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609d99a3 | 1 | .. _submittingpatches: |
1da177e4 | 2 | |
89edeedd JC |
3 | Submitting patches: the essential guide to getting your code into the kernel |
4 | ============================================================================ | |
1da177e4 LT |
5 | |
6 | For a person or company who wishes to submit a change to the Linux | |
7 | kernel, the process can sometimes be daunting if you're not familiar | |
8 | with "the system." This text is a collection of suggestions which | |
9 | can greatly increase the chances of your change being accepted. | |
10 | ||
d00c4559 JC |
11 | This document contains a large number of suggestions in a relatively terse |
12 | format. For detailed information on how the kernel development process | |
5ff4aa70 MCC |
13 | works, see :doc:`development-process`. Also, read :doc:`submit-checklist` |
14 | for a list of items to check before submitting code. If you are submitting | |
15 | a driver, also read :doc:`submitting-drivers`; for device tree binding patches, | |
16 | read :doc:`submitting-patches`. | |
1da177e4 | 17 | |
9f364b60 DD |
18 | This documentation assumes that you're using ``git`` to prepare your patches. |
19 | If you're unfamiliar with ``git``, you would be well-advised to learn how to | |
20 | use it, it will make your life as a kernel developer and in general much | |
21 | easier. | |
1da177e4 | 22 | |
ef227c39 DD |
23 | Obtain a current source tree |
24 | ---------------------------- | |
7994cc15 JC |
25 | |
26 | If you do not have a repository with the current kernel source handy, use | |
9b2c7677 | 27 | ``git`` to obtain one. You'll want to start with the mainline repository, |
5903019b | 28 | which can be grabbed with:: |
7994cc15 | 29 | |
5903019b | 30 | git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git |
7994cc15 JC |
31 | |
32 | Note, however, that you may not want to develop against the mainline tree | |
33 | directly. Most subsystem maintainers run their own trees and want to see | |
5903019b | 34 | patches prepared against those trees. See the **T:** entry for the subsystem |
7994cc15 JC |
35 | in the MAINTAINERS file to find that tree, or simply ask the maintainer if |
36 | the tree is not listed there. | |
37 | ||
5903019b | 38 | .. _describe_changes: |
84da7c08 | 39 | |
ef227c39 DD |
40 | Describe your changes |
41 | --------------------- | |
1da177e4 | 42 | |
7b9828d4 JW |
43 | Describe your problem. Whether your patch is a one-line bug fix or |
44 | 5000 lines of a new feature, there must be an underlying problem that | |
45 | motivated you to do this work. Convince the reviewer that there is a | |
46 | problem worth fixing and that it makes sense for them to read past the | |
47 | first paragraph. | |
48 | ||
49 | Describe user-visible impact. Straight up crashes and lockups are | |
50 | pretty convincing, but not all bugs are that blatant. Even if the | |
51 | problem was spotted during code review, describe the impact you think | |
52 | it can have on users. Keep in mind that the majority of Linux | |
53 | installations run kernels from secondary stable trees or | |
54 | vendor/product-specific trees that cherry-pick only specific patches | |
55 | from upstream, so include anything that could help route your change | |
56 | downstream: provoking circumstances, excerpts from dmesg, crash | |
57 | descriptions, performance regressions, latency spikes, lockups, etc. | |
58 | ||
59 | Quantify optimizations and trade-offs. If you claim improvements in | |
60 | performance, memory consumption, stack footprint, or binary size, | |
61 | include numbers that back them up. But also describe non-obvious | |
62 | costs. Optimizations usually aren't free but trade-offs between CPU, | |
63 | memory, and readability; or, when it comes to heuristics, between | |
64 | different workloads. Describe the expected downsides of your | |
65 | optimization so that the reviewer can weigh costs against benefits. | |
66 | ||
67 | Once the problem is established, describe what you are actually doing | |
68 | about it in technical detail. It's important to describe the change | |
69 | in plain English for the reviewer to verify that the code is behaving | |
70 | as you intend it to. | |
1da177e4 | 71 | |
2ae19aca TT |
72 | The maintainer will thank you if you write your patch description in a |
73 | form which can be easily pulled into Linux's source code management | |
9b2c7677 | 74 | system, ``git``, as a "commit log". See :ref:`explicit_in_reply_to`. |
2ae19aca | 75 | |
7b9828d4 JW |
76 | Solve only one problem per patch. If your description starts to get |
77 | long, that's a sign that you probably need to split up your patch. | |
5903019b | 78 | See :ref:`split_changes`. |
1da177e4 | 79 | |
d89b1945 RD |
80 | When you submit or resubmit a patch or patch series, include the |
81 | complete patch description and justification for it. Don't just | |
82 | say that this is version N of the patch (series). Don't expect the | |
d00c4559 | 83 | subsystem maintainer to refer back to earlier patch versions or referenced |
d89b1945 RD |
84 | URLs to find the patch description and put that into the patch. |
85 | I.e., the patch (series) and its description should be self-contained. | |
d00c4559 | 86 | This benefits both the maintainers and reviewers. Some reviewers |
d89b1945 RD |
87 | probably didn't even receive earlier versions of the patch. |
88 | ||
74a475ac JT |
89 | Describe your changes in imperative mood, e.g. "make xyzzy do frotz" |
90 | instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy | |
91 | to do frotz", as if you are giving orders to the codebase to change | |
92 | its behaviour. | |
93 | ||
d89b1945 | 94 | If the patch fixes a logged bug entry, refer to that bug entry by |
9547c706 JT |
95 | number and URL. If the patch follows from a mailing list discussion, |
96 | give a URL to the mailing list archive; use the https://lkml.kernel.org/ | |
9b2c7677 | 97 | redirector with a ``Message-Id``, to ensure that the links cannot become |
9547c706 JT |
98 | stale. |
99 | ||
100 | However, try to make your explanation understandable without external | |
101 | resources. In addition to giving a URL to a mailing list archive or | |
102 | bug, summarize the relevant points of the discussion that led to the | |
103 | patch as submitted. | |
1da177e4 | 104 | |
0af52703 GU |
105 | If you want to refer to a specific commit, don't just refer to the |
106 | SHA-1 ID of the commit. Please also include the oneline summary of | |
107 | the commit, to make it easier for reviewers to know what it is about. | |
5903019b | 108 | Example:: |
0af52703 GU |
109 | |
110 | Commit e21d2170f36602ae2708 ("video: remove unnecessary | |
111 | platform_set_drvdata()") removed the unnecessary | |
112 | platform_set_drvdata(), but left the variable "dev" unused, | |
113 | delete it. | |
114 | ||
7994cc15 JC |
115 | You should also be sure to use at least the first twelve characters of the |
116 | SHA-1 ID. The kernel repository holds a *lot* of objects, making | |
117 | collisions with shorter IDs a real possibility. Bear in mind that, even if | |
118 | there is no collision with your six-character ID now, that condition may | |
119 | change five years from now. | |
120 | ||
8401aa1f | 121 | If your patch fixes a bug in a specific commit, e.g. you found an issue using |
9b2c7677 | 122 | ``git bisect``, please use the 'Fixes:' tag with the first 12 characters of |
19c3fe28 SC |
123 | the SHA-1 ID, and the one line summary. Do not split the tag across multiple |
124 | lines, tags are exempt from the "wrap at 75 columns" rule in order to simplify | |
125 | parsing scripts. For example:: | |
8401aa1f | 126 | |
19c3fe28 | 127 | Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed") |
8401aa1f | 128 | |
9b2c7677 MCC |
129 | The following ``git config`` settings can be used to add a pretty format for |
130 | outputting the above style in the ``git log`` or ``git show`` commands:: | |
8401aa1f JK |
131 | |
132 | [core] | |
133 | abbrev = 12 | |
134 | [pretty] | |
135 | fixes = Fixes: %h (\"%s\") | |
1da177e4 | 136 | |
5b5bbb8c TR |
137 | An example call:: |
138 | ||
139 | $ git log -1 --pretty=fixes 54a4f0239f2e | |
140 | Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed") | |
141 | ||
5903019b MCC |
142 | .. _split_changes: |
143 | ||
ef227c39 DD |
144 | Separate your changes |
145 | --------------------- | |
1da177e4 | 146 | |
5903019b | 147 | Separate each **logical change** into a separate patch. |
1da177e4 LT |
148 | |
149 | For example, if your changes include both bug fixes and performance | |
150 | enhancements for a single driver, separate those changes into two | |
151 | or more patches. If your changes include an API update, and a new | |
152 | driver which uses that new API, separate those into two patches. | |
153 | ||
154 | On the other hand, if you make a single change to numerous files, | |
155 | group those changes into a single patch. Thus a single logical change | |
156 | is contained within a single patch. | |
157 | ||
d00c4559 JC |
158 | The point to remember is that each patch should make an easily understood |
159 | change that can be verified by reviewers. Each patch should be justifiable | |
160 | on its own merits. | |
161 | ||
1da177e4 | 162 | If one patch depends on another patch in order for a change to be |
5903019b | 163 | complete, that is OK. Simply note **"this patch depends on patch X"** |
1da177e4 LT |
164 | in your patch description. |
165 | ||
7994cc15 JC |
166 | When dividing your change into a series of patches, take special care to |
167 | ensure that the kernel builds and runs properly after each patch in the | |
5903019b | 168 | series. Developers using ``git bisect`` to track down a problem can end up |
7994cc15 JC |
169 | splitting your patch series at any point; they will not thank you if you |
170 | introduce bugs in the middle. | |
171 | ||
5b0ed2c6 XVP |
172 | If you cannot condense your patch set into a smaller set of patches, |
173 | then only post say 15 or so at a time and wait for review and integration. | |
174 | ||
175 | ||
1da177e4 | 176 | |
ef227c39 DD |
177 | Style-check your changes |
178 | ------------------------ | |
0a920b5b AW |
179 | |
180 | Check your patch for basic style violations, details of which can be | |
dca22a63 | 181 | found in |
8c27ceff | 182 | :ref:`Documentation/process/coding-style.rst <codingstyle>`. |
dca22a63 | 183 | Failure to do so simply wastes |
f56d35e7 | 184 | the reviewers time and will get your patch rejected, probably |
0a920b5b AW |
185 | without even being read. |
186 | ||
6de16eba JC |
187 | One significant exception is when moving code from one file to |
188 | another -- in this case you should not modify the moved code at all in | |
189 | the same patch which moves it. This clearly delineates the act of | |
190 | moving the code and your changes. This greatly aids review of the | |
191 | actual differences and allows tools to better track the history of | |
192 | the code itself. | |
193 | ||
194 | Check your patches with the patch style checker prior to submission | |
195 | (scripts/checkpatch.pl). Note, though, that the style checker should be | |
196 | viewed as a guide, not as a replacement for human judgment. If your code | |
197 | looks better with a violation then its probably best left alone. | |
0a920b5b | 198 | |
6de16eba JC |
199 | The checker reports at three levels: |
200 | - ERROR: things that are very likely to be wrong | |
201 | - WARNING: things requiring careful review | |
202 | - CHECK: things requiring thought | |
0a920b5b | 203 | |
6de16eba JC |
204 | You should be able to justify all violations that remain in your |
205 | patch. | |
0a920b5b AW |
206 | |
207 | ||
ef227c39 DD |
208 | Select the recipients for your patch |
209 | ------------------------------------ | |
1da177e4 | 210 | |
ccae8616 JC |
211 | You should always copy the appropriate subsystem maintainer(s) on any patch |
212 | to code that they maintain; look through the MAINTAINERS file and the | |
213 | source code revision history to see who those maintainers are. The | |
214 | script scripts/get_maintainer.pl can be very useful at this step. If you | |
d6eff078 | 215 | cannot find a maintainer for the subsystem you are working on, Andrew |
ccae8616 | 216 | Morton (akpm@linux-foundation.org) serves as a maintainer of last resort. |
1da177e4 | 217 | |
ccae8616 JC |
218 | You should also normally choose at least one mailing list to receive a copy |
219 | of your patch set. linux-kernel@vger.kernel.org functions as a list of | |
220 | last resort, but the volume on that list has caused a number of developers | |
221 | to tune it out. Look in the MAINTAINERS file for a subsystem-specific | |
222 | list; your patch will probably get more attention there. Please do not | |
223 | spam unrelated lists, though. | |
1da177e4 | 224 | |
ccae8616 JC |
225 | Many kernel-related lists are hosted on vger.kernel.org; you can find a |
226 | list of them at http://vger.kernel.org/vger-lists.html. There are | |
227 | kernel-related lists hosted elsewhere as well, though. | |
5b0ed2c6 XVP |
228 | |
229 | Do not send more than 15 patches at once to the vger mailing lists!!! | |
230 | ||
1da177e4 | 231 | Linus Torvalds is the final arbiter of all changes accepted into the |
e00bfcbf | 232 | Linux kernel. His e-mail address is <torvalds@linux-foundation.org>. |
ccae8616 JC |
233 | He gets a lot of e-mail, and, at this point, very few patches go through |
234 | Linus directly, so typically you should do your best to -avoid- | |
e00bfcbf | 235 | sending him e-mail. |
1da177e4 | 236 | |
ccae8616 JC |
237 | If you have a patch that fixes an exploitable security bug, send that patch |
238 | to security@kernel.org. For severe bugs, a short embargo may be considered | |
253508ca | 239 | to allow distributors to get the patch out to users; in such cases, |
eb45fb2f | 240 | obviously, the patch should not be sent to any public lists. See also |
5ff4aa70 | 241 | :doc:`/admin-guide/security-bugs`. |
1da177e4 | 242 | |
ccae8616 | 243 | Patches that fix a severe bug in a released kernel should be directed |
5903019b | 244 | toward the stable maintainers by putting a line like this:: |
1da177e4 | 245 | |
ccae8616 | 246 | Cc: stable@vger.kernel.org |
1da177e4 | 247 | |
8cda4c3a | 248 | into the sign-off area of your patch (note, NOT an email recipient). You |
dca22a63 | 249 | should also read |
8c27ceff | 250 | :ref:`Documentation/process/stable-kernel-rules.rst <stable_kernel_rules>` |
dca22a63 | 251 | in addition to this file. |
1da177e4 | 252 | |
ccae8616 JC |
253 | Note, however, that some subsystem maintainers want to come to their own |
254 | conclusions on which patches should go to the stable trees. The networking | |
255 | maintainer, in particular, would rather not see individual developers | |
256 | adding lines like the above to their patches. | |
5b0ed2c6 | 257 | |
ccae8616 JC |
258 | If changes affect userland-kernel interfaces, please send the MAN-PAGES |
259 | maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at | |
260 | least a notification of the change, so that some information makes its way | |
261 | into the manual pages. User-space API changes should also be copied to | |
5903019b | 262 | linux-api@vger.kernel.org. |
1da177e4 LT |
263 | |
264 | For small patches you may want to CC the Trivial Patch Monkey | |
82d27b2b MH |
265 | trivial@kernel.org which collects "trivial" patches. Have a look |
266 | into the MAINTAINERS file for its current manager. | |
5903019b | 267 | |
82d27b2b | 268 | Trivial patches must qualify for one of the following rules: |
5903019b | 269 | |
9b2c7677 MCC |
270 | - Spelling fixes in documentation |
271 | - Spelling fixes for errors which could break :manpage:`grep(1)` | |
272 | - Warning fixes (cluttering with useless warnings is bad) | |
273 | - Compilation fixes (only if they are actually correct) | |
274 | - Runtime fixes (only if they actually fix things) | |
275 | - Removing use of deprecated functions/macros | |
276 | - Contact detail and documentation fixes | |
277 | - Non-portable code replaced by portable code (even in arch-specific, | |
278 | since people copy, as long as it's trivial) | |
279 | - Any fix by the author/maintainer of the file (ie. patch monkey | |
280 | in re-transmission mode) | |
84da7c08 | 281 | |
1da177e4 LT |
282 | |
283 | ||
ef227c39 DD |
284 | No MIME, no links, no compression, no attachments. Just plain text |
285 | ------------------------------------------------------------------- | |
1da177e4 LT |
286 | |
287 | Linus and other kernel developers need to be able to read and comment | |
288 | on the changes you are submitting. It is important for a kernel | |
289 | developer to be able to "quote" your changes, using standard e-mail | |
290 | tools, so that they may comment on specific portions of your code. | |
291 | ||
9f364b60 DD |
292 | For this reason, all patches should be submitted by e-mail "inline". The |
293 | easiest way to do this is with ``git send-email``, which is strongly | |
294 | recommended. An interactive tutorial for ``git send-email`` is available at | |
295 | https://git-send-email.io. | |
296 | ||
297 | If you choose not to use ``git send-email``: | |
9b2c7677 MCC |
298 | |
299 | .. warning:: | |
300 | ||
301 | Be wary of your editor's word-wrap corrupting your patch, | |
302 | if you choose to cut-n-paste your patch. | |
1da177e4 LT |
303 | |
304 | Do not attach the patch as a MIME attachment, compressed or not. | |
305 | Many popular e-mail applications will not always transmit a MIME | |
306 | attachment as plain text, making it impossible to comment on your | |
307 | code. A MIME attachment also takes Linus a bit more time to process, | |
308 | decreasing the likelihood of your MIME-attached change being accepted. | |
309 | ||
310 | Exception: If your mailer is mangling patches then someone may ask | |
311 | you to re-send them using MIME. | |
312 | ||
5ff4aa70 MCC |
313 | See :doc:`/process/email-clients` for hints about configuring your e-mail |
314 | client so that it sends your patches untouched. | |
1da177e4 | 315 | |
ef227c39 DD |
316 | Respond to review comments |
317 | -------------------------- | |
1da177e4 | 318 | |
0eea2314 | 319 | Your patch will almost certainly get comments from reviewers on ways in |
9f364b60 DD |
320 | which the patch can be improved, in the form of a reply to your email. You must |
321 | respond to those comments; ignoring reviewers is a good way to get ignored in | |
322 | return. You can simply reply to their emails to answer their comments. Review | |
323 | comments or questions that do not lead to a code change should almost certainly | |
0eea2314 JC |
324 | bring about a comment or changelog entry so that the next reviewer better |
325 | understands what is going on. | |
1da177e4 | 326 | |
0eea2314 JC |
327 | Be sure to tell the reviewers what changes you are making and to thank them |
328 | for their time. Code review is a tiring and time-consuming process, and | |
329 | reviewers sometimes get grumpy. Even in that case, though, respond | |
330 | politely and address the problems they have pointed out. | |
1da177e4 | 331 | |
5ff4aa70 | 332 | See :doc:`email-clients` for recommendations on email |
7433ff33 DD |
333 | clients and mailing list etiquette. |
334 | ||
1da177e4 | 335 | |
ef227c39 DD |
336 | Don't get discouraged - or impatient |
337 | ------------------------------------ | |
1da177e4 | 338 | |
0eea2314 JC |
339 | After you have submitted your change, be patient and wait. Reviewers are |
340 | busy people and may not get to your patch right away. | |
1da177e4 | 341 | |
0eea2314 JC |
342 | Once upon a time, patches used to disappear into the void without comment, |
343 | but the development process works more smoothly than that now. You should | |
344 | receive comments within a week or so; if that does not happen, make sure | |
345 | that you have sent your patches to the right place. Wait for a minimum of | |
346 | one week before resubmitting or pinging reviewers - possibly longer during | |
347 | busy times like merge windows. | |
1da177e4 | 348 | |
1da177e4 | 349 | |
ef227c39 DD |
350 | Include PATCH in the subject |
351 | ----------------------------- | |
1da177e4 LT |
352 | |
353 | Due to high e-mail traffic to Linus, and to linux-kernel, it is common | |
354 | convention to prefix your subject line with [PATCH]. This lets Linus | |
355 | and other kernel developers more easily distinguish patches from other | |
356 | e-mail discussions. | |
357 | ||
9f364b60 | 358 | ``git send-email`` will do this for you automatically. |
1da177e4 LT |
359 | |
360 | ||
ef227c39 DD |
361 | Sign your work - the Developer's Certificate of Origin |
362 | ------------------------------------------------------ | |
1da177e4 LT |
363 | |
364 | To improve tracking of who did what, especially with patches that can | |
365 | percolate to their final resting place in the kernel through several | |
366 | layers of maintainers, we've introduced a "sign-off" procedure on | |
367 | patches that are being emailed around. | |
368 | ||
369 | The sign-off is a simple line at the end of the explanation for the | |
370 | patch, which certifies that you wrote it or otherwise have the right to | |
db12fb83 | 371 | pass it on as an open-source patch. The rules are pretty simple: if you |
1da177e4 LT |
372 | can certify the below: |
373 | ||
5903019b MCC |
374 | Developer's Certificate of Origin 1.1 |
375 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
1da177e4 | 376 | |
5903019b | 377 | By making a contribution to this project, I certify that: |
1da177e4 LT |
378 | |
379 | (a) The contribution was created in whole or in part by me and I | |
380 | have the right to submit it under the open source license | |
381 | indicated in the file; or | |
382 | ||
383 | (b) The contribution is based upon previous work that, to the best | |
384 | of my knowledge, is covered under an appropriate open source | |
385 | license and I have the right under that license to submit that | |
386 | work with modifications, whether created in whole or in part | |
387 | by me, under the same open source license (unless I am | |
388 | permitted to submit under a different license), as indicated | |
389 | in the file; or | |
390 | ||
391 | (c) The contribution was provided directly to me by some other | |
392 | person who certified (a), (b) or (c) and I have not modified | |
393 | it. | |
394 | ||
e00bfcbf SB |
395 | (d) I understand and agree that this project and the contribution |
396 | are public and that a record of the contribution (including all | |
397 | personal information I submit with it, including my sign-off) is | |
398 | maintained indefinitely and may be redistributed consistent with | |
399 | this project or the open source license(s) involved. | |
cbd83da8 | 400 | |
5903019b | 401 | then you just add a line saying:: |
1da177e4 | 402 | |
9fd5559c | 403 | Signed-off-by: Random J Developer <random@developer.example.org> |
1da177e4 | 404 | |
af45f32d | 405 | using your real name (sorry, no pseudonyms or anonymous contributions.) |
9f364b60 | 406 | This will be done for you automatically if you use ``git commit -s``. |
7d717887 AS |
407 | Reverts should also include "Signed-off-by". ``git revert -s`` does that |
408 | for you. | |
af45f32d | 409 | |
1da177e4 LT |
410 | Some people also put extra tags at the end. They'll just be ignored for |
411 | now, but you can do this to mark internal company procedures or just | |
e00bfcbf | 412 | point out some special detail about the sign-off. |
1da177e4 | 413 | |
9bf19b78 BP |
414 | Any further SoBs (Signed-off-by:'s) following the author's SoB are from |
415 | people handling and transporting the patch, but were not involved in its | |
416 | development. SoB chains should reflect the **real** route a patch took | |
417 | as it was propagated to the maintainers and ultimately to Linus, with | |
418 | the first SoB entry signalling primary authorship of a single author. | |
419 | ||
1da177e4 | 420 | |
ef227c39 DD |
421 | When to use Acked-by:, Cc:, and Co-developed-by: |
422 | ------------------------------------------------ | |
0a920b5b | 423 | |
0f44cd23 AM |
424 | The Signed-off-by: tag indicates that the signer was involved in the |
425 | development of the patch, or that he/she was in the patch's delivery path. | |
426 | ||
427 | If a person was not directly involved in the preparation or handling of a | |
428 | patch but wishes to signify and record their approval of it then they can | |
d00c4559 | 429 | ask to have an Acked-by: line added to the patch's changelog. |
0f44cd23 AM |
430 | |
431 | Acked-by: is often used by the maintainer of the affected code when that | |
432 | maintainer neither contributed to nor forwarded the patch. | |
433 | ||
434 | Acked-by: is not as formal as Signed-off-by:. It is a record that the acker | |
435 | has at least reviewed the patch and has indicated acceptance. Hence patch | |
436 | mergers will sometimes manually convert an acker's "yep, looks good to me" | |
d00c4559 JC |
437 | into an Acked-by: (but note that it is usually better to ask for an |
438 | explicit ack). | |
0f44cd23 AM |
439 | |
440 | Acked-by: does not necessarily indicate acknowledgement of the entire patch. | |
441 | For example, if a patch affects multiple subsystems and has an Acked-by: from | |
442 | one subsystem maintainer then this usually indicates acknowledgement of just | |
443 | the part which affects that maintainer's code. Judgement should be used here. | |
ef40203a | 444 | When in doubt people should refer to the original discussion in the mailing |
0f44cd23 AM |
445 | list archives. |
446 | ||
ef40203a | 447 | If a person has had the opportunity to comment on a patch, but has not |
5903019b | 448 | provided such comments, you may optionally add a ``Cc:`` tag to the patch. |
ef40203a | 449 | This is the only tag which might be added without an explicit action by the |
d00c4559 JC |
450 | person it names - but it should indicate that this person was copied on the |
451 | patch. This tag documents that potentially interested parties | |
452 | have been included in the discussion. | |
0f44cd23 | 453 | |
24a2bb90 | 454 | Co-developed-by: states that the patch was co-created by multiple developers; |
7e902857 | 455 | it is used to give attribution to co-authors (in addition to the author |
24a2bb90 SC |
456 | attributed by the From: tag) when several people work on a single patch. Since |
457 | Co-developed-by: denotes authorship, every Co-developed-by: must be immediately | |
458 | followed by a Signed-off-by: of the associated co-author. Standard sign-off | |
459 | procedure applies, i.e. the ordering of Signed-off-by: tags should reflect the | |
460 | chronological history of the patch insofar as possible, regardless of whether | |
461 | the author is attributed via From: or Co-developed-by:. Notably, the last | |
462 | Signed-off-by: must always be that of the developer submitting the patch. | |
463 | ||
464 | Note, the From: tag is optional when the From: author is also the person (and | |
465 | email) listed in the From: line of the email header. | |
466 | ||
467 | Example of a patch submitted by the From: author:: | |
468 | ||
469 | <changelog> | |
470 | ||
471 | Co-developed-by: First Co-Author <first@coauthor.example.org> | |
472 | Signed-off-by: First Co-Author <first@coauthor.example.org> | |
473 | Co-developed-by: Second Co-Author <second@coauthor.example.org> | |
474 | Signed-off-by: Second Co-Author <second@coauthor.example.org> | |
475 | Signed-off-by: From Author <from@author.example.org> | |
476 | ||
477 | Example of a patch submitted by a Co-developed-by: author:: | |
478 | ||
479 | From: From Author <from@author.example.org> | |
480 | ||
481 | <changelog> | |
482 | ||
483 | Co-developed-by: Random Co-Author <random@coauthor.example.org> | |
484 | Signed-off-by: Random Co-Author <random@coauthor.example.org> | |
485 | Signed-off-by: From Author <from@author.example.org> | |
486 | Co-developed-by: Submitting Co-Author <sub@coauthor.example.org> | |
487 | Signed-off-by: Submitting Co-Author <sub@coauthor.example.org> | |
82d95343 | 488 | |
ef40203a | 489 | |
ef227c39 DD |
490 | Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes: |
491 | ---------------------------------------------------------------------- | |
