doc: change section title for modules docs

[mirror_frr.git] / doc / developer / workflow.rst

Developing for FRRouting
========================

General note on this document
-----------------------------

This document is "descriptive/post-factual" in that it documents
pratices that are in use; it is not "definitive/pre-factual" in
prescribing practices.

This means that when a procedure changes, it is agreed upon, then put
into practice, and then documented here. If this document doesn't match
reality, it's the document that needs to be updated, not reality.

Git Structure
-------------

The master Git for FRRouting resides on Github at
`https://github.com/frrouting/frr <https://github.com/FRRouting/frr>`__

.. figure:: git_branches.svg
   :alt: git branches continually merging to the left from 3 lanes;
   float-right

   git branches continually merging to the left from 3 lanes;
   float-right

There is one main branch for development and a release branch for each
major release.

New contributions are done against the head of the master branch. The CI
systems will pick up the Github Pull Requests or the new patch from
Patchwork, run some basic build and functional tests.

For each major release (1.0, 1.1 etc) a new release branch is created
based on the master.

There was an attempt to use a "develop" branch automatically maintained
by the CI system. This is not currently in active use, though the system
is operational. If the "develop" branch is in active use and this
paragraph is still here, this document obviously wasn't updated.

Programming language, Tools and Libraries
-----------------------------------------

The core of FRRouting is written in C (gcc or clang supported) and makes
use of GNU compiler extensions. A few non-essential scripts are
implemented in Perl and Python. FRRouting requires the following tools
to build distribution packages: automake, autoconf, texinfo, libtool and
gawk and various libraries (i.e. libpam and libjson-c).

If your contribution requires a new library or other tool, then please
highlight this in your description of the change. Also make sure it’s
supported by all FRRouting platform OSes or provide a way to build
without the library (potentially without the new feature) on the other
platforms.

Documentation should be written in Tex (.texi) or Markdown (.md) format
with a preference for Markdown.

Mailing lists
-------------

Italicized lists are private.

+----------------------------------+--------------------------------+
| Topic                            | List                           |
+==================================+================================+
| Development                      | dev@lists.frrouting.org        |
+----------------------------------+--------------------------------+
| Users & Operators                | frog@lists.frrouting.org       |
+----------------------------------+--------------------------------+
| Announcements                    | announce@lists.frrouting.org   |
+----------------------------------+--------------------------------+
| *Security*                       | security@lists.frrouting.org   |
+----------------------------------+--------------------------------+
| *Technical Steering Committee*   | tsc@lists.frrouting.org        |
+----------------------------------+--------------------------------+

Changelog
~~~~~~~~~

The changelog will be the base for the release notes. A changelog entry
for your changes is usually not required and will be added based on your
commit messages by the maintainers. However, you are free to include an
update to the changelog with some better description. The changelog will
be the base for the release notes.

Submitting Patches and Enhancements
-----------------------------------

Pre-submission Checklist
~~~~~~~~~~~~~~~~~~~~~~~~

-  Format code (see `Developer's Guidelines <#developers-guidelines>`__)
-  Verify and acknowledge license (see `License for
   contributions <#license-for-contributions>`__)
-  Ensure you have properly signed off (see `Signing
   Off <#signing-off>`__)
-  Test building with various configurations:

   -  ``buildtest.sh``

-  Verify building source distribution:

   -  ``make dist`` (and try rebuilding from the resulting tar file)

-  Run unit tests:

   -  ``make test``

-  Document Regression Runs and plans for continued maintenance of the
   feature

License for contributions
~~~~~~~~~~~~~~~~~~~~~~~~~

FRRouting is under a “GPLv2 or later” license. Any code submitted must
be released under the same license (preferred) or any license which
allows redistribution under this GPLv2 license (eg MIT License).

Signing Off
~~~~~~~~~~~

Code submitted to FRRouting must be signed off. We have the same
requirements for using the signed-off-by process as the Linux kernel. In
short, you must include a signed-off-by tag in every patch.

``Signed-off-by:`` this is a developer's certification that he or she
has the right to submit the patch for inclusion into the project. It is
an agreement to the Developer's Certificate of Origin (below). Code
without a proper signoff can not and will not be merged.

