1======================
2Linux Kernel Selftests
3======================
4
5The kernel contains a set of "self tests" under the tools/testing/selftests/
6directory. These are intended to be small tests to exercise individual code
7paths in the kernel. Tests are intended to be run after building, installing
8and booting a kernel.
9
10Kselftest from mainline can be run on older stable kernels. Running tests
11from mainline offers the best coverage. Several test rings run mainline
12kselftest suite on stable releases. The reason is that when a new test
13gets added to test existing code to regression test a bug, we should be
14able to run that test on an older kernel. Hence, it is important to keep
15code that can still test an older kernel and make sure it skips the test
16gracefully on newer releases.
17
18You can find additional information on Kselftest framework, how to
19write new tests using the framework on Kselftest wiki:
20
21https://kselftest.wiki.kernel.org/
22
23On some systems, hot-plug tests could hang forever waiting for cpu and
24memory to be ready to be offlined. A special hot-plug target is created
25to run the full range of hot-plug tests. In default mode, hot-plug tests run
26in safe mode with a limited scope. In limited mode, cpu-hotplug test is
27run on a single cpu as opposed to all hotplug capable cpus, and memory
28hotplug test is run on 2% of hotplug capable memory instead of 10%.
29
30kselftest runs as a userspace process.  Tests that can be written/run in
31userspace may wish to use the `Test Harness`_.  Tests that need to be
32run in kernel space may wish to use a `Test Module`_.
33
34Running the selftests (hotplug tests are run in limited mode)
35=============================================================
36
37To build the tests::
38
39  $ make headers
40  $ make -C tools/testing/selftests
41
42To run the tests::
43
44  $ make -C tools/testing/selftests run_tests
45
46To build and run the tests with a single command, use::
47
48  $ make kselftest
49
50Note that some tests will require root privileges.
51
52Kselftest supports saving output files in a separate directory and then
53running tests. To locate output files in a separate directory two syntaxes
54are supported. In both cases the working directory must be the root of the
55kernel src. This is applicable to "Running a subset of selftests" section
56below.
57
58To build, save output files in a separate directory with O= ::
59
60  $ make O=/tmp/kselftest kselftest
61
62To build, save output files in a separate directory with KBUILD_OUTPUT ::
63
64  $ export KBUILD_OUTPUT=/tmp/kselftest; make kselftest
65
66The O= assignment takes precedence over the KBUILD_OUTPUT environment
67variable.
68
69The above commands by default run the tests and print full pass/fail report.
70Kselftest supports "summary" option to make it easier to understand the test
71results. Please find the detailed individual test results for each test in
72/tmp/testname file(s) when summary option is specified. This is applicable
73to "Running a subset of selftests" section below.
74
75To run kselftest with summary option enabled ::
76
77  $ make summary=1 kselftest
78
79Running a subset of selftests
80=============================
81
82You can use the "TARGETS" variable on the make command line to specify
83single test to run, or a list of tests to run.
84
85To run only tests targeted for a single subsystem::
86
87  $ make -C tools/testing/selftests TARGETS=ptrace run_tests
88
89You can specify multiple tests to build and run::
90
91  $  make TARGETS="size timers" kselftest
92
93To build, save output files in a separate directory with O= ::
94
95  $ make O=/tmp/kselftest TARGETS="size timers" kselftest
96
97To build, save output files in a separate directory with KBUILD_OUTPUT ::
98
99  $ export KBUILD_OUTPUT=/tmp/kselftest; make TARGETS="size timers" kselftest
100
101Additionally you can use the "SKIP_TARGETS" variable on the make command
102line to specify one or more targets to exclude from the TARGETS list.
103
104To run all tests but a single subsystem::
105
106  $ make -C tools/testing/selftests SKIP_TARGETS=ptrace run_tests
107
108You can specify multiple tests to skip::
109
110  $  make SKIP_TARGETS="size timers" kselftest
111
112You can also specify a restricted list of tests to run together with a
113dedicated skiplist::
114
115  $  make TARGETS="bpf breakpoints size timers" SKIP_TARGETS=bpf kselftest
116
117See the top-level tools/testing/selftests/Makefile for the list of all
118possible targets.
119
120Running the full range hotplug selftests
121========================================
122
123To build the hotplug tests::
124
125  $ make -C tools/testing/selftests hotplug
126
127To run the hotplug tests::
128
129  $ make -C tools/testing/selftests run_hotplug
130
131Note that some tests will require root privileges.
132
133
134Install selftests
135=================
136
137You can use the "install" target of "make" (which calls the `kselftest_install.sh`
138tool) to install selftests in the default location (`tools/testing/selftests/kselftest_install`),
139or in a user specified location via the `INSTALL_PATH` "make" variable.
