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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 | |
0e4f07a6 | 13 | works, see :ref:`Documentation/process <development_process_main>`. |
8c27ceff | 14 | Also, read :ref:`Documentation/process/submit-checklist.rst <submitchecklist>` |
dca22a63 | 15 | for a list of items to check before |
d00c4559 | 16 | submitting code. If you are submitting a driver, also read |
8c27ceff | 17 | :ref:`Documentation/process/submitting-drivers.rst <submittingdrivers>`; |
dca22a63 | 18 | for device tree binding patches, read |
858e6845 | 19 | Documentation/devicetree/bindings/submitting-patches.rst. |
1da177e4 | 20 | |
9f364b60 DD |
21 | This documentation assumes that you're using ``git`` to prepare your patches. |
22 | If you're unfamiliar with ``git``, you would be well-advised to learn how to | |
23 | use it, it will make your life as a kernel developer and in general much | |
24 | easier. | |
1da177e4 | 25 | |
ef227c39 DD |
26 | Obtain a current source tree |
27 | ---------------------------- | |
7994cc15 JC |
28 | |
29 | If you do not have a repository with the current kernel source handy, use | |
9b2c7677 | 30 | ``git`` to obtain one. You'll want to start with the mainline repository, |
5903019b | 31 | which can be grabbed with:: |
7994cc15 | 32 | |
5903019b | 33 | git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git |
7994cc15 JC |
34 | |
35 | Note, however, that you may not want to develop against the mainline tree | |
36 | directly. Most subsystem maintainers run their own trees and want to see | |
5903019b | 37 | patches prepared against those trees. See the **T:** entry for the subsystem |
7994cc15 JC |
38 | in the MAINTAINERS file to find that tree, or simply ask the maintainer if |
39 | the tree is not listed there. | |
40 | ||
5903019b | 41 | .. _describe_changes: |
84da7c08 | 42 | |
ef227c39 DD |
43 | Describe your changes |
44 | --------------------- | |
1da177e4 | 45 | |
7b9828d4 JW |
46 | Describe your problem. Whether your patch is a one-line bug fix or |
47 | 5000 lines of a new feature, there must be an underlying problem that | |
48 | motivated you to do this work. Convince the reviewer that there is a | |
49 | problem worth fixing and that it makes sense for them to read past the | |
50 | first paragraph. | |
51 | ||
52 | Describe user-visible impact. Straight up crashes and lockups are | |
53 | pretty convincing, but not all bugs are that blatant. Even if the | |
54 | problem was spotted during code review, describe the impact you think | |
55 | it can have on users. Keep in mind that the majority of Linux | |
56 | installations run kernels from secondary stable trees or | |
57 | vendor/product-specific trees that cherry-pick only specific patches | |
58 | from upstream, so include anything that could help route your change | |
59 | downstream: provoking circumstances, excerpts from dmesg, crash | |
60 | descriptions, performance regressions, latency spikes, lockups, etc. | |
61 | ||
62 | Quantify optimizations and trade-offs. If you claim improvements in | |
63 | performance, memory consumption, stack footprint, or binary size, | |
64 | include numbers that back them up. But also describe non-obvious | |
65 | costs. Optimizations usually aren't free but trade-offs between CPU, | |
66 | memory, and readability; or, when it comes to heuristics, between | |
67 | different workloads. Describe the expected downsides of your | |
68 | optimization so that the reviewer can weigh costs against benefits. | |
69 | ||
70 | Once the problem is established, describe what you are actually doing | |
71 | about it in technical detail. It's important to describe the change | |
72 | in plain English for the reviewer to verify that the code is behaving | |
73 | as you intend it to. | |
1da177e4 | 74 | |
2ae19aca TT |
75 | The maintainer will thank you if you write your patch description in a |
76 | form which can be easily pulled into Linux's source code management | |
9b2c7677 | 77 | system, ``git``, as a "commit log". See :ref:`explicit_in_reply_to`. |
2ae19aca | 78 | |
7b9828d4 JW |
79 | Solve only one problem per patch. If your description starts to get |
80 | long, that's a sign that you probably need to split up your patch. | |
5903019b | 81 | See :ref:`split_changes`. |
1da177e4 | 82 | |
d89b1945 RD |
83 | When you submit or resubmit a patch or patch series, include the |
84 | complete patch description and justification for it. Don't just | |
85 | say that this is version N of the patch (series). Don't expect the | |
d00c4559 | 86 | subsystem maintainer to refer back to earlier patch versions or referenced |
d89b1945 RD |
87 | URLs to find the patch description and put that into the patch. |
88 | I.e., the patch (series) and its description should be self-contained. | |
d00c4559 | 89 | This benefits both the maintainers and reviewers. Some reviewers |
d89b1945 RD |
90 | probably didn't even receive earlier versions of the patch. |
91 | ||
74a475ac JT |
92 | Describe your changes in imperative mood, e.g. "make xyzzy do frotz" |
93 | instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy | |
94 | to do frotz", as if you are giving orders to the codebase to change | |
95 | its behaviour. | |
96 | ||
d89b1945 | 97 | If the patch fixes a logged bug entry, refer to that bug entry by |
9547c706 JT |
98 | number and URL. If the patch follows from a mailing list discussion, |
99 | give a URL to the mailing list archive; use the https://lkml.kernel.org/ | |
9b2c7677 | 100 | redirector with a ``Message-Id``, to ensure that the links cannot become |
9547c706 JT |
101 | stale. |
102 | ||
103 | However, try to make your explanation understandable without external | |
104 | resources. In addition to giving a URL to a mailing list archive or | |
105 | bug, summarize the relevant points of the discussion that led to the | |
106 | patch as submitted. | |
1da177e4 | 107 | |
0af52703 GU |
108 | If you want to refer to a specific commit, don't just refer to the |
109 | SHA-1 ID of the commit. Please also include the oneline summary of | |
110 | the commit, to make it easier for reviewers to know what it is about. | |
5903019b | 111 | Example:: |
0af52703 GU |
112 | |
113 | Commit e21d2170f36602ae2708 ("video: remove unnecessary | |
114 | platform_set_drvdata()") removed the unnecessary | |
115 | platform_set_drvdata(), but left the variable "dev" unused, | |
116 | delete it. | |
117 | ||
7994cc15 JC |
118 | You should also be sure to use at least the first twelve characters of the |
119 | SHA-1 ID. The kernel repository holds a *lot* of objects, making | |
120 | collisions with shorter IDs a real possibility. Bear in mind that, even if | |
121 | there is no collision with your six-character ID now, that condition may | |
122 | change five years from now. | |
123 | ||
8401aa1f | 124 | If your patch fixes a bug in a specific commit, e.g. you found an issue using |
9b2c7677 | 125 | ``git bisect``, please use the 'Fixes:' tag with the first 12 characters of |
19c3fe28 SC |
126 | the SHA-1 ID, and the one line summary. Do not split the tag across multiple |
127 | lines, tags are exempt from the "wrap at 75 columns" rule in order to simplify | |
128 | parsing scripts. For example:: | |
8401aa1f | 129 | |
19c3fe28 | 130 | Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed") |
8401aa1f | 131 | |
9b2c7677 MCC |
132 | The following ``git config`` settings can be used to add a pretty format for |
133 | outputting the above style in the ``git log`` or ``git show`` commands:: | |
8401aa1f JK |
134 | |
135 | [core] | |
136 | abbrev = 12 | |
137 | [pretty] | |
138 | fixes = Fixes: %h (\"%s\") | |
1da177e4 | 139 | |
5b5bbb8c TR |
140 | An example call:: |
141 | ||
142 | $ git log -1 --pretty=fixes 54a4f0239f2e | |
143 | Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed") | |
144 | ||
5903019b MCC |
145 | .. _split_changes: |
146 | ||
ef227c39 DD |
147 | Separate your changes |
148 | --------------------- | |
1da177e4 | 149 | |
5903019b | 150 | Separate each **logical change** into a separate patch. |
1da177e4 LT |
151 | |
152 | For example, if your changes include both bug fixes and performance | |
153 | enhancements for a single driver, separate those changes into two | |
154 | or more patches. If your changes include an API update, and a new | |
155 | driver which uses that new API, separate those into two patches. | |
156 | ||
157 | On the other hand, if you make a single change to numerous files, | |
158 | group those changes into a single patch. Thus a single logical change | |
159 | is contained within a single patch. | |
160 | ||
d00c4559 JC |
161 | The point to remember is that each patch should make an easily understood |
162 | change that can be verified by reviewers. Each patch should be justifiable | |
163 | on its own merits. | |
164 | ||
1da177e4 | 165 | If one patch depends on another patch in order for a change to be |
5903019b | 166 | complete, that is OK. Simply note **"this patch depends on patch X"** |
1da177e4 LT |
167 | in your patch description. |
168 | ||
7994cc15 JC |
169 | When dividing your change into a series of patches, take special care to |
170 | ensure that the kernel builds and runs properly after each patch in the | |
5903019b | 171 | series. Developers using ``git bisect`` to track down a problem can end up |
7994cc15 JC |
172 | splitting your patch series at any point; they will not thank you if you |
173 | introduce bugs in the middle. | |
174 | ||
5b0ed2c6 XVP |
175 | If you cannot condense your patch set into a smaller set of patches, |
176 | then only post say 15 or so at a time and wait for review and integration. | |
177 | ||
178 | ||
1da177e4 | 179 | |
ef227c39 DD |
180 | Style-check your changes |
181 | ------------------------ | |
0a920b5b AW |
182 | |
183 | Check your patch for basic style violations, details of which can be | |
dca22a63 | 184 | found in |
8c27ceff | 185 | :ref:`Documentation/process/coding-style.rst <codingstyle>`. |
dca22a63 | 186 | Failure to do so simply wastes |
f56d35e7 | 187 | the reviewers time and will get your patch rejected, probably |
0a920b5b AW |
188 | without even being read. |
189 | ||
6de16eba JC |
190 | One significant exception is when moving code from one file to |
191 | another -- in this case you should not modify the moved code at all in | |
192 | the same patch which moves it. This clearly delineates the act of | |
193 | moving the code and your changes. This greatly aids review of the | |
194 | actual differences and allows tools to better track the history of | |
195 | the code itself. | |
196 | ||
197 | Check your patches with the patch style checker prior to submission | |
198 | (scripts/checkpatch.pl). Note, though, that the style checker should be | |
199 | viewed as a guide, not as a replacement for human judgment. If your code | |
200 | looks better with a violation then its probably best left alone. | |
