// -*- mode:doc; -*-
// vim: set syntax=asciidoc:

== Contributing to Buildroot

There are many ways in which you can contribute to Buildroot: analyzing
and fixing bugs, analyzing and fixing package build failures detected by
the autobuilders, testing and reviewing patches sent by other
developers, working on the items in our TODO list and sending your own
improvements to Buildroot or its manual. The following sections give a
little more detail on each of these items.

If you are interested in contributing to Buildroot, the first thing you
should do is to subscribe to the Buildroot mailing list. This list is
the main way of interacting with other Buildroot developers and to send
contributions to. If you aren't subscribed yet, then refer to
xref:community-resources[] for the subscription link.

If you are going to touch the code, it is highly recommended to use a
git repository of Buildroot, rather than starting from an extracted
source code tarball. Git is the easiest way to develop from and directly
send your patches to the mailing list. Refer to xref:getting-buildroot[]
for more information on obtaining a Buildroot git tree.

=== Reproducing, analyzing and fixing bugs

A first way of contributing is to have a look at the open bug reports in
the https://bugs.buildroot.org/buglist.cgi?product=buildroot[Buildroot bug
tracker]. As we strive to keep the bug count as small as possible, all
help in reproducing, analyzing and fixing reported bugs is more than
welcome. Don't hesitate to add a comment to bug reports reporting your
findings, even if you don't yet see the full picture.

=== Analyzing and fixing autobuild failures

The Buildroot autobuilders are a set of build machines that continuously
run Buildroot builds based on random configurations. This is done for
all architectures supported by Buildroot, with various toolchains, and
with a random selection of packages. With the large commit activity on
Buildroot, these autobuilders are a great help in detecting problems
very early after commit.

All build results are available at http://autobuild.buildroot.org[],
statistics are at http://autobuild.buildroot.org/stats.php[]. Every day,
an overview of all failed packages is sent to the mailing list.

Detecting problems is great, but obviously these problems have to be
fixed as well. Your contribution is very welcome here! There are
basically two things that can be done:

- Analyzing the problems. The daily summary mails do not contain details
  about the actual failures: in order to see what's going on you have to
  open the build log and check the last output. Having someone doing
  this for all packages in the mail is very useful for other developers,
  as they can make a quick initial analysis based on this output alone.

- Fixing a problem. When fixing autobuild failures, you should follow
  these steps:
  . Check if you can reproduce the problem by building with the same
    configuration. You can do this manually, or use the
    http://git.buildroot.org/buildroot-test/tree/utils/br-reproduce-build[br-reproduce-build]
    script that will automatically clone a Buildroot git repository,
    checkout the correct revision, download and set the right
    configuration, and start the build.
  . Analyze the problem and create a fix.
  . Verify that the problem is really fixed by starting from a clean
    Buildroot tree and only applying your fix.
  . Send the fix to the Buildroot mailing list (see
    xref:submitting-patches[]). In case you created a patch against the
    package sources, you should also send the patch upstream so that the
    problem will be fixed in a later release, and the patch in Buildroot
    can be removed.
    In the commit message of a patch fixing an autobuild failure, add a
    reference to the build result directory, as follows:
---------------------
Fixes http://autobuild.buildroot.org/results/51000a9d4656afe9e0ea6f07b9f8ed374c2e4069
---------------------

=== Reviewing and testing patches

With the amount of patches sent to the mailing list each day, the
maintainer has a very hard job to judge which patches are ready to apply
and which ones aren't. Contributors can greatly help here by reviewing
and testing these patches.

In the review process, do not hesitate to respond to patch submissions
for remarks, suggestions or anything that will help everyone to
understand the patches and make them better. Please use internet
style replies in plain text emails when responding to patch
submissions.

To indicate approval of a patch, there are three formal tags that keep
track of this approval. To add your tag to a patch, reply to it with the
approval tag below the original author's Signed-off-by line. These tags
will be picked up automatically by patchwork (see
xref:apply-patches-patchwork[]) and will be part of the commit log when
the patch is accepted.