If you are unfamiliar with this process, you should read the `official
policy at
kernel.org <https://www.kernel.org/doc/html/latest/process/submitting-patches.html>`__
and you might find this article about `participating in the Linux
community on the Linux Foundation
website <http://www.linuxfoundation.org/content/how-participate-linux-community-0>`__
to be a helpful resource.

In short, when you sign off on a commit, you assert your agreement to
all of the following:

    Developer's Certificate of Origin 1.1

    By making a contribution to this project, I certify that:

    (a) The contribution was created in whole or in part by me and I
        have the right to submit it under the open source license
        indicated in the file; or

    (b) The contribution is based upon previous work that, to the best
        of my knowledge, is covered under an appropriate open source
        license and I have the right under that license to submit that
        work with modifications, whether created in whole or in part by
        me, under the same open source license (unless I am permitted to
        submit under a different license), as indicated in the file; or

    (c) The contribution was provided directly to me by some other
        person who certified (a), (b) or (c) and I have not modified it.

    (d) I understand and agree that this project and the contribution
        are public and that a record of the contribution (including all
        personal information I submit with it, including my sign-off) is
        maintained indefinitely and may be redistributed consistent with
        this project or the open source license(s) involved.

What do I submit my changes against?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We've documented where we would like to have the different fixes applied
at
https://github.com/FRRouting/frr/wiki/Where-Do-I-create-a-Pull-Request-against%3F
If you are unsure where your submission goes, look at that document or
ask a project maintainer.

Github pull requests
~~~~~~~~~~~~~~~~~~~~

The preferred method of submitting changes is a Github pull request.
Code submitted by pull request will be automatically tested by one or
more CI systems. Once the automated tests succeed, other developers will
review your code for quality and correctness. After any concerns are
resolved, your code will be merged into the branch it was submitted
against.

Patch submission via mailing list
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As an alternative submission method, a patch can be mailed to the
development mailing list. Patches received on the mailing list will be
picked up by Patchwork and tested against the latest development branch.

The recommended way to send the patch (or series of NN patches) to the
list is by using ``git send-email`` as follows (assuming they are the N
most recent commit(s) in your git history:

::

    git send-email -NN --annotate --to=dev@lists.frrouting.org

If your commits do not already contain a ``Signed-off-by`` line, then
use the following command to add it (after making sure you agree to the
Developer Certificate of Origin as outlined above):

::

    git send-email -NN --annotate --signoff --to=dev@lists.frrouting.org

Submitting multi-commit patches as a Github pull request is **strongly
encouraged** and increases the probability of your patch getting
reviewed and merged in a timely manner.

After submitting your changes
-----------------------------

-  Watch for Continuous Integration (CI) Test results

   -  You should automatically receive an email with the test results
      within less than 2 hrs of the submission. If you don’t get the
      email, then check status on the github pull request (if submitted
      by pull request) or on Patchwork at
      https://patchwork.frrouting.org (if submitted as patch to mailing
      list).
   -  Please notify the development mailing list if you think something
      doesn’t work.

-  If the tests failed:

   -  In general, expect the community to ignore the submission until
      the tests pass.
   -  It is up to you to fix and resubmit.

      -  This includes fixing existing unit (“make test”) tests if your
         changes broke or changed them.
      -  It also includes fixing distribution packages for the failing
         platforms (ie if new libraries are required).
      -  Feel free to ask for help on the development list.

   -  Go back to the submission process and repeat until the tests pass.

-  If the tests pass:

   -  Wait for reviewers. Someone will review your code or be assigned
      to review your code.
   -  Respond to any comments or concerns the reviewer has.
   -  After all comments and concerns are addressed, expect your patch
      to be merged.

-  Watch out for questions on the mailing list. At this time there will
   be a manual code review and further (longer) tests by various
   community members.
-  Your submission is done once it is merged to the master branch.

Developer's Guidelines
----------------------

Commit messages
~~~~~~~~~~~~~~~

Commit messages should be formatted in the same way as Linux kernel
commit messages. The format is roughly

::

    dir: short summary

    extended summary

``dir`` should be the top level source directory under which the change
was made. For example, a change in bgpd/rfapi would be formatted as:

``bgpd: short summary``

The first line should be no longer than 50 characters. Subsequent lines
should be wrapped to 72 characters.