0a920b5b | 201 | |
6de16eba JC |
202 | The checker reports at three levels: |
203 | - ERROR: things that are very likely to be wrong | |
204 | - WARNING: things requiring careful review | |
205 | - CHECK: things requiring thought | |
0a920b5b | 206 | |
6de16eba JC |
207 | You should be able to justify all violations that remain in your |
208 | patch. | |
0a920b5b AW |
209 | |
210 | ||
ef227c39 DD |
211 | Select the recipients for your patch |
212 | ------------------------------------ | |
1da177e4 | 213 | |
ccae8616 JC |
214 | You should always copy the appropriate subsystem maintainer(s) on any patch |
215 | to code that they maintain; look through the MAINTAINERS file and the | |
216 | source code revision history to see who those maintainers are. The | |
217 | script scripts/get_maintainer.pl can be very useful at this step. If you | |
d6eff078 | 218 | cannot find a maintainer for the subsystem you are working on, Andrew |
ccae8616 | 219 | Morton (akpm@linux-foundation.org) serves as a maintainer of last resort. |
1da177e4 | 220 | |
ccae8616 JC |
221 | You should also normally choose at least one mailing list to receive a copy |
222 | of your patch set. linux-kernel@vger.kernel.org functions as a list of | |
223 | last resort, but the volume on that list has caused a number of developers | |
224 | to tune it out. Look in the MAINTAINERS file for a subsystem-specific | |
225 | list; your patch will probably get more attention there. Please do not | |
226 | spam unrelated lists, though. | |
1da177e4 | 227 | |
ccae8616 JC |
228 | Many kernel-related lists are hosted on vger.kernel.org; you can find a |
229 | list of them at http://vger.kernel.org/vger-lists.html. There are | |
230 | kernel-related lists hosted elsewhere as well, though. | |
5b0ed2c6 XVP |
231 | |
232 | Do not send more than 15 patches at once to the vger mailing lists!!! | |
233 | ||
1da177e4 | 234 | Linus Torvalds is the final arbiter of all changes accepted into the |
e00bfcbf | 235 | Linux kernel. His e-mail address is <torvalds@linux-foundation.org>. |
ccae8616 JC |
236 | He gets a lot of e-mail, and, at this point, very few patches go through |
237 | Linus directly, so typically you should do your best to -avoid- | |
e00bfcbf | 238 | sending him e-mail. |
1da177e4 | 239 | |
ccae8616 JC |
240 | If you have a patch that fixes an exploitable security bug, send that patch |
241 | to security@kernel.org. For severe bugs, a short embargo may be considered | |
253508ca | 242 | to allow distributors to get the patch out to users; in such cases, |
eb45fb2f KK |
243 | obviously, the patch should not be sent to any public lists. See also |
244 | :ref:`Documentation/admin-guide/security-bugs.rst <security-bugs>`. | |
1da177e4 | 245 | |
ccae8616 | 246 | Patches that fix a severe bug in a released kernel should be directed |
5903019b | 247 | toward the stable maintainers by putting a line like this:: |
1da177e4 | 248 | |
ccae8616 | 249 | Cc: stable@vger.kernel.org |
1da177e4 | 250 | |
8cda4c3a | 251 | into the sign-off area of your patch (note, NOT an email recipient). You |
dca22a63 | 252 | should also read |
8c27ceff | 253 | :ref:`Documentation/process/stable-kernel-rules.rst <stable_kernel_rules>` |
dca22a63 | 254 | in addition to this file. |
1da177e4 | 255 | |
ccae8616 JC |
256 | Note, however, that some subsystem maintainers want to come to their own |
257 | conclusions on which patches should go to the stable trees. The networking | |
258 | maintainer, in particular, would rather not see individual developers | |
259 | adding lines like the above to their patches. | |
5b0ed2c6 | 260 | |
ccae8616 JC |
261 | If changes affect userland-kernel interfaces, please send the MAN-PAGES |
262 | maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at | |
263 | least a notification of the change, so that some information makes its way | |
264 | into the manual pages. User-space API changes should also be copied to | |
5903019b | 265 | linux-api@vger.kernel.org. |
1da177e4 LT |
266 | |
267 | For small patches you may want to CC the Trivial Patch Monkey | |
82d27b2b MH |
268 | trivial@kernel.org which collects "trivial" patches. Have a look |
269 | into the MAINTAINERS file for its current manager. | |
5903019b | 270 | |
82d27b2b | 271 | Trivial patches must qualify for one of the following rules: |
5903019b | 272 | |
9b2c7677 MCC |
273 | - Spelling fixes in documentation |
274 | - Spelling fixes for errors which could break :manpage:`grep(1)` | |
275 | - Warning fixes (cluttering with useless warnings is bad) | |
276 | - Compilation fixes (only if they are actually correct) | |
277 | - Runtime fixes (only if they actually fix things) | |
278 | - Removing use of deprecated functions/macros | |
279 | - Contact detail and documentation fixes | |
280 | - Non-portable code replaced by portable code (even in arch-specific, | |
281 | since people copy, as long as it's trivial) | |
282 | - Any fix by the author/maintainer of the file (ie. patch monkey | |
283 | in re-transmission mode) | |
84da7c08 | 284 | |
1da177e4 LT |
285 | |
286 | ||
ef227c39 DD |
287 | No MIME, no links, no compression, no attachments. Just plain text |
288 | ------------------------------------------------------------------- | |
1da177e4 LT |
289 | |
290 | Linus and other kernel developers need to be able to read and comment | |
291 | on the changes you are submitting. It is important for a kernel | |
