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Pacemaker Development

Working with the Pacemaker Code Base

Edition 1

Andrew Beekhof

Red Hat

Ken Gaillot

Red Hat

Legal Notice

Copyright © 2009-2016 Andrew Beekhof.
The text of and illustrations in this document are licensed under a Creative Commons Attribution–Share Alike 3.0 Unported license ("CC-BY-SA")[1].
In accordance with CC-BY-SA, if you distribute this document or an adaptation of it, you must provide the URL for the original version.
In addition to the requirements of this license, the following activities are looked upon favorably:
  1. If you are distributing Open Publication works on hardcopy or CD-ROM, you provide email notification to the authors of your intent to redistribute at least thirty days before your manuscript or media freeze, to give the authors time to provide updated documents. This notification should describe modifications, if any, made to the document.
  2. All substantive modifications (including deletions) be either clearly marked up in the document or else described in an attachment to the document.
  3. Finally, while it is not mandatory under this license, it is considered good form to offer a free copy of any hardcopy or CD-ROM expression of the author(s) work.


This document has guidelines and tips for developers interested in editing Pacemaker source code and submitting changes for inclusion in the project.

Table of Contents

1. Frequently Asked Questions
2. C Coding Guidelines
2.1. C Boilerplate
2.2. Formatting
2.2.1. Whitespace
2.2.2. Line Length
2.2.3. Pointers
2.2.4. Functions
2.2.5. Control Statements (if, else, while, for, switch)
2.2.6. Operators
2.3. Naming Conventions
2.4. vim Settings
3. Python Coding Guidelines
3.1. Python Boilerplate
3.2. Python Compatibility
3.2.1. Python Future Imports
3.2.2. Other Python Compatibility Requirements
3.2.3. Python Usages to Avoid
3.3. Formatting Python Code
A. Revision History

Chapter 1. Frequently Asked Questions

Who is this document intended for?
Anyone who wishes to read and/or edit the Pacemaker source code. Casual contributors should feel free to read just this FAQ, and consult other sections as needed.
Where is the source code for Pacemaker?
The source code for Pacemaker is kept on GitHub, as are all software projects under the ClusterLabs umbrella. Pacemaker uses Git for source code management. If you are a Git newbie, the gittutorial(7) man page is an excellent starting point. If you’re familiar with using Git from the command line, you can create a local copy of the Pacemaker source code with: git clone pacemaker
What are the different Git branches and repositories used for?
  • The master branch is the primary branch used for development.
  • The 1.1 branch contains the latest official release, and normally does not receive any changes. During the release cycle, it will contain release candidates for the next official release, and will receive only bug fixes.
  • The 1.0 repository is a frozen snapshot of the 1.0 release series, and is no longer developed.
  • Messages will be posted to the mailing list during the release cycle, with instructions about which branches to use when submitting requests.
How do I build from the source code?
See in the main checkout directory.
What coding style should I follow?
You’ll be mostly fine if you simply follow the example of existing code. When unsure, see the relevant section of this document for language-specific recommendations. Pacemaker has grown and evolved organically over many years, so you will see much code that doesn’t conform to the current guidelines. We discourage making changes solely to bring code into conformance, as any change requires developer time for review and opens the possibility of adding bugs. However, new code should follow the guidelines, and it is fine to bring lines of older code into conformance when modifying that code for other reasons.
How should I format my Git commit messages?
See existing examples in the git log. The first line should look like change-type: affected-code: explanation where change-type can be Fix or Bug for most bug fixes, Feature for new features, Log for changes to log messages or handling, Doc for changes to documentation or comments, or Test for changes in CTS and regression tests. You will sometimes see Low, Med (or Mid) and High used instead for bug fixes, to indicate the severity. The important thing is that only commits with Feature, Fix, Bug, or High will automatically be included in the change log for the next release. The affected-code is the name of the component(s) being changed, for example, crmd or libcrmcommon (it’s more free-form, so don’t sweat getting it exact). The explanation briefly describes the change. The git project recommends the entire summary line stay under 50 characters, but more is fine if needed for clarity. Except for the most simple and obvious of changes, the summary should be followed by a blank line and then a longer explanation of why the change was made.
How can I test my changes?
Most importantly, Pacemaker has regression tests for most major components; these will automatically be run for any pull requests submitted through GitHub. Additionally, Pacemaker’s Cluster Test Suite (CTS) can be used to set up a test cluster and run a wide variety of complex tests. This document will have more detail on testing in the future.
What is Pacemaker’s license?
Except where noted otherwise in the file itself, the source code for all Pacemaker programs is licensed under version 2 or later of the GNU General Public License (GPLv2+), its headers and libraries under version 2.1 or later of the less restrictive GNU Lesser General Public License (LGPLv2.1+), its documentation under version 4.0 or later of the Creative Commons Attribution-ShareAlike International Public License (CC-BY-SA), and its init scripts under the Revised BSD license. If you find any deviations from this policy, or wish to inquire about alternate licensing arrangements, please e-mail Licensing issues are also discussed on the ClusterLabs wiki.
How can I contribute my changes to the project?
Contributions of bug fixes or new features are very much appreciated! Patches can be submitted as pull requests via GitHub (the preferred method, due to its excellent features), or e-mailed to the mailing list as an attachment in a format Git can import.
What if I still have questions?
Ask on the mailing list for development-related questions, or on the mailing list for general questions about using Pacemaker. Developers often also hang out on freenode’s #clusterlabs IRC channel.

