doc: Add `show ipv6 rpf X:X::X:X` command to docs

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

.. _process-and-workflow:

*******************
Process & Workflow
*******************

.. highlight:: none

FRR is a large project developed by many different groups. This section
documents standards for code style & quality, commit messages, pull requests
and best practices that all contributors are asked to follow.

This chapter 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.

Mailing Lists
=============

The FRR development group maintains multiple mailing lists for use by the
community. 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        |
+----------------------------------+--------------------------------+

The Development list is used to discuss and document general issues related to
project development and governance. The public
`Slack instance <https://frrouting.slack.com>`_ and weekly technical meetings
provide a higher bandwidth channel for discussions.  The results of such
discussions must be reflected in updates, as appropriate, to code (i.e.,
merges), `GitHub issues`_, and for governance or process changes, updates to
the Development list and either this file or information posted at
https://frrouting.org/.

Development & Release Cycle
===========================

Development
-----------

.. figure:: ../figures/git_branches.png
   :align: center
   :scale: 55%
   :alt: Merging Git branches into a central trunk

   Rough outline of FRR development workflow

The master Git for FRR resides on `GitHub`_.

There is one main branch for development, ``master``. For each major release
(2.0, 3.0 etc) a new release branch is created based on the master. Significant
bugfixes should be backported to upcoming and existing release branches no more
than 1 year old. As a general rule new features are not backported to release
branches.

Subsequent point releases based on a major branch are handled with git tags.

Releases
--------
FRR employs a ``<MAJOR>.<MINOR>.<BUGFIX>`` versioning scheme.

``MAJOR``
   Significant new features or multiple minor features. This should mostly
   cover any kind of disruptive change that is visible or "risky" to operators.
   New features or protocols do not necessarily trigger this. (This was changed
   for FRR 7.x after feedback from users that the pace of major version number
   increments was too high.)

``MINOR``
   General incremental development releases, excluding "major" changes
   mentioned above.  Not necessarily fully backwards compatible, as smaller
   (but still visible) changes or deprecated feature removals may still happen.
   However, there shouldn't be any huge "surprises" between minor releases.

``BUGFIX``
   Fixes for actual bugs and/or security issues.  Fully compatible.

Releases are scheduled in a 4-month cycle on the first Tuesday each
March/July/November.  Walking backwards from this date:

 - 6 weeks earlier, ``master`` is frozen for new features, and feature PRs
   are considered lowest priority (regardless of when they were opened.)

 - 4 weeks earlier, the stable branch separates from master (named
   ``dev/MAJOR.MINOR`` at this point) and tagged as ```base_X.Y``.
   Master is unfrozen and new features may again proceed.

   Part of unfreezing master is editing the ``AC_INIT`` statement in
   :file:`configure.ac` to reflect the new development version that master
   now refers to.  This is accompanied by a ``frr-X.Y-dev`` tag on master,
   which should always be on the first commit on master *after* the stable
   branch was forked (even if that is not the edit to ``AC_INIT``; it's more
   important to have it on the very first commit on master after the fork.)

   (The :file:`configure.ac` edit and tag push are considered git housekeeping
   and are pushed directly to ``master``, not through a PR.)

   Below is the snippet of the commands to use in this step.

     .. code-block:: console

        % git remote --verbose
        upstream  git@github.com:frrouting/frr (fetch)
        upstream  git@github.com:frrouting/frr (push)

        % git checkout master
        % git pull upstream master
        % git checkout -b dev/8.2
        % git tag base_8.2
        % git push upstream base_8.2
        % git push upstream dev/8.2
        % git checkout master
        % sed -i 's/8.2-dev/8.3-dev/' configure.ac
        % git add configure.ac
        % git commit -s -m "build: FRR 8.3 development version"
        % git tag -a frr-8.3-dev -m "frr-8.3-dev"
        % git push upstream master
        % git push upstream frr-8.3-dev

   In this step, we also have to update package versions to reflect
   the development version. Versions need to be updated using
   a standard way of development (Pull Requests) based on master branch.

   Only change the version number with no other changes. This will produce
   packages with the a version number that is higher than any previous
   version. Once the release is done, whatever updates we make to changelog
   files on the release branch need to be cherry-picked to the master branch.

   Update essential dates in advance for reference table (below) when
   the next freeze, dev/X.Y, RC, and release phases are scheduled. This should
   go in the ``master`` branch.

 - 2 weeks earlier, a ``frr-X.Y-rc`` release candidate is tagged.

     .. code-block:: console

        % git remote --verbose
        upstream  git@github.com:frrouting/frr (fetch)
        upstream  git@github.com:frrouting/frr (push)

        % git checkout dev/8.2
        % git tag frr-8.2-rc
        % git push upstream frr-8.2-rc

 - on release date, the branch is renamed to ``stable/MAJOR.MINOR``.

The 2 week window between each of these events should be used to run any and
all testing possible for the release in progress.  However, the current
intention is to stick to the schedule even if known issues remain.  This would
hopefully occur only after all avenues of fixing issues are exhausted, but to
achieve this, an as exhaustive as possible list of issues needs to be available
as early as possible, i.e. the first 2-week window.

For reference, the expected release schedule according to the above is:

+---------+------------+------------+------------+------------+------------+
| Release | 2023-03-07 | 2023-07-04 | 2023-10-31 | 2024-02-27 | 2024-06-25 |
+---------+------------+------------+------------+------------+------------+
| RC      | 2023-02-21 | 2023-06-20 | 2023-10-17 | 2024-02-13 | 2024-06-11 |
+---------+------------+------------+------------+------------+------------+
| dev/X.Y | 2023-02-07 | 2023-06-06 | 2023-10-03 | 2024-01-30 | 2024-05-28 |
+---------+------------+------------+------------+------------+------------+
| freeze  | 2023-01-24 | 2023-05-23 | 2023-09-19 | 2024-01-16 | 2024-05-14 |
+---------+------------+------------+------------+------------+------------+

Here is the hint on how to get the dates easily:

   .. code-block:: console

      ~$ # Last freeze date was 2023-09-19
      ~$ date +%F --date='2023-09-19 +119 days' # Next freeze date
      2024-01-16
      ~$ date +%F --date='2024-01-16 +14 days'  # Next dev/X.Y date
      2024-01-30
      ~$ date +%F --date='2024-01-30 +14 days'  # Next RC date
      2024-02-13
      ~$ date +%F --date='2024-02-13 +14 days'  # Next Release date
      2024-02-27

Each release is managed by one or more volunteer release managers from the FRR
community.  These release managers are expected to handle the branch for a period
of one year.  To spread and distribute this workload, this should be rotated for
subsequent releases.  The release managers are currently assumed/expected to
run a release management meeting during the weeks listed above.  Barring other
constraints, this would be scheduled before the regular weekly FRR community
call such that important items can be carried over into that call.

