6. C Development Helpers

6.1. Refactoring

Pacemaker uses an optional tool called coccinelle to do automatic refactoring. coccinelle is a very complicated tool that can be difficult to understand, and the existing documentation makes it pretty tough to get started. Much of the documentation is either aimed at kernel developers or takes the form of grammars.

However, it can apply very complex transformations across an entire source tree. This is useful for tasks like code refactoring, changing APIs (number or type of arguments, etc.), catching functions that should not be called, and changing existing patterns.

coccinelle is driven by input scripts called semantic patches written in its own language. These scripts bear a passing resemblance to source code patches and tell coccinelle how to match and modify a piece of source code. They are stored in devel/coccinelle and each script either contains a single source transformation or several related transformations. In general, we try to keep these as simple as possible.

In Pacemaker development, we use a couple targets in devel/Makefile.am to control coccinelle. The cocci target tries to apply each script to every Pacemaker source file, printing out any changes it would make to the console. The cocci-inplace target does the same but also makes those changes to the source files. A variety of warnings might also be printed. If you aren’t working on a new script, these can usually be ignored.

If you are working on a new coccinelle script, it can be useful (and faster) to skip everything else and only run the new script. The COCCI_FILES variable can be used for this:

$ make -C devel COCCI_FILES=coccinelle/new-file.cocci cocci

This variable is also used for preventing some coccinelle scripts in the Pacemaker source tree from running. Some scripts are disabled because they are not currently fully working or because they are there as templates. When adding a new script, remember to add it to this variable if it should always be run.

One complication when writing coccinelle scripts is that certain Pacemaker source files may not use private functions (those whose name starts with pcmk__). Handling this requires work in both the Makefile and in the coccinelle scripts.

The Makefile deals with this by maintaining two lists of source files: those that may use private functions and those that may not. For those that may, a special argument (-D internal) is added to the coccinelle command line. This creates a virtual dependency named internal.

In the coccinelle scripts, those transformations that modify source code to use a private function also have a dependency on internal. If that dependency was given on the command line, the transformation will be run. Otherwise, it will be skipped.

This means that not all instances of an older style of code will be changed after running a given transformation. Some developer intervention is still necessary to know whether a source code block should have been changed or not.

Probably the easiest way to learn how to use coccinelle is by following other people’s scripts. In addition to the ones in the Pacemaker source directory, there’s several others on the coccinelle website.

6.2. Unit Testing

Where possible, changes to the C side of Pacemaker should be accompanied by unit tests. Much of Pacemaker cannot effectively be unit tested (and there are other testing systems used for those parts), but the lib subdirectory is pretty easy to write tests for.

Pacemaker uses the cmocka unit testing framework which looks a lot like other unit testing frameworks for C and should be fairly familiar. In addition to regular unit tests, cmocka also gives us the ability to use mock functions for unit testing functions that would otherwise be difficult to test.

6.2.1. Organization

Pay close attention to the organization and naming of test cases to ensure the unit tests continue to work as they should.

Tests are spread throughout the source tree, alongside the source code they test. For instance, all the tests for the source code in lib/common/ are in the lib/common/tests directory. If there is no tests subdirectory, there are no tests for that library yet.

Under that directory, there is a Makefile.am and additional subdirectories. Each subdirectory contains the tests for a single library source file. For instance, all the tests for lib/common/strings.c are in the lib/common/tests/strings directory. Note that the test subdirectory does not have a .c suffix. If there is no test subdirectory, there are no tests for that file yet.

Finally, under that directory, there is a Makefile.am and then various source files. Each of these source files tests the single function that it is named after. For instance, lib/common/tests/strings/pcmk__btoa_test.c tests the pcmk__btoa_test() function in lib/common/strings.c. If there is no test source file, there are no tests for that function yet.

The _test suffix on the test source file is important. All tests have this suffix, which means all the compiled test cases will also end with this suffix. That lets us ignore all the compiled tests with a single line in .gitignore:

/lib/*/tests/*/*_test

6.2.2. Adding a test

6.2.2.1. Testing a new function in an already testable source file

Follow these steps if you want to test a function in a source file where there are already other tested functions. For the purposes of this example, we will add a test for the pcmk__scan_port() function in lib/common/strings.c. As you can see, there are already tests for other functions in this same file in the lib/common/tests/strings directory.