292 | developer to be able to "quote" your changes, using standard e-mail | |
293 | tools, so that they may comment on specific portions of your code. | |
294 | ||
9f364b60 DD |
295 | For this reason, all patches should be submitted by e-mail "inline". The |
296 | easiest way to do this is with ``git send-email``, which is strongly | |
297 | recommended. An interactive tutorial for ``git send-email`` is available at | |
298 | https://git-send-email.io. | |
299 | ||
300 | If you choose not to use ``git send-email``: | |
9b2c7677 MCC |
301 | |
302 | .. warning:: | |
303 | ||
304 | Be wary of your editor's word-wrap corrupting your patch, | |
305 | if you choose to cut-n-paste your patch. | |
1da177e4 LT |
306 | |
307 | Do not attach the patch as a MIME attachment, compressed or not. | |
308 | Many popular e-mail applications will not always transmit a MIME | |
309 | attachment as plain text, making it impossible to comment on your | |
310 | code. A MIME attachment also takes Linus a bit more time to process, | |
311 | decreasing the likelihood of your MIME-attached change being accepted. | |
312 | ||
313 | Exception: If your mailer is mangling patches then someone may ask | |
314 | you to re-send them using MIME. | |
315 | ||
8c27ceff | 316 | See :ref:`Documentation/process/email-clients.rst <email_clients>` |
dca22a63 MCC |
317 | for hints about configuring your e-mail client so that it sends your patches |
318 | untouched. | |
1da177e4 | 319 | |
ef227c39 DD |
320 | Respond to review comments |
321 | -------------------------- | |
1da177e4 | 322 | |
0eea2314 | 323 | Your patch will almost certainly get comments from reviewers on ways in |
9f364b60 DD |
324 | which the patch can be improved, in the form of a reply to your email. You must |
325 | respond to those comments; ignoring reviewers is a good way to get ignored in | |
326 | return. You can simply reply to their emails to answer their comments. Review | |
327 | comments or questions that do not lead to a code change should almost certainly | |
0eea2314 JC |
328 | bring about a comment or changelog entry so that the next reviewer better |
329 | understands what is going on. | |
1da177e4 | 330 | |
0eea2314 JC |
331 | Be sure to tell the reviewers what changes you are making and to thank them |
332 | for their time. Code review is a tiring and time-consuming process, and | |
333 | reviewers sometimes get grumpy. Even in that case, though, respond | |
334 | politely and address the problems they have pointed out. | |
1da177e4 | 335 | |
7433ff33 DD |
336 | See :ref:`Documentation/process/email-clients.rst` for recommendations on email |
337 | clients and mailing list etiquette. | |
338 | ||
1da177e4 | 339 | |
ef227c39 DD |
340 | Don't get discouraged - or impatient |
341 | ------------------------------------ | |
1da177e4 | 342 | |
0eea2314 JC |
343 | After you have submitted your change, be patient and wait. Reviewers are |
344 | busy people and may not get to your patch right away. | |
1da177e4 | 345 | |
0eea2314 JC |
346 | Once upon a time, patches used to disappear into the void without comment, |
347 | but the development process works more smoothly than that now. You should | |
348 | receive comments within a week or so; if that does not happen, make sure | |
349 | that you have sent your patches to the right place. Wait for a minimum of | |
350 | one week before resubmitting or pinging reviewers - possibly longer during | |
351 | busy times like merge windows. | |
1da177e4 | 352 | |
1da177e4 | 353 | |
ef227c39 DD |
354 | Include PATCH in the subject |
355 | ----------------------------- | |
1da177e4 LT |
356 | |
357 | Due to high e-mail traffic to Linus, and to linux-kernel, it is common | |
358 | convention to prefix your subject line with [PATCH]. This lets Linus | |
359 | and other kernel developers more easily distinguish patches from other | |
360 | e-mail discussions. | |
361 | ||
9f364b60 | 362 | ``git send-email`` will do this for you automatically. |
1da177e4 LT |
363 | |
364 | ||
ef227c39 DD |
365 | Sign your work - the Developer's Certificate of Origin |
366 | ------------------------------------------------------ | |
1da177e4 LT |
367 | |
368 | To improve tracking of who did what, especially with patches that can | |
369 | percolate to their final resting place in the kernel through several | |
370 | layers of maintainers, we've introduced a "sign-off" procedure on | |
371 | patches that are being emailed around. | |
372 | ||
373 | The sign-off is a simple line at the end of the explanation for the | |
374 | patch, which certifies that you wrote it or otherwise have the right to | |
db12fb83 | 375 | pass it on as an open-source patch. The rules are pretty simple: if you |
1da177e4 LT |
376 | can certify the below: |
377 | ||
5903019b MCC |
378 | Developer's Certificate of Origin 1.1 |
379 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
1da177e4 | 380 | |
5903019b | 381 | By making a contribution to this project, I certify that: |
1da177e4 LT |
382 | |
383 | (a) The contribution was created in whole or in part by me and I | |
384 | have the right to submit it under the open source license | |
385 | indicated in the file; or | |
386 | ||
387 | (b) The contribution is based upon previous work that, to the best | |
388 | of my knowledge, is covered under an appropriate open source | |
389 | license and I have the right under that license to submit that | |
390 | work with modifications, whether created in whole or in part | |