bbb0a424 | 492 | |
d75ef707 DC |
493 | The Reported-by tag gives credit to people who find bugs and report them and it |
494 | hopefully inspires them to help us again in the future. Please note that if | |
495 | the bug was reported in private, then ask for permission first before using the | |
496 | Reported-by tag. | |
ef40203a JC |
497 | |
498 | A Tested-by: tag indicates that the patch has been successfully tested (in | |
499 | some environment) by the person named. This tag informs maintainers that | |
500 | some testing has been performed, provides a means to locate testers for | |
501 | future patches, and ensures credit for the testers. | |
502 | ||
503 | Reviewed-by:, instead, indicates that the patch has been reviewed and found | |
504 | acceptable according to the Reviewer's Statement: | |
505 | ||
5903019b MCC |
506 | Reviewer's statement of oversight |
507 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
ef40203a | 508 | |
5903019b | 509 | By offering my Reviewed-by: tag, I state that: |
ef40203a | 510 | |
5903019b | 511 | (a) I have carried out a technical review of this patch to |
ef40203a JC |
512 | evaluate its appropriateness and readiness for inclusion into |
513 | the mainline kernel. | |
514 | ||
515 | (b) Any problems, concerns, or questions relating to the patch | |
516 | have been communicated back to the submitter. I am satisfied | |
517 | with the submitter's response to my comments. | |
518 | ||
519 | (c) While there may be things that could be improved with this | |
520 | submission, I believe that it is, at this time, (1) a | |
521 | worthwhile modification to the kernel, and (2) free of known | |
522 | issues which would argue against its inclusion. | |
523 | ||
524 | (d) While I have reviewed the patch and believe it to be sound, I | |
525 | do not (unless explicitly stated elsewhere) make any | |
526 | warranties or guarantees that it will achieve its stated | |
527 | purpose or function properly in any given situation. | |
528 | ||
529 | A Reviewed-by tag is a statement of opinion that the patch is an | |
530 | appropriate modification of the kernel without any remaining serious | |
531 | technical issues. Any interested reviewer (who has done the work) can | |
532 | offer a Reviewed-by tag for a patch. This tag serves to give credit to | |
533 | reviewers and to inform maintainers of the degree of review which has been | |
534 | done on the patch. Reviewed-by: tags, when supplied by reviewers known to | |
535 | understand the subject area and to perform thorough reviews, will normally | |
5801da1b | 536 | increase the likelihood of your patch getting into the kernel. |
ef40203a | 537 | |
030f066f KK |
538 | Both Tested-by and Reviewed-by tags, once received on mailing list from tester |
539 | or reviewer, should be added by author to the applicable patches when sending | |
540 | next versions. However if the patch has changed substantially in following | |
541 | version, these tags might not be applicable anymore and thus should be removed. | |
542 | Usually removal of someone's Tested-by or Reviewed-by tags should be mentioned | |
543 | in the patch changelog (after the '---' separator). | |
544 | ||
8543ae12 M |
545 | A Suggested-by: tag indicates that the patch idea is suggested by the person |
546 | named and ensures credit to the person for the idea. Please note that this | |
547 | tag should not be added without the reporter's permission, especially if the | |
548 | idea was not posted in a public forum. That said, if we diligently credit our | |
549 | idea reporters, they will, hopefully, be inspired to help us again in the | |
550 | future. | |
551 | ||
8401aa1f JK |
552 | A Fixes: tag indicates that the patch fixes an issue in a previous commit. It |
553 | is used to make it easy to determine where a bug originated, which can help | |
554 | review a bug fix. This tag also assists the stable kernel team in determining | |
555 | which stable kernel versions should receive your fix. This is the preferred | |
5903019b MCC |
556 | method for indicating a bug fixed by the patch. See :ref:`describe_changes` |
557 | for more details. | |
8401aa1f | 558 | |
f0ea149e LJ |
559 | Note: Attaching a Fixes: tag does not subvert the stable kernel rules |
560 | process nor the requirement to Cc: stable@vger.kernel.org on all stable | |
561 | patch candidates. For more information, please read | |
562 | :ref:`Documentation/process/stable-kernel-rules.rst <stable_kernel_rules>` | |
563 | ||
f58252cd | 564 | .. _the_canonical_patch_format: |
ef40203a | 565 | |
ef227c39 DD |
566 | The canonical patch format |
567 | -------------------------- | |
7994cc15 JC |
568 | |
569 | This section describes how the patch itself should be formatted. Note | |
9b2c7677 | 570 | that, if you have your patches stored in a ``git`` repository, proper patch |
5903019b | 571 | formatting can be had with ``git format-patch``. The tools cannot create |
7994cc15 | 572 | the necessary text, though, so read the instructions below anyway. |
84da7c08 | 573 | |
5903019b | 574 | The canonical patch subject line is:: |
75f8426c | 575 | |
d6b9acc0 | 576 | Subject: [PATCH 001/123] subsystem: summary phrase |
75f8426c PJ |
577 | |
578 | The canonical patch message body contains the following: | |
579 | ||
d19b3e32 JH |
580 | - A ``from`` line specifying the patch author, followed by an empty |
581 | line (only needed if the person sending the patch is not the author). | |
75f8426c | 582 | |
2a076f40 JP |
583 | - The body of the explanation, line wrapped at 75 columns, which will |
584 | be copied to the permanent changelog to describe this patch. | |
75f8426c | 585 | |
