How to contribute to CFEngine

Thanks for considering contributing to CFEngine! We take pull-requests on GitHub and we have a public bug-tracker. Discussion is taking place on GitHub Discussions and on the help-cfengine mailing list. You'll find us chatting on the Libera.chat IRC channel #cfengine.

Normally, bug fixes have a higher chance of getting accepted than new features, but we certainly welcome feature contributions. If you have an idea for a new feature, it might be a good idea to open up a feature ticket in our bug-tracker and send a message to dev-cfengine mailing list, before actually contributing the code, in order to get discussion going.

Merged features and larger changes will be released in the first minor release (i.e. x.y.0). Please note that such pull requests should be ready for merging (i.e. adjusted for any feedback) at least two months before the scheduled release date in order to make it to the first minor release.

If you are not very familiar with Git or GitHub, you can look at our suggested workflow, later in this document.

Pull Requests

Checklist

When submitting your pull request, please make sure you:

Follow our Coding Style.
Address only one issue/feature. Smaller pull requests are generally better. Usually a Pull Request will have only one commit.
Add tests. C functions should have unit tests. Promise types, attributes, and functions should have acceptance tests.
Pay attention to review comments and CI results. We have code analysis and tests which run when you submit your PR. You may have to make some changes.
Check that you don't have any merge conflicts. (Rebase on master or target branch).
Tidy up the commit log by squashing commits and writing good commit messages.
Add one or more ChangeLog Entries to the commit(s).
Become familiar with the Northern.tech AS Contributor statement as described in the AUTHORS file.

Pull request title and description

Use the following format for the PR title:

CFE-1234: Title (3.12)

Omit the first part if there is no related ticket. Omit the last part if the PR is for master branch.

If the PR has only 1 commit, the title and description should match the title and body of the commit message. If the PR has multiple commits, summarize. See: Commit messages.

Multi-repo pull requests

CFEngine is built from several different repositories. Sometimes a change is needed in multiple repositories. When possible, try to make changes compatible with the master version of the other repositories. While our Jenkins Pipeline can handle multiple Pull Requests, Travis does not. If you are making a breaking change in one repository which has to be merged together with another pull request, make this very clear. Put this in the pull request description (first comment);

Merge together:
cfengine/core#1234
cfengine/buildscripts#333

If the change is needed for a bigger feature, make that feature a separate pull request. The bigger PR will likely take some time to get reviewed, and discussed, while smaller changes can be merged quickly.

Commits

Each commit should be a valid change and make sense on its own. It is often a good idea to make commits as small as possible. Normally, each commit should include only 1 bug fix, only 1 refactoring, or only 1 new feature. Tests which test a new feature can be in the same commit as the feature. If you add tests for other issues or features, they should be in a separate commit.

Commit messages

Writing good commit messages, and having a clear history of git commits is important. It helps those reviewing your code, when merging and in the future. Good commit messages also increase the quality of the generated changelogs for each release.

It is important that the commit message is sufficiently explicit/descriptive. As an example:

Fixed execresult function

This is not good, because it doesn't really say what was wrong. Here are some better examples:

Policy function execresult() no longer crashes when passed empty string

Fixed memory leak in policy function execresult()

Commit message example

Here is an example of our commit messages:

Fixed memory leak in: differences(), intersection(), unique()

They all use `FnCallSetOp()` internally, which was lacking free
for some error handling return paths.

Changelog: Title
Ticket: ENT-4586

A commit message consists of 3 parts; a title, a body, and metadata. The 3 parts are separated by empty lines. The body and metadata parts are optional.

The first line of the commit message is called the title. It should not have punctuation (like ./!) on the end of the line. It should not exceed 80 characters. In a short sentence it explains the change in the commit. If the commit includes a change in code, as well as a test, it doesn't need to mention the test. Past tense is preferred, especially when the title is used in the changelog.

