kunit: tool: add --kconfig_add to allow easily tweaking kunitconfigs

E.g. run tests but with KASAN
$ ./tools/testing/kunit/kunit.py run --arch=x86_64 --kconfig_add=CONFIG_KASAN=y

This also works with --kunitconfig
$ ./tools/testing/kunit/kunit.py run --arch=x86_64 --kunitconfig=fs/ext4 --kconfig_add=CONFIG_KASAN=y

This flag is inspired by TuxMake's --kconfig-add, see
https://gitlab.com/Linaro/tuxmake#examples.

Our version just uses "_" as the delimiter for consistency with
pre-existing flags like --build_dir, --make_options, --kernel_args, etc.

Note: this does make it easier to run into a pre-existing edge case:
$ ./tools/testing/kunit/kunit.py run --arch=x86_64 --kconfig_add=CONFIG_KASAN=y
$ ./tools/testing/kunit/kunit.py run --arch=x86_64
This second invocation ^ still has KASAN enabled!

kunit.py won't call olddefconfig if our current .config is already a
superset of the provided kunitconfig.

Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/kunit/kunit_kernel.py

@@ -224,6 +224,7 @@ class LinuxSourceTree(object):
 	      build_dir: str,
 	      load_config=True,
 	      kunitconfig_path='',
+	      kconfig_add: Optional[List[str]]=None,
 	      arch=None,
 	      cross_compile=None,
 	      qemu_config_path=None) -> None:
@@ -249,6 +250,10 @@ class LinuxSourceTree(object):
 				shutil.copyfile(DEFAULT_KUNITCONFIG_PATH, kunitconfig_path)
 
 		self._kconfig = kunit_config.parse_file(kunitconfig_path)
+		if kconfig_add:
+			kconfig = kunit_config.parse_from_string('\n'.join(kconfig_add))
+			self._kconfig.merge_in_entries(kconfig)
+
 
 	def clean(self) -> bool:
 		try: