[python/systemd] allow compiling systemd support into python builds (#36037)

Add GRPC_PYTHON_BUILD_WITH_SYSTEMD environment variable to setup.py

The variable sets the required compile time define and adds the required
link time library to the build process

setup.py

@@ -166,6 +166,11 @@ BUILD_WITH_SYSTEM_RE2 = _env_bool_value("GRPC_PYTHON_BUILD_SYSTEM_RE2", "False")
 # runtime, the shared library must be installed
 BUILD_WITH_SYSTEM_ABSL = os.environ.get("GRPC_PYTHON_BUILD_SYSTEM_ABSL", False)
 
+# Export this variable to enable socket activation functions of systemd
+# You need to have the header files installed
+# and during runtime, the shared library must be installed
+BUILD_WITH_SYSTEMD = os.environ.get("GRPC_PYTHON_BUILD_WITH_SYSTEMD", False)
+
 # Export this variable to force building the python extension with a statically linked libstdc++.
 # At least on linux, this is normally not needed as we can build manylinux-compatible wheels on linux just fine
 # without statically linking libstdc++ (which leads to a slight increase in the wheel size).
@@ -278,6 +283,11 @@ if EXTRA_ENV_LINK_ARGS is None:
 if "darwin" in sys.platform:
     EXTRA_ENV_LINK_ARGS += " -framework CoreFoundation"
 
+# Building with systemd socket activation requires defines and libraries.
+if BUILD_WITH_SYSTEMD:
+    EXTRA_ENV_COMPILE_ARGS += " -DHAVE_LIBSYSTEMD"
+    EXTRA_ENV_LINK_ARGS += " -lsystemd"
+
 EXTRA_COMPILE_ARGS = shlex.split(EXTRA_ENV_COMPILE_ARGS)
 EXTRA_LINK_ARGS = shlex.split(EXTRA_ENV_LINK_ARGS)
 

src/python/grpcio/README.rst

@@ -59,6 +59,10 @@ package named :code:`python-dev`).
   $ cd $REPO_ROOT
   $ git submodule update --init
 
+  # To include systemd socket-activation feature in the build,
+  # first install the `libsystemd-dev` package, then :
+  $ export GRPC_PYTHON_BUILD_WITH_SYSTEMD=1
+
   # For the next two commands do `sudo pip install` if you get permission-denied errors
   $ pip install -r requirements.txt
   $ GRPC_PYTHON_BUILD_WITH_CYTHON=1 pip install .