  • cd into lib/common/tests/strings

  • Add the new file to the the check_PROGRAMS variable in Makefile.am, making it something like this:

    check_PROGRAMS = \
           pcmk__add_word_test             \
           pcmk__btoa_test                 \
           pcmk__scan_port_test
    
  • Create a new pcmk__scan_port_test.c file, copying the copyright and include boilerplate from another file in the same directory.

  • Continue with the steps in Writing the test.

6.2.2.2. Testing a function in a source file without tests

Follow these steps if you want to test a function in a source file where there are not already other tested functions, but there are tests for other files in the same library. For the purposes of this example, we will add a test for the pcmk_acl_required() function in lib/common/acls.c. At the time of this documentation being written, no tests existed for that source file, so there is no lib/common/tests/acls directory.

  • Add to AC_CONFIG_FILES in the top-level configure.ac file so the build process knows to use directory we’re about to create. That variable would now look something like:

    dnl Other files we output
    AC_CONFIG_FILES(Makefile                                            \
                    ...
                    lib/common/tests/Makefile                           \
                    lib/common/tests/acls/Makefile                      \
                    lib/common/tests/agents/Makefile                    \
                    ...
    )
    
  • cd into lib/common/tests

  • Add to the SUBDIRS variable in Makefile.am, making it something like:

    SUBDIRS = agents acls cmdline flags operations strings utils xpath results
    
  • Create a new acls directory, copying the Makefile.am from some other directory.

  • cd into acls

  • Get rid of any existing values for check_PROGRAMS and set it to pcmk_acl_required_test like so:

    check_PROGRAMS = pcmk_acl_required_test
    
  • Follow the steps in Testing a new function in an already testable source file to create the new pcmk_acl_required_test.c file.

6.2.2.3. Testing a function in a library without tests

Adding a test case for a function in a library that doesn’t have any test cases to begin with is only slightly more complicated. In general, the steps are the same as for the previous section, except with an additional layer of directory creation.

For the purposes of this example, we will add a test case for the lrmd_send_resource_alert() function in lib/lrmd/lrmd_alerts.c. Note that this may not be a very good function or even library to write actual unit tests for.

  • Add to AC_CONFIG_FILES in the top-level configure.ac file so the build process knows to use directory we’re about to create. That variable would now look something like:

    dnl Other files we output
    AC_CONFIG_FILES(Makefile                                            \
                    ...
                    lib/lrmd/Makefile                                   \
                    lib/lrmd/tests/Makefile                             \
                    lib/services/Makefile                               \
                    ...
    )
    
  • cd into lib/lrmd

  • Create a SUBDIRS variable in Makefile.am if it doesn’t already exist. Most libraries should not have this variable already.

    SUBDIRS = tests
    
  • Create a new tests directory and add a Makefile.am with the following contents:

    SUBDIRS = lrmd_alerts
    
  • Follow the steps in Testing a function in a source file without tests to create the rest of the new directory structure.

  • Follow the steps in Testing a new function in an already testable source file to create the new lrmd_send_resource_alert_test.c file.

6.2.2.4. Adding to an existing test case

If all you need to do is add additional test cases to an existing file, none of the above work is necessary. All you need to do is find the test source file with the name matching your function and add to it and then follow the instructions in Writing the test.

6.2.3. Writing the test

A test case file contains a fair amount of boilerplate. For this reason, it’s usually easiest to just copy an existing file and adapt it to your needs. However, here’s the basic structure:

/*
 * Copyright 2021 the Pacemaker project contributors
 *
 * The version control history for this file may have further details.
 *
 * This source code is licensed under the GNU Lesser General Public License
 * version 2.1 or later (LGPLv2.1+) WITHOUT ANY WARRANTY.
 */

#include <crm_internal.h>

#include <stdarg.h>
#include <stddef.h>
#include <stdint.h>
#include <setjmp.h>
#include <cmocka.h>

