUFFIX`` macro.
> +
>  A real world example is the i40e poll mode driver which exposes two
>  specializations, one for initialization ``pmd.net.i40e.init`` and the other for
>  the remaining driver logs ``pmd.net.i40e.driver``.
> diff --git a/lib/cfgfile/rte_cfgfile.c b/lib/cfgfile/rte_cfgfile.c
> index 9fa7d010ef..eefba6e408 100644
> --- a/lib/cfgfile/rte_cfgfile.c
> +++ b/lib/cfgfile/rte_cfgfile.c
> @@ -27,11 +27,13 @@ struct rte_cfgfile {
>         struct rte_cfgfile_section *sections;
>  };
>
> +/* Setting up dynamic logging 8< */
>  RTE_LOG_REGISTER_DEFAULT(cfgfile_logtype, INFO);
>
>  #define CFG_LOG(level, fmt, args...)                                   \
>         rte_log(RTE_LOG_ ## level, cfgfile_logtype, "%s(): " fmt "\n",  \
>                 __func__, ## args)
> +/* >8 End of setting up dynamic logging */
>
>  /** when we resize a file structure, how many extra entries
>   * for new sections do we add in */
> --
> 2.39.2
>

Thanks, this doc patch is a good addition in its current form.

Reviewed-by: David Marchand <david.marchand at redhat.com>


Stephen used a little trick with a #define RTE_LOGTYPE_$type
${type}_logtype so that RTE_LOG() is directly usable.
This makes conversion from static to dynamic logtypes rather easy.
Example: https://patchwork.dpdk.org/project/dpdk/patch/20230329234049.11071-5-stephen@networkplumber.org/
It could be something we advertise in this doc later.

Maybe some consistency cleanup (and guidance) would be good too, as
many components have close-yet-somewhat-different log formats (some
log the function name, others write the line number etc...).


-- 
David Marchand