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

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

On Thu, Nov 04, 2021 at 05:01:24PM -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 dependency to follow the
> "Naming convention for dependency variables" from the documentation.
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
> Cleaned up from RFC and support both static and shared.
> 
>  lib/meson.build |  5 +++++
>  meson.build     | 12 ++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/lib/meson.build b/lib/meson.build
> index 499d26060fdd..e6df538bd6ef 100644
> --- a/lib/meson.build
> +++ b/lib/meson.build
> @@ -241,6 +241,11 @@ foreach l:libraries
>  
>      dpdk_libraries = [shared_lib] + dpdk_libraries
>      dpdk_static_libraries = [static_lib] + dpdk_static_libraries
> +    if get_option('default_library') == 'static'
> +        dpdk_libs_deps += static_dep
> +    else
> +        dpdk_libs_deps += shared_dep
> +    endif
>  
>      set_variable('shared_rte_' + name, shared_dep)
>      set_variable('static_rte_' + name, static_dep)
> diff --git a/meson.build b/meson.build
> index 12cb6e0e83f3..032783e4e6cf 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -36,6 +36,7 @@ dpdk_drivers = []
>  dpdk_extra_ldflags = []
>  dpdk_libs_disabled = []
>  dpdk_drvs_disabled = []
> +dpdk_libs_deps = []
>  abi_version_file = files('ABI_VERSION')
>  
>  if host_machine.cpu_family().startswith('x86')
> @@ -97,6 +98,17 @@ configure_file(output: build_cfg,
>  # build pkg-config files for dpdk
>  subdir('buildtools/pkg-config')
>  
> +# If DPDK is being built as subproject then define
> +# variable with the dependency convention
> +if meson.is_subproject()
> +    libdpdk_dep = declare_dependency(
> +        version: meson.project_version(),
> +        compile_args : pkg_extra_cflags,
> +        dependencies: dpdk_libs_deps,
> +        link_args: dpdk_extra_ldflags,
> +    )
> +endif
> +

While the code all looks correct to me, when I tested it out, the resulting
app couldn't link. I tested by moving l2fwd/main.c to a new folder and
adding the following as a meson.build file in it:

  project('l2fwd', 'C')

  dpdk_dep = dependency('libdpdk', fallback : ['libdpdk', 'libdpdk_dep'])
  executable('dpdk-l2fwd', 'main.c',
          dependencies: dpdk_dep)

Even though dependencies should include both the libs to link with and the
include paths, that didn't seem to work in this case - the compile worked
fine with all cflags present, none of the DPDK libraries were given on the
link command - just the extra -ldl etc. args.
Adding "link_with: dpdk_libraries" fixed this and allowed it work for me,
but I'm surpised that it proved necessary. Stephen, does it work for you
with just the dependencies provided?

/Bruce

PS: My testing was done with meson 0.56.2 on Ubuntu 21.10.