/* Put your test-specific includes here */

/* Put your test functions here */

int
main(int argc, char **argv)
{
    /* Register your test functions here */

    cmocka_set_message_output(CM_OUTPUT_TAP);
    return cmocka_run_group_tests(tests, NULL, NULL);
}

Each test-specific function should test one aspect of the library function, though it can include many assertions if there are many ways of testing that one aspect. For instance, there might be multiple ways of testing regular expression matching:

static void
regex(void **state) {
    const char *s1 = "abcd";
    const char *s2 = "ABCD";

    assert_int_equal(pcmk__strcmp(NULL, "a..d", pcmk__str_regex), 1);
    assert_int_equal(pcmk__strcmp(s1, NULL, pcmk__str_regex), 1);
    assert_int_equal(pcmk__strcmp(s1, "a..d", pcmk__str_regex), 0);
}

Each test-specific function must also be registered or it will not be called. This is done with cmocka_unit_test() in the main function:

const struct CMUnitTest tests[] = {
    cmocka_unit_test(regex),
};

6.2.4. Running

If you had to create any new files or directories, you will first need to run ./configure from the top level of the source directory. This will regenerate the Makefiles throughout the tree. If you skip this step, your changes will be skipped and you’ll be left wondering why the output doesn’t match what you expected.

To run the tests, simply run make check after previously building the source with make. The test cases in each directory will be built and then run. This should not take long. If all the tests succeed, you will be back at the prompt. Scrolling back through the history, you should see lines like the following:

PASS: pcmk__strcmp_test 1 - same_pointer
PASS: pcmk__strcmp_test 2 - one_is_null
PASS: pcmk__strcmp_test 3 - case_matters
PASS: pcmk__strcmp_test 4 - case_insensitive
PASS: pcmk__strcmp_test 5 - regex
============================================================================
Testsuite summary for pacemaker 2.1.0
============================================================================
# TOTAL: 33
# PASS:  33
# SKIP:  0
# XFAIL: 0
# FAIL:  0
# XPASS: 0
# ERROR: 0
============================================================================
make[7]: Leaving directory '/home/clumens/src/pacemaker/lib/common/tests/strings'

The testing process will quit on the first failed test, and you will see lines like these:

PASS: pcmk__scan_double_test 3 - trailing_chars
FAIL: pcmk__scan_double_test 4 - typical_case
PASS: pcmk__scan_double_test 5 - double_overflow
PASS: pcmk__scan_double_test 6 - double_underflow
ERROR: pcmk__scan_double_test - exited with status 1
PASS: pcmk__starts_with_test 1 - bad_input
============================================================================
Testsuite summary for pacemaker 2.1.0
============================================================================
# TOTAL: 56
# PASS:  54
# SKIP:  0
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 1
============================================================================
See lib/common/tests/strings/test-suite.log
Please report to users@clusterlabs.org
============================================================================
make[7]: *** [Makefile:1218: test-suite.log] Error 1
make[7]: Leaving directory '/home/clumens/src/pacemaker/lib/common/tests/strings'

The failure is in lib/common/tests/strings/test-suite.log:

ERROR: pcmk__scan_double_test
=============================

1..6
ok 1 - empty_input_string
PASS: pcmk__scan_double_test 1 - empty_input_string
ok 2 - bad_input_string
PASS: pcmk__scan_double_test 2 - bad_input_string
ok 3 - trailing_chars
PASS: pcmk__scan_double_test 3 - trailing_chars
not ok 4 - typical_case
FAIL: pcmk__scan_double_test 4 - typical_case
# 0.000000 != 3.000000
# pcmk__scan_double_test.c:80: error: Failure!
ok 5 - double_overflow
PASS: pcmk__scan_double_test 5 - double_overflow
ok 6 - double_underflow
PASS: pcmk__scan_double_test 6 - double_underflow
# not ok - tests
ERROR: pcmk__scan_double_test - exited with status 1

At this point, you need to determine whether your test case is incorrect or whether the code being tested is incorrect. Fix whichever is wrong and continue.

6.3. Debugging

6.3.1. gdb

If you use gdb for debugging, some helper functions are defined in devel/gdbhelpers, which can be given to gdb using the -x option.

From within the debugger, you can then invoke the pcmk command that will describe the helper functions available.