[GIT PULL] KUnit next update for Linux 6.3-rc1

[Shuah Khan]

Hi Linus,

Please pull the following KUnit next update for Linux 6.3-rc1.

This KUnit update for Linux 6.3-rc1 consists of cleanups, new features,
and documentation updates:

-- adds Function Redirection API to isolate the code being tested from
   other parts of the kernel. functionredirection.rst has the details.

diff is attached.

thanks,
-- Shuah

----------------------------------------------------------------
The following changes since commit 4ec5183ec48656cec489c49f989c508b68b518e3:

  Linux 6.2-rc7 (2023-02-05 13:13:28 -0800)

are available in the Git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest tags/linux-kselftest-kunit-6.3-rc1

for you to fetch changes up to 82649c7c0da431d147a75c6ae768ee42c1053f53:

  kunit: Add printf attribute to fail_current_test_impl (2023-02-08 18:08:14 -0700)

----------------------------------------------------------------
linux-kselftest-kunit-6.3-rc1

This KUnit update for Linux 6.3-rc1 consists of cleanups, new features,
and documentation updates:

-- adds Function Redirection API to isolate the code being tested from
   other parts of the kernel. functionredirection.rst has the details.

----------------------------------------------------------------
Alexander Pantyukhin (2):
      tools/testing/kunit/kunit.py: remove redundant double check
      kunit: kunit.py extract handlers

David Gow (3):
      kunit: Add "hooks" to call into KUnit when it's built as a module
      kunit: Expose 'static stub' API to redirect functions
      kunit: Add printf attribute to fail_current_test_impl

Rae Moar (1):
      lib/hashtable_test.c: add test for the hashtable structure

Sadiya Kazi (1):
      Documentation: Add Function Redirection API docs

 .../dev-tools/kunit/api/functionredirection.rst    | 162 +++++++++++
 Documentation/dev-tools/kunit/api/index.rst        |  13 +-
 Documentation/dev-tools/kunit/usage.rst            |  15 +-
 include/kunit/static_stub.h                        | 113 ++++++++
 include/kunit/test-bug.h                           |  29 +-
 lib/Kconfig.debug                                  |  13 +
 lib/Makefile                                       |   9 +
 lib/hashtable_test.c                               | 317 +++++++++++++++++++++
 lib/kunit/Makefile                                 |   4 +
 lib/kunit/hooks-impl.h                             |  31 ++
 lib/kunit/hooks.c                                  |  21 ++
 lib/kunit/kunit-example-test.c                     |  38 +++
 lib/kunit/static_stub.c                            | 123 ++++++++
 lib/kunit/test.c                                   |  15 +-
 tools/testing/kunit/kunit.py                       | 186 ++++++------
 15 files changed, 966 insertions(+), 123 deletions(-)
 create mode 100644 Documentation/dev-tools/kunit/api/functionredirection.rst
 create mode 100644 include/kunit/static_stub.h
 create mode 100644 lib/hashtable_test.c
 create mode 100644 lib/kunit/hooks-impl.h
 create mode 100644 lib/kunit/hooks.c
 create mode 100644 lib/kunit/static_stub.c
----------------------------------------------------------------diff --git a/Documentation/dev-tools/kunit/api/functionredirection.rst b/Documentation/dev-tools/kunit/api/functionredirection.rst
new file mode 100644
index 000000000000..3791efc2fcca
--- /dev/null
+++ b/Documentation/dev-tools/kunit/api/functionredirection.rst
@@ -0,0 +1,162 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========================
+Function Redirection API
+========================
+
+Overview
+========
+
+When writing unit tests, it's important to be able to isolate the code being
+tested from other parts of the kernel. This ensures the reliability of the test
+(it won't be affected by external factors), reduces dependencies on specific
+hardware or config options (making the test easier to run), and protects the
+stability of the rest of the system (making it less likely for test-specific
+state to interfere with the rest of the system).
+
+While for some code (typically generic data structures, helpers, and other
+"pure functions") this is trivial, for others (like device drivers,
+filesystems, core subsystems) the code is heavily coupled with other parts of
+the kernel.
+
+This coupling is often due to global state in some way: be it a global list of
+devices, the filesystem, or some hardware state. Tests need to either carefully
+manage, isolate, and restore state, or they can avoid it altogether by
+replacing access to and mutation of this state with a "fake" or "mock" variant.
+
+By refactoring access to such state, such as by introducing a layer of
+indirection which can use or emulate a separate set of test state. However,
+such refactoring comes with its own costs (and undertaking significant
+refactoring before being able to write tests is suboptimal).
+
+A simpler way to intercept and replace some of the function calls is to use
+function redirection via static stubs.
+
+
+Static Stubs
+============
+
+Static stubs are a way of redirecting calls to one function (the "real"
+function) to another function (the "replacement" function).
+
+It works by adding a macro to the "real" function which checks to see if a test
+is running, and if a replacement function is available. If so, that function is
+called in place of the original.
+
+Using static stubs is pretty straightforward:
+
+1. Add the KUNIT_STATIC_STUB_REDIRECT() macro to the start of the "real"
+   function.
+
+   This should be the first statement in the function, after any variable
+   declarations. KUNIT_STATIC_STUB_REDIRECT() takes the name of the
+   function, followed by all of the arguments passed to the real function.
+
+   For example:
+
+   .. code-block:: c
+
+	void send_data_to_hardware(const char *str)
+	{
+		KUNIT_STATIC_STUB_REDIRECT(send_data_to_hardware, str);
+		/* real implementation */
+	}
+
+2. Write one or more replacement functions.
+
+   These functions should have the same function signature as the real function.
+   In the event they need to access or modify test-specific state, they can use
+   kunit_get_current_test() to get a struct kunit pointer. This can then
+   be passed to the expectation/assertion macros, or used to look up KUnit
+   resources.
+
+   For example:
+
+   .. code-block:: c
+
+	void fake_send_data_to_hardware(const char *str)
+	{
+		struct kunit *test = kunit_get_current_test();
+		KUNIT_EXPECT_STREQ(test, str, "Hello World!");
+	}
+
+3. Activate the static stub from your test.
+
+   From within a test, the redirection can be enabled with
+   kunit_activate_static_stub(), which accepts a struct kunit pointer,
+   the real function, and the replacement function. You can call this several
+   times with different replacement functions to swap out implementations of the
+   function.
+
+   In our example, this would be
+
+   .. code-block:: c
+
+	kunit_activate_static_stub(test,
+				   send_data_to_hardware,
+				   fake_send_data_to_hardware);
+
+4. Call (perhaps indirectly) the real function.
+
+   Once the redirection is activated, any call to the real function will call
+   the replacement function instead. Such calls may be buried deep in the
+   implementation of another function, but must occur from the test's kthread.
+
+   For example:
+
+   .. code-block:: c
+
+	send_data_to_hardware("Hello World!"); /* Succeeds */
+	send_data_to_hardware("Something else"); /* Fails the test. */
+
+5. (Optionally) disable the stub.
+
+   When you no longer need it, disable the redirection (and hence resume the
+   original behaviour of the 'real' function) using
+   kunit_deactivate_static_stub(). Otherwise, it will be automatically disabled
+   when the test exits.
+
+   For example:
+
+   .. code-block:: c
+
+	kunit_deactivate_static_stub(test, send_data_to_hardware);
+
+
+It's also possible to use these replacement functions to test to see if a
+function is called at all, for example:
+
+.. code-block:: c
+
+	void send_data_to_hardware(const char *str)
+	{
+		KUNIT_STATIC_STUB_REDIRECT(send_data_to_hardware, str);
+		/* real implementation */
+	}
+
+	/* In test file */
+	int times_called = 0;
+	void fake_send_data_to_hardware(const char *str)
+	{
+		times_called++;
+	}
+	...
+	/* In the test case, redirect calls for the duration of the test */
+	kunit_activate_static_stub(test, send_data_to_hardware, fake_send_data_to_hardware);
+
+	send_data_to_hardware("hello");
+	KUNIT_EXPECT_EQ(test, times_called, 1);
+
+	/* Can also deactivate the stub early, if wanted */
+	kunit_deactivate_static_stub(test, send_data_to_hardware);
+
+	send_data_to_hardware("hello again");
+	KUNIT_EXPECT_EQ(test, times_called, 1);
+
+
+
+API Reference
+=============
+
+.. kernel-doc:: include/kunit/static_stub.h
+   :internal:
diff --git a/Documentation/dev-tools/kunit/api/index.rst b/Documentation/dev-tools/kunit/api/index.rst
index 45ce04823f9f..2d8f756aab56 100644
--- a/Documentation/dev-tools/kunit/api/index.rst
+++ b/Documentation/dev-tools/kunit/api/index.rst
@@ -4,17 +4,24 @@
 API Reference
 =============
 .. toctree::
+	:hidden:
 
