kunit: tool: make --kunitconfig repeatable, blindly concat

It's come up a few times that it would be useful to have --kunitconfig
be repeatable [1][2].

This could be done before with a bit of shell-fu, e.g.
$ find fs/ -name '.kunitconfig' -exec cat {} + | \
./tools/testing/kunit/kunit.py run --kunitconfig=/dev/stdin
or equivalently:
$ cat fs/ext4/.kunitconfig fs/fat/.kunitconfig | \
./tools/testing/kunit/kunit.py run --kunitconfig=/dev/stdin

But this can be fairly clunky to use in practice.

And having explicit support in kunit.py opens the door to having more
config fragments of interest, e.g. options for PCI on UML [1], UML
coverage [2], variants of tests [3].
There's another argument to be made that users can just use multiple
--kconfig_add's, but this gets very clunky very fast (e.g. [2]).

Note: there's a big caveat here that some kconfig options might be
incompatible. We try to give a clearish error message in the simple case
where the same option appears multiple times with conflicting values,
but more subtle ones (e.g. mutually exclusive options) will be
potentially very confusing for the user. I don't know we can do better.

Note 2: if you want to combine a --kunitconfig with the default, you
either have to do to specify the current build_dir
> --kunitconfig=.kunit --kunitconfig=additional.config
or
> --kunitconfig=tools/testing/kunit/configs/default.config --kunitconifg=additional.config
each of which have their downsides (former depends on --build_dir,
doesn't work if you don't have a .kunitconfig yet), etc.

Example with conflicting values:
> $ ./tools/testing/kunit/kunit.py config --kunitconfig=lib/kunit --kunitconfig=/dev/stdin <<EOF
> CONFIG_KUNIT_TEST=n
> CONFIG_KUNIT=m
> EOF
> ...
> kunit_kernel.ConfigError: Multiple values specified for 2 options in kunitconfig:
> CONFIG_KUNIT=y
> vs from /dev/stdin
> CONFIG_KUNIT=m
>
> CONFIG_KUNIT_TEST=y
> vs from /dev/stdin
> # CONFIG_KUNIT_TEST is not set

[1] https://lists.freedesktop.org/archives/dri-devel/2022-June/357616.html
[2] https://lore.kernel.org/linux-kselftest/[e-mail]/
[3] https://lore.kernel.org/linux-kselftest/[e-mail]/

Signed-off-by: Daniel Latypov <[e-mail]>
Reviewed-by: Brendan Higgins <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/kunit/kunit.py

···
 	parser.add_argument('--kunitconfig',
 			     help='Path to Kconfig fragment that enables KUnit tests.'
 			     ' If given a directory, (e.g. lib/kunit), "/.kunitconfig" '
-			     'will get  automatically appended.',
-			     metavar='PATH')
+			     'will get  automatically appended. If repeated, the files '
+			     'blindly concatenated, which might not work in all cases.',
+			     action='append', metavar='PATHS')
 	parser.add_argument('--kconfig_add',
 			     help='Additional Kconfig options to append to the '
 			     '.kunitconfig, e.g. CONFIG_KASAN=y. Can be repeated.',
···
 			qemu_args.extend(shlex.split(arg))
 
 	return kunit_kernel.LinuxSourceTree(cli_args.build_dir,
-			kunitconfig_path=cli_args.kunitconfig,
+			kunitconfig_paths=cli_args.kunitconfig,
 			kconfig_add=cli_args.kconfig_add,
 			arch=cli_args.arch,
 			cross_compile=cli_args.cross_compile,

tools/testing/kunit/kunit_config.py

···
 
 from dataclasses import dataclass
 import re
-from typing import Dict, Iterable, Set
+from typing import Dict, Iterable, List, Set, Tuple
 
