Currently utilizing this in an upcoming set of changes for TLDK and all
seems to be working for fallback dependency support under both shared and
static linkage.

Reviewed-by: Ben Magistro <koncept1@gmail.com>
Tested-by: Ben Magistro <koncept1@gmail.com>

On Fri, May 6, 2022 at 10:43 AM Bruce Richardson <bruce.richardson@intel.com>
wrote:

> To allow other projects to easily use DPDK as a subproject, add in the
> necessary dependency definitions. Slightly different definitions are
> necessary for static and shared builds, since for shared builds the
> drivers should not be linked in, and the internal meson dependency
> objects are more complete.
>
> To use DPDK as a subproject fallback i.e. use installed DPDK if present,
> otherwise the shipped one, the following meson statement can be used:
>
> libdpdk = dependency('libdpdk', fallback: ['dpdk', 'dpdk_dep'])
>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---
>  buildtools/subproject/meson.build | 21 +++++++++++++++++++++
>  drivers/meson.build               |  4 ++++
>  lib/meson.build                   |  2 ++
>  meson.build                       |  6 ++++++
>  4 files changed, 33 insertions(+)
>  create mode 100644 buildtools/subproject/meson.build
>
> diff --git a/buildtools/subproject/meson.build
> b/buildtools/subproject/meson.build
> new file mode 100644
> index 0000000000..3192efaa40
> --- /dev/null
> +++ b/buildtools/subproject/meson.build
> @@ -0,0 +1,21 @@
> +# SPDX-License-Identifier: BSD-3-Clause
> +# Copyright(c) 2022 Intel Corporation
> +
> +message('DPDK subproject linking: ' + get_option('default_library'))
> +if get_option('default_library') == 'static'
> +    dpdk_dep = declare_dependency(
> +            version: meson.project_version(),
> +            dependencies: dpdk_static_lib_deps,
> +            # static library deps in DPDK build don't include "link_with"
> parameters,
> +            # so explicitly link-in both libs and drivers
> +            link_with: dpdk_static_libraries,
> +            link_whole: dpdk_drivers,
> +            link_args: dpdk_extra_ldflags)
> +else
> +    dpdk_dep = declare_dependency(
> +            version: meson.project_version(),
> +            # shared library deps include all necessary linking parameters
> +            dependencies: dpdk_shared_lib_deps)
> +endif
> +
> +libdpdk_dep = dpdk_dep
> diff --git a/drivers/meson.build b/drivers/meson.build
> index 1d8123b00c..db4d9c73bd 100644
> --- a/drivers/meson.build
> +++ b/drivers/meson.build
> @@ -245,6 +245,10 @@ foreach subpath:subdirs
>
>          set_variable('shared_@0@'.format(lib_name), shared_dep)
>          set_variable('static_@0@'.format(lib_name), static_dep)
> +        # for drivers, we only need to add dependency objects for static
> libs,
> +        # shared lib drivers are not linked in
> +        dpdk_static_lib_deps += static_dep
> +
>          dependency_name = ''.join(lib_name.split('rte_'))
>          if developer_mode
>              message('drivers/@0@: Defining dependency "@1@"'.format(
> diff --git a/lib/meson.build b/lib/meson.build
> index 24adbe44c9..c648f7d800 100644
> --- a/lib/meson.build
> +++ b/lib/meson.build
> @@ -266,6 +266,8 @@ foreach l:libraries
>
>      set_variable('shared_rte_' + name, shared_dep)
>      set_variable('static_rte_' + name, static_dep)
> +    dpdk_shared_lib_deps += shared_dep
> +    dpdk_static_lib_deps += static_dep
>      if developer_mode
>          message('lib/@0@: Defining dependency "@1@"'.format(l, name))
>      endif
> diff --git a/meson.build b/meson.build
> index 937f6110c0..6085e32a79 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -36,6 +36,8 @@ dpdk_build_root = meson.current_build_dir()
>  dpdk_conf = configuration_data()
>  dpdk_libraries = []
>  dpdk_static_libraries = []
> +dpdk_shared_lib_deps = []
> +dpdk_static_lib_deps = []
>  dpdk_chkinc_headers = []
>  dpdk_driver_classes = []
>  dpdk_drivers = []
> @@ -103,6 +105,10 @@ configure_file(output: build_cfg,
>  # build pkg-config files for dpdk
>  subdir('buildtools/pkg-config')
>
> +if meson.is_subproject()
> +    subdir('buildtools/subproject')
> +endif
> +
>  # final output, list all the libs and drivers to be built
>  # this does not affect any part of the build, for information only.
>  output_message = '\n=================\nLibraries
> Enabled\n=================\n'
> --
> 2.34.1
>
>