From 7170b7ed6acbde523c5d362c8978c60df4c30f30 Mon Sep 17 00:00:00 2001 From: David Gow Date: Sat, 28 Jan 2023 15:10:07 +0800 Subject: kunit: Add "hooks" to call into KUnit when it's built as a module KUnit has several macros and functions intended for use from non-test code. These hooks, currently the kunit_get_current_test() and kunit_fail_current_test() macros, didn't work when CONFIG_KUNIT=m. In order to support this case, the required functions and static data need to be available unconditionally, even when KUnit itself is not built-in. The new 'hooks.c' file is therefore always included, and has both the static key required for kunit_get_current_test(), and a table of function pointers in struct kunit_hooks_table. This is filled in with the real implementations by kunit_install_hooks(), which is kept in hooks-impl.h and called when the kunit module is loaded. This can be extended for future features which require similar "hook" behaviour, such as static stubs, by simply adding new entries to the struct, and the appropriate code to set them. Fixed white-space errors during commit: Shuah Khan Resolved merge conflicts with: db105c37a4d6 ("kunit: Export kunit_running()") This patch supersedes the above. Shuah Khan Signed-off-by: David Gow Reviewed-by: Rae Moar Reviewed-by: Brendan Higgins Signed-off-by: Shuah Khan --- Documentation/dev-tools/kunit/usage.rst | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-) (limited to 'Documentation') 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. -- cgit v1.2.3-70-g09d2 From 9ecc9cdd168e217a42b382468643dde66dfac309 Mon Sep 17 00:00:00 2001 From: Sadiya Kazi Date: Tue, 31 Jan 2023 14:46:41 +0800 Subject: Documentation: Add Function Redirection API docs 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 Co-developed-by: Daniel Latypov Signed-off-by: Daniel Latypov Co-developed-by: David Gow Signed-off-by: David Gow Reviewed-by: Brendan Higgins Signed-off-by: Shuah Khan --- .../dev-tools/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 (limited to 'Documentation') 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 -- cgit v1.2.3-70-g09d2