On Sat, Jan 28, 2023 at 2:49 AM David Gow davidgow@google.com 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 dlatypov@google.com Signed-off-by: Daniel Latypov dlatypov@google.com Signed-off-by: David Gow davidgow@google.com Reviewed-by: Brendan Higgins brendanhiggins@google.com
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/20230128071007.1134942-1-davidgow@go...
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/20221208061841.2186447-2-davidgow@google.com/
- Adapted to use the "hooks" mechanism
- See: https://lore.kernel.org/linux-kselftest/20230128071007.1134942-1-davidgow@go...
- Now works when KUnit itself is compiled as a module (CONFIG_KUNIT=m)
Changes since RFC v2: https://lore.kernel.org/linux-kselftest/20220910212804.670622-2-davidgow@goo...
- 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/20220318021314.3225240-2-davidgow@google.com/
- 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 davidgow@google.com
- */
+#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;
}
[...]