Tested-by:: Indicates that the patch has been tested successfully.
  You are encouraged to specify what kind of testing you performed
  (compile-test on architecture X and Y, runtime test on target A,
  ...). This additional information helps other testers and the
  maintainer.

Reviewed-by:: Indicates that you code-reviewed the patch and did your
  best in spotting problems, but you are not sufficiently familiar with
  the area touched to provide an Acked-by tag. This means that there
  may be remaining problems in the patch that would be spotted by
  someone with more experience in that area. Should such problems be
  detected, your Reviewed-by tag remains appropriate and you cannot
  be blamed.

Acked-by:: Indicates that you code-reviewed the patch and you are
  familiar enough with the area touched to feel that the patch can be
  committed as-is (no additional changes required). In case it later
  turns out that something is wrong with the patch, your Acked-by could
  be considered inappropriate. The difference between Acked-by and
  Reviewed-by is thus mainly that you are prepared to take the blame on
  Acked patches, but not on Reviewed ones.

If you reviewed a patch and have comments on it, you should simply reply
to the patch stating these comments, without providing a Reviewed-by or
Acked-by tag. These tags should only be provided if you judge the patch
to be good as it is.

It is important to note that neither Reviewed-by nor Acked-by imply
that testing has been performed. To indicate that you both reviewed and
tested the patch, provide two separate tags (Reviewed/Acked-by and
Tested-by).

Note also that _any developer_ can provide Tested/Reviewed/Acked-by
tags, without exception, and we encourage everyone to do this. Buildroot
does not have a defined group of _core_ developers, it just so happens
that some developers are more active than others. The maintainer will
value tags according to the track record of their submitter. Tags
provided by a regular contributor will naturally be trusted more than
tags provided by a newcomer. As you provide tags more regularly, your
'trustworthiness' (in the eyes of the maintainer) will go up, but _any_
tag provided is valuable.

Buildroot's Patchwork website can be used to pull in patches for testing
purposes. Please see xref:apply-patches-patchwork[] for more
information on using Buildroot's Patchwork website to apply patches.

[[apply-patches-patchwork]]
==== Applying Patches from Patchwork

The main use of Buildroot's Patchwork website for a developer is for
pulling in patches into their local git repository for testing
purposes.

When browsing patches in the patchwork management interface, an +mbox+
link is provided at the top of the page. Copy this link address and
run the following commands:

---------------------
$ git checkout -b <test-branch-name>
$ wget -O - <mbox-url> | git am
---------------------

Another option for applying patches is to create a bundle. A bundle is
a set of patches that you can group together using the patchwork
interface. Once the bundle is created and the bundle is made public,
you can copy the +mbox+ link for the bundle and apply the bundle
using the above commands.


=== Work on items from the TODO list

If you want to contribute to Buildroot but don't know where to start,
and you don't like any of the above topics, you can always work on items
from the http://elinux.org/Buildroot#Todo_list[Buildroot TODO list].
Don't hesitate to discuss an item first on the mailing list or on IRC.
Do edit the wiki to indicate when you start working on an item, so we
avoid duplicate efforts.

[[submitting-patches]]
=== Submitting patches

[NOTE]
_Please, do not attach patches to bugs, send them to the mailing list
instead_.

If you made some changes to Buildroot and you would like to contribute
them to the Buildroot project, proceed as follows.

==== The formatting of a patch

We expect patches to be formatted in a specific way. This is necessary
to make it easy to review patches, to be able to apply them easily to
the git repository, to make it easy to find back in the history how
and why things have changed, and to make it possible to use +git
bisect+ to locate the origin of a problem.

First of all, it is essential that the patch has a good commit
message. The commit message should start with a separate line with a
brief summary of the change, starting with the name of the affected
package. The body of the commit message should describe _why_ this
change is needed, and if necessary also give details about _how_ it
was done. When writing the commit message, think of how the reviewers
will read it, but also think about how you will read it when you look
at this change again a few years down the line.

