Re: [dpdk-dev] [RFC] build: allow build DPDK as a meson submodule

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Nov 03, 2021 at 03:12:05PM -0700, Stephen Hemminger wrote:
> Some other projects using meson may not be able to use DPDK
> using the standard distribution pkg-config mechanism.
> Meson supports a way to handle this via the subproject
>   https://mesonbuild.com/Subprojects.html
> 
> This patch adds the necessary depedency to follow the
> "Naming convention for depedency variables" from the documentation.
> It has no impact if subproject is not being used.
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

Thanks for this Stephen. Couple of comments inline below.

/Bruce

> ---
>  meson.build | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/meson.build b/meson.build
> index 12cb6e0e83f3..6ce5eda2779f 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -97,6 +97,16 @@ configure_file(output: build_cfg,
>  # build pkg-config files for dpdk
>  subdir('buildtools/pkg-config')
>  
> +# If DPDK is being built as subproject then define
> +# varialble with the dependency convention
> +if meson.is_subproject()

I wonder if we should just omit this check. Defining the extra variable in
case of non-subproject should just be harmless.

> +    libdpdk_dep = declare_dependency(
> +        version: meson.project_version(),
> +        compile_args : pkg_extra_cflags,
> +        dependencies: shared_deps
> +    )

"shared_deps" is almost certainly not the correct variable to use here
without additional changes to guarantee its value. That variable is used in
lib and driver meson.build files to hold the libraries to link for each
shared object, so at this point in the build, it will likely contain only
the dependencies of the final driver built, rather than all the DPDK
libraries. I think it would be safer to define "dpdk_shared_deps" global
variable at the top of this meson.build file and add to that from
lib/meson.build as each library dependency is defined.

> +endif
> +