Chapter 2. C Coding Guidelines

2.1. C Boilerplate

Every C file should start like this:
 * Copyright (C) <YYYY[-YYYY]> Andrew Beekhof <>
 * This source code is licensed under <LICENSE> WITHOUT ANY WARRANTY.
<YYYY> is the year the code was originally created (it is the most important date for copyright purposes, as it establishes priority and the point from which expiration is calculated). If the code is modified in later years, add -YYYY with the most recent year of modification.
<LICENSE> should follow the policy set forth in the COPYING file, generally one of "GNU General Public License version 2 or later (GPLv2+)" or "GNU Lesser General Public License version 2.1 or later (LGPLv2.1+)".

2.2. Formatting

2.2.1. Whitespace

  • Indentation must be 4 spaces, no tabs.
  • Do not leave trailing whitespace.

2.2.2. Line Length

  • Lines should be no longer than 80 characters unless limiting line length significantly impacts readability.

2.2.3. Pointers

  • The * goes by the variable name, not the type:
char *foo;
  • Use a space before the * and after the closing parenthesis in a cast:
char *foo = (char *) bar;

2.2.4. Functions

  • In the function definition, put the return type on its own line, and place the opening brace by itself on a line:
static int
  • For functions with enough arguments that they must break to the next line, align arguments with the first argument:
static int
function_name(int bar, const char *a, const char *b,
              const char *c, const char *d)
  • If a function name gets really long, start the arguments on their own line with 8 spaces of indentation:
static int
        int bar, const char *a, const char *b,
        const char *c, const char *d)

2.2.5. Control Statements (if, else, while, for, switch)

  • The keyword is followed by one space, then left parenthesis without space, condition, right parenthesis, space, opening bracket on the same line. else and else if are on the same line with the ending brace and opening brace, separated by a space:
if (condition1) {
} else if (condition2) {
} else {
  • In a switch statement, case is indented one level, and the body of each case is indented by another level. The opening brace is on the same line as switch.
switch (expression) {
    case 0:
    case 1:

2.2.6. Operators

  • Operators have spaces from both sides. Do not rely on operator precedence; use parentheses when mixing operators with different priority.
  • No space is used after opening parenthesis and before closing parenthesis.
x = a + b - (c * d);

2.3. Naming Conventions

  • Any exposed symbols in libraries (non-static function names, type names, etc.) must begin with a prefix appropriate to the library, for example, crm_, pe_, st_, lrm_.

2.4. vim Settings

Developers who use vim to edit source code can add the following settings to their ~/.vimrc file to follow Pacemaker C coding guidelines:
" follow Pacemaker coding guidelines when editing C source code files
filetype plugin indent on
au FileType c   setlocal expandtab tabstop=4 softtabstop=4 shiftwidth=4 textwidth=80
autocmd BufNewFile,BufRead *.h set filetype=c
let c_space_errors = 1

Chapter 3. Python Coding Guidelines

3.1. Python Boilerplate

Every Python file should start like this:

# Pacemaker targets compatibility with Python 2.6+ and 3.2+
from __future__ import print_function, unicode_literals, absolute_import, division

