build: add definitions for use as Meson subproject

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

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

drivers/meson.build

@@ -246,6 +246,10 @@ 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 testpmd_sources.length() != 0
             testpmd_drivers_sources += testpmd_sources

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

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 = []
@@ -105,6 +107,10 @@ 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'