 CONFIG_IS_NOT_SET_PATTERN = r'^# CONFIG_(\w+) is not set$'
 CONFIG_PATTERN = r'^CONFIG_(\w+)=(\S+|".*")$'
···
 			if value != b:
 				return False
 		return True
+
+	def conflicting_options(self, other: 'Kconfig') -> List[Tuple[KconfigEntry, KconfigEntry]]:
+		diff = []  # type: List[Tuple[KconfigEntry, KconfigEntry]]
+		for name, value in self._entries.items():
+			b = other._entries.get(name)
+			if b and value != b:
+				pair = (KconfigEntry(name, value), KconfigEntry(name, b))
+				diff.append(pair)
+		return diff
 
 	def merge_in_entries(self, other: 'Kconfig') -> None:
 		for name, value in other._entries.items():

tools/testing/kunit/kunit_kernel.py

···
 def get_old_kunitconfig_path(build_dir: str) -> str:
 	return os.path.join(build_dir, OLD_KUNITCONFIG_PATH)
 
+def get_parsed_kunitconfig(build_dir: str,
+			   kunitconfig_paths: Optional[List[str]]=None) -> kunit_config.Kconfig:
+	if not kunitconfig_paths:
+		path = get_kunitconfig_path(build_dir)
+		if not os.path.exists(path):
+			shutil.copyfile(DEFAULT_KUNITCONFIG_PATH, path)
+		return kunit_config.parse_file(path)
+
+	merged = kunit_config.Kconfig()
+
+	for path in kunitconfig_paths:
+		if os.path.isdir(path):
+			path = os.path.join(path, KUNITCONFIG_PATH)
+		if not os.path.exists(path):
+			raise ConfigError(f'Specified kunitconfig ({path}) does not exist')
+
+		partial = kunit_config.parse_file(path)
+		diff = merged.conflicting_options(partial)
+		if diff:
+			diff_str = '\n\n'.join(f'{a}\n  vs from {path}\n{b}' for a, b in diff)
+			raise ConfigError(f'Multiple values specified for {len(diff)} options in kunitconfig:\n{diff_str}')
+		merged.merge_in_entries(partial)
+	return merged
+
 def get_outfile_path(build_dir: str) -> str:
 	return os.path.join(build_dir, OUTFILE_PATH)
 
···
 	def __init__(
 	      self,
 	      build_dir: str,
-	      kunitconfig_path='',
+	      kunitconfig_paths: Optional[List[str]]=None,
 	      kconfig_add: Optional[List[str]]=None,
 	      arch=None,
 	      cross_compile=None,
···
 				qemu_config_path = _default_qemu_config_path(self._arch)
 				_, self._ops = _get_qemu_ops(qemu_config_path, extra_qemu_args, cross_compile)
 
-		if kunitconfig_path:
-			if os.path.isdir(kunitconfig_path):
-				kunitconfig_path = os.path.join(kunitconfig_path, KUNITCONFIG_PATH)
-			if not os.path.exists(kunitconfig_path):
-				raise ConfigError(f'Specified kunitconfig ({kunitconfig_path}) does not exist')
-		else:
-			kunitconfig_path = get_kunitconfig_path(build_dir)
-			if not os.path.exists(kunitconfig_path):
-				shutil.copyfile(DEFAULT_KUNITCONFIG_PATH, kunitconfig_path)
-
-		self._kconfig = kunit_config.parse_file(kunitconfig_path)
+		self._kconfig = get_parsed_kunitconfig(build_dir, kunitconfig_paths)
 		if kconfig_add:
 			kconfig = kunit_config.parse_from_string('\n'.join(kconfig_add))
 			self._kconfig.merge_in_entries(kconfig)

tools/testing/kunit/kunit_tool_test.py

···
 
 	def test_invalid_kunitconfig(self):
 		with self.assertRaisesRegex(kunit_kernel.ConfigError, 'nonexistent.* does not exist'):
-			kunit_kernel.LinuxSourceTree('', kunitconfig_path='/nonexistent_file')
+			kunit_kernel.LinuxSourceTree('', kunitconfig_paths=['/nonexistent_file'])
 
 	def test_valid_kunitconfig(self):
 		with tempfile.NamedTemporaryFile('wt') as kunitconfig:
-			kunit_kernel.LinuxSourceTree('', kunitconfig_path=kunitconfig.name)
+			kunit_kernel.LinuxSourceTree('', kunitconfig_paths=[kunitconfig.name])
 