 	test
 	resource
+	functionredirection
 
-This section documents the KUnit kernel testing API. It is divided into the
+
+This page documents the KUnit kernel testing API. It is divided into the
 following sections:
 
 Documentation/dev-tools/kunit/api/test.rst
 
- - documents all of the standard testing API
+ - Documents all of the standard testing API
 
 Documentation/dev-tools/kunit/api/resource.rst
 
- - documents the KUnit resource API
+ - Documents the KUnit resource API
+
+Documentation/dev-tools/kunit/api/functionredirection.rst
+
+ - Documents the KUnit Function Redirection API
diff --git a/Documentation/dev-tools/kunit/usage.rst b/Documentation/dev-tools/kunit/usage.rst
index 48f8196d5aad..9faf2b4153fc 100644
--- a/Documentation/dev-tools/kunit/usage.rst
+++ b/Documentation/dev-tools/kunit/usage.rst
@@ -648,10 +648,9 @@ We can do this via the ``kunit_test`` field in ``task_struct``, which we can
 access using the ``kunit_get_current_test()`` function in ``kunit/test-bug.h``.
 
 ``kunit_get_current_test()`` is safe to call even if KUnit is not enabled. If
-KUnit is not enabled, was built as a module (``CONFIG_KUNIT=m``), or no test is
-running in the current task, it will return ``NULL``. This compiles down to
-either a no-op or a static key check, so will have a negligible performance
-impact when no test is running.
+KUnit is not enabled, or if no test is running in the current task, it will
+return ``NULL``. This compiles down to either a no-op or a static key check,
+so will have a negligible performance impact when no test is running.
 
 The example below uses this to implement a "mock" implementation of a function, ``foo``:
 
@@ -726,8 +725,6 @@ structures as shown below:
 	#endif
 
 ``kunit_fail_current_test()`` is safe to call even if KUnit is not enabled. If
-KUnit is not enabled, was built as a module (``CONFIG_KUNIT=m``), or no test is
-running in the current task, it will do nothing. This compiles down to either a
-no-op or a static key check, so will have a negligible performance impact when
-no test is running.
-
+KUnit is not enabled, or if no test is running in the current task, it will do
+nothing. This compiles down to either a no-op or a static key check, so will
+have a negligible performance impact when no test is running.
diff --git a/include/kunit/static_stub.h b/include/kunit/static_stub.h
new file mode 100644
index 000000000000..9b80150a5d62
--- /dev/null
+++ b/include/kunit/static_stub.h
@@ -0,0 +1,113 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * KUnit function redirection (static stubbing) API.
+ *
+ * Copyright (C) 2022, Google LLC.
+ * Author: David Gow <davidgow@xxxxxxxxxx>
+ */
+#ifndef _KUNIT_STATIC_STUB_H
+#define _KUNIT_STATIC_STUB_H
+
+#if !IS_ENABLED(CONFIG_KUNIT)
+
+/* If CONFIG_KUNIT is not enabled, these stubs quietly disappear. */
+#define KUNIT_TRIGGER_STATIC_STUB(real_fn_name, args...) do {} while (0)
+
+#else
+
+#include <kunit/test.h>
+#include <kunit/test-bug.h>
+
+#include <linux/compiler.h> /* for {un,}likely() */
+#include <linux/sched.h> /* for task_struct */
+
+
+/**
+ * KUNIT_STATIC_STUB_REDIRECT() - call a replacement 'static stub' if one exists
+ * @real_fn_name: The name of this function (as an identifier, not a string)
+ * @args: All of the arguments passed to this function
+ *
+ * This is a function prologue which is used to allow calls to the current
+ * function to be redirected by a KUnit test. KUnit tests can call
+ * kunit_activate_static_stub() to pass a replacement function in. The
+ * replacement function will be called by KUNIT_TRIGGER_STATIC_STUB(), which
+ * will then return from the function. If the caller is not in a KUnit context,
+ * the function will continue execution as normal.
+ *
+ * Example:
+ *
+ * .. code-block:: c
+ *
+ *	int real_func(int n)
+ *	{
+ *		KUNIT_STATIC_STUB_REDIRECT(real_func, n);
+ *		return 0;
+ *	}
+ *
+ *	int replacement_func(int n)
+ *	{
+ *		return 42;
+ *	}
+ *
+ *	void example_test(struct kunit *test)
+ *	{
+ *		kunit_activate_static_stub(test, real_func, replacement_func);
+ *		KUNIT_EXPECT_EQ(test, real_func(1), 42);
+ *	}
+ *
+ */
+#define KUNIT_STATIC_STUB_REDIRECT(real_fn_name, args...)		\
+do {									\
+	typeof(&real_fn_name) replacement;				\
+	struct kunit *current_test = kunit_get_current_test();		\
+									\
+	if (likely(!current_test))					\
+		break;							\
+									\
+	replacement = kunit_hooks.get_static_stub_address(current_test,	\
+							&real_fn_name);	\
+									\
+	if (unlikely(replacement))					\
+		return replacement(args);				\
+} while (0)
+
+/* Helper function for kunit_activate_static_stub(). The macro does
+ * typechecking, so use it instead.
+ */
+void __kunit_activate_static_stub(struct kunit *test,
+				  void *real_fn_addr,
+				  void *replacement_addr);
+
+/**
+ * kunit_activate_static_stub() - replace a function using static stubs.
+ * @test: A pointer to the 'struct kunit' test context for the current test.
+ * @real_fn_addr: The address of the function to replace.
+ * @replacement_addr: The address of the function to replace it with.
+ *
+ * When activated, calls to real_fn_addr from within this test (even if called
+ * indirectly) will instead call replacement_addr. The function pointed to by
+ * real_fn_addr must begin with the static stub prologue in
+ * KUNIT_TRIGGER_STATIC_STUB() for this to work. real_fn_addr and
+ * replacement_addr must have the same type.
+ *
+ * The redirection can be disabled again with kunit_deactivate_static_stub().
+ */
+#define kunit_activate_static_stub(test, real_fn_addr, replacement_addr) do {	\
+	typecheck_fn(typeof(&real_fn_addr), replacement_addr);			\
+	__kunit_activate_static_stub(test, real_fn_addr, replacement_addr);	\
+} while (0)
+
+
+/**
+ * kunit_deactivate_static_stub() - disable a function redirection
+ * @test: A pointer to the 'struct kunit' test context for the current test.
+ * @real_fn_addr: The address of the function to no-longer redirect
+ *
+ * Deactivates a redirection configured with kunit_activate_static_stub(). After
+ * this function returns, calls to real_fn_addr() will execute the original
+ * real_fn, not any previously-configured replacement.
+ */
+void kunit_deactivate_static_stub(struct kunit *test, void *real_fn_addr);
+
+#endif
+#endif
diff --git a/include/kunit/test-bug.h b/include/kunit/test-bug.h
index c1b2e14eab64..30ca541b6ff2 100644
--- a/include/kunit/test-bug.h
+++ b/include/kunit/test-bug.h
@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * KUnit API allowing dynamic analysis tools to interact with KUnit tests
+ * KUnit API providing hooks for non-test code to interact with tests.
  *
  * Copyright (C) 2020, Google LLC.
  * Author: Uriel Guajardo <urielguajardo@xxxxxxxxxx>
@@ -9,7 +9,7 @@
 #ifndef _KUNIT_TEST_BUG_H
 #define _KUNIT_TEST_BUG_H
 