Bugfixes are applied to the two most recent releases.  It is expected that
each bugfix backported should include some reasoning for its inclusion
as well as receiving approval by the release managers for that release before
accepted into the release branch.  This does not necessarily preclude backporting of
bug fixes to older than the two most recent releases.

Security fixes are backported to all releases less than or equal to at least one
year old. Security fixes may also be backported to older releases depending on
severity.

For detailed instructions on how to produce an FRR release, refer to
:ref:`frr-release-procedure`.


Long term support branches ( LTS )
-----------------------------------------

This kind of branch is not yet officially supported, and need experimentation
before being effective.

Previous definition of releases prevents long term support of previous releases.
For instance, bug and security fixes are not applied if the stable branch is too
old.

Because the FRR users have a need to backport bug and security fixes after the
stable branch becomes too old, there is a need to provide support on a long term
basis on that stable branch. If that support is applied on that stable branch,
then that branch is a long term support branch.

Having a LTS branch requires extra-work and requires one person to be in charge
of that maintenance branch for a certain amount of time. The amount of time will
be by default set to 4 months, and can be increased. 4 months stands for the time
between two releases, this time can be applied to the decision to continue with a
LTS release or not. In all cases, that time period will be well-defined and
published. Also, a self nomination from a person that proposes to handle the LTS
branch is required. The work can be shared by multiple people. In all cases, there
must be at least one person that is in charge of the maintenance branch. The person
on people responsible for a maintenance branch must be a FRR maintainer. Note that
they may choose to abandon support for the maintenance branch at any time. If
no one takes over the responsibility of the LTS branch, then the support will be
discontinued.

The LTS branch duties are the following ones:

- organise meetings on a (bi-)weekly or monthly basis, the handling of issues
  and pull requested relative to that branch. When time permits, this may be done
  during the regularly scheduled FRR meeting.

- ensure the stability of the branch, by using and eventually adapting the
  checking the CI tools of FRR ( indeed, maintaining may lead to create
  maintenance branches for topotests or for CI).

It will not be possible to backport feature requests to LTS branches. Actually, it
is a false good idea to use LTS for that need. Introducing feature requests may
break the paradigm where all more recent releases should also include the feature
request. This would require the LTS maintainer to ensure that all more recent
releases have support for this feature request. Moreover, introducing features
requests may result in breaking the stability of the branch. LTS branches are first
done to bring long term support for stability.

Development Branches
--------------------

Occassionally the community will desire the ability to work together
on a feature that is considered useful to FRR.  In this case the
parties may ask the Maintainers for the creation of a development
branch in the main FRR repository.  Requirements for this to happen
are:

- A one paragraph description of the feature being implemented to
  allow for the facilitation of discussion about the feature.  This
  might include pointers to relevant RFC's or presentations that
  explain what is planned.  This is intended to set a somewhat
  low bar for organization.
- A branch maintainer must be named.  This person is responsible for
  keeping the branch up to date, and general communication about the
  project with the other FRR Maintainers.  Additionally this person
  must already be a FRR Maintainer.
- Commits to this branch must follow the normal PR and commit process
  as outlined in other areas of this document.  The goal of this is
  to prevent the current state where large features are submitted
  and are so large they are difficult to review.

After a development branch has completed the work together, a final
review can be made and the branch merged into master.  If a development
branch is becomes un-maintained or not being actively worked on after
three months then the Maintainers can decide to remove the branch.

Debian Branches
---------------

The Debian project contains "official" packages for FRR.  While FRR
Maintainers may participate in creating these, it is entirely the Debian
project's decision what to ship and how to work on this.

As a courtesy and for FRR's benefit, this packaging work is currently visible
in git branches named ``debian/*`` on the main FRR git repository.  These
branches are for the exclusive use by people involved in Debian packaging work
for FRR.  Direct commit access may be handed out and FRR git rules (review,
testing, etc.) do not apply.  Do not push to these branches without talking
to the people noted under ``Maintainer:`` and ``Uploaders:`` in
``debian/control`` on the target branch -- even if you are a FRR Maintainer.

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.

Accords: non-code community consensus
=====================================

The FRR repository has a place for "accords" - these are items of
consideration for FRR that influence how we work as a community, but either
haven't resulted in code *yet*, or may *never* result in code being written.
They are placed in the ``doc/accords/`` directory.

The general idea is to simply pass small blurbs of text through our normal PR
procedures, giving them the same visibility, comment and review mechanisms as
code PRs - and changing them later is another PR.  Please refer to the README
file in ``doc/accords/`` for further details.  The file names of items in that
directory are hopefully helpful in determining whether some of them might be
relevant to your work.

Submitting Patches and Enhancements
===================================

FRR accepts patches using GitHub pull requests.

The base branch for new contributions and non-critical bug fixes should be
``master``. Please ensure your pull request is based on this branch when you
submit it.

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.

The title of the pull request should provide a high level technical
summary of the included patches.  The description should provide
additional details that will help the reviewer to understand the context
of the included patches.

Squash commits
--------------

Before merging make sure a PR has squashed the following kinds of commits:

- Fixes/review feedback
- Typos
- Merges and rebases
- Work in progress

This helps to automatically generate human-readable changelog messages.

Commit Guidelines
-----------------

There is a built-in commit linter. Basic rules:

- Commit messages must be prefixed with the name of the changed subsystem, followed
  by a colon and a space and start with an imperative verb.

   `Check <https://github.com/FRRouting/frr/tree/master/.github/commitlint.config.js>`_ all
   the supported subsystems.

