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 ======================
 Linux Kernel Selftests
 ======================
 
 The kernel contains a set of "self tests" under the tools/testing/selftests/
 directory. These are intended to be small tests to exercise individual code
 paths in the kernel. Tests are intended to be run after building, installing
 and booting a kernel.
 
 Kselftest from mainline can be run on older stable kernels. Running tests
 from mainline offers the best coverage. Several test rings run mainline
 kselftest suite on stable releases. The reason is that when a new test
 gets added to test existing code to regression test a bug, we should be
 able to run that test on an older kernel. Hence, it is important to keep
 code that can still test an older kernel and make sure it skips the test
 gracefully on newer releases.
 
 You can find additional information on Kselftest framework, how to
 write new tests using the framework on Kselftest wiki:
 
 https://kselftest.wiki.kernel.org/
 
 On some systems, hot-plug tests could hang forever waiting for cpu and
 memory to be ready to be offlined. A special hot-plug target is created
 to run the full range of hot-plug tests. In default mode, hot-plug tests run
 in safe mode with a limited scope. In limited mode, cpu-hotplug test is
 run on a single cpu as opposed to all hotplug capable cpus, and memory
 hotplug test is run on 2% of hotplug capable memory instead of 10%.
 
 kselftest runs as a userspace process.  Tests that can be written/run in
 userspace may wish to use the `Test Harness`_.  Tests that need to be
 run in kernel space may wish to use a `Test Module`_.
 
 Running the selftests (hotplug tests are run in limited mode)
 =============================================================
 
 To build the tests::
 
   $ make -C tools/testing/selftests
 
 To run the tests::
 
   $ make -C tools/testing/selftests run_tests
 
 To build and run the tests with a single command, use::
 
   $ make kselftest
 
 Note that some tests will require root privileges.
 
 Kselftest supports saving output files in a separate directory and then
 running tests. To locate output files in a separate directory two syntaxes
 are supported. In both cases the working directory must be the root of the
 kernel src. This is applicable to "Running a subset of selftests" section
 below.
 
 To build, save output files in a separate directory with O= ::
 
   $ make O=/tmp/kselftest kselftest
 
 To build, save output files in a separate directory with KBUILD_OUTPUT ::
 
   $ export KBUILD_OUTPUT=/tmp/kselftest; make kselftest
 
 The O= assignment takes precedence over the KBUILD_OUTPUT environment
 variable.
 
 The above commands by default run the tests and print full pass/fail report.
 Kselftest supports "summary" option to make it easier to understand the test
 results. Please find the detailed individual test results for each test in
 /tmp/testname file(s) when summary option is specified. This is applicable
 to "Running a subset of selftests" section below.
 
 To run kselftest with summary option enabled ::
 
   $ make summary=1 kselftest
 
 Running a subset of selftests
 =============================
 
 You can use the "TARGETS" variable on the make command line to specify
 single test to run, or a list of tests to run.
 
 To run only tests targeted for a single subsystem::
 
   $ make -C tools/testing/selftests TARGETS=ptrace run_tests
 
 You can specify multiple tests to build and run::
 
   $  make TARGETS="size timers" kselftest
 
 To build, save output files in a separate directory with O= ::
 
   $ make O=/tmp/kselftest TARGETS="size timers" kselftest
 
 To build, save output files in a separate directory with KBUILD_OUTPUT ::
 
   $ export KBUILD_OUTPUT=/tmp/kselftest; make TARGETS="size timers" kselftest
 
 Additionally you can use the "SKIP_TARGETS" variable on the make command
 line to specify one or more targets to exclude from the TARGETS list.
 
 To run all tests but a single subsystem::
 
   $ make -C tools/testing/selftests SKIP_TARGETS=ptrace run_tests
 
 You can specify multiple tests to skip::
 
   $  make SKIP_TARGETS="size timers" kselftest
 
 You can also specify a restricted list of tests to run together with a
 dedicated skiplist::
 
   $  make TARGETS="bpf breakpoints size timers" SKIP_TARGETS=bpf kselftest
 
 See the top-level tools/testing/selftests/Makefile for the list of all
 possible targets.
 
 Running the full range hotplug selftests
 ========================================
 
 To build the hotplug tests::
 
   $ make -C tools/testing/selftests hotplug
 
 To run the hotplug tests::
 
   $ make -C tools/testing/selftests run_hotplug
 
 Note that some tests will require root privileges.
 