Source file header
~~~~~~~~~~~~~~~~~~

New files need to have a Copyright header (see `License for
contributions <#license-for-contributions>`__ above) added to the file.
Preferred form of the header is as follows:

::

    /*
     * Title/Function of file
     * Copyright (C) YEAR  Author’s Name
     *
     * This program is free software; you can redistribute it and/or modify it
     * under the terms of the GNU General Public License as published by the Free
     * Software Foundation; either version 2 of the License, or (at your option)
     * any later version.
     *
     * This program is distributed in the hope that it will be useful, but WITHOUT
     * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
     * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
     * more details.
     *
     * You should have received a copy of the GNU General Public License along
     * with this program; see the file COPYING; if not, write to the Free Software
     * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
     */

    #include <zebra.h>

Adding copyright claims to existing files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When adding copyright claims for modifications to an existing file,
please preface the claim with "Portions: " on a line before it and
indent the "Copyright ..." string. If such a case already exists, add
your indented claim immediately after. E.g.:

::

    Portions:
      Copyright (C) 2010 Entity A ....
      Copyright (C) 2016 Your name [optional brief change description]

Code formatting
~~~~~~~~~~~~~~~

FRR uses Linux kernel style except where noted below. Code which does
not comply with these style guidelines will not be accepted.

To assist with compliance, in the project root there is a .clang-format
configuration file which can be used with the ``clang-format`` tool from
the LLVM project. In the ``tools/`` directory there is a Python script
named ``indent.py`` that wraps clang-format and handles some edge cases
specific to FRR. If you are submitting a new file, it is recommended to
run that script over the new file after ensuring that the latest stable
release of ``clang-format`` is in your PATH.

**Whitespace changes in untouched parts of the code are not acceptable
in patches that change actual code.** To change/fix formatting issues,
please create a separate patch that only does formatting changes and
nothing else.

Style documentation
^^^^^^^^^^^^^^^^^^^

Kernel and BSD styles are documented externally:

-  https://www.kernel.org/doc/html/latest/process/coding-style.html
-  http://man.openbsd.org/style

For GNU coding style, use ``indent`` with the following invocation:

::

    indent -nut -nfc1 file_for_submission.c

Exceptions
^^^^^^^^^^

FRR project code comes from a variety of sources, so there are some
stylistic exceptions in place. They are organized here by branch.

**For ``master``:**

BSD coding style applies to:

-  ``ldpd/``

``babeld`` uses, approximately, the following style:

-  K&R style braces
-  Indents are 4 spaces
-  Function return types are on their own line

**For ``stable/3.0`` and ``stable/2.0``:**

GNU coding style apply to the following parts:

-  ``lib/``
-  ``zebra/``
-  ``bgpd/``
-  ``ospfd/``
-  ``ospf6d/``
-  ``isisd/``
-  ``ripd/``
-  ``ripngd/``
-  ``vtysh/``

BSD coding style applies to:

