CONTRIBUTING.md

   1 # LTTng-tools contributor's guide
   2
   3 Being an open source project, the LTTng-tools project welcomes
   4 contributions from anyone. This guide walks you through the process
   5 of contributing a patch to LTTng-tools.
   6
   7
   8 ## Getting the source code
   9
  10 The LTTng-tools project uses [Git](https://git-scm.com/) for version
  11 control. The upstream Git repository URL is:
  12
  13     git://git.lttng.org/lttng-tools.git
  14
  15
  16 ## Coding standard
  17
  18 See CodingStyle for guidelines style and design guidelines.
  19
  20 Although the LTTng-tools code base is primarily written in C, it does
  21 contain shell, Perl, and Python code as well. There is no official coding
  22 standard for these languages. However, using a style consistent with the
  23 rest of the code written in that language is strongly encouraged.
  24
  25
  26 ## Creating and sending a patch
  27
  28 LTTng-tools's development flow is primarily email-based, although we
  29 also accept pull requests on our
  30 [GitHub mirror](https://github.com/lttng/lttng-tools) and
  31 [Gerrit Code Review](https://review.lttng.org). If you're going
  32 to create GitHub pull requests, make sure you still follow the
  33 guidelines below.
  34
  35 Like a lot of open source projects, patches are submitted and reviewed
  36 on its development mailing list,
  37 [`lttng-dev`](http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev)
  38 (`lttng-dev@lists.lttng.org`). The mailing list is also used to share
  39 and comment on <abbr title="Request for Comments">RFC</abbr>s and answer
  40 user questions.
  41
  42 Once your changes have been committed to your local branch, you may use
  43 Git's [`format-patch`](https://git-scm.com/docs/git-format-patch) command
  44 to generate a patch file. The following command line generates a
  45 patch from the latest commit:
  46
  47     git format-patch -N1 -s --subject-prefix="PATCH lttng-tools"
  48
  49 The custom `PATCH lttng-tools` subject prefix is mandatory when
  50 submitting patches that apply to the LTTng-tools project.
  51
  52 The patch's subject (the commit message's first line) should:
  53
  54   * Begin with an uppercase letter.
  55   * Be written in the present tense.
  56   * _Not_ exceed 72 characters in length.
  57   * _Not_ end with a period.
  58
  59 In the case of bug fixes, the patch's subject must be prefixed with
  60 `Fix:` and a suitable sub-system name. For instance, a patch
  61 addressing a bug in the session daemon should start with `Fix:
  62 sessiond:`. Patches targeting shared code can either use the namespace
  63 of the interface or of the internal library, whichever is more
  64 precise.
  65
  66 A non-exhaustive list of common sub-system prefixes follows:
  67
  68   * `relayd` (relay daemon).
  69   * `sessiond` (session daemon).
  70   * `lttng` (LTTng CLI client).
  71   * `ust-consumerd` (user space consumer daemon).
  72   * `kernel-consumerd` (kernel space consumer daemon).
  73   * `consumerd` (common consumer daemon).
  74   * `common` (internal `libcommon`).
  75   * `trace-chunk` (internal `lttng_trace_chunk_*` interface).
  76   * `lttng-ctl` (`liblttng-ctl` library).
  77   * `mi` (LTTng client's machine interface).
  78
  79 When possible, the commit title should describe the issue _as
  80 observed_ and not the underlying cause. For instance, prefer `Fix:
  81 sessiond: hang on SIGTERM after session rotation` to `Fix: sessiond:
  82 unchecked status on exit`.
  83
  84 The commit message's body must be as detailed as possible and explain
  85 the reasons behind the proposed change. Keep in mind that this message
  86 will be read in a number of years and must still be clear. Any related
  87 [bug report(s)](https://bugs.lttng.org/projects/lttng-tools/issues)
  88 should be mentioned at the end of the message using the `#123` format,
  89 where `123` is the bug number:
  90
  91   * Use `Refs: #123` if the patch is related to bug 123, but does not
  92     fix it yet.
  93   * Use `Fixes: #123` to signify that this patch fixes the bug.