140
141To install selftests in default location::
142
143   $ make -C tools/testing/selftests install
144
145To install selftests in a user specified location::
146
147   $ make -C tools/testing/selftests install INSTALL_PATH=/some/other/path
148
149Running installed selftests
150===========================
151
152Found in the install directory, as well as in the Kselftest tarball,
153is a script named `run_kselftest.sh` to run the tests.
154
155You can simply do the following to run the installed Kselftests. Please
156note some tests will require root privileges::
157
158   $ cd kselftest_install
159   $ ./run_kselftest.sh
160
161To see the list of available tests, the `-l` option can be used::
162
163   $ ./run_kselftest.sh -l
164
165The `-c` option can be used to run all the tests from a test collection, or
166the `-t` option for specific single tests. Either can be used multiple times::
167
168   $ ./run_kselftest.sh -c bpf -c seccomp -t timers:posix_timers -t timer:nanosleep
169
170For other features see the script usage output, seen with the `-h` option.
171
172Timeout for selftests
173=====================
174
175Selftests are designed to be quick and so a default timeout is used of 45
176seconds for each test. Tests can override the default timeout by adding
177a settings file in their directory and set a timeout variable there to the
178configured a desired upper timeout for the test. Only a few tests override
179the timeout with a value higher than 45 seconds, selftests strives to keep
180it that way. Timeouts in selftests are not considered fatal because the
181system under which a test runs may change and this can also modify the
182expected time it takes to run a test. If you have control over the systems
183which will run the tests you can configure a test runner on those systems to
184use a greater or lower timeout on the command line as with the `-o` or
185the `--override-timeout` argument. For example to use 165 seconds instead
186one would use:
187
188   $ ./run_kselftest.sh --override-timeout 165
189
190You can look at the TAP output to see if you ran into the timeout. Test
191runners which know a test must run under a specific time can then optionally
192treat these timeouts then as fatal.
193
194Packaging selftests
195===================
196
197In some cases packaging is desired, such as when tests need to run on a
198different system. To package selftests, run::
199
200   $ make -C tools/testing/selftests gen_tar
201
202This generates a tarball in the `INSTALL_PATH/kselftest-packages` directory. By
203default, `.gz` format is used. The tar compression format can be overridden by
204specifying a `FORMAT` make variable. Any value recognized by `tar's auto-compress`_
205option is supported, such as::
206
207    $ make -C tools/testing/selftests gen_tar FORMAT=.xz
208
209`make gen_tar` invokes `make install` so you can use it to package a subset of
210tests by using variables specified in `Running a subset of selftests`_
211section::
212
213    $ make -C tools/testing/selftests gen_tar TARGETS="bpf" FORMAT=.xz
214
215.. _tar's auto-compress: https://www.gnu.org/software/tar/manual/html_node/gzip.html#auto_002dcompress
216
217Contributing new tests
218======================
219
220In general, the rules for selftests are
221
222 * Do as much as you can if you're not root;
223
224 * Don't take too long;
225
226 * Don't break the build on any architecture, and
227
228 * Don't cause the top-level "make run_tests" to fail if your feature is
229   unconfigured.
230
231Contributing new tests (details)
232================================
233
234 * In your Makefile, use facilities from lib.mk by including it instead of
235   reinventing the wheel. Specify flags and binaries generation flags on
236   need basis before including lib.mk. ::
237
238    CFLAGS = $(KHDR_INCLUDES)
239    TEST_GEN_PROGS := close_range_test
240    include ../lib.mk
241
242 * Use TEST_GEN_XXX if such binaries or files are generated during
243   compiling.
244
245   TEST_PROGS, TEST_GEN_PROGS mean it is the executable tested by
246   default.
247
248   TEST_CUSTOM_PROGS should be used by tests that require custom build
249   rules and prevent common build rule use.
250
251   TEST_PROGS are for test shell scripts. Please ensure shell script has
252   its exec bit set. Otherwise, lib.mk run_tests will generate a warning.
253
254   TEST_CUSTOM_PROGS and TEST_PROGS will be run by common run_tests.
255
256   TEST_PROGS_EXTENDED, TEST_GEN_PROGS_EXTENDED mean it is the
257   executable which is not tested by default.
258   TEST_FILES, TEST_GEN_FILES mean it is the file which is used by
259   test.
260
261 * First use the headers inside the kernel source and/or git repo, and then the
262   system headers.  Headers for the kernel release as opposed to headers
263   installed by the distro on the system should be the primary focus to be able
264   to find regressions. Use KHDR_INCLUDES in Makefile to include headers from
265   the kernel source.
266
267 * If a test needs specific kernel config options enabled, add a config file in
268   the test directory to enable them.
269
270   e.g: tools/testing/selftests/android/config
271
272 * Create a .gitignore file inside test directory and add all generated objects
273   in it.
