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 based on
  29 [Gerrit Code Review](https://review.lttng.org), although we also accept
  30 e-mail based patch series on the
  31 [`lttng-dev` mailing list](https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev)
  32 and pull requests on our [GitHub mirror](https://github.com/lttng/lttng-tools).
  33 If you're going to create GitHub pull requests, make sure you still follow the
  34 guidelines below.
  35
  36 The mailing list is also used to share and comment on
  37 <abbr title="Request for Comments">RFC</abbr>s and answer
  38 user questions.
  39
  40 Once your changes have been comitted to your local branch, you may use the
  41 [git-review](https://opendev.org/opendev/git-review) plugin to submit them
  42 directly to [Gerrit](https://review.lttng.org) using the following command:
  43
  44     git review
  45
  46 Please note that you will need to create an account on [Gerrit](https://review.lttng.org)
  47 and add an SSH public key.
  48
  49 For e-mail based patches you may use Git's
  50 [`format-patch`](https://git-scm.com/docs/git-format-patch) command
  51 to generate a patch file. The following command line generates a
  52 patch from the latest commit:
  53
  54     git format-patch -N1 -s --subject-prefix="PATCH lttng-tools"
  55
  56 The custom `PATCH lttng-tools` subject prefix is mandatory when
  57 submitting patches that apply to the LTTng-tools project.
  58
  59 The patch's subject (the commit message's first line) should:
  60
  61   * Begin with an uppercase letter.
  62   * Be written in the present tense.
  63   * _Not_ exceed 72 characters in length.
  64   * _Not_ end with a period.
  65
  66 In the case of bug fixes, the patch's subject must be prefixed with
  67 `Fix:` and a suitable sub-system name. For instance, a patch
  68 addressing a bug in the session daemon should start with `Fix:
  69 sessiond:`. Patches targeting shared code can either use the namespace
  70 of the interface or of the internal library, whichever is more
  71 precise.
  72
  73 A non-exhaustive list of common sub-system prefixes follows:
  74
  75   * `relayd` (relay daemon).
  76   * `sessiond` (session daemon).
  77   * `lttng` (LTTng CLI client).
  78   * `ust-consumerd` (user space consumer daemon).
  79   * `kernel-consumerd` (kernel space consumer daemon).
  80   * `consumerd` (common consumer daemon).
  81   * `common` (internal `libcommon`).
  82   * `trace-chunk` (internal `lttng_trace_chunk_*` interface).
  83   * `lttng-ctl` (`liblttng-ctl` library).
  84   * `mi` (LTTng client's machine interface).
  85
  86 When possible, the commit title should describe the issue _as
  87 observed_ and not the underlying cause. For instance, prefer `Fix:
  88 sessiond: hang on SIGTERM after session rotation` to `Fix: sessiond:
  89 unchecked status on exit`.
  90
  91 The commit message's body must be as detailed as possible and explain
  92 the reasons behind the proposed change. Keep in mind that this message
  93 will be read in a number of years and must still be clear. Any related
  94 [bug report(s)](https://bugs.lttng.org/projects/lttng-tools/issues)
  95 should be mentioned at the end of the message using the `#123` format,
  96 where `123` is the bug number:
  97
  98   * Use `Refs: #123` if the patch is related to bug 123, but does not
  99     fix it yet.
 100   * Use `Fixes: #123` to signify that this patch fixes the bug.
 101
 102 In the case of bug fixes, the following structure must be used:
 103
 104   * Observed issue
 105   * Cause
 106   * Solution
 107   * **Optional**: Known drawbacks
 108
 109 A short commit message can be used when submitting typo fixes or minor
 110 cleanups that don't introduce behaviour changes.
 111
 112 When submitting a patch that affects existing code, implement changes
 113 to the existing code as prelude patches in a patch series. Explain why
 114 those changes are needed and how they make follow-up changes
 115 easier/possible.
 116
 117 Make sure to **sign-off** your submitted patches (the `-s` argument to
 118 Git's `commit` and `format-patch` commands).
 119
 120 Here's a complete example:
 121
 122 ~~~ text
 123 Fix: relayd: missing thingy in the doodad folder on error
 124
 125 Observed issue
 126 ==============
 127 After a communication error, the relay daemon will not produce
 128 a thingy in the doodad folder. This results in the knickknack
 129 baring the foo.
 130
 131 Steps to reproduce (list of commands or narrative description).
 132
 133 Cause
 134 =====
 135 The thingy_do_the_doodad() callback is only invoked when
 136 the thread responsible for receiving messages and dispatching
 137 them to the correct actors encounters an emoji.
 138
 139 However, an emoji is not guaranteed to be present in the ELF
 140 section header [1].
 141
 142 Solution
 143 ========
 144 Flushing the doodad on every reception of a thingo ensures that
 145 the thingy is present in the doodad folder even if a communication
 146 error occurs.
 147
 148 Known drawbacks
 149 ===============
 150 Flushing the doodad too often may spam the widget and result in
 151 degradation of the gizmo. This doesn't matter right now since
 152 it happens exactly once per blue moon.
 153
 154 If this becomes a serious issue, we could machine learn the MVP
 155 through the big O terminal.
 156
 157 References
 158 ==========
 159 [1] https://www.thedocs.com/elf/proving-my-point-unambiguously.aspx
 160
 161 Fixes: #321
 162 Refs: #456
 163 Refs: #1987
 164
 165 Signed-off-by: Jeanne Mance <jmeance@lttng.org>
 166 ~~~
 167
 168 Please note that patches should be **as focused as possible**. Do not,
 169 for instance, fix a bug and correct the indentation of an unrelated
 170 block of code as part of the same patch.
 171
 172 The project contains a script, [`extras/checkpatch.pl`](extras/checkpatch.pl),
 173 that performs a number of checks on a patch to ensure it is ready for
 174 submission. Run this script on your patch and correct any reported
 175 errors before posting it to the mailing list:
 176
 177     extras/checkpatch.pl --no-tree 0001-Fix...patch
 178
 179 Once you are confident your patch meets the required guidelines,
 180 you may use Git's [`send-email`](https://git-scm.com/docs/git-send-email)
 181 command to send your patch to the mailing list:
 182
 183     git send-email --suppress-cc=self --to lttng-dev@lists.lttng.org *.patch
 184
 185 Make sure you are
 186 [subscribed](http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev)
 187 to the mailing list to follow and take part in discussions about your
 188 changes. You may join the file to an email as an attachment if you can't
 189 send the patch directly using <code>git&nbsp;send&#8209;email</code>.
 190
 191
 192 ## Reviews
 193
 194 Once your patch has been posted to the mailing list or as a GitHub
 195 pull request, other contributors may propose modifications.
 196 This is completely normal. This collaborative code review is an integral
 197 part of the open source development process in general and LTTng-tools
 198 makes no exception.
 199
 200 Keep in mind that reviewing patches is a time-consuming process and,
 201 as such, may not be done right away. The delays may be affected by the
 202 current release cycle phase and the complexity of the proposed changes.
 203 If you think your patch might have been forgotten, please mention it on
 204 the [`#lttng`](irc://irc.oftc.net/lttng) IRC channel rather than
 205 resubmitting.
 206
 207
 208 ## Release cycle
 209
 210 The LTTng-tools project follows a release cycle that alternates between
 211 development and release candidate (RC) phases. The master branch is
 212 feature-frozen during RC phases: only bug fixes are accepted during
 213 this period. However, patches adding new functionality may still be
 214 submitted and reviewed during the RC. The upcoming features and release
 215 dates are posted in a monthly digest on the mailing list.