391 | by me, under the same open source license (unless I am | |
392 | permitted to submit under a different license), as indicated | |
393 | in the file; or | |
394 | ||
395 | (c) The contribution was provided directly to me by some other | |
396 | person who certified (a), (b) or (c) and I have not modified | |
397 | it. | |
398 | ||
e00bfcbf SB |
399 | (d) I understand and agree that this project and the contribution |
400 | are public and that a record of the contribution (including all | |
401 | personal information I submit with it, including my sign-off) is | |
402 | maintained indefinitely and may be redistributed consistent with | |
403 | this project or the open source license(s) involved. | |
cbd83da8 | 404 | |
5903019b | 405 | then you just add a line saying:: |
1da177e4 | 406 | |
9fd5559c | 407 | Signed-off-by: Random J Developer <random@developer.example.org> |
1da177e4 | 408 | |
af45f32d | 409 | using your real name (sorry, no pseudonyms or anonymous contributions.) |
9f364b60 | 410 | This will be done for you automatically if you use ``git commit -s``. |
af45f32d | 411 | |
1da177e4 LT |
412 | Some people also put extra tags at the end. They'll just be ignored for |
413 | now, but you can do this to mark internal company procedures or just | |
e00bfcbf | 414 | point out some special detail about the sign-off. |
1da177e4 LT |
415 | |
416 | ||
ef227c39 DD |
417 | When to use Acked-by:, Cc:, and Co-developed-by: |
418 | ------------------------------------------------ | |
0a920b5b | 419 | |
0f44cd23 AM |
420 | The Signed-off-by: tag indicates that the signer was involved in the |
421 | development of the patch, or that he/she was in the patch's delivery path. | |
422 | ||
423 | If a person was not directly involved in the preparation or handling of a | |
424 | patch but wishes to signify and record their approval of it then they can | |
d00c4559 | 425 | ask to have an Acked-by: line added to the patch's changelog. |
0f44cd23 AM |
426 | |
427 | Acked-by: is often used by the maintainer of the affected code when that | |
428 | maintainer neither contributed to nor forwarded the patch. | |
429 | ||
430 | Acked-by: is not as formal as Signed-off-by:. It is a record that the acker | |
431 | has at least reviewed the patch and has indicated acceptance. Hence patch | |
432 | mergers will sometimes manually convert an acker's "yep, looks good to me" | |
d00c4559 JC |
433 | into an Acked-by: (but note that it is usually better to ask for an |
434 | explicit ack). | |
0f44cd23 AM |
435 | |
436 | Acked-by: does not necessarily indicate acknowledgement of the entire patch. | |
437 | For example, if a patch affects multiple subsystems and has an Acked-by: from | |
438 | one subsystem maintainer then this usually indicates acknowledgement of just | |
439 | the part which affects that maintainer's code. Judgement should be used here. | |
ef40203a | 440 | When in doubt people should refer to the original discussion in the mailing |
0f44cd23 AM |
441 | list archives. |
442 | ||
ef40203a | 443 | If a person has had the opportunity to comment on a patch, but has not |
5903019b | 444 | provided such comments, you may optionally add a ``Cc:`` tag to the patch. |
ef40203a | 445 | This is the only tag which might be added without an explicit action by the |
d00c4559 JC |
446 | person it names - but it should indicate that this person was copied on the |
447 | patch. This tag documents that potentially interested parties | |
448 | have been included in the discussion. | |
0f44cd23 | 449 | |
24a2bb90 SC |
450 | Co-developed-by: states that the patch was co-created by multiple developers; |
451 | it is a used to give attribution to co-authors (in addition to the author | |
452 | attributed by the From: tag) when several people work on a single patch. Since | |
453 | Co-developed-by: denotes authorship, every Co-developed-by: must be immediately | |
454 | followed by a Signed-off-by: of the associated co-author. Standard sign-off | |
455 | procedure applies, i.e. the ordering of Signed-off-by: tags should reflect the | |
456 | chronological history of the patch insofar as possible, regardless of whether | |
457 | the author is attributed via From: or Co-developed-by:. Notably, the last | |
458 | Signed-off-by: must always be that of the developer submitting the patch. | |
459 | ||
460 | Note, the From: tag is optional when the From: author is also the person (and | |
461 | email) listed in the From: line of the email header. | |
462 | ||
463 | Example of a patch submitted by the From: author:: | |
464 | ||
465 | <changelog> | |
466 | ||
467 | Co-developed-by: First Co-Author <first@coauthor.example.org> | |
468 | Signed-off-by: First Co-Author <first@coauthor.example.org> | |
469 | Co-developed-by: Second Co-Author <second@coauthor.example.org> | |
470 | Signed-off-by: Second Co-Author <second@coauthor.example.org> | |
471 | Signed-off-by: From Author <from@author.example.org> | |
472 | ||
473 | Example of a patch submitted by a Co-developed-by: author:: | |
474 | ||
475 | From: From Author <from@author.example.org> | |
476 | ||
477 | <changelog> | |
478 | ||
479 | Co-developed-by: Random Co-Author <random@coauthor.example.org> | |
480 | Signed-off-by: Random Co-Author <random@coauthor.example.org> | |
481 | Signed-off-by: From Author <from@author.example.org> | |
482 | Co-developed-by: Submitting Co-Author <sub@coauthor.example.org> | |