Second, the patch itself should do only one change, but do it
completely. Two unrelated or weakly related changes should usually be
done in two separate patches. This usually means that a patch affects
only a single package. If several changes are related, it is often
still possible to split them up in small patches and apply them in a
specific order. Small patches make it easier to review, and often
make it easier to understand afterwards why a change was done.
However, each patch must be complete. It is not allowed that the
build is broken when only the first but not the second patch is
applied. This is necessary to be able to use +git bisect+ afterwards.

Of course, while you're doing your development, you're probably going
back and forth between packages, and certainly not committing things
immediately in a way that is clean enough for submission. So most
developers rewrite the history of commits to produce a clean set of
commits that is appropriate for submission. To do this, you need to
use _interactive rebasing_. You can learn about it
https://git-scm.com/book/en/v2/Git-Tools-Rewriting-History[in the Pro
Git book]. Sometimes, it is even easier to discard you history with
+git reset --soft origin/master+ and select individual changes with
+git add -i+ or +git add -p+.

Finally, the patch should be signed off. This is done by adding
+Signed-off-by: Your Real Name <your@email.address>+ at the end of the
commit message. +git commit -s+ does that for you, if configured
properly. The +Signed-off-by+ tag means that you publish the patch
under the Buildroot license (i.e. GPLv2, except for package patches,
which have the upstream license), and that you are allowed to do so.
See http://developercertificate.org/[the Developer Certificate of
Origin] for details.

When adding new packages, you should submit every package in a
separate patch. This patch should have the update to
+package/Config.in+, the package +Config.in+ file, the +.mk+ file, the
+.hash+ file, any init script, and all package patches. If the package
has many sub-options, these are sometimes better added as separate
follow-up patches. The summary line should be something like
+<packagename>: new package+. The body of the commit message can be
empty for simple packages, or it can contain the description of the
package (like the Config.in help text). If anything special has to be
done to build the package, this should also be explained explicitly in
the commit message body.

When you bump a package to a new version, you should also submit a
separate patch for each package. Don't forget to update the +.hash+
file, or add it if it doesn't exist yet. Also don't forget to check if
the +_LICENSE+ and +_LICENSE_FILES+ are still valid. The summary line
should be something like +<packagename>: bump to version <new
version>+. If the new version only contains security updates compared
to the existing one, the summary should be +<packagename>: security
bump to version <new version>+ and the commit message body should show
the CVE numbers that are fixed. If some package patches can be removed
in the new version, it should be explained explicitly why they can be
removed, preferably with the upstream commit ID. Also any other
required changes should be explained explicitly, like configure
options that no longer exist or are no longer needed.

==== Preparing a patch series

Starting from the changes committed in your local git view, _rebase_
your development branch on top of the upstream tree before generating
a patch set. To do so, run:

---------------------
$ git fetch --all --tags
$ git rebase origin/master
---------------------

Now, you are ready to generate then submit your patch set.

To generate it, run:

---------------------
$ git format-patch -M -n -s -o outgoing origin/master
---------------------

This will generate patch files in the +outgoing+ subdirectory,
automatically adding the +Signed-off-by+ line.

Once patch files are generated, you can review/edit the commit message
before submitting them, using your favorite text editor.

Lastly, send/submit your patch set to the Buildroot mailing list:

---------------------
$ git send-email --to buildroot@buildroot.org outgoing/*
---------------------

Note that +git+ should be configured to use your mail account.
To configure +git+, see +man git-send-email+ or google it.

If you do not use +git send-email+, make sure posted *patches are not
line-wrapped*, otherwise they cannot easily be applied. In such a case,
fix your e-mail client, or better yet, learn to use +git send-email+.

==== Cover letter

If you want to present the whole patch set in a separate mail, add
+--cover-letter+ to the +git format-patch+ command (see +man
git-format-patch+ for further information). This will generate a
template for an introduction e-mail to your patch series.

