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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 | LTTng-tools uses the | |
19 | [Linux kernel coding style](http://www.kernel.org/doc/Documentation/CodingStyle) | |
20 | with one addition: single-line `if`/`for`/`while` statements must be | |
21 | wrapped in braces. | |
22 | ||
23 | Example: | |
24 | ||
25 | ~~~ c | |
26 | /* not good */ | |
27 | if (this == that) | |
28 | goto fail; | |
29 | ||
30 | /* good */ | |
31 | if (this == that) { | |
32 | goto fail; | |
33 | } | |
34 | ~~~ | |
35 | ||
36 | Although the LTTng-tools code base is primarily written in C, it does | |
37 | contain shell, Perl, and Python code as well. There is no official coding | |
38 | standard for these languages. However, using a style consistent with the | |
39 | rest of the code written in that language is strongly encouraged. | |
40 | ||
41 | ||
42 | ## Creating and sending a patch | |
43 | ||
44 | LTTng-tools's development flow is primarily email-based, although we | |
45 | also accept pull requests on our | |
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46 | [GitHub mirror](https://github.com/lttng/lttng-tools) and |
47 | [Gerrit Code Review](https://review.lttng.org). If you're going | |
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48 | to create GitHub pull requests, make sure you still follow the |
49 | guidelines below. | |
50 | ||
51 | Like a lot of open source projects, patches are submitted and reviewed | |
52 | on its development mailing list, | |
53 | [`lttng-dev`](http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev) | |
54 | (`lttng-dev@lists.lttng.org`). The mailing list is also used to share | |
55 | and comment on <abbr title="Request for Comments">RFC</abbr>s and answer | |
56 | user questions. | |
57 | ||
58 | Once your changes have been committed to your local branch, you may use | |
59 | Git's [`format-patch`](https://git-scm.com/docs/git-format-patch) command | |
60 | to generate a patch file. The following command line generates a | |
61 | patch from the latest commit: | |
62 | ||
63 | git format-patch -N1 -s --subject-prefix="PATCH lttng-tools" | |
64 | ||
65 | The custom `PATCH lttng-tools` subject prefix is mandatory when | |
66 | submitting patches that apply to the LTTng-tools project. | |
67 | ||
68 | The patch's subject (the commit message's first line) should: | |
69 | ||
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70 | * Begin with an uppercase letter. |
71 | * Be written in the present tense. | |
72 | * _Not_ exceed 72 characters in length. | |
73 | * _Not_ end with a period. | |
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75 | In the case of bug fixes, the patch's subject must be prefixed with |
76 | `Fix:` and a suitable sub-system name. For instance, a patch | |
77 | addressing a bug in the session daemon should start with `Fix: | |
78 | sessiond:`. Patches targeting shared code can either use the namespace | |
79 | of the interface or of the internal library, whichever is more | |
80 | precise. | |
81 | ||
82 | A non-exhaustive list of common sub-system prefixes follows: | |
83 | ||
84 | * `relayd` (relay daemon). | |
85 | * `sessiond` (session daemon). | |
86 | * `lttng` (LTTng CLI client). | |
87 | * `ust-consumerd` (user space consumer daemon). | |
88 | * `kernel-consumerd` (kernel space consumer daemon). | |
89 | * `consumerd` (common consumer daemon). | |
90 | * `common` (internal `libcommon`). | |
91 | * `trace-chunk` (internal `lttng_trace_chunk_*` interface). | |
92 | * `lttng-ctl` (`liblttng-ctl` library). | |
93 | * `mi` (LTTng client's machine interface). | |
94 | ||
95 | When possible, the commit title should describe the issue _as | |
96 | observed_ and not the underlying cause. For instance, prefer `Fix: | |
97 | sessiond: hang on SIGTERM after session rotation` to `Fix: sessiond: | |
98 | unchecked status on exit`. | |
99 | ||
100 | The commit message's body must be as detailed as possible and explain | |
101 | the reasons behind the proposed change. Keep in mind that this message | |
102 | will be read in a number of years and must still be clear. Any related | |
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103 | [bug report(s)](https://bugs.lttng.org/projects/lttng-tools/issues) |
104 | should be mentioned at the end of the message using the `#123` format, | |
105 | where `123` is the bug number: | |
106 | ||
107 | * Use `Refs: #123` if the patch is related to bug 123, but does not | |
108 | fix it yet. | |
109 | * Use `Fixes: #123` to signify that this patch fixes the bug. | |
110 | ||
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111 | In the case of bug fixes, the following structure must be used: |
112 | ||
113 | * Observed issue | |
114 | * Cause | |
115 | * Solution | |
116 | * **Optional**: Known drawbacks | |
117 | ||
118 | A short commit message can be used when submitting typo fixes or minor | |