483 | Signed-off-by: Submitting Co-Author <sub@coauthor.example.org> | |
82d95343 | 484 | |
ef40203a | 485 | |
ef227c39 DD |
486 | Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes: |
487 | ---------------------------------------------------------------------- | |
bbb0a424 | 488 | |
d75ef707 DC |
489 | The Reported-by tag gives credit to people who find bugs and report them and it |
490 | hopefully inspires them to help us again in the future. Please note that if | |
491 | the bug was reported in private, then ask for permission first before using the | |
492 | Reported-by tag. | |
ef40203a JC |
493 | |
494 | A Tested-by: tag indicates that the patch has been successfully tested (in | |
495 | some environment) by the person named. This tag informs maintainers that | |
496 | some testing has been performed, provides a means to locate testers for | |
497 | future patches, and ensures credit for the testers. | |
498 | ||
499 | Reviewed-by:, instead, indicates that the patch has been reviewed and found | |
500 | acceptable according to the Reviewer's Statement: | |
501 | ||
5903019b MCC |
502 | Reviewer's statement of oversight |
503 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
ef40203a | 504 | |
5903019b | 505 | By offering my Reviewed-by: tag, I state that: |
ef40203a | 506 | |
5903019b | 507 | (a) I have carried out a technical review of this patch to |
ef40203a JC |
508 | evaluate its appropriateness and readiness for inclusion into |
509 | the mainline kernel. | |
510 | ||
511 | (b) Any problems, concerns, or questions relating to the patch | |
512 | have been communicated back to the submitter. I am satisfied | |
513 | with the submitter's response to my comments. | |
514 | ||
515 | (c) While there may be things that could be improved with this | |
516 | submission, I believe that it is, at this time, (1) a | |
517 | worthwhile modification to the kernel, and (2) free of known | |
518 | issues which would argue against its inclusion. | |
519 | ||
520 | (d) While I have reviewed the patch and believe it to be sound, I | |
521 | do not (unless explicitly stated elsewhere) make any | |
522 | warranties or guarantees that it will achieve its stated | |
523 | purpose or function properly in any given situation. | |
524 | ||
525 | A Reviewed-by tag is a statement of opinion that the patch is an | |
526 | appropriate modification of the kernel without any remaining serious | |
527 | technical issues. Any interested reviewer (who has done the work) can | |
528 | offer a Reviewed-by tag for a patch. This tag serves to give credit to | |
529 | reviewers and to inform maintainers of the degree of review which has been | |
530 | done on the patch. Reviewed-by: tags, when supplied by reviewers known to | |
531 | understand the subject area and to perform thorough reviews, will normally | |
5801da1b | 532 | increase the likelihood of your patch getting into the kernel. |
ef40203a | 533 | |
8543ae12 M |
534 | A Suggested-by: tag indicates that the patch idea is suggested by the person |
535 | named and ensures credit to the person for the idea. Please note that this | |
536 | tag should not be added without the reporter's permission, especially if the | |
537 | idea was not posted in a public forum. That said, if we diligently credit our | |
538 | idea reporters, they will, hopefully, be inspired to help us again in the | |
539 | future. | |
540 | ||
8401aa1f JK |
541 | A Fixes: tag indicates that the patch fixes an issue in a previous commit. It |
542 | is used to make it easy to determine where a bug originated, which can help | |
543 | review a bug fix. This tag also assists the stable kernel team in determining | |
544 | which stable kernel versions should receive your fix. This is the preferred | |
5903019b MCC |
545 | method for indicating a bug fixed by the patch. See :ref:`describe_changes` |
546 | for more details. | |
8401aa1f | 547 | |
f58252cd | 548 | .. _the_canonical_patch_format: |
ef40203a | 549 | |
ef227c39 DD |
550 | The canonical patch format |
551 | -------------------------- | |
7994cc15 JC |
552 | |
553 | This section describes how the patch itself should be formatted. Note | |
9b2c7677 | 554 | that, if you have your patches stored in a ``git`` repository, proper patch |
5903019b | 555 | formatting can be had with ``git format-patch``. The tools cannot create |
7994cc15 | 556 | the necessary text, though, so read the instructions below anyway. |
84da7c08 | 557 | |
5903019b | 558 | The canonical patch subject line is:: |
75f8426c | 559 | |
d6b9acc0 | 560 | Subject: [PATCH 001/123] subsystem: summary phrase |
75f8426c PJ |
561 | |
562 | The canonical patch message body contains the following: | |
563 | ||
d19b3e32 JH |
564 | - A ``from`` line specifying the patch author, followed by an empty |
565 | line (only needed if the person sending the patch is not the author). | |
75f8426c | 566 | |
2a076f40 JP |
567 | - The body of the explanation, line wrapped at 75 columns, which will |
568 | be copied to the permanent changelog to describe this patch. | |
75f8426c | 569 | |
d19b3e32 JH |
570 | - An empty line. |
571 | ||
5903019b | 572 | - The ``Signed-off-by:`` lines, described above, which will |
75f8426c PJ |
573 | also go in the changelog. |
574 | ||
5903019b | 575 | - A marker line containing simply ``---``. |
75f8426c PJ |
576 | |
577 | - Any additional comments not suitable for the changelog. | |
578 | ||
9b2c7677 | 579 | - The actual patch (``diff`` output). |
