1 .. _submittingpatches: 1 .. _submittingpatches:
2 2
3 Submitting patches: the essential guide to get 3 Submitting patches: the essential guide to getting your code into the kernel
4 ============================================== 4 ============================================================================
5 5
6 For a person or company who wishes to submit a 6 For a person or company who wishes to submit a change to the Linux
7 kernel, the process can sometimes be daunting 7 kernel, the process can sometimes be daunting if you're not familiar
8 with "the system." This text is a collection 8 with "the system." This text is a collection of suggestions which
9 can greatly increase the chances of your chang 9 can greatly increase the chances of your change being accepted.
10 10
11 This document contains a large number of sugge 11 This document contains a large number of suggestions in a relatively terse
12 format. For detailed information on how the k 12 format. For detailed information on how the kernel development process
13 works, see Documentation/process/development-p 13 works, see Documentation/process/development-process.rst. Also, read
14 Documentation/process/submit-checklist.rst 14 Documentation/process/submit-checklist.rst
15 for a list of items to check before submitting 15 for a list of items to check before submitting code.
16 For device tree binding patches, read 16 For device tree binding patches, read
17 Documentation/devicetree/bindings/submitting-p 17 Documentation/devicetree/bindings/submitting-patches.rst.
18 18
19 This documentation assumes that you're using ` 19 This documentation assumes that you're using ``git`` to prepare your patches.
20 If you're unfamiliar with ``git``, you would b 20 If you're unfamiliar with ``git``, you would be well-advised to learn how to
21 use it, it will make your life as a kernel dev 21 use it, it will make your life as a kernel developer and in general much
22 easier. 22 easier.
23 23
24 Some subsystems and maintainer trees have addi 24 Some subsystems and maintainer trees have additional information about
25 their workflow and expectations, see 25 their workflow and expectations, see
26 :ref:`Documentation/process/maintainer-handboo 26 :ref:`Documentation/process/maintainer-handbooks.rst <maintainer_handbooks_main>`.
27 27
28 Obtain a current source tree 28 Obtain a current source tree
29 ---------------------------- 29 ----------------------------
30 30
31 If you do not have a repository with the curre 31 If you do not have a repository with the current kernel source handy, use
32 ``git`` to obtain one. You'll want to start w 32 ``git`` to obtain one. You'll want to start with the mainline repository,
33 which can be grabbed with:: 33 which can be grabbed with::
34 34
35 git clone git://git.kernel.org/pub/scm/linux 35 git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
36 36
37 Note, however, that you may not want to develo 37 Note, however, that you may not want to develop against the mainline tree
38 directly. Most subsystem maintainers run thei 38 directly. Most subsystem maintainers run their own trees and want to see
39 patches prepared against those trees. See the 39 patches prepared against those trees. See the **T:** entry for the subsystem
40 in the MAINTAINERS file to find that tree, or 40 in the MAINTAINERS file to find that tree, or simply ask the maintainer if
41 the tree is not listed there. 41 the tree is not listed there.
42 42
43 .. _describe_changes: 43 .. _describe_changes:
44 44
45 Describe your changes 45 Describe your changes
46 --------------------- 46 ---------------------
47 47
48 Describe your problem. Whether your patch is 48 Describe your problem. Whether your patch is a one-line bug fix or
49 5000 lines of a new feature, there must be an 49 5000 lines of a new feature, there must be an underlying problem that
50 motivated you to do this work. Convince the r 50 motivated you to do this work. Convince the reviewer that there is a
51 problem worth fixing and that it makes sense f 51 problem worth fixing and that it makes sense for them to read past the
52 first paragraph. 52 first paragraph.
53 53
54 Describe user-visible impact. Straight up cra 54 Describe user-visible impact. Straight up crashes and lockups are
55 pretty convincing, but not all bugs are that b 55 pretty convincing, but not all bugs are that blatant. Even if the
56 problem was spotted during code review, descri 56 problem was spotted during code review, describe the impact you think
57 it can have on users. Keep in mind that the m 57 it can have on users. Keep in mind that the majority of Linux
58 installations run kernels from secondary stabl 58 installations run kernels from secondary stable trees or
59 vendor/product-specific trees that cherry-pick 59 vendor/product-specific trees that cherry-pick only specific patches
60 from upstream, so include anything that could 60 from upstream, so include anything that could help route your change
61 downstream: provoking circumstances, excerpts 61 downstream: provoking circumstances, excerpts from dmesg, crash
62 descriptions, performance regressions, latency 62 descriptions, performance regressions, latency spikes, lockups, etc.
63 63
64 Quantify optimizations and trade-offs. If you 64 Quantify optimizations and trade-offs. If you claim improvements in
65 performance, memory consumption, stack footpri 65 performance, memory consumption, stack footprint, or binary size,
66 include numbers that back them up. But also d 66 include numbers that back them up. But also describe non-obvious
67 costs. Optimizations usually aren't free but 67 costs. Optimizations usually aren't free but trade-offs between CPU,
68 memory, and readability; or, when it comes to 68 memory, and readability; or, when it comes to heuristics, between
69 different workloads. Describe the expected do 69 different workloads. Describe the expected downsides of your
70 optimization so that the reviewer can weigh co 70 optimization so that the reviewer can weigh costs against benefits.
