[LTP] [PATCH 03/10] Rewrite writing tests guidelines documentation
Andrea Cervesato
andrea.cervesato@suse.de
Wed Mar 20 17:20:47 CET 2024
From: Andrea Cervesato <andrea.cervesato@suse.com>
The writing tests guidelines documentation has been adapted into
the RST format, as well as fixing typos and syntax errors.
make check errors messages are documented here, after being
previously inside user guidelines.
---
doc_new/developers/writing_tests.rst | 517 +++++++++++++++++++++++++++++++++++
1 file changed, 517 insertions(+)
diff --git a/doc_new/developers/writing_tests.rst b/doc_new/developers/writing_tests.rst
index ba0188aee..7b4b70bd0 100644
--- a/doc_new/developers/writing_tests.rst
+++ b/doc_new/developers/writing_tests.rst
@@ -3,6 +3,343 @@
Writing tests
=============
+This document describes LTP guidelines and it's intended for anybody who wants
+to write or to modify a LTP testcase. It's not a definitive guide and it's not,
+by any means, a substitute for common sense.
+
+Guide to clean and understandable code
+--------------------------------------
+
+Testcases require that the source code is easy to follow. When a test starts to
+fail, the failure has to be analyzed and clean test codebase makes this task
+much easier and quicker.
+
+Keep things simple
+~~~~~~~~~~~~~~~~~~
+
+It's worth to keep testcases simple or, better, as simple as possible.
+
+The kernel and libc are tricky beasts and the complexity imposed by their
+interfaces is quite high. Concentrate on the interface you want to test and
+follow the UNIX philosophy.
+
+It's a good idea to make the test as self-contained as possible too, ideally
+tests should not depend on tools or libraries that are not widely available.
+
+Do not reinvent the wheel!
+
+* Use LTP standard interface
+* Do not add custom PASS/FAIL reporting functions
+* Do not write Makefiles from scratch, use LTP build system instead
+* Etc.
+
+Keep functions and variable names short
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Choosing a good name for an API functions or even variables is a difficult
+task do not underestimate it.
+
+There are a couple of customary names for different things that help people to
+understand code, for example:
+
+* For loop variables are usually named with a single letter ``i``, ``j``, ...
+* File descriptors ``fd`` or ``fd_foo``.
+* Number of bytes stored in file are usually named as ``size`` or ``len``
+* Etc.
+
+Do not overcomment
+~~~~~~~~~~~~~~~~~~
+
+Comments can sometimes save your day, but they can easily do more harm than
+good. There has been several cases where comments and actual implementation
+drifted slowly apart which yielded into API misuses and hard to find bugs.
+Remember there is only one thing worse than no documentation: wrong
+documentation.
+
+Ideally, everybody should write code that is obvious, which unfortunately isn't
+always possible. If there is a code that requires to be commented, keep it
+short and to the point. These comments should explain *why* and not *how*
+things are done.
+
+Never ever comment the obvious.
+
+In case of LTP testcases, it's customary to add an asciidoc formatted comment
+paragraph with highlevel test description at the beginning of the file right
+under the GPL SPDX header. This helps other people to understand the overall
+goal of the test before they dive into the technical details. It's also
+exported into generated documentation hence it should mostly explain what is
+tested.
+
+DRY (Code duplication)
+~~~~~~~~~~~~~~~~~~~~~~
+
+Copy & paste is a good servant but very poor master. If you are about to copy a
+large part of the code from one testcase to another, think what would happen if
+you find bug in the code that has been copied all around the tree. What about
+moving it to a library instead?
+
+The same goes for short but complicated parts, whenever you are about to copy &
+paste a syscall wrapper that packs arguments accordingly to machine
+architecture or similarly complicated code, put it into a header instead.
+
+C coding style
+--------------
+
+LTP adopted `Linux kernel coding style <https://www.kernel.org/doc/html/latest/process/coding-style.html>`_.
+Run ``make check`` in the test's directory and/or use ``make check-$TCID``, it
+uses (among other checks) our vendored version of
+`checkpatch.pl <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/scripts/checkpatch.pl>`_
+script from kernel git tree.
+
+.. note::
+ If ``make check`` does not report any problems, the code still may be wrong
+ as all tools used for checking only look for common mistakes.
+
+The following linting code can be found when we run ``make check``:
+
+.. list-table::
+ :header-rows: 1
+
+ * - Linting code
+ - Message
+ - Explanation
+
+ * - LTP-001
+ - Library source files have ``tst_`` prefix
+ - API source code is inside headers in ``include/{empty}*.h``,
+ ``include/lapi/{empty}*.h`` (backward compatibility for old kernel and
+ libc) and C sources in ``lib/{empty}*.c``. Files must have ``tst_``
+ prefix.