The body can be several sentences. They should have proper punctuation, ending sentences in ./!. Wrap lines before 80 characters, so the width of git log is consistent. It should explain the change in detail, and can give examples, implementation details, etc.

Using some markdown syntax is okay, but not required. Commit messages and changelog entries are considered plain text. Sometimes markdown can make them more clear, and the automatic pull request description on GitHub looks nicer.

The metadata part is one or more lines of Keyword: Value. We mainly use 3 keywords:

Changelog: Title
Ticket: CFE-1234
Signed-off-by: Ole Herman Schumacher Elgesem <ole@northern.tech>

(Signed-off-by is added by git commit -s).

One exception is the line automatically added by git cherry-pick -x, which looks like this:

(cherry picked from commit fca949fdb4b9691338e316b3675d8e5a4e9082b9)

If your change only affects one feature, component or part of the git repo, you can prefix the title:

CONTRIBUTING.md: Improved instructions for commit messages

This is helpful because it clearly communicates that the change only affects this markdown file. The same can be said for only affecting one component(binary):

cf-net: Fixed networking issues on windows

Changelog

Most new features and fixes should have an entry in the ChangeLog file. We have an automatic way of generating them before the release, by properly formatting commit messages.

To write arbitrary message in the ChangeLog: Changelog: <message>
To use the commit title line in the ChangeLog: Changelog: Title
To use the entire commit message in the ChangeLog: Changelog: Commit
To not generate an entry in the ChangeLog: Changelog: None

Changelog entry is in past tense, and explains the impact to users. Changelog entries should be written in a way that is understandable by our users. This means that references to implementation details are not appropriate, leave this for the non-changelog part of the commit message. It is the behavior change which is important. Changes which don't affect users, like changes in tests or in tools which are not packaged, should not have a changelog entry.

All changelog entries should also include a reference to a ticket: Ticket: CFE-1234

Note that the Changelog and Ticket entries must be in a commit message and not the description of a PR.

Sometimes is necessary to redact a Changelog entry, for example a commit needs to be reverted, or it's already been mentioned in another Changelog entry in another repository. When this is necessary, use the Cancel-Changelog keyword with the commit of the entry you wish to redact: Cancel-changelog: 19cd387

Bug tracker tickets

Most changes should have a ticket number, referring to a ticket on our bug tracker:

https://northerntech.atlassian.net/

Add it to the commit message as in the example above.

Coding Style

Our coding style is loosely based on Allman-4 and the Google C++ Style Guide. Keep in mind that these are guidelines, there will always be some situations where exceptions are appropriate.

Formatting / Whitespace

Feel free to use clang-format to format new code you submit. (Our configuration is in .clang-format).
4 spaces per indentation, no tabs.
Fold new code at 78 columns.
- Do not break string literals. Prefer having strings on a single line, in order to improve search-ability(grep). If they do not fit on a single line, try breaking on punctuation. You can surpass the 78 column limit if necessary.

Use single spaces around operators, but not before semicolon:

int a = 2 + 3;
int b = 2 * (a - 2);
if (a > b)

Place pointer star to the right, next to the name it belongs to:
```
int *a;
char *b, *c;
const char *const d;
```
Curly brackets on separate lines.
- Except in a do-while loop, to avoid confusion with a while loop:
```
do
{
    // ...
} while (condition);
```
- Except at the end of a struct type definition:
```
typedef struct _Name
{
    // ...
} Name;
```

Type casts should be separated with one space from the value:

bool ok = true;
int res = (int) ok;
char *msg = (char *) malloc(64 * sizeof(char *));

Indentation in (auto)make files

Automake is based on make.
In make and automake files, tabs have a special meaning.
- Some places you have to use tabs, other places you cannot use tabs.
Always use tabs for make targets (required by make):
```
run-coverage:
<TAB>-$(MAKE) check -k
```

For consistency, always use tabs to indent multi line lists (optional in make):

AM_CFLAGS = \
<TAB>$(OPENSSL_CFLAGS) \
<TAB>$(PCRE2_CFLAGS) \
<TAB>$(ENTERPRISE_CFLAGS)

Inside an if, you cannot indent with tabs (lines will be silently skipped):
```
if !BUILTIN_EXTENSIONS
bin_PROGRAMS = cf-key
cf_key_LDADD = libcf-key.la
cf_key_SOURCES =
endif
```
We prefer to not indent at all in these cases, if you have to, use 4 spaces.