75f8426c PJ |
580 | |
581 | The Subject line format makes it very easy to sort the emails | |
582 | alphabetically by subject line - pretty much any email reader will | |
583 | support that - since because the sequence number is zero-padded, | |
584 | the numerical and alphabetic sort is the same. | |
585 | ||
5903019b | 586 | The ``subsystem`` in the email's Subject should identify which |
d6b9acc0 PJ |
587 | area or subsystem of the kernel is being patched. |
588 | ||
5903019b MCC |
589 | The ``summary phrase`` in the email's Subject should concisely |
590 | describe the patch which that email contains. The ``summary | |
591 | phrase`` should not be a filename. Do not use the same ``summary | |
592 | phrase`` for every patch in a whole patch series (where a ``patch | |
593 | series`` is an ordered sequence of multiple, related patches). | |
d6b9acc0 | 594 | |
5903019b | 595 | Bear in mind that the ``summary phrase`` of your email becomes a |
2ae19aca | 596 | globally-unique identifier for that patch. It propagates all the way |
9b2c7677 | 597 | into the ``git`` changelog. The ``summary phrase`` may later be used in |
2ae19aca | 598 | developer discussions which refer to the patch. People will want to |
5903019b | 599 | google for the ``summary phrase`` to read discussion regarding that |
2ae19aca TT |
600 | patch. It will also be the only thing that people may quickly see |
601 | when, two or three months later, they are going through perhaps | |
9b2c7677 MCC |
602 | thousands of patches using tools such as ``gitk`` or ``git log |
603 | --oneline``. | |
2ae19aca | 604 | |
5903019b | 605 | For these reasons, the ``summary`` must be no more than 70-75 |
2ae19aca TT |
606 | characters, and it must describe both what the patch changes, as well |
607 | as why the patch might be necessary. It is challenging to be both | |
608 | succinct and descriptive, but that is what a well-written summary | |
609 | should do. | |
610 | ||
5903019b | 611 | The ``summary phrase`` may be prefixed by tags enclosed in square |
e12d7462 AH |
612 | brackets: "Subject: [PATCH <tag>...] <summary phrase>". The tags are |
613 | not considered part of the summary phrase, but describe how the patch | |
2ae19aca TT |
614 | should be treated. Common tags might include a version descriptor if |
615 | the multiple versions of the patch have been sent out in response to | |
616 | comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for | |
617 | comments. If there are four patches in a patch series the individual | |
618 | patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures | |
619 | that developers understand the order in which the patches should be | |
620 | applied and that they have reviewed or applied all of the patches in | |
621 | the patch series. | |
d6b9acc0 | 622 | |
5903019b | 623 | A couple of example Subjects:: |
d6b9acc0 | 624 | |
e12d7462 AH |
625 | Subject: [PATCH 2/5] ext2: improve scalability of bitmap searching |
626 | Subject: [PATCH v2 01/27] x86: fix eflags tracking | |
75f8426c | 627 | |
5903019b | 628 | The ``from`` line must be the very first line in the message body, |
75f8426c PJ |
629 | and has the form: |
630 | ||
24a2bb90 | 631 | From: Patch Author <author@example.com> |
75f8426c | 632 | |
5903019b MCC |
633 | The ``from`` line specifies who will be credited as the author of the |
634 | patch in the permanent changelog. If the ``from`` line is missing, | |
635 | then the ``From:`` line from the email header will be used to determine | |
75f8426c PJ |
636 | the patch author in the changelog. |
637 | ||
638 | The explanation body will be committed to the permanent source | |
639 | changelog, so should make sense to a competent reader who has long | |
640 | since forgotten the immediate details of the discussion that might | |
2ae19aca TT |
641 | have led to this patch. Including symptoms of the failure which the |
642 | patch addresses (kernel log messages, oops messages, etc.) is | |
643 | especially useful for people who might be searching the commit logs | |
644 | looking for the applicable patch. If a patch fixes a compile failure, | |
645 | it may not be necessary to include _all_ of the compile failures; just | |
646 | enough that it is likely that someone searching for the patch can find | |
5903019b | 647 | it. As in the ``summary phrase``, it is important to be both succinct as |
2ae19aca | 648 | well as descriptive. |
75f8426c | 649 | |
5903019b | 650 | The ``---`` marker line serves the essential purpose of marking for patch |
75f8426c PJ |
651 | handling tools where the changelog message ends. |
652 | ||
5903019b | 653 | One good use for the additional comments after the ``---`` marker is for |
9b2c7677 MCC |
654 | a ``diffstat``, to show what files have changed, and the number of |
655 | inserted and deleted lines per file. A ``diffstat`` is especially useful | |
2ae19aca TT |
656 | on bigger patches. Other comments relevant only to the moment or the |
657 | maintainer, not suitable for the permanent changelog, should also go | |
5903019b | 658 | here. A good example of such comments might be ``patch changelogs`` |
2ae19aca TT |
659 | which describe what has changed between the v1 and v2 version of the |
660 | patch. | |
661 | ||
9b2c7677 MCC |
662 | If you are going to include a ``diffstat`` after the ``---`` marker, please |
663 | use ``diffstat`` options ``-p 1 -w 70`` so that filenames are listed from | |