+
+ * - LTP-002
+ - ``TST_RET`` and ``TST_ERR`` are never modified by test library functions
+ - The test author is guaranteed that the test API will not modify these
+ variables. This prevents silent errors where the return value and
+ errno are overwritten before the test has chance to check them.
+
+ The macros which are clearly intended to update these variables. That
+ is ``TEST`` and those in ``tst_test_macros.h``. Are of course allowed to
+ update these variables.
+
+ * - LTP-003
+ - Externally visible library symbols have the ``tst_`` prefix
+ - Functions, types and variables in the public test API should have the
+ ``tst_`` prefix. With some exceptions for symbols already prefixed with
+ ``safe_`` or ``ltp_``.
+
+ Static (private) symbols should not have the prefix.
+
+ * - LTP-004
+ - Test executable symbols are marked ``static``
+ - Test executables should not export symbols unnecessarily. This means
+ that all top-level variables and functions should be marked with the
+ ``static`` keyword. The only visible symbols should be those included
+ from shared object files.
+
+ * - LTP-005
+ - Array must terminate with a sentinel value (i.e. ``NULL`` or ``{}``)
+ - When defining arrays in the ``struct tst_test`` structure, we need to
+ end the array items with a sentinel ``NULL`` value.
+
+Shell coding style
+------------------
+
+When writing testcases in shell, write in *portable shell* only, it's a good
+idea to try to run the test using alternative shell (alternative to bash, for
+example dash) too.
+
+*Portable shell* means Shell Command Language as defined by POSIX with an
+exception of few widely used extensions, namely **local** keyword used inside of
+functions and ``-o`` and ``-a`` test parameters (that are marked as obsolete in
+POSIX).
+
+You can either try to run the testcases in Debian which has ``/bin/sh`` pointing
+to ``dash`` by default, or to install ``dash`` on your favorite distribution,
+then use it to run tests. If your distribution lacks ``dash`` package, you can
+always compile it from `sources <http://gondor.apana.org.au/~herbert/dash/files/>`_.
+
+Run ``make check`` in the test's directory and/or use ``make check-$TCID.sh``.
+It uses (among other checks) our vendored version of
+`checkbashism.pl <https://salsa.debian.org/debian/devscripts/raw/master/scripts/checkbashisms.pl>`_
+from Debian that is used to check for non-portable shell code.
+
+.. note::
+
+ If ``make check`` does not report any problems the code still may be wrong,
+ as ``checkbashisms.pl`` is used for checking only common mistakes.
+
+Here there are some common sense style rules for shell
+
+* Keep lines under 80 chars
+* Use tabs for indentation
+* Keep things simple, avoid unnecessary subshells
+* Don't do confusing things (i.e. don't name your functions like common shell
+ commands, etc.)
+* Quote variables
+* Be consistent
+
+3 Backwards compatibility
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+LTP test should be as backward compatible as possible. Think of an enterprise
+distributions with long term support (more than five years since the initial
+release) or of an embedded platform that needs to use several years old
+toolchain supplied by the manufacturer.
+
+Therefore LTP test for more current features should be able to cope with older
+systems. It should at least compile fine and if it's not appropriate for the
+configuration it should return ``TCONF``.
+
+There are several types of checks we use:
+
+* The *configure script* is usually used to detect availability of a function
+ declarations in system headers. It's used to disable tests at compile time or
+ to enable fallback definitions.
+
+* Checking the ``errno`` value is another type of runtime check. Most of the
+ syscalls returns either ``EINVAL`` or ``ENOSYS`` when syscall was not
+ implemented or was disabled upon kernel compilation.
+
+* LTP has kernel version detection that can be used to disable tests at runtime.
+ Unfortunately, the kernel version does not always corresponds to a well
+ defined feature set, as distributions tend to backport hundreds of patches
+ while the kernel version stays the same. Use with caution.
+
+* Lately, we added a kernel ``.config`` parser. A test can define a boolean
+ expression of kernel config variables that has to be satisfied in order to run
+ a test. At the moment, this is mostly used for kernel namespaces.
+
+* Sometimes it makes sense to define a few macros instead of creating a
+ configure test. One example is Linux specific POSIX clock ids in
+ ``include/lapi/posix_clocks.h``
+
+Dealing with messed up legacy code
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+LTP still contains a lot of old and messy code and we are cleaning it up as
+fast as we can but, despite the decade of efforts, there is still a lot of it.