274
275 * Add new test name in TARGETS in selftests/Makefile::
276
277    TARGETS += android
278
279 * All changes should pass::
280
281    kselftest-{all,install,clean,gen_tar}
282    kselftest-{all,install,clean,gen_tar} O=abo_path
283    kselftest-{all,install,clean,gen_tar} O=rel_path
284    make -C tools/testing/selftests {all,install,clean,gen_tar}
285    make -C tools/testing/selftests {all,install,clean,gen_tar} O=abs_path
286    make -C tools/testing/selftests {all,install,clean,gen_tar} O=rel_path
287
288Test Module
289===========
290
291Kselftest tests the kernel from userspace.  Sometimes things need
292testing from within the kernel, one method of doing this is to create a
293test module.  We can tie the module into the kselftest framework by
294using a shell script test runner.  ``kselftest/module.sh`` is designed
295to facilitate this process.  There is also a header file provided to
296assist writing kernel modules that are for use with kselftest:
297
298- ``tools/testing/selftests/kselftest_module.h``
299- ``tools/testing/selftests/kselftest/module.sh``
300
301Note that test modules should taint the kernel with TAINT_TEST. This will
302happen automatically for modules which are in the ``tools/testing/``
303directory, or for modules which use the ``kselftest_module.h`` header above.
304Otherwise, you'll need to add ``MODULE_INFO(test, "Y")`` to your module
305source. selftests which do not load modules typically should not taint the
306kernel, but in cases where a non-test module is loaded, TEST_TAINT can be
307applied from userspace by writing to ``/proc/sys/kernel/tainted``.
308
309How to use
310----------
311
312Here we show the typical steps to create a test module and tie it into
313kselftest.  We use kselftests for lib/ as an example.
314
3151. Create the test module
316
3172. Create the test script that will run (load/unload) the module
318   e.g. ``tools/testing/selftests/lib/printf.sh``
319
3203. Add line to config file e.g. ``tools/testing/selftests/lib/config``
321
3224. Add test script to makefile  e.g. ``tools/testing/selftests/lib/Makefile``
323
3245. Verify it works:
325
326.. code-block:: sh
327
328   # Assumes you have booted a fresh build of this kernel tree
329   cd /path/to/linux/tree
330   make kselftest-merge
331   make modules
332   sudo make modules_install
333   make TARGETS=lib kselftest
334
335Example Module
336--------------
337
338A bare bones test module might look like this:
339
340.. code-block:: c
341
342   // SPDX-License-Identifier: GPL-2.0+
343
344   #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
345
346   #include "../tools/testing/selftests/kselftest_module.h"
347
348   KSTM_MODULE_GLOBALS();
349
350   /*
351    * Kernel module for testing the foobinator
352    */
353
354   static int __init test_function()
355   {
356           ...
357   }
358
359   static void __init selftest(void)
360   {
361           KSTM_CHECK_ZERO(do_test_case("", 0));
362   }
363
364   KSTM_MODULE_LOADERS(test_foo);
365   MODULE_AUTHOR("John Developer <jd@fooman.org>");
366   MODULE_LICENSE("GPL");
367   MODULE_INFO(test, "Y");
368
369Example test script
370-------------------
371
372.. code-block:: sh
373
374    #!/bin/bash
375    # SPDX-License-Identifier: GPL-2.0+
376    $(dirname $0)/../kselftest/module.sh "foo" test_foo
377
378
379Test Harness
380============
381
382The kselftest_harness.h file contains useful helpers to build tests.  The
383test harness is for userspace testing, for kernel space testing see `Test
384Module`_ above.
385
386The tests from tools/testing/selftests/seccomp/seccomp_bpf.c can be used as
387example.
388
389Example
390-------
391
392.. kernel-doc:: tools/testing/selftests/kselftest_harness.h
393    :doc: example
394
395
396Helpers
397-------
398
399.. kernel-doc:: tools/testing/selftests/kselftest_harness.h
400    :functions: TH_LOG TEST TEST_SIGNAL FIXTURE FIXTURE_DATA FIXTURE_SETUP
401                FIXTURE_TEARDOWN TEST_F TEST_HARNESS_MAIN FIXTURE_VARIANT
402                FIXTURE_VARIANT_ADD
403
404Operators
405---------
406
407.. kernel-doc:: tools/testing/selftests/kselftest_harness.h
408    :doc: operators
409
410.. kernel-doc:: tools/testing/selftests/kselftest_harness.h
411    :functions: ASSERT_EQ ASSERT_NE ASSERT_LT ASSERT_LE ASSERT_GT ASSERT_GE
412                ASSERT_NULL ASSERT_TRUE ASSERT_NULL ASSERT_TRUE ASSERT_FALSE
413                ASSERT_STREQ ASSERT_STRNE EXPECT_EQ EXPECT_NE EXPECT_LT
414                EXPECT_LE EXPECT_GT EXPECT_GE EXPECT_NULL EXPECT_TRUE
415                EXPECT_FALSE EXPECT_STREQ EXPECT_STRNE
416