- Commit messages must start with a capital letter
- Commit messages must not end with a period ``.``

Why was my pull request closed?
-------------------------------

Pull requests older than 180 days will be closed. Exceptions can be made for
pull requests that have active review comments, or that are awaiting other
dependent pull requests. Closed pull requests are easy to recreate, and little
work is lost by closing a pull request that subsequently needs to be reopened.

We want to limit the total number of pull requests in flight to:

- Maintain a clean project
- Remove old pull requests that would be difficult to rebase as the underlying code has changed over time
- Encourage code velocity

.. _license-for-contributions:

License for Contributions
-------------------------
FRR 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).
It is forbidden to push any code that prevents from using GPLv3 license. This
becomes a community rule, as FRR produces binaries that links with Apache 2.0
libraries. Apache 2.0 and GPLv2 license are incompatible, if put together.
Please see `<http://www.apache.org/licenses/GPL-compatibility.html>`_ for
more information. This rule guarantees the user to distribute FRR binary code
without any licensing issues.

Pre-submission Checklist
------------------------
-  Format code (see `Code Formatting <#code-formatting>`__)
-  Verify and acknowledge license (see :ref:`license-for-contributions`)
-  Ensure you have properly signed off (see :ref:`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``

- In the case of a major new feature or other significant change, document
  plans for continued maintenance of the feature.  In addition it is a
  requirement that automated testing must be written that exercises
  the new feature within our existing CI infrastructure.  Also the
  addition of automated testing to cover any pull request is encouraged.

- All new code must use the current latest version of acceptable code.

   - If a daemon is converted to YANG, then new code must use YANG.
   - DEFPY's must be used for new cli
   - Typesafe lists must be used
   - printf formatting changes must be used

.. _signing-off:

Signing Off
-----------
Code submitted to FRR 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.

An easy way to do this is to use ``git commit -s`` where ``-s`` will automatically
append a signed-off line to the end of your commit message. Also, if you commit
and forgot to add the line you can use ``git commit --amend -s`` to add the
signed-off line to the last commit.

``Signed-off-by`` is a developer's certification that they have the right to
submit the patch for inclusion into the project. It is an agreement to the
:ref:`Developer's Certificate of Origin <developers-certificate-of-origin>`.
Code without a proper ``Signed-off-by`` line cannot 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>`_.
You might also find
`this article <http://www.linuxfoundation.org/content/how-participate-linux-community-0>`_
about participating in the Linux community on the Linux Foundation website to
be a helpful resource.

.. _developers-certificate-of-origin:

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.

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.
   -  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.  Use e-mail or
      add a comment via github to respond or to let the reviewer know how
      their comment or concern is addressed.
   -  An author must never delete or manually dismiss someone else's comments
      or review.  (A review may be overridden by agreement in the weekly
      technical meeting.)
   -  When you have addressed someone's review comments, please click the
      "re-request review" button (in the top-right corner of the PR page, next
      to the reviewer's name, an icon that looks like "reload")
   -  The responsibility for keeping a PR moving rests with the author at
      least as long as there are either negative CI results or negative review
      comments.  If you forget to mark a review comment as addressed (by
      clicking re-request review), the reviewer may very well not notice and
      won't come back to your PR.
   -  Automatically generated comments, e.g., those generated by CI systems,
      may be deleted by authors and others when such comments are not the most
      recent results from that automated comment source.
   -  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.

Programming Languages, Tools and Libraries
==========================================

The core of FRR 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. FRR 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 FRR 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 reStructuredText. Sphinx extensions may be
utilized but pure ReST is preferred where possible. See
:ref:`documentation`.

Use of C++
----------

While C++ is not accepted for core components of FRR, extensions, modules or
other distinct components may want to use C++ and include FRR header files.
There is no requirement on contributors to work to retain C++ compatibility,
but fixes for C++ compatibility are welcome.

This implies that the burden of work to keep C++ compatibility is placed with
the people who need it, and they may provide it at their leisure to the extent
it is useful to them.  So, if only a subset of header files, or even parts of
a header file are made available to C++, this is perfectly fine.

Code Reviews
============

Code quality is paramount for any large program. Consequently we require
reviews of all submitted patches by at least one person other than the
submitter before the patch is merged.

Because of the nature of the software, FRR's maintainer list (i.e. those with
commit permissions) tends to contain employees / members of various
organizations. In order to prevent conflicts of interest, we use an honor
system in which submissions from an individual representing one company should
be merged by someone unaffiliated with that company.

Guidelines for code review
--------------------------

- As a rule of thumb, the depth of the review should be proportional to the
  scope and / or impact of the patch.

- Anyone may review a patch.

- When using GitHub reviews, marking "Approve" on a code review indicates
  willingness to merge the PR.

- For individuals with merge rights, marking "Changes requested" is equivalent
  to a NAK.

- For a PR you marked with "Changes requested", please respond to updates in a
  timely manner to avoid impeding the flow of development.

- Rejected or obsolete PRs are generally closed by the submitter based
  on requests and/or agreement captured in a PR comment.  The comment
  may originate with a reviewer or document agreement reached on Slack,
  the Development mailing list, or the weekly technical meeting.

- Reviewers may ask for new automated testing if they feel that the
  code change is large enough/significant enough to warrant such
  a requirement.

For project members with merge permissions, the following patterns have
emerged:

- a PR with any reviews requesting changes may not be merged.

- a PR with any negative CI result may not be merged.

- an open "yellow" review mark ("review requested, but not done") should be
  given some time (a few days up to weeks, depending on the size of the PR),
  but is not a merge blocker.

- a "textbubble" review mark ("review comments, but not positive/negative")
  should be read through but is not a merge blocker.

- non-trivial PRs are generally given some time (again depending on the size)
  for people to mark an interest in reviewing.  Trivial PRs may be merged
  immediately when CI is green.


Coding Practices & Style
========================

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 :file:`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.

The purpose of commit messages is to briefly summarize what the commit is
changing. Therefore, the extended summary portion should be in the form of an
English paragraph. Brief examples of program output are acceptable but if
present should be short (on the order of 10 lines) and clearly demonstrate what
has changed. The goal should be that someone with only passing familiarity with
the code in question can understand what is being changed.

