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============================================
Contributing to Ceph: A Guide for Developers
============================================
:Author: Loic Dachary
:Author: Nathan Cutler
:License: Creative Commons Attribution-ShareAlike (CC BY-SA)
.. note:: The old (pre-2016) developer documentation has been moved to :doc:`/dev/index-old`.
.. contents::
:depth: 3
Introduction
============
This guide has two aims. First, it should lower the barrier to entry for
software developers who wish to get involved in the Ceph project. Second,
it should serve as a reference for Ceph developers.
We assume that readers are already familiar with Ceph (the distributed
object store and file system designed to provide excellent performance,
reliability and scalability). If not, please refer to the `project website`_
and especially the `publications list`_.
.. _`project website`: http://ceph.com
.. _`publications list`: https://ceph.com/resources/publications/
Since this document is to be consumed by developers, who are assumed to
have Internet access, topics covered elsewhere, either within the Ceph
documentation or elsewhere on the web, are treated by linking. If you
notice that a link is broken or if you know of a better link, please
`report it as a bug`_.
.. _`report it as a bug`: http://tracker.ceph.com/projects/ceph/issues/new
Essentials (tl;dr)
==================
This chapter presents essential information that every Ceph developer needs
to know.
Leads
-----
The Ceph project is led by Sage Weil. In addition, each major project
component has its own lead. The following table shows all the leads and
their nicks on `GitHub`_:
.. _github: https://github.com/
========= =============== =============
Scope Lead GitHub nick
========= =============== =============
Ceph Sage Weil liewegas
RADOS Samuel Just athanatos
RGW Yehuda Sadeh yehudasa
RBD Josh Durgin jdurgin
CephFS Gregory Farnum gregsfortytwo
Build/Ops Ken Dreyer ktdreyer
========= =============== =============
The Ceph-specific acronyms in the table are explained under
`Architecture`_, below.
History
-------
See the `History chapter of the Wikipedia article`_.
.. _`History chapter of the Wikipedia article`: https://en.wikipedia.org/wiki/Ceph_%28software%29#History
Licensing
---------
Ceph is free software.
Unless stated otherwise, the Ceph source code is distributed under the terms of
the LGPL2.1. For full details, see `the file COPYING in the top-level
directory of the source-code tree`_.
.. _`the file COPYING in the top-level directory of the source-code tree`:
https://github.com/ceph/ceph/blob/master/COPYING
Source code repositories
------------------------
The source code of Ceph lives on `GitHub`_ in a number of repositories below
the `Ceph "organization"`_.
.. _`Ceph "organization"`: https://github.com/ceph
To make a meaningful contribution to the project as a developer, a working
knowledge of git_ is essential.
.. _git: https://git-scm.com/documentation
Although the `Ceph "organization"`_ includes several software repositories,
this document covers only one: https://github.com/ceph/ceph.
Issue tracker
-------------
Although `GitHub`_ is used for code, Ceph-related issues (Bugs, Features,
Backports, Documentation, etc.) are tracked at http://tracker.ceph.com,
which is powered by `Redmine`_.
.. _Redmine: http://www.redmine.org
The tracker has a Ceph project with a number of subprojects loosely
corresponding to the project components listed in `Architecture`_.
Mere `registration`_ in the tracker automatically grants permissions
sufficient to open new issues and comment on existing ones.
.. _registration: http://tracker.ceph.com/account/register
To report a bug or propose a new feature, `jump to the Ceph project`_ and
click on `New issue`_.
.. _`jump to the Ceph project`: http://tracker.ceph.com/projects/ceph
.. _`New issue`: http://tracker.ceph.com/projects/ceph/issues/new
Mailing list
------------
Ceph development email discussions take place on the mailing list
``ceph-devel@vger.kernel.org``. The list is open to all. Subscribe by
sending a message to ``majordomo@vger.kernel.org`` with the line: ::
subscribe ceph-devel
in the body of the message.
There are also `other Ceph-related mailing lists`_.
.. _`other Ceph-related mailing lists`: https://ceph.com/resources/mailing-list-irc/
IRC
---
In addition to mailing lists, the Ceph community also communicates in real
time using `Internet Relay Chat`_.
.. _`Internet Relay Chat`: http://www.irchelp.org/
See https://ceph.com/resources/mailing-list-irc/ for how to set up your IRC
client and a list of channels.
Submitting patches
------------------
The canonical instructions for submitting patches are contained in the
`the file CONTRIBUTING.rst in the top-level directory of the source-code
tree`_. There may be some overlap between this guide and that file.
.. _`the file CONTRIBUTING.rst in the top-level directory of the source-code tree`:
https://github.com/ceph/ceph/blob/master/CONTRIBUTING.rst
All newcomers are encouraged to read that file carefully.
Building from source
--------------------
See instructions at :doc:`/install/build-ceph`.
Development-mode cluster
------------------------
You can start a development-mode Ceph cluster, after compiling the source,
with:
.. code::
cd src
install -d -m0755 out dev/osd0
./vstart.sh -n -x -l
# check that it's there
./ceph health
Basic workflow
==============
.. epigraph::
Without bugs, there would be no software, and without software, there would
be no software developers.
--Unknown
Having already introduced the `Issue tracker`_ and the `Source code
repositories`_, and having touched upon `Submitting patches`_, we now
describe these in more detail in the context of basic Ceph development
workflows.