-#if IS_BUILTIN(CONFIG_KUNIT)
+#if IS_ENABLED(CONFIG_KUNIT)
 
 #include <linux/jump_label.h> /* For static branch */
 #include <linux/sched.h>
@@ -17,6 +17,12 @@
 /* Static key if KUnit is running any tests. */
 DECLARE_STATIC_KEY_FALSE(kunit_running);
 
+/* Hooks table: a table of function pointers filled in when kunit loads */
+extern struct kunit_hooks_table {
+	__printf(3, 4) void (*fail_current_test)(const char*, int, const char*, ...);
+	void *(*get_static_stub_address)(struct kunit *test, void *real_fn_addr);
+} kunit_hooks;
+
 /**
  * kunit_get_current_test() - Return a pointer to the currently running
  *			      KUnit test.
@@ -43,33 +49,20 @@ static inline struct kunit *kunit_get_current_test(void)
  * kunit_fail_current_test() - If a KUnit test is running, fail it.
  *
  * If a KUnit test is running in the current task, mark that test as failed.
- *
- * This macro will only work if KUnit is built-in (though the tests
- * themselves can be modules). Otherwise, it compiles down to nothing.
  */
 #define kunit_fail_current_test(fmt, ...) do {					\
 		if (static_branch_unlikely(&kunit_running)) {			\
-			__kunit_fail_current_test(__FILE__, __LINE__,		\
+			/* Guaranteed to be non-NULL when kunit_running true*/	\
+			kunit_hooks.fail_current_test(__FILE__, __LINE__,	\
 						  fmt, ##__VA_ARGS__);		\
 		}								\
 	} while (0)
 
-
-extern __printf(3, 4) void __kunit_fail_current_test(const char *file, int line,
-						    const char *fmt, ...);
-
 #else
 
 static inline struct kunit *kunit_get_current_test(void) { return NULL; }
 
-/* We define this with an empty helper function so format string warnings work */
-#define kunit_fail_current_test(fmt, ...) \
-		__kunit_fail_current_test(__FILE__, __LINE__, fmt, ##__VA_ARGS__)
-
-static inline __printf(3, 4) void __kunit_fail_current_test(const char *file, int line,
-							    const char *fmt, ...)
-{
-}
+#define kunit_fail_current_test(fmt, ...) do {} while (0)
 
 #endif
 
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 02ee440f7be3..6a7ce60c8412 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2497,6 +2497,19 @@ config LIST_KUNIT_TEST
 
 	  If unsure, say N.
 
+config HASHTABLE_KUNIT_TEST
+	tristate "KUnit Test for Kernel Hashtable structures" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  This builds the hashtable KUnit test suite.
+	  It tests the basic functionality of the API defined in
+	  include/linux/hashtable.h. For more information on KUnit and
+	  unit tests in general please refer to the KUnit documentation
+	  in Documentation/dev-tools/kunit/.
+
+	  If unsure, say N.
+
 config LINEAR_RANGES_TEST
 	tristate "KUnit test for linear_ranges"
 	depends on KUNIT
diff --git a/lib/Makefile b/lib/Makefile
index 4d9461bfea42..b25a324fa326 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -126,6 +126,14 @@ CFLAGS_test_fpu.o += $(FPU_CFLAGS)
 obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/
 