Commit messages consisting entirely of program output are *unacceptable*. These
do not describe the behavior changed. For example, putting VTYSH output or the
result of test runs as the sole content of commit messages is unacceptable.

You must also sign off on your commit.

.. seealso:: :ref:`signing-off`


Source File Header
------------------

New files must have a copyright header (see :ref:`license-for-contributions`
above) added to the file. The header should be:

.. code-block:: c

    /*
     * 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>

Please copy-paste this header verbatim. In particular:

- Do not replace "This program" with "FRR"
- Do not change the address of the FSF
- keep ``#include <zebra.h>``.  The absolute first header included in any C
  file **must** be either ``zebra.h`` or ``config.h`` (with HAVE_CONFIG_H guard)

Adding Copyright Claims to Existing Files
-----------------------------------------

When adding copyright claims for modifications to an existing file, please
add a ``Portions:`` section as shown below. If this section already exists, add
your new claim at the end of the list.

.. code-block:: c

    /*
     * Title/Function of file
     * Copyright (C) YEAR  Author’s Name
     * Portions:
     *     Copyright (C) 2010 Entity A ....
     *     Copyright (C) 2016 Your name [optional brief change description]
     * ...
     */

Defensive coding requirements
-----------------------------

In general, code submitted into FRR will be rejected if it uses unsafe
programming practices.  While there is no enforced overall ruleset, the
following requirements have achieved consensus:

- ``strcpy``, ``strcat`` and ``sprintf`` are unacceptable without exception.
  Use ``strlcpy``, ``strlcat`` and ``snprintf`` instead.  (Rationale:  even if
  you know the operation cannot overflow the buffer, a future code change may
  inadvertedly introduce an overflow.)

- buffer size arguments, particularly to ``strlcpy`` and ``snprintf``, must
  use ``sizeof()`` whereever possible.  Particularly, do not use a size
  constant in these cases.  (Rationale:  changing a buffer to another size
  constant may leave the write operations on a now-incorrect size limit.)

- For stack allocated structs and arrays that should be zero initialized,
  prefer initializer expressions over ``memset()`` wherever possible. This
  helps prevent ``memset()`` calls being missed in branches, and eliminates the
  error class of an incorrect ``size`` argument to ``memset()``.

  For example, instead of:

  .. code-block:: c

     struct foo mystruct;
     ...
     memset(&mystruct, 0x00, sizeof(struct foo));

  Prefer:

  .. code-block:: c

     struct foo mystruct = {};

- Do not zero initialize stack allocated values that must be initialized with a
  nonzero value in order to be used. This way the compiler and memory checking
  tools can catch uninitialized value use that would otherwise be suppressed by
  the (incorrect) zero initialization.

Other than these specific rules, coding practices from the Linux kernel as
well as CERT or MISRA C guidelines may provide useful input on safe C code.
However, these rules are not applied as-is;  some of them expressly collide
with established practice.


Container implementations
^^^^^^^^^^^^^^^^^^^^^^^^^

In particular to gain defensive coding benefits from better compiler type
checks, there is a set of replacement container data structures to be found
in :file:`lib/typesafe.h`.  They're documented under :ref:`lists`.

Unfortunately, the FRR codebase is quite large, and migrating existing code to
use these new structures is a tedious and far-reaching process (even if it
can be automated with coccinelle, the patches would touch whole swaths of code
and create tons of merge conflicts for ongoing work.)  Therefore, little
existing code has been migrated.

However, both **new code and refactors of existing code should use the new
containers**.  If there are any reasons this can't be done, please work to
remove these reasons (e.g. by adding necessary features to the new containers)
rather than falling back to the old code.

In order of likelyhood of removal, these are the old containers:

- :file:`nhrpd/list.*`, ``hlist_*`` ⇒ ``DECLARE_LIST``
- :file:`nhrpd/list.*`, ``list_*`` ⇒ ``DECLARE_DLIST``
- :file:`lib/skiplist.*`, ``skiplist_*`` ⇒ ``DECLARE_SKIPLIST``
- :file:`lib/*_queue.h` (BSD), ``SLIST_*`` ⇒ ``DECLARE_LIST``
- :file:`lib/*_queue.h` (BSD), ``LIST_*`` ⇒ ``DECLARE_DLIST``
- :file:`lib/*_queue.h` (BSD), ``STAILQ_*`` ⇒ ``DECLARE_LIST``
- :file:`lib/*_queue.h` (BSD), ``TAILQ_*`` ⇒ ``DECLARE_DLIST``
- :file:`lib/hash.*`, ``hash_*`` ⇒ ``DECLARE_HASH``
- :file:`lib/linklist.*`, ``list_*`` ⇒ ``DECLARE_DLIST``
- open-coded linked lists ⇒ ``DECLARE_LIST``/``DECLARE_DLIST``


Code Formatting
---------------

C Code
^^^^^^

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

The project provides multiple tools to allow you to correctly style your code
as painlessly as possible, primarily built around ``clang-format``.

clang-format
   In the project root there is a :file:`.clang-format` configuration file
   which can be used with the ``clang-format`` source formatter tool from the
   LLVM project. Most of the time, this is the easiest and smartest tool to
   use. It can be run in a variety of ways. If you point it at a C source file
   or directory of source files, it will format all of them. In the LLVM source
   tree there are scripts that allow you to integrate it with ``git``, ``vim``
   and ``emacs``, and there are third-party plugins for other editors. The
   ``git`` integration is particularly useful; suppose you have some changes in
   your git index. Then, with the integration installed, you can do the
   following:

   ::

      git clang-format

   This will format *only* the changes present in your index. If you have just
   made a few commits and would like to correctly style only the changes made
   in those commits, you can use the following syntax:

   ::

      git clang-format HEAD~X

   Where X is one more than the number of commits back from the tip of your
   branch you would like ``clang-format`` to look at (similar to specifying the
   target for a rebase).

   The ``vim`` plugin is particularly useful. It allows you to select lines in
   visual line mode and press a key binding to invoke ``clang-format`` on only
   those lines.

   When using ``clang-format``, it is recommended to use the latest version.
   Each consecutive version generally has better handling of various edge
   cases. You may notice on occasion that two consecutive runs of
   ``clang-format`` over the same code may result in changes being made on the
   second run. This is an unfortunate artifact of the tool. Please check with
   the kernel style guide if in doubt.