119 | cleanups that don't introduce behaviour changes. | |
120 | ||
121 | When submitting a patch that affects existing code, implement changes | |
122 | to the existing code as prelude patches in a patch series. Explain why | |
123 | those changes are needed and how they make follow-up changes | |
124 | easier/possible. | |
125 | ||
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126 | Make sure to **sign-off** your submitted patches (the `-s` argument to |
127 | Git's `commit` and `format-patch` commands). | |
128 | ||
129 | Here's a complete example: | |
130 | ||
131 | ~~~ text | |
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132 | Fix: relayd: missing thingy in the doodad folder on error |
133 | ||
134 | Observed issue | |
135 | ============== | |
136 | After a communication error, the relay daemon will not produce | |
137 | a thingy in the doodad folder. This results in the knickknack | |
138 | baring the foo. | |
139 | ||
140 | Steps to reproduce (list of commands or narrative description). | |
141 | ||
142 | Cause | |
143 | ===== | |
144 | The thingy_do_the_doodad() callback is only invoked when | |
145 | the thread responsible for receiving messages and dispatching | |
146 | them to the correct actors encounters an emoji. | |
147 | ||
148 | However, an emoji is not guaranteed to be present in the ELF | |
149 | section header [1]. | |
150 | ||
151 | Solution | |
152 | ======== | |
153 | Flushing the doodad on every reception of a thingo ensures that | |
154 | the thingy is present in the doodad folder even if a communication | |
155 | error occurs. | |
156 | ||
157 | Known drawbacks | |
158 | =============== | |
159 | Flushing the doodad too often may spam the widget and result in | |
160 | degradation of the gizmo. This doesn't matter right now since | |
161 | it happens exactly once per blue moon. | |
162 | ||
163 | If this becomes a serious issue, we could machine learn the MVP | |
164 | through the big O terminal. | |
165 | ||
166 | References | |
167 | ========== | |
168 | [1] https://www.thedocs.com/elf/proving-my-point-unambiguously.aspx | |
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169 | |
170 | Fixes: #321 | |
171 | Refs: #456 | |
172 | Refs: #1987 | |
173 | ||
174 | Signed-off-by: Jeanne Mance <jmeance@lttng.org> | |
175 | ~~~ | |
176 | ||
177 | Please note that patches should be **as focused as possible**. Do not, | |
178 | for instance, fix a bug and correct the indentation of an unrelated | |
179 | block of code as part of the same patch. | |
180 | ||
181 | The project contains a script, [`extras/checkpatch.pl`](extras/checkpatch.pl), | |
182 | that performs a number of checks on a patch to ensure it is ready for | |
183 | submission. Run this script on your patch and correct any reported | |
184 | errors before posting it to the mailing list: | |
185 | ||
186 | extras/checkpatch.pl --no-tree 0001-Fix...patch | |
187 | ||
188 | Once you are confident your patch meets the required guidelines, | |
189 | you may use Git's [`send-email`](https://git-scm.com/docs/git-send-email) | |
190 | command to send your patch to the mailing list: | |
191 | ||
192 | git send-email --suppress-cc=self --to lttng-dev@lists.lttng.org *.patch | |
193 | ||
194 | Make sure you are | |
195 | [subscribed](http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev) | |
196 | to the mailing list to follow and take part in discussions about your | |
197 | changes. You may join the file to an email as an attachment if you can't | |
198 | send the patch directly using <code>git send‑email</code>. | |
199 | ||
200 | ||
201 | ## Reviews | |
202 | ||
203 | Once your patch has been posted to the mailing list or as a GitHub | |
204 | pull request, other contributors may propose modifications. | |
205 | This is completely normal. This collaborative code review is an integral | |
206 | part of the open source development process in general and LTTng-tools | |
207 | makes no exception. | |
208 | ||
209 | Keep in mind that reviewing patches is a time-consuming process and, | |
210 | as such, may not be done right away. The delays may be affected by the | |
211 | current release cycle phase and the complexity of the proposed changes. | |
212 | If you think your patch might have been forgotten, please mention it on | |
213 | the [`#lttng`](irc://irc.oftc.net/lttng) IRC channel rather than | |
214 | resubmitting. | |
215 | ||
216 | ||
217 | ## Release cycle | |
218 | ||
219 | The LTTng-tools project follows a release cycle that alternates between | |
220 | development and release candidate (RC) phases. The master branch is | |
221 | feature-frozen during RC phases: only bug fixes are accepted during | |
222 | this period. However, patches adding new functionality may still be | |
223 | submitted and reviewed during the RC. The upcoming features and release | |
224 | dates are posted in a monthly digest on the mailing list. |