Readability / Maintainability

Keep in mind that code should be readable by non C experts. If you are a Guru, try to restrain yourself, only do magic when absolutely necessary.

Avoid code duplication. Make a variable or a function instead of copy-pasting the same patterns.
- Helper functions which are only used in the same file should be declared static.
- If you want to test the static functions, you can #include the .c file in the unit test.
Avoid abbreviations.
Welcome to "modern" C (C99).
- Declare variables where they are needed, not at the beginning of a function / block.
- Declare index inside for loop:
```
for (int i = 0; i < n; ++i)
```
Conditionals:
- Don't include assignments inside expressions. Put them on the line before.
  - Unless they avoid great repetition.
- Always use curly braces:
```
if (ready)
{
    printf("Ready!\n");
}
```
- A conditional with an empty body should have curly braces, and a comment:
```
while (ready)
{
    // Log message already printed above
}
```

Switch-case deliberate fall through: It should be explicitly indicated with a specific comment: // fall through or /* fall through */

switch(x) {
case 1:
case 2:
    // ...
// fall through
// Optional comment explaining why
case 3:
    // ...
    break;
default:
    // ...
    break;
}

Variable names:
- Describe what the variable is.
- Are English words with underscores: string_index
- Boolean variable names should make an if/while sensible: if (more_data) / while (more_data)
Function names:
- Are CamelCase (with first letter capital).
- Describe what the function does.
Namespaces:
- Don't exist in C.
- But we can pretend, using underscores in function names:
  - StrList_BinarySearch()
Structs:
- Names are CamelCase (with first letter capital).
- Use the common typedef pattern:
```
typedef struct _Point
{
    float x;
    float y;
} Point;
```
  Don't add a trailing _t or similar for typedefs.
- Structs and functions which modify them are similar to classes and methods in other languages.
  - Method names should start with the struct name.
  - The first parameter should be the "self" pointer:
```
void SeqAppend(Seq *seq, void *item);
```
Document using Doxygen (within reason), preferably in the .c files, not the header files.

Safety / Correctness

Minimize use of global variables.
Use pure functions when possible:
- Functions with no / few side effects are easier to reuse.
- Use const parameters to show that they are not altered.

Functions which expect their arguments to be non-NULL should assert this at the top:

size_t SeqLength(const Seq *seq)
{
    assert(seq != NULL);
    return seq->length;
}

Not necessary all the time, avoid duplication. A wrapper like this doesn't need the asserts:

bool SaveXmlDocAsFile(xmlDocPtr doc, const char *file, const Attributes *a, NewLineMode new_line_mode)
{
    return SaveAsFile(&SaveXmlCallback, doc, file, a, new_line_mode);
}

It's more appropriate to put the asserts close to the code which dereferences the pointers.

Variable initialization:
- Don't initialize variables unless they need an initial value. Unnecessary initialization silences important compiler warnings.
- Put the declaration and initialization in the same statement (line).
```
time_t now = time(NULL);
```
Constants:
- Constify what can be const.
- A pointer to an immutable string:
```
const char *string;
```
- An immutable pointer to a mutable string:
```
char *const string;
```
- An immutable pointer to an immutable string:
```
const char *const string;
```
- The const keyword applies to the left, unless it is the first, then it applies to the right.