A 'cover letter' may be useful to introduce the changes you propose
in the following cases:

* large number of commits in the series;

* deep impact of the changes in the rest of the project;

* RFC footnote:[RFC: (Request for comments) change proposal];

* whenever you feel it will help presenting your work, your choices,
  the review process, etc.

==== Patch revision changelog

When improvements are requested, the new revision of each commit
should include a changelog of the modifications between each
submission. Note that when your patch series is introduced by a cover
letter, an overall changelog may be added to the cover letter in
addition to the changelog in the individual commits.
The best thing to rework a patch series is by interactive rebasing:
+git rebase -i origin/master+. Consult the git manual for more
information.

When added to the individual commits, this changelog is added when
editing the commit message. Below the +Signed-off-by+ section, add
+---+ and your changelog.

Although the changelog will be visible for the reviewers in the mail
thread, as well as in http://patchwork.buildroot.org[patchwork], +git+
will automatically ignores lines below +---+ when the patch will be
merged. This is the intended behavior: the changelog is not meant to
be preserved forever in the +git+ history of the project.

Hereafter the recommended layout:

---------------
Patch title: short explanation, max 72 chars

A paragraph that explains the problem, and how it manifests itself. If
the problem is complex, it is OK to add more paragraphs. All paragraphs
should be wrapped at 72 characters.

A paragraph that explains the root cause of the problem. Again, more
than on paragraph is OK.

Finally, one or more paragraphs that explain how the problem is solved.
Don't hesitate to explain complex solutions in detail.

Signed-off-by: John DOE <john.doe@example.net>

---
Changes v2 -> v3:
  - foo bar  (suggested by Jane)
  - bar buz

Changes v1 -> v2:
  - alpha bravo  (suggested by John)
  - charly delta
---------------

Any patch revision should include the version number. The version number
is simply composed of the letter +v+ followed by an +integer+ greater or
equal to two (i.e. "PATCH v2", "PATCH v3" ...).

This can be easily handled with +git format-patch+ by using the option
+--subject-prefix+:

---------------------
$ git format-patch --subject-prefix "PATCH v4" \
    -M -s -o outgoing origin/master
---------------------

Since git version 1.8.1, you can also use +-v <n>+ (where <n> is the
version number):

---------------------
$ git format-patch -v4 -M -s -o outgoing origin/master
---------------------

When you provide a new version of a patch, please mark the old one as
superseded in http://patchwork.buildroot.org[patchwork]. You need to
create an account on http://patchwork.buildroot.org[patchwork] to be
able to modify the status of your patches. Note that you can only change
the status of patches you submitted yourself, which means the email
address you register in http://patchwork.buildroot.org[patchwork] should
match the one you use for sending patches to the mailing list.

You can also add the +--in-reply-to <message-id>+ option when
submitting a patch to the mailing list. The id of the mail to reply to
can be found under the "Message Id" tag on
http://patchwork.buildroot.org[patchwork].  The advantage of
*in-reply-to* is that patchwork will automatically mark the previous
version of the patch as superseded.

[[reporting-bugs]]
=== Reporting issues/bugs or getting help

Before reporting any issue, please check in
xref:community-resources[the mailing list archive] whether someone has
already reported and/or fixed a similar problem.

However you choose to report bugs or get help, either by
opening a bug in the xref:community-resources[bug tracker] or by
xref:community-resources[sending a mail to the mailing list], there are
a number of details to provide in order to help people reproduce and
find a solution to the issue.

Try to think as if you were trying to help someone else; in
that case, what would you need?

Here is a short list of details to provide in such case:

* host machine (OS/release)
* version of Buildroot
* target for which the build fails
* package(s) for which the build fails
* the command that fails and its output
* any information you think that may be relevant

Additionally, you should add the +.config+ file (or if you know how, a
+defconfig+; see xref:customize-store-buildroot-config[]).

If some of these details are too large, do not hesitate to use a
pastebin service. Note that not all available pastebin services will
preserve Unix-style line terminators when downloading raw pastes.
Following pastebin services are known to work correctly:
- https://gist.github.com/
- http://code.bulix.org/