  94
  95 In the case of bug fixes, the following structure must be used:
  96
  97   * Observed issue
  98   * Cause
  99   * Solution
 100   * **Optional**: Known drawbacks
 101
 102 A short commit message can be used when submitting typo fixes or minor
 103 cleanups that don't introduce behaviour changes.
 104
 105 When submitting a patch that affects existing code, implement changes
 106 to the existing code as prelude patches in a patch series. Explain why
 107 those changes are needed and how they make follow-up changes
 108 easier/possible.
 109
 110 Make sure to **sign-off** your submitted patches (the `-s` argument to
 111 Git's `commit` and `format-patch` commands).
 112
 113 Here's a complete example:
 114
 115 ~~~ text
 116 Fix: relayd: missing thingy in the doodad folder on error
 117
 118 Observed issue
 119 ==============
 120 After a communication error, the relay daemon will not produce
 121 a thingy in the doodad folder. This results in the knickknack
 122 baring the foo.
 123
 124 Steps to reproduce (list of commands or narrative description).
 125
 126 Cause
 127 =====
 128 The thingy_do_the_doodad() callback is only invoked when
 129 the thread responsible for receiving messages and dispatching
 130 them to the correct actors encounters an emoji.
 131
 132 However, an emoji is not guaranteed to be present in the ELF
 133 section header [1].
 134
 135 Solution
 136 ========
 137 Flushing the doodad on every reception of a thingo ensures that
 138 the thingy is present in the doodad folder even if a communication
 139 error occurs.
 140
 141 Known drawbacks
 142 ===============
 143 Flushing the doodad too often may spam the widget and result in
 144 degradation of the gizmo. This doesn't matter right now since
 145 it happens exactly once per blue moon.
 146
 147 If this becomes a serious issue, we could machine learn the MVP
 148 through the big O terminal.
 149
 150 References
 151 ==========
 152 [1] https://www.thedocs.com/elf/proving-my-point-unambiguously.aspx
 153
 154 Fixes: #321
 155 Refs: #456
 156 Refs: #1987
 157
 158 Signed-off-by: Jeanne Mance <jmeance@lttng.org>
 159 ~~~
 160
 161 Please note that patches should be **as focused as possible**. Do not,
 162 for instance, fix a bug and correct the indentation of an unrelated
 163 block of code as part of the same patch.
 164
 165 The project contains a script, [`extras/checkpatch.pl`](extras/checkpatch.pl),
 166 that performs a number of checks on a patch to ensure it is ready for
 167 submission. Run this script on your patch and correct any reported
 168 errors before posting it to the mailing list:
 169
 170     extras/checkpatch.pl --no-tree 0001-Fix...patch
 171
 172 Once you are confident your patch meets the required guidelines,
 173 you may use Git's [`send-email`](https://git-scm.com/docs/git-send-email)
 174 command to send your patch to the mailing list:
 175
 176     git send-email --suppress-cc=self --to lttng-dev@lists.lttng.org *.patch
 177
 178 Make sure you are
 179 [subscribed](http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev)
 180 to the mailing list to follow and take part in discussions about your
 181 changes. You may join the file to an email as an attachment if you can't
 182 send the patch directly using <code>git&nbsp;send&#8209;email</code>.
 183
 184
 185 ## Reviews
 186
 187 Once your patch has been posted to the mailing list or as a GitHub
 188 pull request, other contributors may propose modifications.
 189 This is completely normal. This collaborative code review is an integral
 190 part of the open source development process in general and LTTng-tools
 191 makes no exception.
 192
 193 Keep in mind that reviewing patches is a time-consuming process and,
 194 as such, may not be done right away. The delays may be affected by the
 195 current release cycle phase and the complexity of the proposed changes.
 196 If you think your patch might have been forgotten, please mention it on
 197 the [`#lttng`](irc://irc.oftc.net/lttng) IRC channel rather than
 198 resubmitting.
 199
 200
 201 ## Release cycle
 202
 203 The LTTng-tools project follows a release cycle that alternates between
 204 development and release candidate (RC) phases. The master branch is
 205 feature-frozen during RC phases: only bug fixes are accepted during
 206 this period. However, patches adding new functionality may still be
 207 submitted and reviewed during the RC. The upcoming features and release
 208 dates are posted in a monthly digest on the mailing list.