Types:

Assign and compare using the correct "type" literal:

float temperature = 0.0;
int dollars = 10;
char string_terminator = '\0';
char *name = NULL;
if (name == NULL && dollars <= 0 && temperature <= -10.0)
{
    // :(
}

Conditions:
- Use explicit comparisons:
```
if (data != NULL)
```
- Have the literal (constant) to the right side, so it reads well:
```
if (age >= 33)
```
- NEVER compare to true: ~~if (data == true)~~ (true is 1)
Error handling:
- Functions which can fail should return error code (int) or success/failure (bool).
  - Compiler can enforce checking of return value, output of function can be in an output parameter (pointer).
  - Functions which have valid positive return values can use negative numbers for errors.
- true(bool) and 0(int) should signify success.
- Only return an error code (int) when there are multiple different return values for different errors. If a function can only return 0 (success) or -1 (error) use bool instead.
Destroy functions should accept NULL pointers (similar to free()).
Don't use static variables that change, since they are not thread-safe.
Sizes of stack-allocated buffers should be deduced using sizeof(). Never hard-code the size (like CF_BUFSIZE).
Avoid using type casts, unless absolutely necessary.
- Usually a compiler warning is better satisfied with correct code rather than using a type cast.

String formatting

Type	Format string
`char *`	`%s`
`int`	`%d`
`unsigned int`	`%du`
`long`	`%l`
`unsigned long`	`%lu`
`size_t`	`%zu`
`ssize_t`	`%zd`
`intmax_t`	`%jd`
`uintmax_t`	`%ju`

See man 3 printf for a more complete table. For other integer types without a format, cast signed types to intmax_t and unsigned types to uintmax_t.

Logging Conventions

CFEngine outputs messages about what it's doing using the Log() function. It takes a LogLevel enum, mapping closely to syslog priorities. Please try to do the following when writing output messages.

Log levels

LOG_LEVEL_CRIT: For critical errors, where process cannot / should not continue running, exit immediately.
LOG_LEVEL_ERR: Promise failed or other errors that are definitely considered bad / not normal.
LOG_LEVEL_WARNING: Something unusual happened that the user should investigate. Should be severe enough to warrant investigating further, but not as severe as a definitive error/bug.
LOG_LEVEL_NOTICE: Important information (not errors) that must not be missed by the user. For example cf-agent uses it in files promises when change tracking is enabled and the file changes.
LOG_LEVEL_INFO: Useful high level information about what the process is doing. Examples:
- Changes performed to the system, for example when a promise has been repaired.
- Server denies access to client based on access_rules.
LOG_LEVEL_VERBOSE: Log human readable progress info useful to users (i.e. sysadmins). Also errors that are unimportant or expected in certain cases.
LOG_LEVEL_DEBUG: Log anything else (for example various progress info). Try to avoid "Entering function Foo()", but rather use for "While copying, got reply '%s' from server".

Please keep in mind that some components like cf-serverd handle very large sets of data / connections and logs can become spammy. In some cases it might be appropriate to create error / warning summaries instead of outputting a log message every time an event occurs.

Logging Guidelines

Do not decorate with symbols or indentation in messages and do not terminate the message with punctuation. Let Log() enforce the common formatting rules.
When quoting strings, use single quotes, e.g. "Some stuff '%s' happened in '%s'.
Keep in mind context, e.g. write "While copying, insufficient permissions" rather than "Insufficient permissions".
Use output sparingly, and use levels appropriately. Verbose logging tends to get very verbose.
Use platform-independent GetErrorStr() for strerror(errno). Write for example Log(LOG_LEVEL_ERR, "Failed to open ... (fopen: %s)", GetErrorStr());
Normally, try to keep each message to one line of output, produced by one call to Log().
Normally, do not circumvent Log() by writing to stdout or stderr.

Code Overview

The CFEngine codebase can be usefully thought of as a few separate components: utilities (libutils), parsing (libpromises), evaluation (libpromises), actuation (mostly in cf-agent), network (libcfnet).