+If you start modifying old or a messy testcase and your changes are more
+complicated than simple typo fixes, you should convert the test into a new
+library first.
+
+It's also much easier to review the changes if you split them into a smaller
+logical groups. The same goes for moving files: if you need to rename or to move
+files, do it in a separate patch.
+
+License
+~~~~~~~
+
+Code contributed to LTP should be licensed under GPLv2+ (GNU GPL version 2 or
+any later version).
+
+Use ``SPDX-License-Identifier: GPL-2.0-or-later``
+
+LTP Structure
+-------------
+
+The structure of LTP is quite simple. Each test is a binary written either in
+portable shell or C. The test gets a configuration via environment variables
+and/or command line parameters, it prints additional information into the
+stdout and reports overall success/failure via the exit value.
+
+Tests are generally placed under the ``testcases/`` directory. Everything that
+is a syscall or (slightly confusingly) libc syscall wrapper, goes under
+``testcases/kernel/syscalls/``.
+
+There is also ``testcases/open_posix_testsuite/`` which is a well maintained
+fork of the Open POSIX testsuite project, that has been dead since 2005.
+
+We also have a number of directories with tests for more specific features, such
+as containers, etc.
+
+Runtest Files
+~~~~~~~~~~~~~
+
+The list of tests to be executed is stored in runtest files under the
+``runtest/`` directory. The default set of runtest files to be executed is
+stored in ``scenario_groups/default``. When you add a test, you should add
+corresponding entries into some runtest file(s) as well.
+
+Each line of runtest file contains one test. The first item is the test name.
+All other items, separated by space will be executed as a command.
+
+.. code-block:: bash
+
+ shell_test01 echo "SUCCESS" | shell_pipe01.sh
+ splice02 splice02 -s 20
+
+Blank lines and lines starting with a ``#`` (comments) are ignored.
+
+Syscalls tests, placed under ``testcases/kernel/syscalls/``, use
+``runtest/syscalls`` file. For kernel related tests for memory management we
+have ``runtest/mm``, etc.
+
+.. note::
+
+ runtest files should have one entry per a test. Creating a
+ wrapper that runs all your tests and adding it as a single test
+ into runtest file is strongly discouraged.
+
+Datafiles
+---------
+
+If your test needs data files, these should be put into a subdirectory
+named ``datafiles`` and installed into the ``testcases/data/$TCID`` directory.
+This will require to add ``INSTALL_DIR := testcases/data/TCID`` into
+``datafiles/Makefile``.
+
+You can obtain path to datafiles via ``$TST_DATAROOT`` provided by ``test.sh``
+or via C function ``tst_dataroot()`` provided by libltp:
+
+.. code-block:: c
+
+ const char *dataroot = tst_dataroot();
+
+Datafiles can also be accessed as ``$LTPROOT/testcases/data/$TCID/...``,
+but ``$TST_DATAROOT`` and ``tst_dataroot()`` are preferred, as these can be used
+when running testcases directly in git tree as well as from install location.
+
+Subexecutables
+~~~~~~~~~~~~~~
+
+If your test needs to execute a binary, place it in the same directory of the
+testcase and name the binary with ``$TESTNAME_`` prefix, where ``$TESTNAME`` is
+the name of the test binary. Once the test is executed by the framework, the
+path to the directory with all LTP binaries is added to the ``$PATH`` and you
+can execute it via its name.
+
+.. note::
+
+ If you need to execute a test from the LTP tree, you can add ``PATH`` to
+ the current directory with ``PATH="$PATH:$PWD" ./foo01``.
+
+Test Contribution Checklist
+---------------------------
+
+#. Test compiles and it runs fine (check with ``-i 10`` and ``-i 0`` too)
+#. ``make check`` should not emit any warnings for the test you are working on
+ (hint: run it in the test's directory and/or use ``make check-$TCID``)
+#. The runtest entries are in place
+#. New test binaries are added into the corresponding ``.gitignore`` files
+#. Patches apply over the latest git
+
+About .gitignore files
+~~~~~~~~~~~~~~~~~~~~~~
+
+There are numerous ``.gitignore`` files in the LTP tree. Usually, there is a
+``.gitignore`` file for a group of tests. The reason of this setup is simple:
+it's easier to maintain a ``.gitignore`` file per tests' directory, rather
+than having a single file in the project root directory. In this way, we don't
+have to update all the gitignore files when moving directories, and they get
+deleted automatically when a directory with tests is removed.