 obj-$(CONFIG_KUNIT) += kunit/
+# Include the KUnit hooks unconditionally. They'll compile to nothing if
+# CONFIG_KUNIT=n, otherwise will be a small table of static data (static key,
+# function pointers) which need to be built-in even when KUnit is a module.
+ifeq ($(CONFIG_KUNIT), m)
+obj-y += kunit/hooks.o
+else
+obj-$(CONFIG_KUNIT) += kunit/hooks.o
+endif
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG
@@ -369,6 +377,7 @@ obj-$(CONFIG_PLDMFW) += pldmfw/
 CFLAGS_bitfield_kunit.o := $(DISABLE_STRUCTLEAK_PLUGIN)
 obj-$(CONFIG_BITFIELD_KUNIT) += bitfield_kunit.o
 obj-$(CONFIG_LIST_KUNIT_TEST) += list-test.o
+obj-$(CONFIG_HASHTABLE_KUNIT_TEST) += hashtable_test.o
 obj-$(CONFIG_LINEAR_RANGES_TEST) += test_linear_ranges.o
 obj-$(CONFIG_BITS_TEST) += test_bits.o
 obj-$(CONFIG_CMDLINE_KUNIT_TEST) += cmdline_kunit.o
diff --git a/lib/hashtable_test.c b/lib/hashtable_test.c
new file mode 100644
index 000000000000..1d1b3288dee2
--- /dev/null
+++ b/lib/hashtable_test.c
@@ -0,0 +1,317 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for the Kernel Hashtable structures.
+ *
+ * Copyright (C) 2022, Google LLC.
+ * Author: Rae Moar <rmoar@xxxxxxxxxx>
+ */
+#include <kunit/test.h>
+
+#include <linux/hashtable.h>
+
+struct hashtable_test_entry {
+	int key;
+	int data;
+	struct hlist_node node;
+	int visited;
+};
+
+static void hashtable_test_hash_init(struct kunit *test)
+{
+	/* Test the different ways of initialising a hashtable. */
+	DEFINE_HASHTABLE(hash1, 2);
+	DECLARE_HASHTABLE(hash2, 3);
+
+	/* When using DECLARE_HASHTABLE, must use hash_init to
+	 * initialize the hashtable.
+	 */
+	hash_init(hash2);
+
+	KUNIT_EXPECT_TRUE(test, hash_empty(hash1));
+	KUNIT_EXPECT_TRUE(test, hash_empty(hash2));
+}
+
+static void hashtable_test_hash_empty(struct kunit *test)
+{
+	struct hashtable_test_entry a;
+	DEFINE_HASHTABLE(hash, 1);
+
+	KUNIT_EXPECT_TRUE(test, hash_empty(hash));
+
+	a.key = 1;
+	a.data = 13;
+	hash_add(hash, &a.node, a.key);
+
+	/* Hashtable should no longer be empty. */
+	KUNIT_EXPECT_FALSE(test, hash_empty(hash));
+}
+
+static void hashtable_test_hash_hashed(struct kunit *test)
+{
+	struct hashtable_test_entry a, b;
+	DEFINE_HASHTABLE(hash, 4);
+
+	a.key = 1;
+	a.data = 13;
+	hash_add(hash, &a.node, a.key);
+	b.key = 1;
+	b.data = 2;
+	hash_add(hash, &b.node, b.key);
+
+	KUNIT_EXPECT_TRUE(test, hash_hashed(&a.node));
+	KUNIT_EXPECT_TRUE(test, hash_hashed(&b.node));
+}
+
+static void hashtable_test_hash_add(struct kunit *test)
+{
+	struct hashtable_test_entry a, b, *x;
+	int bkt;
+	DEFINE_HASHTABLE(hash, 3);
+
+	a.key = 1;
+	a.data = 13;
+	a.visited = 0;
+	hash_add(hash, &a.node, a.key);
+	b.key = 2;
+	b.data = 10;
+	b.visited = 0;
+	hash_add(hash, &b.node, b.key);
+
+	hash_for_each(hash, bkt, x, node) {
+		x->visited++;
+		if (x->key == a.key)
+			KUNIT_EXPECT_EQ(test, x->data, 13);
+		else if (x->key == b.key)
+			KUNIT_EXPECT_EQ(test, x->data, 10);
+		else
+			KUNIT_FAIL(test, "Unexpected key in hashtable.");
+	}
+
+	/* Both entries should have been visited exactly once. */
+	KUNIT_EXPECT_EQ(test, a.visited, 1);
+	KUNIT_EXPECT_EQ(test, b.visited, 1);
+}
+
+static void hashtable_test_hash_del(struct kunit *test)
+{
+	struct hashtable_test_entry a, b, *x;
+	DEFINE_HASHTABLE(hash, 6);
+
+	a.key = 1;
+	a.data = 13;
+	hash_add(hash, &a.node, a.key);
+	b.key = 2;
+	b.data = 10;
+	b.visited = 0;
+	hash_add(hash, &b.node, b.key);
+
+	hash_del(&b.node);
+	hash_for_each_possible(hash, x, node, b.key) {
+		x->visited++;
+		KUNIT_EXPECT_NE(test, x->key, b.key);
+	}
+
+	/* The deleted entry should not have been visited. */
+	KUNIT_EXPECT_EQ(test, b.visited, 0);
+
+	hash_del(&a.node);
+
+	/* The hashtable should be empty. */
+	KUNIT_EXPECT_TRUE(test, hash_empty(hash));
+}
+
+static void hashtable_test_hash_for_each(struct kunit *test)
+{
+	struct hashtable_test_entry entries[3];
+	struct hashtable_test_entry *x;
+	int bkt, i, j, count;
+	DEFINE_HASHTABLE(hash, 3);
+
+	/* Add three entries to the hashtable. */
+	for (i = 0; i < 3; i++) {
+		entries[i].key = i;
+		entries[i].data = i + 10;
+		entries[i].visited = 0;
+		hash_add(hash, &entries[i].node, entries[i].key);
+	}
+
+	count = 0;
+	hash_for_each(hash, bkt, x, node) {
+		x->visited += 1;
+		KUNIT_ASSERT_GE_MSG(test, x->key, 0, "Unexpected key in hashtable.");
+		KUNIT_ASSERT_LT_MSG(test, x->key, 3, "Unexpected key in hashtable.");
+		count++;
+	}
+
+	/* Should have visited each entry exactly once. */
+	KUNIT_EXPECT_EQ(test, count, 3);
+	for (j = 0; j < 3; j++)
+		KUNIT_EXPECT_EQ(test, entries[j].visited, 1);
+}
+
+static void hashtable_test_hash_for_each_safe(struct kunit *test)
+{
+	struct hashtable_test_entry entries[3];
+	struct hashtable_test_entry *x;
+	struct hlist_node *tmp;
+	int bkt, i, j, count;
+	DEFINE_HASHTABLE(hash, 3);
+
+	/* Add three entries to the hashtable. */
+	for (i = 0; i < 3; i++) {
