Add a simple way of redirecting calls to functions by including a
special prologue in the "real" function which checks to see if the
replacement function should be called (and, if so, calls it).
To redirect calls to a function, make the first (non-declaration) line
of the function:
KUNIT_STATIC_STUB_REDIRECT(function_name, [function arguments]);
(This will compile away to nothing if KUnit is not enabled, otherwise it
will check if a redirection is active, call the replacement function,
and return. This check is protected by a static branch, so has very
little overhead when there are no KUnit tests running.)
Calls to the real function can be redirected to a replacement using:
kunit_activate_static_stub(test, real_fn, replacement_fn);
The redirection will only affect calls made from within the kthread of
the current test, and will be automatically disabled when the test
completes. It can also be manually disabled with
kunit_deactivate_static_stub().
The 'example' KUnit test suite has a more complete example.
Co-developed-by: Daniel Latypov <[email protected]>
Signed-off-by: Daniel Latypov <[email protected]>
Signed-off-by: David Gow <[email protected]>
Reviewed-by: Brendan Higgins <[email protected]>
---
This patch depends upon the 'hooks' implementation in
https://lore.kernel.org/linux-kselftest/[email protected]/
Note that checkpatch.pl does warn about control flow in the
KUNIT_STATIC_STUB_REDIRECT() macro. This is an intentional design choice
(we think it makes the feature easier to use), though if there are
strong objections, we can of course reconsider.
Changes since v1:
https://lore.kernel.org/all/[email protected]/
- Adapted to use the "hooks" mechanism
- See: https://lore.kernel.org/linux-kselftest/[email protected]/
- Now works when KUnit itself is compiled as a module (CONFIG_KUNIT=m)
Changes since RFC v2:
https://lore.kernel.org/linux-kselftest/[email protected]/
- Now uses the kunit_get_current_test() function, which uses the static
key to reduce overhead.
- Thanks Kees for the suggestion.
- Note that this does prevent redirections from working when
CONFIG_KUNIT=m -- this is a restriction of kunit_get_current_test()
which will be removed in a future patch.
- Several tidy-ups to the inline documentation.
Changes since RFC v1:
https://lore.kernel.org/lkml/[email protected]/
- Use typecheck_fn() to fix typechecking in some cases (thanks Brendan)
---
include/kunit/static_stub.h | 113 ++++++++++++++++++++++++++++++
include/kunit/test-bug.h | 1 +
lib/kunit/Makefile | 1 +
lib/kunit/hooks-impl.h | 2 +
lib/kunit/kunit-example-test.c | 38 ++++++++++
lib/kunit/static_stub.c | 123 +++++++++++++++++++++++++++++++++
6 files changed, 278 insertions(+)
create mode 100644 include/kunit/static_stub.h
create mode 100644 lib/kunit/static_stub.c
diff --git a/include/kunit/static_stub.h b/include/kunit/static_stub.h
new file mode 100644
index 000000000000..047b68d65f1a
--- /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 <[email protected]>
+ */
+#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;
+ * }
+ *
+ * void 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 2b505a95b641..30ca541b6ff2 100644
--- a/include/kunit/test-bug.h
+++ b/include/kunit/test-bug.h
@@ -20,6 +20,7 @@ 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;
/**
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index deeb46cc879b..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 \
diff --git a/lib/kunit/hooks-impl.h b/lib/kunit/hooks-impl.h
index d911f40f76db..ec745a39832c 100644
--- a/lib/kunit/hooks-impl.h
+++ b/lib/kunit/hooks-impl.h
@@ -16,12 +16,14 @@
/* List of declarations. */
void __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/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 <[email protected]>
+ */
+
+#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);
--
2.39.1.456.gfc5497dd1b-goog
From: Sadiya Kazi <[email protected]>
Added a new page (functionredirection.rst) that describes the Function
Redirection (static stubbing) API. This page will be expanded if we add,
for example, ftrace-based stubbing.
In addition,
1. Updated the api/index.rst page to create an entry for function
redirection api
2. Updated the toctree to be hidden, reducing redundancy on the
generated page.
Signed-off-by: Sadiya Kazi <[email protected]>
Co-developed-by: Daniel Latypov <[email protected]>
Signed-off-by: Daniel Latypov <[email protected]>
Co-developed-by: David Gow <[email protected]>
Signed-off-by: David Gow <[email protected]>
Reviewed-by: Brendan Higgins <[email protected]>
---
Note that this document reworks some elements of the KUnit website's "mocking"
page at http://kunit.dev/mocking.html written by Daniel Latypov, and used with
his permission.