d19b3e32 JH |
586 | - An empty line. |
587 | ||
5903019b | 588 | - The ``Signed-off-by:`` lines, described above, which will |
75f8426c PJ |
589 | also go in the changelog. |
590 | ||
5903019b | 591 | - A marker line containing simply ``---``. |
75f8426c PJ |
592 | |
593 | - Any additional comments not suitable for the changelog. | |
594 | ||
9b2c7677 | 595 | - The actual patch (``diff`` output). |
75f8426c PJ |
596 | |
597 | The Subject line format makes it very easy to sort the emails | |
598 | alphabetically by subject line - pretty much any email reader will | |
599 | support that - since because the sequence number is zero-padded, | |
600 | the numerical and alphabetic sort is the same. | |
601 | ||
5903019b | 602 | The ``subsystem`` in the email's Subject should identify which |
d6b9acc0 PJ |
603 | area or subsystem of the kernel is being patched. |
604 | ||
5903019b MCC |
605 | The ``summary phrase`` in the email's Subject should concisely |
606 | describe the patch which that email contains. The ``summary | |
607 | phrase`` should not be a filename. Do not use the same ``summary | |
608 | phrase`` for every patch in a whole patch series (where a ``patch | |
609 | series`` is an ordered sequence of multiple, related patches). | |
d6b9acc0 | 610 | |
5903019b | 611 | Bear in mind that the ``summary phrase`` of your email becomes a |
2ae19aca | 612 | globally-unique identifier for that patch. It propagates all the way |
9b2c7677 | 613 | into the ``git`` changelog. The ``summary phrase`` may later be used in |
2ae19aca | 614 | developer discussions which refer to the patch. People will want to |
5903019b | 615 | google for the ``summary phrase`` to read discussion regarding that |
2ae19aca TT |
616 | patch. It will also be the only thing that people may quickly see |
617 | when, two or three months later, they are going through perhaps | |
9b2c7677 MCC |
618 | thousands of patches using tools such as ``gitk`` or ``git log |
619 | --oneline``. | |
2ae19aca | 620 | |
5903019b | 621 | For these reasons, the ``summary`` must be no more than 70-75 |
2ae19aca TT |
622 | characters, and it must describe both what the patch changes, as well |
623 | as why the patch might be necessary. It is challenging to be both | |
624 | succinct and descriptive, but that is what a well-written summary | |
625 | should do. | |
626 | ||
5903019b | 627 | The ``summary phrase`` may be prefixed by tags enclosed in square |
e12d7462 AH |
628 | brackets: "Subject: [PATCH <tag>...] <summary phrase>". The tags are |
629 | not considered part of the summary phrase, but describe how the patch | |
2ae19aca TT |
630 | should be treated. Common tags might include a version descriptor if |
631 | the multiple versions of the patch have been sent out in response to | |
632 | comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for | |
633 | comments. If there are four patches in a patch series the individual | |
634 | patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures | |
635 | that developers understand the order in which the patches should be | |
636 | applied and that they have reviewed or applied all of the patches in | |
637 | the patch series. | |
d6b9acc0 | 638 | |
5903019b | 639 | A couple of example Subjects:: |
d6b9acc0 | 640 | |
e12d7462 AH |
641 | Subject: [PATCH 2/5] ext2: improve scalability of bitmap searching |
642 | Subject: [PATCH v2 01/27] x86: fix eflags tracking | |
75f8426c | 643 | |
5903019b | 644 | The ``from`` line must be the very first line in the message body, |
75f8426c PJ |
645 | and has the form: |
646 | ||
24a2bb90 | 647 | From: Patch Author <author@example.com> |
75f8426c | 648 | |
5903019b MCC |
649 | The ``from`` line specifies who will be credited as the author of the |
650 | patch in the permanent changelog. If the ``from`` line is missing, | |
651 | then the ``From:`` line from the email header will be used to determine | |
75f8426c PJ |
652 | the patch author in the changelog. |
653 | ||
654 | The explanation body will be committed to the permanent source | |
655 | changelog, so should make sense to a competent reader who has long | |
656 | since forgotten the immediate details of the discussion that might | |
2ae19aca TT |
657 | have led to this patch. Including symptoms of the failure which the |
658 | patch addresses (kernel log messages, oops messages, etc.) is | |
659 | especially useful for people who might be searching the commit logs | |
660 | looking for the applicable patch. If a patch fixes a compile failure, | |
661 | it may not be necessary to include _all_ of the compile failures; just | |
662 | enough that it is likely that someone searching for the patch can find | |
5903019b | 663 | it. As in the ``summary phrase``, it is important to be both succinct as |
2ae19aca | 664 | well as descriptive. |
75f8426c | 665 | |
5903019b | 666 | The ``---`` marker line serves the essential purpose of marking for patch |
75f8426c PJ |
667 | handling tools where the changelog message ends. |
668 | ||
5903019b | 669 | One good use for the additional comments after the ``---`` marker is for |
9b2c7677 MCC |
670 | a ``diffstat``, to show what files have changed, and the number of |
671 | inserted and deleted lines per file. A ``diffstat`` is especially useful | |
2ae19aca TT |
672 | on bigger patches. Other comments relevant only to the moment or the |
673 | maintainer, not suitable for the permanent changelog, should also go | |
5903019b | 674 | here. A good example of such comments might be ``patch changelogs`` |
2ae19aca TT |
675 | which describe what has changed between the v1 and v2 version of the |
676 | patch. | |
677 | ||
9b2c7677 MCC |