 
 Install selftests
 =================
 
 You can use the "install" target of "make" (which calls the `kselftest_install.sh`
 tool) to install selftests in the default location (`tools/testing/selftests/kselftest_install`),
 or in a user specified location via the `INSTALL_PATH` "make" variable.
 
 To install selftests in default location::
 
    $ make -C tools/testing/selftests install
 
 To install selftests in a user specified location::
 
    $ make -C tools/testing/selftests install INSTALL_PATH=/some/other/path
 
 Running installed selftests
 ===========================
 
 Found in the install directory, as well as in the Kselftest tarball,
 is a script named `run_kselftest.sh` to run the tests.
 
 You can simply do the following to run the installed Kselftests. Please
 note some tests will require root privileges::
 
    $ cd kselftest_install
    $ ./run_kselftest.sh
 
 To see the list of available tests, the `-l` option can be used::
 
    $ ./run_kselftest.sh -l
 
 The `-c` option can be used to run all the tests from a test collection, or
 the `-t` option for specific single tests. Either can be used multiple times::
 
    $ ./run_kselftest.sh -c bpf -c seccomp -t timers:posix_timers -t timer:nanosleep
 
 For other features see the script usage output, seen with the `-h` option.
 
 Packaging selftests
 ===================
 
 In some cases packaging is desired, such as when tests need to run on a
 different system. To package selftests, run::
 
    $ make -C tools/testing/selftests gen_tar
 
 This generates a tarball in the `INSTALL_PATH/kselftest-packages` directory. By
 default, `.gz` format is used. The tar compression format can be overridden by
 specifying a `FORMAT` make variable. Any value recognized by `tar's auto-compress`_
 option is supported, such as::
 
     $ make -C tools/testing/selftests gen_tar FORMAT=.xz
 
 `make gen_tar` invokes `make install` so you can use it to package a subset of
 tests by using variables specified in `Running a subset of selftests`_
 section::
 
     $ make -C tools/testing/selftests gen_tar TARGETS="bpf" FORMAT=.xz
 
 .. _tar's auto-compress: https://www.gnu.org/software/tar/manual/html_node/gzip.html#auto_002dcompress
 
 Contributing new tests
 ======================
 
 In general, the rules for selftests are
 
  * Do as much as you can if you're not root;
 
  * Don't take too long;
 
  * Don't break the build on any architecture, and
 
  * Don't cause the top-level "make run_tests" to fail if your feature is
    unconfigured.
 
 Contributing new tests (details)
 ================================
 
  * In your Makefile, use facilities from lib.mk by including it instead of
    reinventing the wheel. Specify flags and binaries generation flags on
    need basis before including lib.mk. ::
 
     CFLAGS = $(KHDR_INCLUDES)
     TEST_GEN_PROGS := close_range_test
     include ../lib.mk
 
  * Use TEST_GEN_XXX if such binaries or files are generated during
    compiling.
 
    TEST_PROGS, TEST_GEN_PROGS mean it is the executable tested by
    default.
 
    TEST_CUSTOM_PROGS should be used by tests that require custom build
    rules and prevent common build rule use.
 
    TEST_PROGS are for test shell scripts. Please ensure shell script has
    its exec bit set. Otherwise, lib.mk run_tests will generate a warning.
 
    TEST_CUSTOM_PROGS and TEST_PROGS will be run by common run_tests.
 
    TEST_PROGS_EXTENDED, TEST_GEN_PROGS_EXTENDED mean it is the
    executable which is not tested by default.
    TEST_FILES, TEST_GEN_FILES mean it is the file which is used by
    test.
 
  * First use the headers inside the kernel source and/or git repo, and then the
    system headers.  Headers for the kernel release as opposed to headers
    installed by the distro on the system should be the primary focus to be able
    to find regressions. Use KHDR_INCLUDES in Makefile to include headers from
    the kernel source.
 
  * If a test needs specific kernel config options enabled, add a config file in
    the test directory to enable them.
 
    e.g: tools/testing/selftests/android/config
 
  * Create a .gitignore file inside test directory and add all generated objects
    in it.
 
