kunit: tool: yield output from run_kernel in real time

Currently, `run_kernel()` dumps all the kernel output to a file
(.kunit/test.log) and then opens the file and yields it to callers.
This made it easier to respect the requested timeout, if any.

But it means that we can't yield the results in real time, either to the
parser or to stdout (if --raw_output is set).

This change spins up a background thread to enforce the timeout, which
allows us to yield the kernel output in real time, while also copying it
to the .kunit/test.log file.
It's also careful to ensure that the .kunit/test.log file is complete,
even in the kunit_parser throws an exception/otherwise doesn't consume
every line, see the new `finally` block and unit test.

For example:

$ ./tools/testing/kunit/kunit.py run --arch=x86_64 --raw_output
<configure + build steps>
...
<can now see output from QEMU in real time>

This does not currently have a visible effect when --raw_output is not
passed, as kunit_parser.py currently only outputs everything at the end.
But that could change, and this patch is a necessary step towards
showing parsed test results in real time.

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

tools/testing/kunit/kunit_kernel.py

···
 import os
 import shutil
 import signal
-from typing import Iterator, Optional, Tuple
+import threading
+from typing import Iterator, List, Optional, Tuple
 
 import kunit_config
 import kunit_parser
···
 		if stderr:  # likely only due to build warnings
 			print(stderr.decode())
 
-	def run(self, params, timeout, build_dir, outfile) -> None:
-		pass
+	def start(self, params: List[str], build_dir: str) -> subprocess.Popen:
+		raise RuntimeError('not implemented!')
 
 
 class LinuxSourceTreeOperationsQemu(LinuxSourceTreeOperations):
···
 		kconfig.parse_from_string(self._kconfig)
 		base_kunitconfig.merge_in_entries(kconfig)
 
-	def run(self, params, timeout, build_dir, outfile):
+	def start(self, params: List[str], build_dir: str) -> subprocess.Popen:
 		kernel_path = os.path.join(build_dir, self._kernel_path)
 		qemu_command = ['qemu-system-' + self._qemu_arch,
 				'-nodefaults',
···
 				'-nographic',
 				'-serial stdio'] + self._extra_qemu_params
 		print('Running tests with:\n$', ' '.join(qemu_command))
-		with open(outfile, 'w') as output:
-			process = subprocess.Popen(' '.join(qemu_command),
-						   stdin=subprocess.PIPE,
-						   stdout=output,
-						   stderr=subprocess.STDOUT,
-						   text=True, shell=True)
-		try:
-			process.wait(timeout=timeout)
-		except Exception as e:
-			print(e)
-			process.terminate()
-		return process
+		return subprocess.Popen(' '.join(qemu_command),
+					   stdin=subprocess.PIPE,
+					   stdout=subprocess.PIPE,
+					   stderr=subprocess.STDOUT,
+					   text=True, shell=True)
 
 class LinuxSourceTreeOperationsUml(LinuxSourceTreeOperations):
 	"""An abstraction over command line operations performed on a source tree."""
···
 		kunit_parser.print_with_timestamp(
 			'Starting Kernel with all configs takes a few minutes...')
 
-	def run(self, params, timeout, build_dir, outfile):
+	def start(self, params: List[str], build_dir: str) -> subprocess.Popen:
 		"""Runs the Linux UML binary. Must be named 'linux'."""
 		linux_bin = get_file_path(build_dir, 'linux')
-		outfile = get_outfile_path(build_dir)
-		with open(outfile, 'w') as output:
-			process = subprocess.Popen([linux_bin] + params,
-						   stdin=subprocess.PIPE,
-						   stdout=output,
-						   stderr=subprocess.STDOUT,
-						   text=True)
-			process.wait(timeout)
+		return subprocess.Popen([linux_bin] + params,
+					   stdin=subprocess.PIPE,
+					   stdout=subprocess.PIPE,
+					   stderr=subprocess.STDOUT,
+					   text=True)
 
 def get_kconfig_path(build_dir) -> str:
 	return get_file_path(build_dir, KCONFIG_PATH)
···
 		args.extend(['mem=1G', 'console=tty', 'kunit_shutdown=halt'])
 		if filter_glob:
 			args.append('kunit.filter_glob='+filter_glob)
-		outfile = get_outfile_path(build_dir)
-		self._ops.run(args, timeout, build_dir, outfile)
-		subprocess.call(['stty', 'sane'])
-		with open(outfile, 'r') as file:
-			for line in file:
+
+		process = self._ops.start(args, build_dir)
+		assert process.stdout is not None  # tell mypy it's set
+
+		# Enforce the timeout in a background thread.
+		def _wait_proc():
+			try:
+				process.wait(timeout=timeout)
+			except Exception as e:
+				print(e)
+				process.terminate()
+				process.wait()
+		waiter = threading.Thread(target=_wait_proc)
+		waiter.start()
+
+		output = open(get_outfile_path(build_dir), 'w')
+		try:
+			# Tee the output to the file and to our caller in real time.
+			for line in process.stdout:
+				output.write(line)
 				yield line
+		# This runs even if our caller doesn't consume every line.
+		finally:
+			# Flush any leftover output to the file
+			output.write(process.stdout.read())
+			output.close()
+			process.stdout.close()
+
+			waiter.join()
+			subprocess.call(['stty', 'sane'])
 
 	def signal_handler(self, sig, frame) -> None:
 		logging.error('Build interruption occurred. Cleaning console.')

tools/testing/kunit/kunit_tool_test.py

···
 import itertools
 import json
 import signal
+import subprocess
 import os
 
 import kunit_config
···
 	def test_invalid_arch(self):
 		with self.assertRaisesRegex(kunit_kernel.ConfigError, 'not a valid arch, options are.*x86_64'):
 			kunit_kernel.LinuxSourceTree('', arch='invalid')
+
+	def test_run_kernel_hits_exception(self):
+		def fake_start(unused_args, unused_build_dir):
+			return subprocess.Popen(['echo "hi\nbye"'], shell=True, text=True, stdout=subprocess.PIPE)
+
+		with tempfile.TemporaryDirectory('') as build_dir:
+			tree = kunit_kernel.LinuxSourceTree(build_dir, load_config=False)
+			mock.patch.object(tree._ops, 'start', side_effect=fake_start).start()
+
+			with self.assertRaises(ValueError):
+				for line in tree.run_kernel(build_dir=build_dir):
+					self.assertEqual(line, 'hi\n')
+					raise ValueError('uh oh, did not read all output')
+
+			with open(kunit_kernel.get_outfile_path(build_dir), 'rt') as outfile:
+				self.assertEqual(outfile.read(), 'hi\nbye\n', msg='Missing some output')
 
 	# TODO: add more test cases.