Since around 2016, the structure of the codebase has undergone some change. The goal of the restructuring is to isolate separate components with explicit dependencies, and provide better unit test coverage.

For a general introduction to the tools, please read the man pages/documentation.

libcompat

These are replacement functions in cases where autoconf cannot find a function it expected to find on the platform. CFEngine takes an approach of relying on the platform (typically POSIX) as much as possible, rather than creating its own system abstraction layer.

libutils

Contains generally useful data structures or utilities. The key point about libutils is that it is free of dependencies (except libcompat), so it does not know about any CFEngine structures or global state found in libpromises. Some examples of often used files (not meant to be an exhaustive list):

sequence.h: Collection of ordered elements (Loosely based on glib GSequence).
map.h: General purpose map (hash table).
set.h: General purpose set, a wrapper of Map.
writer.h: Stream writer abstraction over strings and FILEs.
string_lib.h: General purpose string utilities.
logging.h: Log functions, use Log() instead of printf.
ip_address.h: IP address parsing.
file_lib.h: General purpose file utilities.
misc_lib.h: Really general utilities.

libcfnet

Contains the networking layer for CFEngine. All of this was in libpromises previously. Ideally it would be completely separate, without depending on libpromises, but we're not there yet. See JIRA Epic CFE-2735 for details on status.

libpromises

This is the remainder of the old src directory, that which has not been categorized. The roadmap for the project remains to leave libpromises as a component for evaluation.

cf3.defs.h: Contains structure definitions used widely.
generic_agent.h: Common code for all agent binaries.
parser.h: Parse a policy file.
syntax.h: Syntax utilities and type checking.
mod_???.c: Syntax definitions for all promise types (actuation modules).
eval_context.h: Header for EvalContext, keeper of evaluation state.
expand.c: Evaluates promises.
policy.h: Policy document object model, essentially the AST output of the parsing stage.
evalfunction.c: Where all the built-in functions are implemented.
locks.h: Manages various persistent locks, kept in a local database.
sysinfo.c: Detects hard classes from the environment (OS, IP, etc.)

Things which should be moved out of libpromises:

crypto.h: Crypto utilities for some reason still tied to evaluation state.
files_???: File utilities we haven't been able to decouple from evaluation.

Things you should not use in libpromises

cf3.extern.h: Remaining global variables.
prototypes3.h: The original singular header file.
item_lib.h: Item is a special purpose list that has been abused for unintended purposes.
assoc.h: An lval-rval pair, deprecated in favor of EvalContext symbol table.
scope.h: Old symbol table, this will move into EvalContext.

cf-agent

See the documentation for an introduction to cf-agent and the other components. Since cf-agent is (arguably) the most important component here is a more technical description of how it works, both during first time setup (bootstrap) and regular operation. Note that most of the binaries evaluate policy so there are many similarities to cf-agent.

Lifecycle of cf-agent

The following outlines the normal execution of a cf-agent run.

Read options and gather these in GenericAgentConfig.
Create an EvalContext and call GenericAgentConfigApply(ctx, config).
Discover environment and set hard classes, apply to EvalContext.
Parse input policy file, get a Policy object.
Run static checks on Policy object.
Evaluate each Bundle in bundlesequence.
Write reports to disk.

Bootstrapping cf-agent

The following outlines the steps taken by agent during a successful bootstrap to a policy server.

Remove all files in inputs directory
Write built-in inputs/failsafe.cf
Write policy server address or hostname, as was the argument to --bootstrap option, to policy_server.dat.
If the host was bootstrapped to the machine's own IP address, then it is a policy server, and the file state/am_policy_hub is touched as marker.
cf-agent runs using failsafe.cf as input file:
1. Runs cf-key to generate localhost.{priv,pub} keys inside ppkeys directory.
2. Fetches policy files from the policy server.
3. Starts cf-execd
4. Runs cf-agent -f update.cf
Agent finishes.
cf-execd continues to run cf-agent periodically with policy from inputs directory.