2ae19aca | 664 | the top of the kernel source tree and don't use too much horizontal |
9b2c7677 | 665 | space (easily fit in 80 columns, maybe with some indentation). (``git`` |
8e3072a2 | 666 | generates appropriate diffstats by default.) |
75f8426c PJ |
667 | |
668 | See more details on the proper patch format in the following | |
669 | references. | |
670 | ||
5903019b MCC |
671 | .. _explicit_in_reply_to: |
672 | ||
ef227c39 DD |
673 | Explicit In-Reply-To headers |
674 | ---------------------------- | |
d7ac8d85 CM |
675 | |
676 | It can be helpful to manually add In-Reply-To: headers to a patch | |
5903019b | 677 | (e.g., when using ``git send-email``) to associate the patch with |
d7ac8d85 CM |
678 | previous relevant discussion, e.g. to link a bug fix to the email with |
679 | the bug report. However, for a multi-patch series, it is generally | |
680 | best to avoid using In-Reply-To: to link to older versions of the | |
681 | series. This way multiple versions of the patch don't become an | |
682 | unmanageable forest of references in email clients. If a link is | |
683 | helpful, you can use the https://lkml.kernel.org/ redirector (e.g., in | |
684 | the cover email text) to link to an earlier version of the patch series. | |
685 | ||
75f8426c | 686 | |
ef227c39 DD |
687 | Providing base tree information |
688 | ------------------------------- | |
e8686a40 KR |
689 | |
690 | When other developers receive your patches and start the review process, | |
691 | it is often useful for them to know where in the tree history they | |
692 | should place your work. This is particularly useful for automated CI | |
693 | processes that attempt to run a series of tests in order to establish | |
694 | the quality of your submission before the maintainer starts the review. | |
695 | ||
696 | If you are using ``git format-patch`` to generate your patches, you can | |
697 | automatically include the base tree information in your submission by | |
698 | using the ``--base`` flag. The easiest and most convenient way to use | |
699 | this option is with topical branches:: | |
700 | ||
701 | $ git checkout -t -b my-topical-branch master | |
702 | Branch 'my-topical-branch' set up to track local branch 'master'. | |
703 | Switched to a new branch 'my-topical-branch' | |
704 | ||
705 | [perform your edits and commits] | |
706 | ||
707 | $ git format-patch --base=auto --cover-letter -o outgoing/ master | |
708 | outgoing/0000-cover-letter.patch | |
709 | outgoing/0001-First-Commit.patch | |
710 | outgoing/... | |
711 | ||
712 | When you open ``outgoing/0000-cover-letter.patch`` for editing, you will | |
713 | notice that it will have the ``base-commit:`` trailer at the very | |
714 | bottom, which provides the reviewer and the CI tools enough information | |
715 | to properly perform ``git am`` without worrying about conflicts:: | |
716 | ||
717 | $ git checkout -b patch-review [base-commit-id] | |
718 | Switched to a new branch 'patch-review' | |
719 | $ git am patches.mbox | |
720 | Applying: First Commit | |
721 | Applying: ... | |
722 | ||
723 | Please see ``man git-format-patch`` for more information about this | |
724 | option. | |
725 | ||
726 | .. note:: | |
727 | ||
728 | The ``--base`` feature was introduced in git version 2.9.0. | |
729 | ||
730 | If you are not using git to format your patches, you can still include | |
731 | the same ``base-commit`` trailer to indicate the commit hash of the tree | |
732 | on which your work is based. You should add it either in the cover | |
733 | letter or in the first patch of the series and it should be placed | |
734 | either below the ``---`` line or at the very bottom of all other | |
735 | content, right before your email signature. | |
736 | ||
737 | ||
89edeedd JC |
738 | References |
739 | ---------- | |
5b0ed2c6 XVP |
740 | |
741 | Andrew Morton, "The perfect patch" (tpp). | |
e7b4311e | 742 | <https://www.ozlabs.org/~akpm/stuff/tpp.txt> |
5b0ed2c6 | 743 | |
8e9cb8fd | 744 | Jeff Garzik, "Linux kernel patch submission format". |
5aff7c46 | 745 | <https://web.archive.org/web/20180829112450/http://linux.yyz.us/patch-format.html> |
5b0ed2c6 | 746 | |
8e9cb8fd | 747 | Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer". |
f5039935 | 748 | <http://www.kroah.com/log/linux/maintainer.html> |
9b2c7677 | 749 | |
f5039935 | 750 | <http://www.kroah.com/log/linux/maintainer-02.html> |
9b2c7677 | 751 | |
f5039935 | 752 | <http://www.kroah.com/log/linux/maintainer-03.html> |
9b2c7677 | 753 | |
f5039935 | 754 | <http://www.kroah.com/log/linux/maintainer-04.html> |
9b2c7677 | 755 | |
f5039935 | 756 | <http://www.kroah.com/log/linux/maintainer-05.html> |
9b2c7677 | 757 | |
7e0dae61 | 758 | <http://www.kroah.com/log/linux/maintainer-06.html> |
5b0ed2c6 | 759 | |
bc7455fa | 760 | NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people! |
37c703f4 | 761 | <https://lkml.org/lkml/2005/7/11/336> |
5b0ed2c6 | 762 | |
8c27ceff MCC |
763 | Kernel Documentation/process/coding-style.rst: |
764 | :ref:`Documentation/process/coding-style.rst <codingstyle>` | |
5b0ed2c6 | 765 | |
8e9cb8fd | 766 | Linus Torvalds's mail on the canonical patch format: |
5b0ed2c6 | 767 | <http://lkml.org/lkml/2005/4/7/183> |
9536727e AK |
768 | |
769 | Andi Kleen, "On submitting kernel patches" | |
25985edc | 770 | Some strategies to get difficult or controversial changes in. |
9b2c7677 | 771 | |
9536727e | 772 | http://halobates.de/on-submitting-patches.pdf |