   One stylistic problem with the FRR codebase is the use of ``DEFUN`` macros
   for defining CLI commands. ``clang-format`` will happily format these macro
   invocations, but the result is often unsightly and difficult to read.
   Consequently, FRR takes a more relaxed position with how these are
   formatted. In general you should lean towards using the style exemplified in
   the section on :ref:`command-line-interface`. Because ``clang-format``
   mangles this style, there is a Python script named ``tools/indent.py`` that
   wraps ``clang-format`` and handles ``DEFUN`` macros as well as some other
   edge cases specific to FRR. If you are submitting a new file, it is
   recommended to run that script over the new file, preferably after ensuring
   that the latest stable release of ``clang-format`` is in your ``PATH``.

   Documentation on ``clang-format`` and its various integrations is maintained
   on the LLVM website.

   https://clang.llvm.org/docs/ClangFormat.html

checkpatch.sh
   In the Linux kernel source tree there is a Perl script used to check
   incoming patches for style errors. FRR uses an adapted version of this
   script for the same purpose. It can be found at
   :file:`tools/checkpatch.sh`. This script takes a git-formatted diff or
   patch file, applies it to a clean FRR tree, and inspects the result to catch
   potential style errors. Running this script on your patches before
   submission is highly recommended. The CI system runs this script as well and
   will comment on the PR with the results if style errors are found.

   It is run like this::

      ./checkpatch.sh <patch> <tree>

   Reports are generated on ``stderr`` and the exit code indicates whether
   issues were found (2, 1) or not (0).

   Where ``<patch>`` is the path to the diff or patch file and ``<tree>`` is
   the path to your FRR source tree. The tree should be on the branch that you
   intend to submit the patch against. The script will make a best-effort
   attempt to save the state of your working tree and index before applying the
   patch, and to restore it when it is done, but it is still recommended that
   you have a clean working tree as the script does perform a hard reset on
   your tree during its run.

   The script reports two classes of issues, namely WARNINGs and ERRORs. Please
   pay attention to both of them. The script will generally report WARNINGs
   where it cannot be 100% sure that a particular issue is real. In most cases
   WARNINGs indicate an issue that needs to be fixed. Sometimes the script will
   report false positives; these will be handled in code review on a
   case-by-case basis. Since the script only looks at changed lines,
   occasionally changing one part of a line can cause the script to report a
   style issue already present on that line that is unrelated to the change.
   When convenient it is preferred that these be cleaned up inline, but this is
   not required.

   In general, a developer should heed the information reported by checkpatch.
   However, some flexibility is needed for cases where human judgement yields
   better clarity than the script. Accordingly, it may be appropriate to
   ignore some checkpatch.sh warnings per discussion among the submitter(s)
   and reviewer(s) of a change. Misreporting of errors by the script is
   possible. When this occurs, the exception should be handled either by
   patching checkpatch to correct the false error report, or by documenting the
   exception in this document under :ref:`style-exceptions`. If the incorrect
   report is likely to appear again, a checkpatch update is preferred.

   If the script finds one or more WARNINGs it will exit with 1. If it finds
   one or more ERRORs it will exit with 2.


Please remember that while FRR provides these tools for your convenience,
responsibility for properly formatting your code ultimately lies on the
shoulders of the submitter. As such, it is recommended to double-check the
results of these tools to avoid delays in merging your submission.

In some cases, these tools modify or flag the format in ways that go beyond or
even conflict [#tool_style_conflicts]_ with the canonical documented Linux
kernel style. In these cases, the Linux kernel style takes priority;
non-canonical issues flagged by the tools are not compulsory but rather are
opportunities for discussion among the submitter(s) and reviewer(s) of a change.

**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.

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


Historically, FRR used fixed-width integral types that do not exist in any
standard but were defined by most platforms at some point. Officially these
types are not guaranteed to exist. Therefore, please use the fixed-width
integral types introduced in the C99 standard when contributing new code to
FRR. If you need to convert a large amount of code to use the correct types,
there is a shell script in :file:`tools/convert-fixedwidth.sh` that will do the
necessary replacements.

+-----------+--------------------------+
| Incorrect | Correct                  |
+===========+==========================+
| u_int8_t  | uint8_t                  |
+-----------+--------------------------+
| u_int16_t | uint16_t                 |
+-----------+--------------------------+
| u_int32_t | uint32_t                 |
+-----------+--------------------------+
| u_int64_t | uint64_t                 |
+-----------+--------------------------+
| u_char    | uint8_t or unsigned char |
+-----------+--------------------------+
| u_short   | unsigned short           |
+-----------+--------------------------+
| u_int     | unsigned int             |
+-----------+--------------------------+
| u_long    | unsigned long            |
+-----------+--------------------------+

FRR also uses unnamed struct fields, enabled with ``-fms-extensions`` (cf.
https://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html).  The following two
patterns can/should be used where contextually appropriate:

.. code-block:: c

   struct outer {
           struct inner;
   };

.. code-block:: c

   struct outer {
           union {
                   struct inner;
                   struct inner inner_name;
           };
   };


.. _style-exceptions:

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/``


Python Code
^^^^^^^^^^^

Format all Python code with `black <https://github.com/psf/black>`_.

In a line::

   python3 -m black <file.py>

Run this on any Python files you modify before committing.

FRR's Python code has been formatted with black version 19.10b.


YANG
^^^^

FRR uses YANG to define data models for its northbound interface. YANG models
should follow conventions used by the IETF standard models. From a practical
standpoint, this corresponds to the output produced by the ``yanglint`` tool
included in the ``libyang`` project, which is used by FRR to parse and validate
YANG models. You should run the following command on all YANG documents you
write:

.. code-block:: console

   yanglint -f yang <model>

The output of this command should be identical to the input file. The sole
exception to this is comments. ``yanglint`` does not support comments and will
strip them from its output. You may include comments in your YANG documents,
but they should be indented appropriately (use spaces). Where possible,
comments should be eschewed in favor of a suitable ``description`` statement.

In short, a diff between your input file and the output of ``yanglint`` should
either be empty or contain only comments.