Changes since v1:
https://lore.kernel.org/all/[email protected]/
- Fix a bunch of typos (Thanks, Daniel)
- Remove a redundant comment (Thanks, Daniel)
- Reword a few things to be clearer, especially about global state.
---
.../kunit/api/functionredirection.rst | 162 ++++++++++++++++++
Documentation/dev-tools/kunit/api/index.rst | 13 +-
2 files changed, 172 insertions(+), 3 deletions(-)
create mode 100644 Documentation/dev-tools/kunit/api/functionredirection.rst
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
--
2.39.1.456.gfc5497dd1b-goog
On Sat, Jan 28, 2023 at 2:49 AM David Gow <[email protected]> wrote:
>
> Add a simple way of redirecting calls to functions by including a
> special prologue in the "real" function which checks to see if the
> replacement function should be called (and, if so, calls it).
>
> To redirect calls to a function, make the first (non-declaration) line
> of the function:
>
> KUNIT_STATIC_STUB_REDIRECT(function_name, [function arguments]);
>
> (This will compile away to nothing if KUnit is not enabled, otherwise it
> will check if a redirection is active, call the replacement function,
> and return. This check is protected by a static branch, so has very
> little overhead when there are no KUnit tests running.)
>
> Calls to the real function can be redirected to a replacement using:
>
> kunit_activate_static_stub(test, real_fn, replacement_fn);
>
> The redirection will only affect calls made from within the kthread of
> the current test, and will be automatically disabled when the test
> completes. It can also be manually disabled with
> kunit_deactivate_static_stub().
>
> The 'example' KUnit test suite has a more complete example.
>
> Co-developed-by: Daniel Latypov <[email protected]>
> Signed-off-by: Daniel Latypov <[email protected]>
> Signed-off-by: David Gow <[email protected]>
> Reviewed-by: Brendan Higgins <[email protected]>
Still looks good overall to me, but I see one nit:
> ---
>
> This patch depends upon the 'hooks' implementation in
> https://lore.kernel.org/linux-kselftest/[email protected]/
>
> Note that checkpatch.pl does warn about control flow in the
> KUNIT_STATIC_STUB_REDIRECT() macro. This is an intentional design choice
> (we think it makes the feature easier to use), though if there are
> strong objections, we can of course reconsider.
>
> Changes since v1:
> https://lore.kernel.org/all/[email protected]/
> - Adapted to use the "hooks" mechanism
> - See: https://lore.kernel.org/linux-kselftest/[email protected]/
> - Now works when KUnit itself is compiled as a module (CONFIG_KUNIT=m)
>
> Changes since RFC v2:
> https://lore.kernel.org/linux-kselftest/[email protected]/
> - Now uses the kunit_get_current_test() function, which uses the static
> key to reduce overhead.
> - Thanks Kees for the suggestion.
> - Note that this does prevent redirections from working when
> CONFIG_KUNIT=m -- this is a restriction of kunit_get_current_test()
> which will be removed in a future patch.
> - Several tidy-ups to the inline documentation.
>
> Changes since RFC v1:
> https://lore.kernel.org/lkml/[email protected]/
> - Use typecheck_fn() to fix typechecking in some cases (thanks Brendan)
>
> ---
> include/kunit/static_stub.h | 113 ++++++++++++++++++++++++++++++
> include/kunit/test-bug.h | 1 +
> lib/kunit/Makefile | 1 +
> lib/kunit/hooks-impl.h | 2 +
> lib/kunit/kunit-example-test.c | 38 ++++++++++
> lib/kunit/static_stub.c | 123 +++++++++++++++++++++++++++++++++
> 6 files changed, 278 insertions(+)
> create mode 100644 include/kunit/static_stub.h
> create mode 100644 lib/kunit/static_stub.c
>
> diff --git a/include/kunit/static_stub.h b/include/kunit/static_stub.h
> new file mode 100644
> index 000000000000..047b68d65f1a
> --- /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 <[email protected]>
> + */
> +#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;
> + * }
> + *
> + * void replacement_func(int n)
nit: Pretty sure the return type should be `int`
> + * {
> + * return 42;
> + * }
[...]