  * Add new test name in TARGETS in selftests/Makefile::
 
     TARGETS += android
 
  * All changes should pass::
 
     kselftest-{all,install,clean,gen_tar}
     kselftest-{all,install,clean,gen_tar} O=abo_path
     kselftest-{all,install,clean,gen_tar} O=rel_path
     make -C tools/testing/selftests {all,install,clean,gen_tar}
     make -C tools/testing/selftests {all,install,clean,gen_tar} O=abs_path
     make -C tools/testing/selftests {all,install,clean,gen_tar} O=rel_path
 
 Test Module
 ===========
 
 Kselftest tests the kernel from userspace.  Sometimes things need
 testing from within the kernel, one method of doing this is to create a
 test module.  We can tie the module into the kselftest framework by
 using a shell script test runner.  ``kselftest/module.sh`` is designed
 to facilitate this process.  There is also a header file provided to
 assist writing kernel modules that are for use with kselftest:
 
 - ``tools/testing/selftests/kselftest_module.h``
 - ``tools/testing/selftests/kselftest/module.sh``
 
 Note that test modules should taint the kernel with TAINT_TEST. This will
 happen automatically for modules which are in the ``tools/testing/``
 directory, or for modules which use the ``kselftest_module.h`` header above.
 Otherwise, you'll need to add ``MODULE_INFO(test, "Y")`` to your module
 source. selftests which do not load modules typically should not taint the
 kernel, but in cases where a non-test module is loaded, TEST_TAINT can be
 applied from userspace by writing to ``/proc/sys/kernel/tainted``.
 
 How to use
 ----------
 
 Here we show the typical steps to create a test module and tie it into
 kselftest.  We use kselftests for lib/ as an example.
 
 1. Create the test module
 
 2. Create the test script that will run (load/unload) the module
    e.g. ``tools/testing/selftests/lib/printf.sh``
 
 3. Add line to config file e.g. ``tools/testing/selftests/lib/config``
 
 4. Add test script to makefile  e.g. ``tools/testing/selftests/lib/Makefile``
 
 5. Verify it works:
 
 .. code-block:: sh
 
    # Assumes you have booted a fresh build of this kernel tree
    cd /path/to/linux/tree
    make kselftest-merge
    make modules
    sudo make modules_install
    make TARGETS=lib kselftest
 
 Example Module
 --------------
 
 A bare bones test module might look like this:
 
 .. code-block:: c
 
    // SPDX-License-Identifier: GPL-2.0+
 
    #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
    #include "../tools/testing/selftests/kselftest/module.h"
 
    KSTM_MODULE_GLOBALS();
 
    /*
     * Kernel module for testing the foobinator
     */
 
    static int __init test_function()
    {
            ...
    }
 
    static void __init selftest(void)
    {
            KSTM_CHECK_ZERO(do_test_case("", 0));
    }
 
    KSTM_MODULE_LOADERS(test_foo);
    MODULE_AUTHOR("John Developer <jd@fooman.org>");
    MODULE_LICENSE("GPL");
    MODULE_INFO(test, "Y");
 
 Example test script
 -------------------
 
 .. code-block:: sh
 
     #!/bin/bash
     # SPDX-License-Identifier: GPL-2.0+
     $(dirname $0)/../kselftest/module.sh "foo" test_foo
 
 
 Test Harness
 ============
 
 The kselftest_harness.h file contains useful helpers to build tests.  The
 test harness is for userspace testing, for kernel space testing see `Test
 Module`_ above.
 
 The tests from tools/testing/selftests/seccomp/seccomp_bpf.c can be used as
 example.
 
 Example
 -------
 
 .. kernel-doc:: tools/testing/selftests/kselftest_harness.h
     :doc: example
 
 
 Helpers
 -------
 
 .. kernel-doc:: tools/testing/selftests/kselftest_harness.h
     :functions: TH_LOG TEST TEST_SIGNAL FIXTURE FIXTURE_DATA FIXTURE_SETUP
                 FIXTURE_TEARDOWN TEST_F TEST_HARNESS_MAIN FIXTURE_VARIANT
                 FIXTURE_VARIANT_ADD
 
 Operators
 ---------
 
 .. kernel-doc:: tools/testing/selftests/kselftest_harness.h
     :doc: operators
 
 .. kernel-doc:: tools/testing/selftests/kselftest_harness.h
     :functions: ASSERT_EQ ASSERT_NE ASSERT_LT ASSERT_LE ASSERT_GT ASSERT_GE
                 ASSERT_NULL ASSERT_TRUE ASSERT_NULL ASSERT_TRUE ASSERT_FALSE
                 ASSERT_STREQ ASSERT_STRNE EXPECT_EQ EXPECT_NE EXPECT_LT
                 EXPECT_LE EXPECT_GT EXPECT_GE EXPECT_NULL EXPECT_TRUE
                 EXPECT_FALSE EXPECT_STREQ EXPECT_STRNE

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