.. ditaa::
Upstream Code Your Local Environment
/----------\ git clone /-------------\
| Ceph | -------------------------> | ceph/master |
\----------/ \-------------/
^ |
| | git branch fix_1
| git merge |
| v
/----------------\ git commit --amend /-------------\
| make check |---------------------> | ceph/fix_1 |
| ceph--qa--suite| \-------------/
\----------------/ |
^ | fix changes
| | make check
| review | ceph--workbench ceph--qa--suite
| | git commit
| v
/--------------\ /-------------\
| github |<---------------------- | ceph/fix_1 |
| pull request | git push \-------------/
\--------------/
Issue tracker conventions
-------------------------
When you start working on an existing issue, it's nice to let the other
developers know this - to avoid duplication of labor. Typically, this is
done by changing the :code:`Assignee` field (to yourself) and changing the
:code:`Status` to *In progress*. Newcomers to the Ceph community typically do not
have sufficient privileges to update these fields, however: they can
simply update the issue with a brief note.
.. table:: Meanings of some commonly used statuses
================ ===========================================
Status Meaning
================ ===========================================
New Initial status
In Progress Somebody is working on it
Need Review Pull request is open with a fix
Pending Backport Fix has been merged, backport(s) pending
Resolved Fix and backports (if any) have been merged
================ ===========================================
Pull requests
-------------
The Ceph source code is maintained in the `ceph/ceph repository` on
`GitHub`_.
.. _`ceph/ceph project on GitHub`: https://github.com/ceph/ceph
The `GitHub`_ web interface provides a key feature for contributing code
to the project: the *pull request*.
Newcomers who are uncertain how to use pull requests may read
`this GitHub pull request tutorial`_.
.. _`this GitHub pull request tutorial`:
https://help.github.com/articles/using-pull-requests/
For some ideas on what constitutes a "good" pull request, see
the `Git Commit Good Practice`_ article at the `OpenStack Project Wiki`_.
.. _`Git Commit Good Practice`: https://wiki.openstack.org/wiki/GitCommitMessages
.. _`OpenStack Project Wiki`: https://wiki.openstack.org/wiki/Main_Page
Make check tests
----------------
After compiling Ceph, the ``make check`` command can be used to run a
series of tests. They cover various aspects of Ceph and each of them
must:
* bind ports that do not conflict with other tests
* not require root access
* not require more than one machine to run
* complete within a few minutes
Integration tests
-----------------
When a test requires multiple machines, root access or lasts for a
longer time (for example, to simulate a realistic Ceph deployment), it
is deemed to be an integration test. Integration tests are defined
in the `ceph-qa-suite repository`_ and run with the `teuthology
framework`_.
A number of integration tests are run on a regular basis against the
official Ceph repositories (on the master development branch and the
stable branches). The results are visible at `sepia
<http://pulpito.ceph.com/>`_ and `sepia.ovh
<http://pulpito.ovh.sepia.ceph.com:8081/>`_ and are also reported on
the `ceph-qa mailing list <http://ceph.com/resources/mailing-list-irc/>`_
for analysis.
Some Ceph developers have access to the hardware running these tests
(either bare metal or OpenStack provisioned) and are allowed to
schedule integration tests there (the developer nick shows in the test
results URL).
Ceph developers who have access to an OpenStack tenant can use the
`ceph-workbench ceph-qa-suite`_ command to run integration tests and
publish the results at http://teuthology-logs.public.ceph.com. This
allows reviewers to verify that changes to the code base do not cause
regressions, or to analyze test failures when they do occur.
.. _`ceph-qa-suite repository`: https://github.com/ceph/ceph-qa-suite
.. _`teuthology framework`: https://github.com/ceph/teuthology
.. _`ceph-workbench ceph-qa-suite`: http://ceph-workbench.readthedocs.org/
Architecture
============
Ceph is a collection of components built on top of RADOS and provide
services (RBD, RGW, CephFS) and APIs (S3, Swift, POSIX) for the user to
store and retrieve data.
See :doc:`/architecture` for an overview of Ceph architecture. The
following sections treat each of the major architectural components
in more detail, with links to code and tests.
.. FIXME The following are just stubs. These need to be developed into
detailed descriptions of the various high-level components (RADOS, RGW,
etc.) with breakdowns of their respective subcomponents.
.. FIXME Later, in the Testing chapter I would like to take another look
at these components/subcomponents with a focus on how they are tested.
RADOS
-----
RADOS stands for "Reliable, Autonomic Distributed Object Store". In a Ceph
cluster, all data are stored in objects, and RADOS is the component responsible
for that.
RADOS itself can be further broken down into Monitors, Object Storage Daemons
(OSDs), and client APIs (librados). Monitors and OSDs are introduced at
:doc:`/start/intro`. The client library is explained at
:doc:`/rados/api/index`.
RGW
---
RGW stands for RADOS Gateway. Using the embedded HTTP server civetweb_, RGW
provides a REST interface to RADOS objects.
.. _civetweb: https://github.com/civetweb/civetweb
A more thorough introduction to RGW can be found at :doc:`/radosgw/index`.
RBD
---
RBD stands for RADOS Block Device. It enables a Ceph cluster to store disk
images, and includes in-kernel code enabling RBD images to be mounted.
To delve further into RBD, see :doc:`/rbd/rbd`.
CephFS
------
CephFS is a distributed file system that enables a Ceph cluster to be used as a NAS.
File system metadata is managed by Meta Data Server (MDS) daemons. The Ceph
file system is explained in more detail at :doc:`/cephfs/index`.
.. WIP
.. ===
..
.. Building RPM packages
.. ---------------------
..
.. Ceph is regularly built and packaged for a number of major Linux
.. distributions. At the time of this writing, these included CentOS, Debian,
.. Fedora, openSUSE, and Ubuntu.
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