Specific Exceptions
^^^^^^^^^^^^^^^^^^^

Most of the time checkpatch errors should be corrected. Occasionally as a group
maintainers will decide to ignore certain stylistic issues. Usually this is
because correcting the issue is not possible without large unrelated code
changes. When an exception is made, if it is unlikely to show up again and
doesn't warrant an update to checkpatch, it is documented here.

+------------------------------------------+---------------------------------------------------------------+
| Issue                                    | Ignore Reason                                                 |
+==========================================+===============================================================+
| DEFPY_HIDDEN, DEFPY_ATTR: complex macros | DEF* macros cannot be wrapped in parentheses without updating |
| should be wrapped in parentheses         | all usages of the macro, which would be highly disruptive.    |
+------------------------------------------+---------------------------------------------------------------+

Types of configurables
----------------------

.. note::

   This entire section essentially just argues to not make configuration
   unnecessarily involved for the user.  Rather than rules, this is more of
   a list of conclusions intended to help make FRR usable for operators.


Almost every feature FRR has comes with its own set of switches and options.
There are several stages at which configuration can be applied.  In order of
preference, these are:

-  at configuration/runtime, through YANG.

   This is the preferred way for all FRR knobs.  Not all daemons and features
   are fully YANGified yet, so in some cases new features cannot rely on a
   YANG interface.  If a daemon already implements a YANG interface (even
   partial), new CLI options must be implemented through a YANG model.

   .. warning::

      Unlike everything else in this section being guidelines with some slack,
      implementing and using a YANG interface for new CLI options in (even
      partially!) YANGified daemons is a hard requirement.


-  at configuration/runtime, through the CLI.

   The "good old" way for all regular configuration.  More involved for users
   to automate *correctly* than YANG.

-  at startup, by loading additional modules.

   If a feature introduces a dependency on additional libraries (e.g. libsnmp,
   rtrlib, etc.), this is the best way to encapsulate the dependency.  Having
   a separate module allows the distribution to create a separate package
   with the extra dependency, so FRR can still be installed without pulling
   everything in.

   A module may also be appropriate if a feature is large and reasonably well
   isolated.  Reducing the amount of running the code is a security benefit,
   so even if there are no new external dependencies, modules can be useful.

   While modules cannot currently be loaded at runtime, this is a tradeoff
   decision that was made to allow modules to change/extend code that is very
   hard to (re)adjust at runtime.  If there is a case for runtime (un)loading
   of modules, this tradeoff can absolutely be reevaluated.

-  at startup, with command line options.

   This interface is only appropriate for options that have an effect very
   early in FRR startup, i.e. before configuration is loaded.  Anything that
   affects configuration load itself should be here, as well as options
   changing the environment FRR runs in.

   If a tunable can be changed at runtime, a command line option is only
   acceptable if the configured value has an effect before configuration is
   loaded (e.g. zebra reads routes from the kernel before loading config, so
   the netlink buffer size is an appropriate command line option.)

-  at compile time, with ``./configure`` options.

   This is the absolute last preference for tunables, since the distribution
   needs to make the decision for the user and/or the user needs to rebuild
   FRR in order to change the option.

   "Good" configure options do one of three things:

   -  set distribution-specific parameters, most prominently all the path
      options.  File system layout is a distribution/packaging choice, so the
      user would hopefully never need to adjust these.

   -  changing toolchain behavior, e.g. instrumentation, warnings,
      optimizations and sanitizers.

   -  enabling/disabling parts of the build, especially if they need
      additional dependencies.  Being able to build only parts of FRR, or
      without some library, is useful.  **The only effect these options should
      have is adding or removing files from the build result.**  If a knob
      in this category causes the same binary to exist in different variants,
      it is likely implemented incorrectly!

      .. note::

         This last guideline is currently ignored by several configure options.
         ``vtysh`` in general depends on the entire list of enabled daemons,
         and options like ``--enable-bgp-vnc`` and ``--enable-ospfapi`` change
         daemons internally.  Consider this more of an "ideal" than a "rule".


Whenever adding new knobs, please try reasonably hard to go up as far as
possible on the above list.  Especially ``./configure`` flags are often enough
the "easy way out" but should be avoided when at all possible.  To a lesser
degree, the same applies to command line options.


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.

Custom syntax-like block macros
-------------------------------

FRR uses some macros that behave like the ``for`` or ``if`` C keywords.  These
macros follow these patterns:

- loop-style macros are named ``frr_each_*`` (and ``frr_each``)
- single run macros are named ``frr_with_*``
- to avoid confusion, ``frr_with_*`` macros must always use a ``{ ... }``
  block even if the block only contains one statement.  The ``frr_each``
  constructs are assumed to be well-known enough to use normal ``for`` rules.
- ``break``, ``return`` and ``goto`` all work correctly.  For loop-style
  macros, ``continue`` works correctly too.

Both the ``each`` and ``with`` keywords are inspired by other (more
higher-level) programming languages that provide these constructs.

There are also some older iteration macros, e.g. ``ALL_LIST_ELEMENTS`` and
``FOREACH_AFI_SAFI``.  These macros in some cases do **not** fulfill the above
pattern (e.g. ``break`` does not work in ``FOREACH_AFI_SAFI`` because it
expands to 2 nested loops.)

Static Analysis and Sanitizers
------------------------------
Clang/LLVM and GCC come with a variety of tools that can be used to help find
bugs in FRR.

clang-analyze
   This is a static analyzer that scans the source code looking for patterns
   that are likely to be bugs. The tool is run automatically on pull requests
   as part of CI and new static analysis warnings will be placed in the CI
   results. FRR aims for absolutely zero static analysis errors. While the
   project is not quite there, code that introduces new static analysis errors
   is very unlikely to be merged.

AddressSanitizer
   This is an excellent tool that provides runtime instrumentation for
   detecting memory errors. As part of CI FRR is built with this
   instrumentation and run through a series of tests to look for any results.
   Testing your own code with this tool before submission is encouraged. You
   can enable it by passing::

      --enable-address-sanitizer

   to ``configure``.