Testing

It is extremely important to have automated tests for all code, and normally all new code should be covered by tests, though sometimes it can be hard to mock up the environment.

There are two types of tests in CFEngine. Unit tests are generally preferable to acceptance tests because they are more targeted and take less time to run. Most tests can be run using make check. See Unsafe Tests below.

Unit tests. Unit tests are a great way of testing some new module (header file). Ideally, the new functionality is written so that the environment can be easily injected and results readily verified.
Acceptance tests. These are tests that run cf-agent on a policy file that contains test and check bundles, i.e. it uses CFEngine to both make a change and check it. See also script tests/acceptance/testall.

Tip: In order to trigger assert() calls in the code, build with --enable-debug (passed to either ./autogen.sh or ./configure). If you get very large binary sizes you can also pass CFLAGS='-g -O0' to reduce that.

Code Coverage

We strive to always increase code coverage. If you wish to generate code coverage information then you must autogen or configure with --enable-debug and --enable-coverage as well as ensure lcov is installed (typically an lcov package is available in a distribution). We use gcov to instrument and process coverage information. .gcno files are generated at compile-time and will not be regenerated if the source code does not change. So be careful about cleaning those files. .gcda files are like index files which can be used to generate the .gcov files which lcov uses to generate lcov.info and the HTML report in the coverage-html directory. Many IDEs and editors expect a /coverage/lcov.info summary of coverage information. After running make check you can run make coverage and generate this lcov.info summary for use with other tools. If you wish to only run a few tests which will add to coverage data you can update lcov.info with make collect-coverage which will only collect coverage data, not compile or run any tests.

For the atom editor, install the package atom-lcov-info.

Unsafe Tests

Note that some acceptance tests are considered to be unsafe because they modify the system they are running on. One example is the tests for the "users" promise type, which does real manipulation of the user database on the system. Due to their potential to do damage to the host system, these tests are not run unless explicitly asked for. Normally, this is something you would want to do in a VM, so you can restore the OS to a pristine state afterwards.

To run all tests, including the unsafe ones, you either need to be logged in as root or have "sudo" configured to not ask for a password. Then run the following:

$ UNSAFE_TESTS=1 GAINROOT=sudo make check

Again: DO NOT do this on your main computer! Always use a test machine, preferable in a VM.

C Platform Macros

It's important to have portability in a consistent way. In general we use autoconf to test for features (like system headers, defines, specific functions). So try to use the autoconf macros HAVE_DECL_X, HAVE_STRUCT_Y, HAVE_MYFUNCTION etc. See the autoconf manual existing tests section.

It is preferable to write feature-specific ifdefs, instead of OS-specific, but it's not always easy. If necessary use these platform-specific macros in C code:

Any Windows system: Use _WIN32. Don't use NT.
mingw-based Win32 build: Use __MINGW32__. Don't use MINGW.
Cygwin-based Win32 build: Use __CYGWIN__. Don't use CFCYG.
OS X: Use __APPLE__. Don't use DARWIN.
FreeBSD: Use __FreeBSD__. Don't use FREEBSD.
NetBSD: Use __NetBSD__. Don't use NETBSD.
OpenBSD: Use __OpenBSD__. Don't use OPENBSD.
AIX: Use _AIX. Don't use AIX.
Solaris: Use __sun. Don't use SOLARIS.
Linux: Use __linux__. Don't use LINUX.
HP/UX: Use __hpux (two underscores!). Don't use hpux.

Finally, it's best to avoid polluting the code logic with many ifdefs. Try restricting ifdefs in the header files, or in the beginning of the C files.

Suggested git / GitHub workflow

For very small / simple changes, you can open a PR by clicking the edit buttons in the GitHub UI. For most changes, it is preferable to work locally, using git. This is a suggested outline for those unfamiliar with working with GitHub. It does, however, assume a familiarity with the basics of using git so it does not attempt to provide every detail of that.