+
+Testing pre-release kernel features
+-----------------------------------
+
+Tests for features not yet in the mainline kernel release are accepted. However,
+they must be added only to the **staging** runtest file. Once a feature is part
+of the stable kernel ABI, the associated test must be moved out of staging.
+
Testing builds with GitHub Actions
----------------------------------
@@ -18,3 +355,183 @@ check ``.github/workflows/ci.yml``.
different distributions on their **newest releases**.
The CI also checks for code linting, running ``make check`` in the whole
LTP project.
+
+LTP C And Shell Test API Comparison
+-----------------------------------
+
+.. list-table::
+ :header-rows: 1
+
+ * - C API ``struct tst_test`` members
+ - Shell API ``$TST_*`` variables
+
+ * - .all_filesystems
+ - TST_ALL_FILESYSTEMS
+
+ * - .bufs
+ - \-
+
+ * - .caps
+ - \-
+
+ * - .child_needs_reinit
+ - not applicable
+
+ * - .cleanup
+ - TST_CLEANUP
+
+ * - .dev_extra_opts
+ - TST_DEV_EXTRA_OPTS
+
+ * - .dev_fs_opts
+ - TST_DEV_FS_OPTS
+
+ * - .dev_fs_type
+ - TST_FS_TYPE
+
+ * - .dev_min_size
+ - not applicable
+
+ * - .format_device
+ - TST_FORMAT_DEVICE
+
+ * - .max_runtime
+ - \-
+
+ * - .min_cpus
+ - not applicable
+
+ * - .min_kver
+ - TST_MIN_KVER
+
+ * - .min_mem_avail
+ - not applicable
+
+ * - .mnt_flags
+ - TST_MNT_PARAMS
+
+ * - .min_swap_avail
+ - not applicable
+
+ * - .mntpoint | .mnt_data
+ - TST_MNTPOINT
+
+ * - .mount_device
+ - TST_MOUNT_DEVICE
+
+ * - .needs_cgroup_ctrls
+ - \-
+
+ * - .needs_checkpoints
+ - TST_NEEDS_CHECKPOINTS
+
+ * - .needs_cmds
+ - TST_NEEDS_CMDS
+
+ * - .needs_devfs
+ - \-
+
+ * - .needs_device
+ - TST_NEEDS_DEVICE
+
+ * - .needs_drivers
+ - TST_NEEDS_DRIVERS
+
+ * - .needs_kconfigs
+ - TST_NEEDS_KCONFIGS
+
+ * - .needs_overlay
+ - \-
+
+ * - .needs_rofs
+ - \-
+
+ * - .needs_root
+ - TST_NEEDS_ROOT
+
+ * - .needs_tmpdir
+ - TST_NEEDS_TMPDIR
+
+ * - .options
+ - TST_PARSE_ARGS | TST_OPTS
+
+ * - .resource_files
+ - \-
+
+ * - .restore_wallclock
+ - not applicable
+
+ * - .sample
+ - \-
+
+ * - .save_restore
+ - \-
+
+ * - .scall
+ - not applicable
+
+ * - .setup
+ - TST_SETUP
+
+ * - .skip_filesystems
+ - TST_SKIP_FILESYSTEMS
+
+ * - .skip_in_compat
+ - \-
+
+ * - .skip_in_lockdown
+ - TST_SKIP_IN_LOCKDOWN
+
+ * - .skip_in_secureboot
+ - TST_SKIP_IN_SECUREBOOT
+
+ * - .supported_archs
+ - not applicable
+
+ * - .tags
+ - \-
+
+ * - .taint_check
+ - \-
+
+ * - .tcnt
+ - TST_CNT
+
+ * - .tconf_msg
+ - not applicable
+
+ * - .test | .test_all
+ - TST_TESTFUNC
+
+ * - .test_variants
+ - \-
+
+ * - .timeout
+ - TST_TIMEOUT
+
+ * - .tst_hugepage
+ - not applicable
+
+ * - .ulimit
+ - not applicable
+
+ * - not applicable
+ - TST_NEEDS_KCONFIGS_IFS
+
+ * - not applicable
+ - TST_NEEDS_MODULE
+
+ * - not applicable
+ - TST_POS_ARGS
+
+ * - not applicable
+ - TST_USAGE
+
+.. list-table::
+ :header-rows: 1
+
+ * - C API other structs
+ - Shell API ``$TST_*`` variables
+
+ * - struct tst_device
+ - TST_DEVICE
--
2.35.3
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