+		entries[i].key = i;
+		entries[i].data = i + 10;
+		entries[i].visited = 0;
+		hash_add(hash, &entries[i].node, entries[i].key);
+	}
+
+	count = 0;
+	hash_for_each_safe(hash, bkt, tmp, x, node) {
+		x->visited += 1;
+		KUNIT_ASSERT_GE_MSG(test, x->key, 0, "Unexpected key in hashtable.");
+		KUNIT_ASSERT_LT_MSG(test, x->key, 3, "Unexpected key in hashtable.");
+		count++;
+
+		/* Delete entry during loop. */
+		hash_del(&x->node);
+	}
+
+	/* Should have visited each entry exactly once. */
+	KUNIT_EXPECT_EQ(test, count, 3);
+	for (j = 0; j < 3; j++)
+		KUNIT_EXPECT_EQ(test, entries[j].visited, 1);
+}
+
+static void hashtable_test_hash_for_each_possible(struct kunit *test)
+{
+	struct hashtable_test_entry entries[4];
+	struct hashtable_test_entry *x, *y;
+	int buckets[2];
+	int bkt, i, j, count;
+	DEFINE_HASHTABLE(hash, 5);
+
+	/* Add three entries with key = 0 to the hashtable. */
+	for (i = 0; i < 3; i++) {
+		entries[i].key = 0;
+		entries[i].data = i;
+		entries[i].visited = 0;
+		hash_add(hash, &entries[i].node, entries[i].key);
+	}
+
+	/* Add an entry with key = 1. */
+	entries[3].key = 1;
+	entries[3].data = 3;
+	entries[3].visited = 0;
+	hash_add(hash, &entries[3].node, entries[3].key);
+
+	count = 0;
+	hash_for_each_possible(hash, x, node, 0) {
+		x->visited += 1;
+		KUNIT_ASSERT_GE_MSG(test, x->data, 0, "Unexpected data in hashtable.");
+		KUNIT_ASSERT_LT_MSG(test, x->data, 4, "Unexpected data in hashtable.");
+		count++;
+	}
+
+	/* Should have visited each entry with key = 0 exactly once. */
+	for (j = 0; j < 3; j++)
+		KUNIT_EXPECT_EQ(test, entries[j].visited, 1);
+
+	/* Save the buckets for the different keys. */
+	hash_for_each(hash, bkt, y, node) {
+		KUNIT_ASSERT_GE_MSG(test, y->key, 0, "Unexpected key in hashtable.");
+		KUNIT_ASSERT_LE_MSG(test, y->key, 1, "Unexpected key in hashtable.");
+		buckets[y->key] = bkt;
+	}
+
+	/* If entry with key = 1 is in the same bucket as the entries with
+	 * key = 0, check it was visited. Otherwise ensure that only three
+	 * entries were visited.
+	 */
+	if (buckets[0] == buckets[1]) {
+		KUNIT_EXPECT_EQ(test, count, 4);
+		KUNIT_EXPECT_EQ(test, entries[3].visited, 1);
+	} else {
+		KUNIT_EXPECT_EQ(test, count, 3);
+		KUNIT_EXPECT_EQ(test, entries[3].visited, 0);
+	}
+}
+
+static void hashtable_test_hash_for_each_possible_safe(struct kunit *test)
+{
+	struct hashtable_test_entry entries[4];
+	struct hashtable_test_entry *x, *y;
+	struct hlist_node *tmp;
+	int buckets[2];
+	int bkt, i, j, count;
+	DEFINE_HASHTABLE(hash, 5);
+
+	/* Add three entries with key = 0 to the hashtable. */
+	for (i = 0; i < 3; i++) {
+		entries[i].key = 0;
+		entries[i].data = i;
+		entries[i].visited = 0;
+		hash_add(hash, &entries[i].node, entries[i].key);
+	}
+
+	/* Add an entry with key = 1. */
+	entries[3].key = 1;
+	entries[3].data = 3;
+	entries[3].visited = 0;
+	hash_add(hash, &entries[3].node, entries[3].key);
+
+	count = 0;
+	hash_for_each_possible_safe(hash, x, tmp, node, 0) {
+		x->visited += 1;
+		KUNIT_ASSERT_GE_MSG(test, x->data, 0, "Unexpected data in hashtable.");
+		KUNIT_ASSERT_LT_MSG(test, x->data, 4, "Unexpected data in hashtable.");
+		count++;
+
+		/* Delete entry during loop. */
+		hash_del(&x->node);
+	}
+
+	/* Should have visited each entry with key = 0 exactly once. */
+	for (j = 0; j < 3; j++)
+		KUNIT_EXPECT_EQ(test, entries[j].visited, 1);
+
+	/* Save the buckets for the different keys. */
+	hash_for_each(hash, bkt, y, node) {
+		KUNIT_ASSERT_GE_MSG(test, y->key, 0, "Unexpected key in hashtable.");
+		KUNIT_ASSERT_LE_MSG(test, y->key, 1, "Unexpected key in hashtable.");
+		buckets[y->key] = bkt;
+	}
+
+	/* If entry with key = 1 is in the same bucket as the entries with
+	 * key = 0, check it was visited. Otherwise ensure that only three
+	 * entries were visited.
+	 */
+	if (buckets[0] == buckets[1]) {
+		KUNIT_EXPECT_EQ(test, count, 4);
+		KUNIT_EXPECT_EQ(test, entries[3].visited, 1);
+	} else {
+		KUNIT_EXPECT_EQ(test, count, 3);
+		KUNIT_EXPECT_EQ(test, entries[3].visited, 0);
+	}
+}
+
+static struct kunit_case hashtable_test_cases[] = {
+	KUNIT_CASE(hashtable_test_hash_init),
+	KUNIT_CASE(hashtable_test_hash_empty),
+	KUNIT_CASE(hashtable_test_hash_hashed),
+	KUNIT_CASE(hashtable_test_hash_add),
+	KUNIT_CASE(hashtable_test_hash_del),
+	KUNIT_CASE(hashtable_test_hash_for_each),
+	KUNIT_CASE(hashtable_test_hash_for_each_safe),
+	KUNIT_CASE(hashtable_test_hash_for_each_possible),
+	KUNIT_CASE(hashtable_test_hash_for_each_possible_safe),
+	{},
+};
+
+static struct kunit_suite hashtable_test_module = {
+	.name = "hashtable",
+	.test_cases = hashtable_test_cases,
+};
+
+kunit_test_suites(&hashtable_test_module);
+
+MODULE_LICENSE("GPL");
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index 29aff6562b42..da665cd4ea12 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -2,6 +2,7 @@ obj-$(CONFIG_KUNIT) +=			kunit.o
 
