Re: [PATCH] build/eal: add OS defines for C conditional checks

[Jerin Jacob <jerinjacobk@gmail.com>]

On Fri, Dec 10, 2021 at 8:23 PM Bruce Richardson
<bruce.richardson@intel.com> wrote:
>
> Define a set of macros in the build configuration to allow C runtime
> code to check the current OS environment. This saves the user having to
> use ifdefs for e.g. disabling particular tests on Windows. See included
> documentation changes for usage examples.
>
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>

Acked-by: Jerin Jacob <jerinj@marvell.com>


> ---
>  doc/guides/contributing/coding_style.rst | 42 ++++++++++++++++++++++--
>  lib/eal/meson.build                      |  7 ++++
>  2 files changed, 47 insertions(+), 2 deletions(-)
>
> diff --git a/doc/guides/contributing/coding_style.rst b/doc/guides/contributing/coding_style.rst
> index 0ec37c019b..e52ecb2b60 100644
> --- a/doc/guides/contributing/coding_style.rst
> +++ b/doc/guides/contributing/coding_style.rst
> @@ -136,6 +136,12 @@ For example:
>  Conditional Compilation
>  ~~~~~~~~~~~~~~~~~~~~~~~
>
> +.. note::
> +
> + Conditional compilation should be used only when absolutely necessary, as it increases the number of target binaries that need to be built and tested.
> + See below for details of some utility macros/defines available to allow ifdefs/macros to be replaced by C conditional in some cases.
> +
> +
>  * When code is conditionally compiled using ``#ifdef`` or ``#if``, a comment may be added following the matching
>    ``#endif`` or ``#else`` to permit the reader to easily discern where conditionally compiled code regions end.
>  * This comment should be used only for (subjectively) long regions, regions greater than 20 lines, or where a series of nested ``#ifdef``'s may be confusing to the reader.
> @@ -165,9 +171,41 @@ Conditional Compilation
>   /* Or here. */
>   #endif /* !COMPAT_43 */
>
> -.. note::
> +Defines to Avoid Conditional Compilation
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +In many cases in DPDK, one wants to optionally compile code based on the target platform,
> +or runtime environment.
> +While this can be done using the conditional compilation directives,
> +e.g. ``#ifdef RTE_EXEC_ENV_LINUX``, present in DPDK for many releases,
> +this can also be done in many cases using regular ``if`` statements and the following defines:
> +
> +* ``RTE_ENV_FREEBSD``, ``RTE_ENV_LINUX``, ``RTE_ENV_WINDOWS`` - these define ids for each operating system environment.
> +* ``RTE_EXEC_ENV`` - this defines the id of the current environment, i.e. one of the items in list above.
> +* ``RTE_EXEC_ENV_IS_FREEBSD``, ``RTE_EXEC_ENV_IS_LINUX``, ``RTE_EXEC_ENV_IS_WINDOWS`` - 0/1 values indicating if the current environment is that specified,
> +  shortcuts for checking e.g. ``RTE_EXEC_ENV == RTE_ENV_WINDOWS``
> +
> +Examples of use:
> +
> +.. code-block:: c
> +
> +  /* report a unit tests as unsupported on Windows */
> +  if (RTE_EXEC_ENV_IS_WINDOWS)
> +     return TEST_SKIPPED;
> +
> +  /* set different default values depending on OS Environment */
> +  switch (RTE_EXEC_ENV) {
> +     case RTE_ENV_FREEBSD:
> +         default = x;
> +         break;
> +     case RTE_ENV_LINUX:
> +         default = y;
> +         break;
> +     case RTE_ENV_WINDOWS:
> +         default = z;
> +         break;
> +  }
>
> - Conditional compilation should be used only when absolutely necessary, as it increases the number of target binaries that need to be built and tested.
>
>  C Types
>  -------
> diff --git a/lib/eal/meson.build b/lib/eal/meson.build
> index 1722924f67..056beb9461 100644
> --- a/lib/eal/meson.build
> +++ b/lib/eal/meson.build
> @@ -10,6 +10,13 @@ if not is_windows
>      subdir('unix')
>  endif
>
> +exec_envs = {'freebsd': 0, 'linux': 1, 'windows': 2}
> +foreach env, id:exec_envs
> +    dpdk_conf.set('RTE_ENV_' + env.to_upper(), id)
> +    dpdk_conf.set10('RTE_EXEC_ENV_IS_' + env.to_upper(), (exec_env == env))
> +endforeach
> +dpdk_conf.set('RTE_EXEC_ENV', exec_envs[exec_env])
> +
>  dpdk_conf.set('RTE_EXEC_ENV_' + exec_env.to_upper(), 1)
>  subdir(exec_env)
>
> --
> 2.32.0
>