 	def test_dir_kunitconfig(self):
 		with tempfile.TemporaryDirectory('') as dir:
 			with open(os.path.join(dir, '.kunitconfig'), 'w'):
 				pass
-			kunit_kernel.LinuxSourceTree('', kunitconfig_path=dir)
+			kunit_kernel.LinuxSourceTree('', kunitconfig_paths=[dir])
+
+	def test_multiple_kunitconfig(self):
+		want_kconfig = kunit_config.Kconfig()
+		want_kconfig.add_entry('KUNIT', 'y')
+		want_kconfig.add_entry('KUNIT_TEST', 'm')
+
+		with tempfile.TemporaryDirectory('') as dir:
+			other = os.path.join(dir, 'otherkunitconfig')
+			with open(os.path.join(dir, '.kunitconfig'), 'w') as f:
+				f.write('CONFIG_KUNIT=y')
+			with open(other, 'w') as f:
+				f.write('CONFIG_KUNIT_TEST=m')
+				pass
+
+			tree = kunit_kernel.LinuxSourceTree('', kunitconfig_paths=[dir, other])
+			self.assertTrue(want_kconfig.is_subset_of(tree._kconfig), msg=tree._kconfig)
+
+
+	def test_multiple_kunitconfig_invalid(self):
+		with tempfile.TemporaryDirectory('') as dir:
+			other = os.path.join(dir, 'otherkunitconfig')
+			with open(os.path.join(dir, '.kunitconfig'), 'w') as f:
+				f.write('CONFIG_KUNIT=y')
+			with open(other, 'w') as f:
+				f.write('CONFIG_KUNIT=m')
+
+			with self.assertRaisesRegex(kunit_kernel.ConfigError, '(?s)Multiple values.*CONFIG_KUNIT'):
+				kunit_kernel.LinuxSourceTree('', kunitconfig_paths=[dir, other])
+
 
 	def test_kconfig_add(self):
 		want_kconfig = kunit_config.Kconfig()
···
 		kunit.main(['run', '--kunitconfig=mykunitconfig'])
 		# Just verify that we parsed and initialized it correctly here.
 		self.mock_linux_init.assert_called_once_with('.kunit',
-						kunitconfig_path='mykunitconfig',
+						kunitconfig_paths=['mykunitconfig'],
 						kconfig_add=None,
 						arch='um',
 						cross_compile=None,
···
 		kunit.main(['config', '--kunitconfig=mykunitconfig'])
 		# Just verify that we parsed and initialized it correctly here.
 		self.mock_linux_init.assert_called_once_with('.kunit',
-						kunitconfig_path='mykunitconfig',
+						kunitconfig_paths=['mykunitconfig'],
 						kconfig_add=None,
 						arch='um',
 						cross_compile=None,
 						qemu_config_path=None,
 						extra_qemu_args=[])
 
+	@mock.patch.object(kunit_kernel, 'LinuxSourceTree')
+	def test_run_multiple_kunitconfig(self, mock_linux_init):
+		mock_linux_init.return_value = self.linux_source_mock
+		kunit.main(['run', '--kunitconfig=mykunitconfig', '--kunitconfig=other'])
+		# Just verify that we parsed and initialized it correctly here.
+		mock_linux_init.assert_called_once_with('.kunit',
+							kunitconfig_paths=['mykunitconfig', 'other'],
+							kconfig_add=None,
+							arch='um',
+							cross_compile=None,
+							qemu_config_path=None,
+							extra_qemu_args=[])
+
 	def test_run_kconfig_add(self):
 		kunit.main(['run', '--kconfig_add=CONFIG_KASAN=y', '--kconfig_add=CONFIG_KCSAN=y'])
 		# Just verify that we parsed and initialized it correctly here.
 		self.mock_linux_init.assert_called_once_with('.kunit',
-						kunitconfig_path=None,
+						kunitconfig_paths=None,
 						kconfig_add=['CONFIG_KASAN=y', 'CONFIG_KCSAN=y'],
 						arch='um',
 						cross_compile=None,
···
 		kunit.main(['run', '--arch=x86_64', '--qemu_args', '-m 2048'])
 		# Just verify that we parsed and initialized it correctly here.
 		self.mock_linux_init.assert_called_once_with('.kunit',
-						kunitconfig_path=None,
+						kunitconfig_paths=None,
 						kconfig_add=None,
 						arch='x86_64',
 						cross_compile=None,