-  ``ldpd/``

Documentation
~~~~~~~~~~~~~

FRRouting is a large and complex software project developed by many
different people over a long period of time. Without adequate
documentation, it can be exceedingly difficult to understand code
segments, APIs and other interfaces. In the interest of keeping the
project healthy and maintainable, you should make every effort to
document your code so that other people can understand what it does
without needing to closely read the code itself.

Some specific guidelines that contributors should follow are:

-  Functions exposed in header files should have descriptive comments
   above their signatures in the header file. At a minimum, a function
   comment should contain information about the return value,
   parameters, and a general summary of the function's purpose.
   Documentation on parameter values can be omitted if it is (very)
   obvious what they are used for.

Function comments must follow the style for multiline comments laid out
in the kernel style guide.

Example:

::

    /*
     * Determines whether or not a string is cool.
     *
     * @param text - the string to check for coolness
     * @param is_clccfc - whether capslock is cruise control for cool
     * @return 7 if the text is cool, 0 otherwise
     */
    int check_coolness(const char *text, bool is_clccfc);

The Javadoc-style annotations are not required, but you should still
strive to make it equally clear what parameters and return values are
used for.

-  Static functions should have descriptive comments in the same form as
   above if what they do is not immediately obvious. Use good
   engineering judgement when deciding whether a comment is necessary.
   If you are unsure, document your code.

-  Global variables, static or not, should have a comment describing
   their use.

-  **For new code in ``lib/``, these guidelines are hard requirements.**

If you are contributing code that adds significant user-visible
functionality or introduces a new API, please document it in ``doc/``.
Markdown and LaTeX are acceptable formats, although Markdown is
currently preferred for new documentation. This may change in the near
future.

Finally, if you come across some code that is undocumented and feel like
going above and beyond, document it! We absolutely appreciate and accept
patches that document previously undocumented code.

Compile-time conditional code
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Many users access FRR via binary packages from 3rd party sources;
compile-time code puts inclusion/exclusion in the hands of the package
maintainer. Please think very carefully before making code conditional
at compile time, as it increases regression testing, maintenance
burdens, and user confusion. In particular, please avoid gratuitous
``--enable-…`` switches to the configure script - in general, code
should be of high quality and in working condition, or it shouldn’t be
in FRR at all.

When code must be compile-time conditional, try have the compiler make
it conditional rather than the C pre-processor so that it will still be
checked by the compiler, even if disabled. For example,

::

    if (SOME_SYMBOL)
          frobnicate();

is preferred to

::

    #ifdef SOME_SYMBOL
    frobnicate ();
    #endif /* SOME_SYMBOL */

Note that the former approach requires ensuring that ``SOME_SYMBOL``
will be defined (watch your ``AC_DEFINE``\ s).

Debug-guards in code
~~~~~~~~~~~~~~~~~~~~

Debugging statements are an important methodology to allow developers to
fix issues found in the code after it has been released. The caveat here
is that the developer must remember that people will be using the code
at scale and in ways that can be unexpected for the original
implementor. As such debugs **MUST** be guarded in such a way that they
can be turned off. FRR has the ability to turn on/off debugs from the
CLI and it is expected that the developer will use this convention to
allow control of their debugs.

CLI changes
~~~~~~~~~~~

CLI's are a complicated ugly beast. Additions or changes to the CLI
should use a DEFUN to encapsulate one setting as much as is possible.
Additionally as new DEFUN's are added to the system, documentation
should be provided for the new commands.

Backwards Compatibility
~~~~~~~~~~~~~~~~~~~~~~~

As a general principle, changes to CLI and code in the lib/ directory
should be made in a backwards compatible fashion. This means that
changes that are purely stylistic in nature should be avoided, e.g.,
renaming an existing macro or library function name without any
functional change. When adding new parameters to common functions, it is
also good to consider if this too should be done in a backward
compatible fashion, e.g., by preserving the old form in addition to
adding the new form.

This is not to say that minor or even major functional changes to CLI
and common code should be avoided, but rather that the benefit gained
from a change should be weighed against the added cost/complexity to
existing code. Also, that when making such changes, it is good to
preserve compatibility when possible to do so without introducing
maintenance overhead/cost. It is also important to keep in mind,
existing code includes code that may reside in private repositories (and
is yet to be submitted) or code that has yet to be migrated from Quagga
to FRR.

That said, compatibility measures can (and should) be removed when
either:

-  they become a significant burden, e.g. when data structures change
   and the compatibility measure would need a complex adaptation layer
   or becomes flat-out impossible
-  some measure of time (dependent on the specific case) has passed, so
   that the compatibility grace period is considered expired.

In all cases, compatibility pieces should be marked with
compiler/preprocessor annotations to print warnings at compile time,
pointing to the appropriate update path. A ``-Werror`` build should fail
if compatibility bits are used.

Miscellaneous
~~~~~~~~~~~~~

When in doubt, follow the guidelines in the Linux kernel style guide, or
ask on the development mailing list / public Slack instance.