 kunit-objs +=				test.o \
 					resource.o \
+					static_stub.o \
 					string-stream.o \
 					assert.o \
 					try-catch.o \
@@ -11,6 +12,9 @@ ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
 kunit-objs +=				debugfs.o
 endif
 
+# KUnit 'hooks' are built-in even when KUnit is built as a module.
+lib-y +=				hooks.o
+
 obj-$(CONFIG_KUNIT_TEST) +=		kunit-test.o
 
 # string-stream-test compiles built-in only.
diff --git a/lib/kunit/hooks-impl.h b/lib/kunit/hooks-impl.h
new file mode 100644
index 000000000000..4e71b2d0143b
--- /dev/null
+++ b/lib/kunit/hooks-impl.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Declarations for hook implementations.
+ *
+ * These will be set as the function pointers in struct kunit_hook_table,
+ * found in include/kunit/test-bug.h.
+ *
+ * Copyright (C) 2023, Google LLC.
+ * Author: David Gow <davidgow@xxxxxxxxxx>
+ */
+
+#ifndef _KUNIT_HOOKS_IMPL_H
+#define _KUNIT_HOOKS_IMPL_H
+
+#include <kunit/test-bug.h>
+
+/* List of declarations. */
+void __printf(3, 4) __kunit_fail_current_test_impl(const char *file,
+						   int line,
+						   const char *fmt, ...);
+void *__kunit_get_static_stub_address_impl(struct kunit *test, void *real_fn_addr);
+
+/* Code to set all of the function pointers. */
+static inline void kunit_install_hooks(void)
+{
+	/* Install the KUnit hook functions. */
+	kunit_hooks.fail_current_test = __kunit_fail_current_test_impl;
+	kunit_hooks.get_static_stub_address = __kunit_get_static_stub_address_impl;
+}
+
+#endif /* _KUNIT_HOOKS_IMPL_H */
diff --git a/lib/kunit/hooks.c b/lib/kunit/hooks.c
new file mode 100644
index 000000000000..365d98d4953c
--- /dev/null
+++ b/lib/kunit/hooks.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit 'Hooks' implementation.
+ *
+ * This file contains code / structures which should be built-in even when
+ * KUnit itself is built as a module.
+ *
+ * Copyright (C) 2022, Google LLC.
+ * Author: David Gow <davidgow@xxxxxxxxxx>
+ */
+
+
+#include <kunit/test-bug.h>
+
+DEFINE_STATIC_KEY_FALSE(kunit_running);
+EXPORT_SYMBOL(kunit_running);
+
+/* Function pointers for hooks. */
+struct kunit_hooks_table kunit_hooks;
+EXPORT_SYMBOL(kunit_hooks);
+
diff --git a/lib/kunit/kunit-example-test.c b/lib/kunit/kunit-example-test.c
index 66cc4e2365ec..cd8b7e51d02b 100644
--- a/lib/kunit/kunit-example-test.c
+++ b/lib/kunit/kunit-example-test.c
@@ -7,6 +7,7 @@
  */
 
 #include <kunit/test.h>
+#include <kunit/static_stub.h>
 
 /*
  * This is the most fundamental element of KUnit, the test case. A test case
@@ -130,6 +131,42 @@ static void example_all_expect_macros_test(struct kunit *test)
 	KUNIT_ASSERT_GT_MSG(test, sizeof(int), 0, "Your ints are 0-bit?!");
 }
 
+/* This is a function we'll replace with static stubs. */
+static int add_one(int i)
+{
+	/* This will trigger the stub if active. */
+	KUNIT_STATIC_STUB_REDIRECT(add_one, i);
+
+	return i + 1;
+}
+
+/* This is used as a replacement for the above function. */
+static int subtract_one(int i)
+{
+	/* We don't need to trigger the stub from the replacement. */
+
+	return i - 1;
+}
+
+/*
+ * This test shows the use of static stubs.
+ */
+static void example_static_stub_test(struct kunit *test)
+{
+	/* By default, function is not stubbed. */
+	KUNIT_EXPECT_EQ(test, add_one(1), 2);
+
+	/* Replace add_one() with subtract_one(). */
+	kunit_activate_static_stub(test, add_one, subtract_one);
+
+	/* add_one() is now replaced. */
+	KUNIT_EXPECT_EQ(test, add_one(1), 0);
+
+	/* Return add_one() to normal. */
+	kunit_deactivate_static_stub(test, add_one);
+	KUNIT_EXPECT_EQ(test, add_one(1), 2);
+}
+
 /*
  * Here we make a list of all the test cases we want to add to the test suite
  * below.
@@ -145,6 +182,7 @@ static struct kunit_case example_test_cases[] = {
 	KUNIT_CASE(example_skip_test),
 	KUNIT_CASE(example_mark_skipped_test),
 	KUNIT_CASE(example_all_expect_macros_test),
+	KUNIT_CASE(example_static_stub_test),
 	{}
 };
 
diff --git a/lib/kunit/static_stub.c b/lib/kunit/static_stub.c
new file mode 100644
index 000000000000..92b2cccd5e76
--- /dev/null
+++ b/lib/kunit/static_stub.c
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit function redirection (static stubbing) API.
+ *
+ * Copyright (C) 2022, Google LLC.
+ * Author: David Gow <davidgow@xxxxxxxxxx>
+ */
+
+#include <kunit/test.h>
+#include <kunit/static_stub.h>
+#include "hooks-impl.h"
+
+
+/* Context for a static stub. This is stored in the resource data. */
+struct kunit_static_stub_ctx {
+	void *real_fn_addr;
+	void *replacement_addr;
+};
+
+static void __kunit_static_stub_resource_free(struct kunit_resource *res)
+{
+	kfree(res->data);
+}
+
+/* Matching function for kunit_find_resource(). match_data is real_fn_addr. */
+static bool __kunit_static_stub_resource_match(struct kunit *test,
+						struct kunit_resource *res,
+						void *match_real_fn_addr)
+{
+	/* This pointer is only valid if res is a static stub resource. */
+	struct kunit_static_stub_ctx *ctx = res->data;
+
+	/* Make sure the resource is a static stub resource. */
+	if (res->free != &__kunit_static_stub_resource_free)
+		return false;
+
+	return ctx->real_fn_addr == match_real_fn_addr;
+}
+
+/* Hook to return the address of the replacement function. */
+void *__kunit_get_static_stub_address_impl(struct kunit *test, void *real_fn_addr)
+{
+	struct kunit_resource *res;
+	struct kunit_static_stub_ctx *ctx;
+	void *replacement_addr;
+
+	res = kunit_find_resource(test,
+				  __kunit_static_stub_resource_match,
+				  real_fn_addr);
+
+	if (!res)
+		return NULL;
+
+	ctx = res->data;
+	replacement_addr = ctx->replacement_addr;
+	kunit_put_resource(res);
+	return replacement_addr;
+}
+
+void kunit_deactivate_static_stub(struct kunit *test, void *real_fn_addr)
+{
+	struct kunit_resource *res;
+
+	KUNIT_ASSERT_PTR_NE_MSG(test, real_fn_addr, NULL,
+				"Tried to deactivate a NULL stub.");
+
+	/* Look up the existing stub for this function. */
+	res = kunit_find_resource(test,
+				  __kunit_static_stub_resource_match,
+				  real_fn_addr);
+
+	/* Error out if the stub doesn't exist. */
+	KUNIT_ASSERT_PTR_NE_MSG(test, res, NULL,
+				"Tried to deactivate a nonexistent stub.");
+
+	/* Free the stub. We 'put' twice, as we got a reference
+	 * from kunit_find_resource()
+	 */
+	kunit_remove_resource(test, res);
+	kunit_put_resource(res);
+}
+EXPORT_SYMBOL_GPL(kunit_deactivate_static_stub);
+
+/* Helper function for kunit_activate_static_stub(). The macro does
+ * typechecking, so use it instead.
+ */
+void __kunit_activate_static_stub(struct kunit *test,
+				  void *real_fn_addr,
+				  void *replacement_addr)
+{
+	struct kunit_static_stub_ctx *ctx;
+	struct kunit_resource *res;
+
+	KUNIT_ASSERT_PTR_NE_MSG(test, real_fn_addr, NULL,
+				"Tried to activate a stub for function NULL");
+
+	/* If the replacement address is NULL, deactivate the stub. */
+	if (!replacement_addr) {
+		kunit_deactivate_static_stub(test, replacement_addr);
+		return;
+	}
+
+	/* Look up any existing stubs for this function, and replace them. */
+	res = kunit_find_resource(test,
+				  __kunit_static_stub_resource_match,
+				  real_fn_addr);
+	if (res) {
+		ctx = res->data;
+		ctx->replacement_addr = replacement_addr;
+
+		/* We got an extra reference from find_resource(), so put it. */
+		kunit_put_resource(res);
+	} else {
+		ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
+		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx);
+		ctx->real_fn_addr = real_fn_addr;
+		ctx->replacement_addr = replacement_addr;
+		res = kunit_alloc_resource(test, NULL,
+				     &__kunit_static_stub_resource_free,
+				     GFP_KERNEL, ctx);
+	}
+}
+EXPORT_SYMBOL_GPL(__kunit_activate_static_stub);
diff --git a/lib/kunit/test.c b/lib/kunit/test.c
index 890ba5b3a981..c9e15bb60058 100644
--- a/lib/kunit/test.c
+++ b/lib/kunit/test.c
@@ -17,17 +17,14 @@
 #include <linux/sched.h>
 