678 | If you are going to include a ``diffstat`` after the ``---`` marker, please |
679 | use ``diffstat`` options ``-p 1 -w 70`` so that filenames are listed from | |
2ae19aca | 680 | the top of the kernel source tree and don't use too much horizontal |
9b2c7677 | 681 | space (easily fit in 80 columns, maybe with some indentation). (``git`` |
8e3072a2 | 682 | generates appropriate diffstats by default.) |
75f8426c PJ |
683 | |
684 | See more details on the proper patch format in the following | |
685 | references. | |
686 | ||
5903019b MCC |
687 | .. _explicit_in_reply_to: |
688 | ||
ef227c39 DD |
689 | Explicit In-Reply-To headers |
690 | ---------------------------- | |
d7ac8d85 CM |
691 | |
692 | It can be helpful to manually add In-Reply-To: headers to a patch | |
5903019b | 693 | (e.g., when using ``git send-email``) to associate the patch with |
d7ac8d85 CM |
694 | previous relevant discussion, e.g. to link a bug fix to the email with |
695 | the bug report. However, for a multi-patch series, it is generally | |
696 | best to avoid using In-Reply-To: to link to older versions of the | |
697 | series. This way multiple versions of the patch don't become an | |
698 | unmanageable forest of references in email clients. If a link is | |
699 | helpful, you can use the https://lkml.kernel.org/ redirector (e.g., in | |
700 | the cover email text) to link to an earlier version of the patch series. | |
701 | ||
75f8426c | 702 | |
ef227c39 DD |
703 | Providing base tree information |
704 | ------------------------------- | |
e8686a40 KR |
705 | |
706 | When other developers receive your patches and start the review process, | |
707 | it is often useful for them to know where in the tree history they | |
708 | should place your work. This is particularly useful for automated CI | |
709 | processes that attempt to run a series of tests in order to establish | |
710 | the quality of your submission before the maintainer starts the review. | |
711 | ||
712 | If you are using ``git format-patch`` to generate your patches, you can | |
713 | automatically include the base tree information in your submission by | |
714 | using the ``--base`` flag. The easiest and most convenient way to use | |
715 | this option is with topical branches:: | |
716 | ||
717 | $ git checkout -t -b my-topical-branch master | |
718 | Branch 'my-topical-branch' set up to track local branch 'master'. | |
719 | Switched to a new branch 'my-topical-branch' | |
720 | ||
721 | [perform your edits and commits] | |
722 | ||
723 | $ git format-patch --base=auto --cover-letter -o outgoing/ master | |
724 | outgoing/0000-cover-letter.patch | |
725 | outgoing/0001-First-Commit.patch | |
726 | outgoing/... | |
727 | ||
728 | When you open ``outgoing/0000-cover-letter.patch`` for editing, you will | |
729 | notice that it will have the ``base-commit:`` trailer at the very | |
730 | bottom, which provides the reviewer and the CI tools enough information | |
731 | to properly perform ``git am`` without worrying about conflicts:: | |
732 | ||
733 | $ git checkout -b patch-review [base-commit-id] | |
734 | Switched to a new branch 'patch-review' | |
735 | $ git am patches.mbox | |
736 | Applying: First Commit | |
737 | Applying: ... | |
738 | ||
739 | Please see ``man git-format-patch`` for more information about this | |
740 | option. | |
741 | ||
742 | .. note:: | |
743 | ||
744 | The ``--base`` feature was introduced in git version 2.9.0. | |
745 | ||
746 | If you are not using git to format your patches, you can still include | |
747 | the same ``base-commit`` trailer to indicate the commit hash of the tree | |
748 | on which your work is based. You should add it either in the cover | |
749 | letter or in the first patch of the series and it should be placed | |
750 | either below the ``---`` line or at the very bottom of all other | |
751 | content, right before your email signature. | |
752 | ||
753 | ||
89edeedd JC |
754 | References |
755 | ---------- | |
5b0ed2c6 XVP |
756 | |
757 | Andrew Morton, "The perfect patch" (tpp). | |
e7b4311e | 758 | <https://www.ozlabs.org/~akpm/stuff/tpp.txt> |
5b0ed2c6 | 759 | |
8e9cb8fd | 760 | Jeff Garzik, "Linux kernel patch submission format". |
5aff7c46 | 761 | <https://web.archive.org/web/20180829112450/http://linux.yyz.us/patch-format.html> |
5b0ed2c6 | 762 | |
8e9cb8fd | 763 | Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer". |
f5039935 | 764 | <http://www.kroah.com/log/linux/maintainer.html> |
9b2c7677 | 765 | |
f5039935 | 766 | <http://www.kroah.com/log/linux/maintainer-02.html> |
9b2c7677 | 767 | |
f5039935 | 768 | <http://www.kroah.com/log/linux/maintainer-03.html> |
9b2c7677 | 769 | |
f5039935 | 770 | <http://www.kroah.com/log/linux/maintainer-04.html> |
9b2c7677 | 771 | |
f5039935 | 772 | <http://www.kroah.com/log/linux/maintainer-05.html> |
9b2c7677 | 773 | |
7e0dae61 | 774 | <http://www.kroah.com/log/linux/maintainer-06.html> |
5b0ed2c6 | 775 | |
bc7455fa | 776 | NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people! |
05a5f51c | 777 | <https://lore.kernel.org/r/20050711.125305.08322243.davem@davemloft.net> |
5b0ed2c6 | 778 | |
8c27ceff MCC |
779 | Kernel Documentation/process/coding-style.rst: |
780 | :ref:`Documentation/process/coding-style.rst <codingstyle>` | |
5b0ed2c6 | 781 | |
8e9cb8fd | 782 | Linus Torvalds's mail on the canonical patch format: |
05a5f51c | 783 | <https://lore.kernel.org/r/Pine.LNX.4.58.0504071023190.28951@ppc970.osdl.org> |
9536727e AK |
784 | |
785 | Andi Kleen, "On submitting kernel patches" | |
25985edc | 786 | Some strategies to get difficult or controversial changes in. |
9b2c7677 | 787 | |
9536727e | 788 | http://halobates.de/on-submitting-patches.pdf |