ThreadSanitizer
   Similar to AddressSanitizer, this tool provides runtime instrumentation for
   detecting data races. If you are working on or around multithreaded code,
   extensive testing with this instrumtation enabled is *highly* recommended.
   You can enable it by passing::

      --enable-thread-sanitizer

   to ``configure``.

MemorySanitizer
   Similar to AddressSanitizer, this tool provides runtime instrumentation for
   detecting use of uninitialized heap memory. Testing your own code with this
   tool before submission is encouraged. You can enable it by passing::

      --enable-memory-sanitizer

   to ``configure``.

All of the above tools are available in the Clang/LLVM toolchain since 3.4.
AddressSanitizer and ThreadSanitizer are available in recent versions of GCC,
but are no longer actively maintained. MemorySanitizer is not available in GCC.

.. note::

   The different Sanitizers are mostly incompatible with each other.  Please
   refer to GCC/LLVM documentation for details.

frr-format plugin
   This is a GCC plugin provided with FRR that does extended type checks for
   ``%pFX``-style printfrr extensions.  To use this plugin,

   1. install GCC plugin development files, e.g.::

         apt-get install gcc-10-plugin-dev

   2. **before** running ``configure``, compile the plugin with::

         make -C tools/gcc-plugins CXX=g++-10

   (Edit the GCC version to what you're using, it should work for GCC 9 or
   newer.)

   After this, the plugin should be automatically picked up by ``configure``.
   The plugin does not change very frequently, so you can keep it around across
   work on different FRR branches.  After a ``git clean -x``, the ``make`` line
   will need to be run again.  You can also add ``--with-frr-format`` to the
   ``configure`` line to make sure the plugin is used, otherwise if something
   is not set up correctly it might be silently ignored.

   .. warning::

      Do **not** enable this plugin for package/release builds.  It is intended
      for developer/debug builds only.  Since it modifies the compiler, it may
      cause silent corruption of the executable files.

      Using the plugin also changes the string for ``PRI[udx]64`` from the
      system value to ``%L[udx]`` (normally ``%ll[udx]`` or ``%l[udx]``.)

Additionally, the FRR codebase is regularly scanned with Coverity.
Unfortunately Coverity does not have the ability to handle scanning pull
requests, but after code is merged it will send an email notifying project
members with Coverity access of newly introduced defects.

Executing non-installed dynamic binaries
----------------------------------------

Since FRR uses the GNU autotools build system, it inherits its shortcomings.
To execute a binary directly from the build tree under a wrapper like
`valgrind`, `gdb` or `strace`, use::

   ./libtool --mode=execute valgrind [--valgrind-opts] zebra/zebra [--zebra-opts]

While replacing valgrind/zebra as needed.  The `libtool` script is found in
the root of the build directory after `./configure` has completed.  Its purpose
is to correctly set up `LD_LIBRARY_PATH` so that libraries from the build tree
are used.  (On some systems, `libtool` is also available from PATH, but this is
not always the case.)

.. _cli-workflow:

CLI changes
-----------

CLI's are a complicated ugly beast. Additions or changes to the CLI should use
a DEFPY to encapsulate one setting as much as is possible.  Additionally as new
DEFPY'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.

For CLI commands, the deprecation period is 1 year.

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. To
avoid compilation issues in released code, such compiler/preprocessor
annotations must be ignored non-development branches. For example:

.. code-block:: c

   #if CONFDATE > 20180403
   CPP_NOTICE("Use of <XYZ> is deprecated, please use <ABC>")
   #endif

Preferably, the shell script :file:`tools/fixup-deprecated.py` will be
updated along with making non-backwards compatible code changes, or an
alternate script should be introduced, to update the code to match the
change.  When the script is updated, there is no need to preserve the
deprecated code. Note that this does not apply to user interface
changes, just internal code, macros and libraries.

Miscellaneous
-------------

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

JSON Output
^^^^^^^^^^^

New JSON output in FRR needs to be backed by schema, in particular a YANG model.
When adding new JSON, first search for an existing YANG model, either in FRR or
a standard model (e.g., IETF) and use that model as the basis for any JSON
structure and *especially* for key names and canonical values formats.

If no YANG model exists to support the JSON then an FRR YANG model needs to be
added to or created to support the JSON format.

* All JSON keys are to be ``camelCased``, with no spaces. YANG modules almost
  always use ``kebab-case`` (i.e., all lower case with hyphens to separate
  words), so these identifiers need to be mapped to ``camelCase`` by removing
  the hyphen (or symbol) and capitalizing the following letter, for
  example "router-id" becomes "routerId"
* Commands which output JSON should produce ``{}`` if they have nothing to
  display
* In general JSON commands include a ``json`` keyword typically at the end of
  the CLI command (e.g., ``show ip ospf json``)

Use of const
^^^^^^^^^^^^

Please consider using ``const`` when possible: it's a useful hint to
callers about the limits to side-effects from your apis, and it makes
it possible to use your apis in paths that involve ``const``
objects. If you encounter existing apis that *could* be ``const``,
consider including changes in your own pull-request.

Help with specific warnings
^^^^^^^^^^^^^^^^^^^^^^^^^^^

FRR's configure script enables a whole batch of extra warnings, some of which
may not be obvious in how to fix.  Here are some notes on specific warnings:

* ``-Wstrict-prototypes``:  you probably just forgot the ``void`` in a function
  declaration with no parameters, i.e. ``static void foo() {...}`` rather than
  ``static void foo(void) {...}``.

  Without the ``void``, in C, it's a function with *unspecified* parameters
  (and varargs calling convention.)  This is a notable difference to C++, where
  the ``void`` is optional and an empty parameter list means no parameters.

* ``"strict match required"`` from the frr-format plugin:  check if you are
  using a cast in a printf parameter list.  The frr-format plugin cannot
  access correct full type information for casts like
  ``printfrr(..., (uint64_t)something, ...)`` and will print incorrect
  warnings particularly if ``uint64_t``, ``size_t`` or ``ptrdiff_t`` are
  involved.  The problem is *not* triggered with a variable or function return
  value of the exact same type (without a cast).