 #include "debugfs.h"
+#include "hooks-impl.h"
 #include "string-stream.h"
 #include "try-catch-impl.h"
 
-DEFINE_STATIC_KEY_FALSE(kunit_running);
-EXPORT_SYMBOL_GPL(kunit_running);
-
-#if IS_BUILTIN(CONFIG_KUNIT)
 /*
- * Fail the current test and print an error message to the log.
+ * Hook to fail the current test and print an error message to the log.
  */
-void __kunit_fail_current_test(const char *file, int line, const char *fmt, ...)
+void __printf(3, 4) __kunit_fail_current_test_impl(const char *file, int line, const char *fmt, ...)
 {
 	va_list args;
 	int len;
@@ -54,8 +51,6 @@ void __kunit_fail_current_test(const char *file, int line, const char *fmt, ...)
 	kunit_err(current->kunit_test, "%s:%d: %s", file, line, buffer);
 	kunit_kfree(current->kunit_test, buffer);
 }
-EXPORT_SYMBOL_GPL(__kunit_fail_current_test);
-#endif
 
 /*
  * Enable KUnit tests to run.
@@ -778,6 +773,9 @@ EXPORT_SYMBOL_GPL(kunit_cleanup);
 
 static int __init kunit_init(void)
 {
+	/* Install the KUnit hook functions. */
+	kunit_install_hooks();
+
 	kunit_debugfs_init();
 #ifdef CONFIG_MODULES
 	return register_module_notifier(&kunit_mod_nb);
@@ -789,6 +787,7 @@ late_initcall(kunit_init);
 
 static void __exit kunit_exit(void)
 {
+	memset(&kunit_hooks, 0, sizeof(kunit_hooks));
 #ifdef CONFIG_MODULES
 	unregister_module_notifier(&kunit_mod_nb);
 #endif
diff --git a/tools/testing/kunit/kunit.py b/tools/testing/kunit/kunit.py
index 43fbe96318fe..741f15420467 100755
--- a/tools/testing/kunit/kunit.py
+++ b/tools/testing/kunit/kunit.py
@@ -77,11 +77,8 @@ def config_tests(linux: kunit_kernel.LinuxSourceTree,
 	config_start = time.time()
 	success = linux.build_reconfig(request.build_dir, request.make_options)
 	config_end = time.time()
-	if not success:
-		return KunitResult(KunitStatus.CONFIG_FAILURE,
-				   config_end - config_start)
-	return KunitResult(KunitStatus.SUCCESS,
-			   config_end - config_start)
+	status = KunitStatus.SUCCESS if success else KunitStatus.CONFIG_FAILURE
+	return KunitResult(status, config_end - config_start)
 
 def build_tests(linux: kunit_kernel.LinuxSourceTree,
 		request: KunitBuildRequest) -> KunitResult:
@@ -92,14 +89,8 @@ def build_tests(linux: kunit_kernel.LinuxSourceTree,
 				     request.build_dir,
 				     request.make_options)
 	build_end = time.time()
-	if not success:
-		return KunitResult(KunitStatus.BUILD_FAILURE,
-				   build_end - build_start)
-	if not success:
-		return KunitResult(KunitStatus.BUILD_FAILURE,
-				   build_end - build_start)
-	return KunitResult(KunitStatus.SUCCESS,
-			   build_end - build_start)
+	status = KunitStatus.SUCCESS if success else KunitStatus.BUILD_FAILURE
+	return KunitResult(status, build_end - build_start)
 
 def config_and_build_tests(linux: kunit_kernel.LinuxSourceTree,
 			   request: KunitBuildRequest) -> KunitResult:
@@ -145,7 +136,7 @@ def exec_tests(linux: kunit_kernel.LinuxSourceTree, request: KunitExecRequest) -
 		tests = _list_tests(linux, request)
 		if request.run_isolated == 'test':
 			filter_globs = tests
-		if request.run_isolated == 'suite':
+		elif request.run_isolated == 'suite':
 			filter_globs = _suites_from_test_list(tests)
 			# Apply the test-part of the user's glob, if present.
 			if '.' in request.filter_glob:
@@ -395,6 +386,95 @@ def tree_from_args(cli_args: argparse.Namespace) -> kunit_kernel.LinuxSourceTree
 			extra_qemu_args=qemu_args)
 