Forking

You will be working with three git repositories: the central one on Github, your fork on Github and your local clone.

Within Github, make your fork of the central CFEngine repository using the fork icon on the Github CFEngine repository page. Your fork lives at https://github.com/your-username/core (by default).

Cloning

Clone your fork, there is a "Clone or Download" button, which shows the necessary information. For example:

$ git clone --recursive https://github.com/your-username/core
$ cd core

(If you have set up your GitHub profile with your SSH key, you can use the SSH URLs instead, which might be more convenient).

Replace your-username with your GitHub username, here and later. --recursive is needed to clone submodules, without it, you would have to run these commands separately:

$ git submodule init
$ git submodule update

Set up remote references

Now, add a remote reference to the upstream repository:

$ git remote add upstream https://github.com/cfengine/core

The result should look like this:

$ git remote -v
origin	https://github.com/olehermanse/core (fetch)
origin	https://github.com/olehermanse/core (push)
upstream	https://github.com/cfengine/core (fetch)
upstream	https://github.com/cfengine/core (push)

origin is your fork. This is the default for pushing and pulling. upstream is the central repository, managed by the CFEngine GitHub organization. You (probably) don't have access to push to upstream. Using these names are just a convention, you could change them, but we don't recommend it.

Branching

Never work in the master branch; always use a separate branch for your topic. Prepare your topic on this topic-focussed branch. When it is ready, push it to your Github fork.

$ git checkout master
$ git checkout -b mytopic

You can now make your changes. Build and test them when done:

$ ./autogen.sh --enable-debug && make -j4 && (cd tests/unit/ && make check)

Running all the tests is quite slow, because of many acceptance tests. Locally, it is usually sufficient to run unit tests, and select acceptance tests. Then, commit and push normally:

$ git add -p
$ git commit
$ git push

The default behavior of git push may or may not work for you, you can also specify where to push manually:

$ git push --set-upstream origin mytopic

On your fork at Github you should now see an additional branch mytopic. This is what you use for the pull request there. Pushing more commits or force pushing changed commits to the same branch will automatically update an open Pull Request which uses that branch.

Cleaning up the commit history - rebasing and squashing

Resolving conflicts using rebase

After you branched from upstream/master it is possible that someone else (or even you) commit conflicting changes to the master branch. To resolve these conflicts in your PR branch, use:

$ git fetch --all
$ git rebase upstream/master

This will stop at the conflicting commit, and give you instructions to proceed. You will have to resolve conflicts and then run:

$ git rebase --continue

This might happen multiple times (1 for each commit). Once done, you will have to force push your changes to the PR branch:

$ git push -f

Interactive rebase

We want the commit history to be as easy to read and understand as possible. Sometimes we make more commits than necessary, and we want to squash them (combine them). A good tool for this is interactive rebase.

On your PR branch, run:

$ git rebase -i upstream/master

This will open an editor (usually vi or emacs), with a list of your commits:

pick ac07e6d27 Added new policy function isrealdir()
pick 001bd420b Fixed mistake in isrealdir()

# Commented out instructions ....

upstream/master will be used as a starting point, and the commits / commands will be applied tofrom top to bottom of this list. To combine the 2 commits, replace pick with squash on the second line:

pick ac07e6d27 Added new policy function isrealdir()
squash 001bd420b Fixed mistake in isrealdir()

# Commented out instructions ....

This will squash the second commit into the first one (the one above). Save and close. Another editor will open, allowing you to update the commit message(s). Update it to reflect the current state of this commit, then save and close.

Once you get comfortable with interactive rebase you can make more advanced changes, like squashing multiple commits, reordering commits, or dropping some commits. You may create conflicts, that you have to resolve, as described above.