__copyright__ = "Copyright (C) <YYYY[-YYYY]> Andrew Beekhof <>"
If the file is meant to be directly executed, the first line (<SHEBANG>) should be #!/usr/bin/python. If it is meant to be imported, omit this line.
<BRIEF-DESCRIPTION> is obviously a brief description of the file’s purpose. The string may contain any other information typically used in a Python file docstring.
The import statement is discussed further in Section 3.2.1, “Python Future Imports”.
<YYYY> is the year the code was originally created (it is the most important date for copyright purposes, as it establishes priority and the point from which expiration is calculated). If the code is modified in later years, add -YYYY with the most recent year of modification.
<LICENSE> should follow the policy set forth in the COPYING file, generally one of "GNU General Public License version 2 or later (GPLv2+)" or "GNU Lesser General Public License version 2.1 or later (LGPLv2.1+)".

3.2. Python Compatibility

Pacemaker targets compatibility with Python 2.6 and later, and Python 3.2 and later. These versions have added features to be more compatible with each other, allowing us to support both the 2 and 3 series with the same code. It is a good idea to test any changes with both Python 2 and 3.

3.2.1. Python Future Imports

The future imports used in Section 3.1, “Python Boilerplate” mean:
  • All print statements must use parentheses, and printing without a newline is accomplished with the end=' ' parameter rather than a trailing comma.
  • All string literals will be treated as Unicode (the u prefix is unnecessary, and must not be used, because it is not available in Python 3.2).
  • Local modules must be imported using from . import (rather than just import). To import one item from a local module, use from .modulename import (rather than from modulename import).
  • Division using / will always return a floating-point result (use // if you want the integer floor instead).

3.2.2. Other Python Compatibility Requirements

  • When specifying an exception variable, always use as instead of a comma (e.g. except Exception as e or except (TypeError, IOError) as e). Use e.args to access the error arguments (instead of iterating over or subscripting e).
  • Use in (not has_key()) to determine if a dictionary has a particular key.
  • Always use the I/O functions from the io module rather than the native I/O functions (e.g. rather than open()).
  • When opening a file, always use the t (text) or b (binary) mode flag.
  • When creating classes, always specify a parent class to ensure that it is a "new-style" class (e.g. class Foo(object): rather than class Foo:)
  • Be aware of the bytes type added in Python 3. Many places where strings are used in Python 2 use bytes or bytearrays in Python 3 (for example, the pipes used with subprocess.Popen()). Code should handle both possibilities.
  • Be aware that the items(), keys(), and values() methods of dictionaries return lists in Python 2 and views in Python 3. In many case, no special handling is required, but if the code needs to use list methods on the result, cast the result to list first.
  • Do not name variables with or as.
  • Do not raise or catch strings as exceptions (e.g. raise "Bad thing").
  • Do not use the cmp parameter of sorting functions (use key instead, if needed) or the __cmp__() method of classes (implement rich comparison methods such as __lt__() instead, if needed).
  • Do not use the buffer type.
  • Do not use features not available in all targeted Python versions. Common examples include:
    • The argparse, html, ipaddress, sysconfig, and UserDict modules
    • The collections.OrderedDict class
    • The function
    • The subprocess.DEVNULL constant
    • subprocess module-specific exceptions
    • Set literals ({1, 2, 3})

3.2.3. Python Usages to Avoid

Avoid the following if possible, otherwise research the compatibility issues involved (hacky workarounds are often available):
  • long integers
  • octal integer literals
  • mixed binary and string data in one data file or variable
  • metaclasses
  • locale.strcoll and locale.strxfrm
  • the configparser and ConfigParser modules
  • importing compatibility modules such as six (so we don’t have to add them to Pacemaker’s dependencies)

3.3. Formatting Python Code

  • Indentation must be 4 spaces, no tabs.
  • Do not leave trailing whitespace.
  • Lines should be no longer than 80 characters unless limiting line length significantly impacts readability. For Python, this limitation is flexible since breaking a line often impacts readability, but definitely keep it under 120 characters.
  • Where not conflicting with this style guide, it is recommended (but not required) to follow PEP 8.
  • It is recommended (but not required) to format Python code such that pylint --disable=line-too-long,too-many-lines,too-many-instance-attributes,too-many-arguments,too-many-statements produces minimal complaints (even better if you don’t need to disable all those checks).

Revision History

Revision History
Revision 1-0Tue Jul 26 2016Ken Gaillot
Convert coding guidelines and developer FAQ to Publican document
Revision 1-1Mon Aug 29 2016Ken Gaillot
Add Python coding guidelines, and more about licensing