  Since these cases are very rare, community consensus is to just work around
  the warning even though the code might be correct.  If you are running into
  this, your options are:

  1. try to avoid the cast altogether, maybe using a different printf format
     specifier (e.g. ``%lu`` instead of ``%zu`` or ``PRIu64``).
  2. fix the type(s) of the function/variable/struct member being printed
  3. create a temporary variable with the value and print that without a cast
     (this is the last resort and was not necessary anywhere so far.)


.. _documentation:

Documentation
=============

FRR uses Sphinx+RST as its documentation system. The document you are currently
reading was generated by Sphinx from RST source in
:file:`doc/developer/workflow.rst`. The documentation is structured as follows:

+-----------------------+-------------------------------------------+
| Directory             | Contents                                  |
+=======================+===========================================+
| :file:`doc/user`      | User documentation; configuration guides; |
|                       | protocol overviews                        |
+-----------------------+-------------------------------------------+
| :file:`doc/developer` | Developer's documentation; API specs;     |
|                       | datastructures; architecture overviews;   |
|                       | project management procedure              |
+-----------------------+-------------------------------------------+
| :file:`doc/manpages`  | Source for manpages                       |
+-----------------------+-------------------------------------------+
| :file:`doc/figures`   | Images and diagrams                       |
+-----------------------+-------------------------------------------+
| :file:`doc/extra`     | Miscellaneous Sphinx extensions, scripts, |
|                       | customizations, etc.                      |
+-----------------------+-------------------------------------------+

Each of these directories, with the exception of :file:`doc/figures` and
:file:`doc/extra`, contains a Sphinx-generated Makefile and configuration
script :file:`conf.py` used to set various document parameters. The makefile
can be used for a variety of targets; invoke `make help` in any of these
directories for a listing of available output formats. For convenience, there
is a top-level :file:`Makefile.am` that has targets for PDF and HTML
documentation for both developer and user documentation, respectively. That
makefile is also responsible for building manual pages packed with distribution
builds.

Indent and styling should follow existing conventions:

- 3 spaces for indents under directives
- Cross references may contain only lowercase alphanumeric characters and
  hyphens ('-')
- Lines wrapped to 80 characters where possible

Characters for header levels should follow Python documentation guide:

- ``#`` with overline, for parts
- ``*`` with overline, for chapters
- ``=``, for sections
- ``-``, for subsections
- ``^``, for subsubsections
- ``"``, for paragraphs

After you have made your changes, please make sure that you can invoke
``make latexpdf`` and ``make html`` with no warnings.

The documentation is currently incomplete and needs love. If you find a broken
cross-reference, figure, dead hyperlink, style issue or any other nastiness we
gladly accept documentation patches.

To build the docs, please ensure you have installed a recent version of
`Sphinx <http://www.sphinx-doc.org/en/stable/install.html>`_. If you want to
build LaTeX or PDF docs, you will also need a full LaTeX distribution
installed.

Code
----

FRR 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:

  .. code-block:: c

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

  Function comments should make it 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 make significant changes to portions of the codebase covered in the
Developer's Manual, add a major subsystem or feature, or gain arcane mastery of
some undocumented or poorly documented part of the codebase, please document
your work so others can benefit. If you add a major feature or introduce a new
API, please document the architecture and API to the best of your abilities in
the Developer's Manual, using good judgement when choosing where to place it.

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.

User
----

If you are contributing code that adds significant user-visible functionality
please document how to use it in :file:`doc/user`. Use good judgement when
choosing where to place documentation. For example, instructions on how to use
your implementation of a new BGP draft should go in the BGP chapter instead of
being its own chapter. If you are adding a new protocol daemon, please create a
new chapter.

FRR Specific Markup
-------------------

FRR has some customizations applied to the Sphinx markup that go a long way
towards making documentation easier to use, write and maintain.

CLI Commands
^^^^^^^^^^^^

When documenting CLI please use the ``.. clicmd::`` directive. This directive
will format the command and generate index entries automatically. For example,
the command :clicmd:`show pony` would be documented as follows:

.. code-block:: rest

   .. clicmd:: show pony

      Prints an ASCII pony. Example output:::

              >>\.
             /_  )`.
            /  _)`^)`.   _.---. _
           (_,' \  `^-)""      `.\
                 |  | \
                 \              / |
                / \  /.___.'\  (\ (_
               < ,"||     \ |`. \`-'
                \\ ()      )|  )/
         hjw    |_>|>     /_] //
                  /_]        /_]


When documented this way, CLI commands can be cross referenced with the
``:clicmd:`` inline markup like so:

.. code-block:: rest

   :clicmd:`show pony`

This is very helpful for users who want to quickly remind themselves what a
particular command does.

When documenting a cli that has a ``no`` form, please do not include the ``no``
form. I.e. ``no show pony`` would not be documented anywhere. Since most
commands have ``no`` forms, users should be able to infer these or get help
from vtysh's completions.

When documenting commands that have lots of possible variants, just document
the single command in summary rather than enumerating each possible variant.
E.g. for ``show pony [foo|bar]``, do not:

.. code-block:: rest

   .. clicmd:: show pony
   .. clicmd:: show pony foo
   .. clicmd:: show pony bar

Do:

.. code-block:: rest

   .. clicmd:: show pony [foo|bar]


Configuration Snippets
^^^^^^^^^^^^^^^^^^^^^^

When putting blocks of example configuration please use the
``.. code-block::`` directive and specify ``frr`` as the highlighting language,
as in the following example. This will tell Sphinx to use a custom Pygments
lexer to highlight FRR configuration syntax.

.. code-block:: rest

   .. code-block:: frr

      !
      ! Example configuration file.
      !
      log file /tmp/log.log
      service integrated-vtysh-config
      !
      ip route 1.2.3.0/24 reject
      ipv6 route de:ea:db:ee:ff::/64 reject
      !


.. _GitHub: https://github.com/frrouting/frr
.. _GitHub issues: https://github.com/frrouting/frr/issues

.. rubric:: Footnotes

.. [#tool_style_conflicts] For example, lines over 80 characters are allowed
   for text strings to make it possible to search the code for them: please
   see `Linux kernel style (breaking long lines and strings) <https://www.kernel.org/doc/html/v4.10/process/coding-style.html#breaking-long-lines-and-strings>`_
   and `Issue #1794 <https://github.com/FRRouting/frr/issues/1794>`_.