Keeping master up to date

Switch to local master branch:

$ git checkout master

Download changes from all remotes:

$ git fetch --all

Apply changes from the upstream master branch to our local master branch:

$ git rebase upstream/master

(You can also use git pull, but I find rebase a little easier when there are conflicts. git pull is a combination of git fetch and git merge.)

Inspect the results:

$ git log

(Press q to quit git log).

The latest (top) commit, should include master and upstream/master in parenthesis. This indicates that your local branch is up to date with upstream. If there are additional commits after the upstream/master commit, it means you committed some things on master, perhaps by accident. You can remove them, by doing:

$ git branch master-with-extra-commits
$ git reset --hard upstream/master

You can, optionally, push your updated master branch to your GitHub fork:

$ git push

If you've already pushed some of the extra commits (on accident), you may have to add --force:

$ git push --force

However, normally this should not be necessary (!).

Updating git submodule(s)

git has some commands for working with submodules, for example:

$ git submodule update

This will update the submodule, checking out the correct commit for your current for your current branch.

Please note that a submodule is like a normal git repo, with the SHA committed to the parent repo. In many situations, the easiest approach is to cd into the submodule and run normal git commands in there. You can add remotes, push, pull, rebase, fetch, etc. inside the submodule. If you want to make changes to a submodule (for example libntech). Follow the same general steps inside that folder. (Fork that repo on GitHub, set up your fork as a remote etc.)

If you need to make changes to the libntech submodule, you will need to submit a PR to that repo:

https://github.com/NorthernTechHQ/libntech

The libntech PR has to be merged, before we can test your changes in core.

Advanced topics

This section is not for new contributors, but rather contains more specific guides which are useful to link to in some circumstances.

Git

Cherry-picking/backporting commits

Determine the commit to backport, use the first 6 or so characters of the sha1 (to make it unique). E.g. 80f198 for 80f198baeddcd5d1b9556d9a4890b648fe3c12c5

First checkout the branch you are backporting to:
$ git checkout --track upstream/<branch such as 3.10.x>

Next create a branch in which to work and for a PR:

$ git checkout -b backport-some-commit

If you are cherry picking your own commit simply use -x option

$ git cherry-pick -x 80f198

-x adds: `"(cherry picked from commit 80f198baeddcd5d1b9556d9a4890b648fe3c12c5)"``

If you are cherry picking someone elses commit, use the -s option to make your involvement more obvious.

$ git cherry-pick -x -s 80f198

-s --signoff adds: "Signed-off-by: Committer Name <committer.email@northern.tech>"

Submit your change as a PR:

$ git push --set-upstream origin backport-some-commit

In the GitHub web UI you will need to create the PR and select the correct branch to submit to. If the cherry pick applied cleanly and you have merge rights, you may merge the change. If significant or risky changes were introduced in order to backport, ask for code review before merging.

Cryptographically signing git commits

Automatic Git commit signing with GPG on OSX
(Open a Pull Request to add instructions for other platforms).

Emacs users

There is an Elisp snippet in contrib/cfengine-code-style.el which defines the project's coding style. Please use it when working with source code. The easiest way to do so is to add:

(add-to-list 'load-path "<core checkout directory>/contrib")
(require 'cfengine-code-style)

and run:

ln -s contrib/dir-locals.el .dir-locals.el

Windows atexit()

On Windows the atexit function works but the functions registered there are executed after or concurrently with DLL unloading. If registered functions rely on DLLs such as pthreads to do locking/unlocking deadlock scenarios can occur when exit is called.

In order to make behavior more explicit and predictable we migrated to always using a homegrown atexit system. RegisterCleanupFunction instead of atexit and DoCleanupAndExit instead of exit.

If _Exit or _exit need to be called that is fine as they don't call atexit or cleanup functions.

In some cases such as when exiting a forked process or in executables which don't register cleanup functions, exit() may be used but a comment should be added noting that this issue was considered.

Files

CONTRIBUTING.md

Latest commit

History