 
+def run_handler(cli_args):
+	if not os.path.exists(cli_args.build_dir):
+		os.mkdir(cli_args.build_dir)
+
+	linux = tree_from_args(cli_args)
+	request = KunitRequest(build_dir=cli_args.build_dir,
+					make_options=cli_args.make_options,
+					jobs=cli_args.jobs,
+					raw_output=cli_args.raw_output,
+					json=cli_args.json,
+					timeout=cli_args.timeout,
+					filter_glob=cli_args.filter_glob,
+					kernel_args=cli_args.kernel_args,
+					run_isolated=cli_args.run_isolated)
+	result = run_tests(linux, request)
+	if result.status != KunitStatus.SUCCESS:
+		sys.exit(1)
+
+
+def config_handler(cli_args):
+	if cli_args.build_dir and (
+			not os.path.exists(cli_args.build_dir)):
+		os.mkdir(cli_args.build_dir)
+
+	linux = tree_from_args(cli_args)
+	request = KunitConfigRequest(build_dir=cli_args.build_dir,
+						make_options=cli_args.make_options)
+	result = config_tests(linux, request)
+	stdout.print_with_timestamp((
+		'Elapsed time: %.3fs\n') % (
+			result.elapsed_time))
+	if result.status != KunitStatus.SUCCESS:
+		sys.exit(1)
+
+
+def build_handler(cli_args):
+	linux = tree_from_args(cli_args)
+	request = KunitBuildRequest(build_dir=cli_args.build_dir,
+					make_options=cli_args.make_options,
+					jobs=cli_args.jobs)
+	result = config_and_build_tests(linux, request)
+	stdout.print_with_timestamp((
+		'Elapsed time: %.3fs\n') % (
+			result.elapsed_time))
+	if result.status != KunitStatus.SUCCESS:
+		sys.exit(1)
+
+
+def exec_handler(cli_args):
+	linux = tree_from_args(cli_args)
+	exec_request = KunitExecRequest(raw_output=cli_args.raw_output,
+					build_dir=cli_args.build_dir,
+					json=cli_args.json,
+					timeout=cli_args.timeout,
+					filter_glob=cli_args.filter_glob,
+					kernel_args=cli_args.kernel_args,
+					run_isolated=cli_args.run_isolated)
+	result = exec_tests(linux, exec_request)
+	stdout.print_with_timestamp((
+		'Elapsed time: %.3fs\n') % (result.elapsed_time))
+	if result.status != KunitStatus.SUCCESS:
+		sys.exit(1)
+
+
+def parse_handler(cli_args):
+	if cli_args.file is None:
+		sys.stdin.reconfigure(errors='backslashreplace')  # pytype: disable=attribute-error
+		kunit_output = sys.stdin
+	else:
+		with open(cli_args.file, 'r', errors='backslashreplace') as f:
+			kunit_output = f.read().splitlines()
+	# We know nothing about how the result was created!
+	metadata = kunit_json.Metadata()
+	request = KunitParseRequest(raw_output=cli_args.raw_output,
+					json=cli_args.json)
+	result, _ = parse_tests(request, metadata, kunit_output)
+	if result.status != KunitStatus.SUCCESS:
+		sys.exit(1)
+
+
+subcommand_handlers_map = {
+	'run': run_handler,
+	'config': config_handler,
+	'build': build_handler,
+	'exec': exec_handler,
+	'parse': parse_handler
+}
+
+
 def main(argv):
 	parser = argparse.ArgumentParser(
 			description='Helps writing and running KUnit tests.')
@@ -438,78 +518,14 @@ def main(argv):
 	if get_kernel_root_path():
 		os.chdir(get_kernel_root_path())
 
-	if cli_args.subcommand == 'run':
-		if not os.path.exists(cli_args.build_dir):
-			os.mkdir(cli_args.build_dir)
-
-		linux = tree_from_args(cli_args)
-		request = KunitRequest(build_dir=cli_args.build_dir,
-				       make_options=cli_args.make_options,
-				       jobs=cli_args.jobs,
-				       raw_output=cli_args.raw_output,
-				       json=cli_args.json,
-				       timeout=cli_args.timeout,
-				       filter_glob=cli_args.filter_glob,
-				       kernel_args=cli_args.kernel_args,
-				       run_isolated=cli_args.run_isolated)
-		result = run_tests(linux, request)
-		if result.status != KunitStatus.SUCCESS:
-			sys.exit(1)
-	elif cli_args.subcommand == 'config':
-		if cli_args.build_dir and (
-				not os.path.exists(cli_args.build_dir)):
-			os.mkdir(cli_args.build_dir)
-
-		linux = tree_from_args(cli_args)
-		request = KunitConfigRequest(build_dir=cli_args.build_dir,
-					     make_options=cli_args.make_options)
-		result = config_tests(linux, request)
-		stdout.print_with_timestamp((
-			'Elapsed time: %.3fs\n') % (
-				result.elapsed_time))
-		if result.status != KunitStatus.SUCCESS:
-			sys.exit(1)
-	elif cli_args.subcommand == 'build':
-		linux = tree_from_args(cli_args)
-		request = KunitBuildRequest(build_dir=cli_args.build_dir,
-					    make_options=cli_args.make_options,
-					    jobs=cli_args.jobs)
-		result = config_and_build_tests(linux, request)
-		stdout.print_with_timestamp((
-			'Elapsed time: %.3fs\n') % (
-				result.elapsed_time))
-		if result.status != KunitStatus.SUCCESS:
-			sys.exit(1)
-	elif cli_args.subcommand == 'exec':
-		linux = tree_from_args(cli_args)
-		exec_request = KunitExecRequest(raw_output=cli_args.raw_output,
-						build_dir=cli_args.build_dir,
-						json=cli_args.json,
-						timeout=cli_args.timeout,
-						filter_glob=cli_args.filter_glob,
-						kernel_args=cli_args.kernel_args,
-						run_isolated=cli_args.run_isolated)
-		result = exec_tests(linux, exec_request)
-		stdout.print_with_timestamp((
-			'Elapsed time: %.3fs\n') % (result.elapsed_time))
-		if result.status != KunitStatus.SUCCESS:
-			sys.exit(1)
-	elif cli_args.subcommand == 'parse':
-		if cli_args.file is None:
-			sys.stdin.reconfigure(errors='backslashreplace')  # pytype: disable=attribute-error
-			kunit_output = sys.stdin
-		else:
-			with open(cli_args.file, 'r', errors='backslashreplace') as f:
-				kunit_output = f.read().splitlines()
-		# We know nothing about how the result was created!
-		metadata = kunit_json.Metadata()
-		request = KunitParseRequest(raw_output=cli_args.raw_output,
-					    json=cli_args.json)
-		result, _ = parse_tests(request, metadata, kunit_output)
-		if result.status != KunitStatus.SUCCESS:
-			sys.exit(1)
-	else:
+	subcomand_handler = subcommand_handlers_map.get(cli_args.subcommand, None)
+
+	if subcomand_handler is None:
 		parser.print_help()
+		return
+
+	subcomand_handler(cli_args)
+
 
 if __name__ == '__main__':
 	main(sys.argv[1:])