71 71
72 Once the problem is established, describe what 72 Once the problem is established, describe what you are actually doing
73 about it in technical detail. It's important 73 about it in technical detail. It's important to describe the change
74 in plain English for the reviewer to verify th 74 in plain English for the reviewer to verify that the code is behaving
75 as you intend it to. 75 as you intend it to.
76 76
77 The maintainer will thank you if you write you 77 The maintainer will thank you if you write your patch description in a
78 form which can be easily pulled into Linux's s 78 form which can be easily pulled into Linux's source code management
79 system, ``git``, as a "commit log". See :ref: 79 system, ``git``, as a "commit log". See :ref:`the_canonical_patch_format`.
80 80
81 Solve only one problem per patch. If your des 81 Solve only one problem per patch. If your description starts to get
82 long, that's a sign that you probably need to 82 long, that's a sign that you probably need to split up your patch.
83 See :ref:`split_changes`. 83 See :ref:`split_changes`.
84 84
85 When you submit or resubmit a patch or patch s 85 When you submit or resubmit a patch or patch series, include the
86 complete patch description and justification f 86 complete patch description and justification for it. Don't just
87 say that this is version N of the patch (serie 87 say that this is version N of the patch (series). Don't expect the
88 subsystem maintainer to refer back to earlier 88 subsystem maintainer to refer back to earlier patch versions or referenced
89 URLs to find the patch description and put tha 89 URLs to find the patch description and put that into the patch.
90 I.e., the patch (series) and its description s 90 I.e., the patch (series) and its description should be self-contained.
91 This benefits both the maintainers and reviewe 91 This benefits both the maintainers and reviewers. Some reviewers
92 probably didn't even receive earlier versions 92 probably didn't even receive earlier versions of the patch.
93 93
94 Describe your changes in imperative mood, e.g. 94 Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
95 instead of "[This patch] makes xyzzy do frotz" 95 instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
96 to do frotz", as if you are giving orders to t 96 to do frotz", as if you are giving orders to the codebase to change
97 its behaviour. 97 its behaviour.
98 98
99 If you want to refer to a specific commit, don 99 If you want to refer to a specific commit, don't just refer to the
100 SHA-1 ID of the commit. Please also include th 100 SHA-1 ID of the commit. Please also include the oneline summary of
101 the commit, to make it easier for reviewers to 101 the commit, to make it easier for reviewers to know what it is about.
102 Example:: 102 Example::
103 103
104 Commit e21d2170f36602ae2708 ("video: r 104 Commit e21d2170f36602ae2708 ("video: remove unnecessary
105 platform_set_drvdata()") removed the u 105 platform_set_drvdata()") removed the unnecessary
106 platform_set_drvdata(), but left the v 106 platform_set_drvdata(), but left the variable "dev" unused,
107 delete it. 107 delete it.
108 108
109 You should also be sure to use at least the fi 109 You should also be sure to use at least the first twelve characters of the
110 SHA-1 ID. The kernel repository holds a *lot* 110 SHA-1 ID. The kernel repository holds a *lot* of objects, making
111 collisions with shorter IDs a real possibility 111 collisions with shorter IDs a real possibility. Bear in mind that, even if
112 there is no collision with your six-character 112 there is no collision with your six-character ID now, that condition may
113 change five years from now. 113 change five years from now.
114 114
115 If related discussions or any other background 115 If related discussions or any other background information behind the change
116 can be found on the web, add 'Link:' tags poin 116 can be found on the web, add 'Link:' tags pointing to it. If the patch is a
117 result of some earlier mailing list discussion 117 result of some earlier mailing list discussions or something documented on the
118 web, point to it. 118 web, point to it.
119 119
120 When linking to mailing list archives, prefera 120 When linking to mailing list archives, preferably use the lore.kernel.org
121 message archiver service. To create the link U 121 message archiver service. To create the link URL, use the contents of the
122 ``Message-ID`` header of the message without t 122 ``Message-ID`` header of the message without the surrounding angle brackets.
123 For example:: 123 For example::
124 124
125 Link: https://lore.kernel.org/30th.anniver 125 Link: https://lore.kernel.org/30th.anniversary.repost@klaava.Helsinki.FI
126 126
127 Please check the link to make sure that it is 127 Please check the link to make sure that it is actually working and points
128 to the relevant message. 128 to the relevant message.
129 129
130 However, try to make your explanation understa 130 However, try to make your explanation understandable without external
131 resources. In addition to giving a URL to a ma 131 resources. In addition to giving a URL to a mailing list archive or bug,
132 summarize the relevant points of the discussio 132 summarize the relevant points of the discussion that led to the
133 patch as submitted. 133 patch as submitted.
134 134
135 In case your patch fixes a bug, use the 'Close 135 In case your patch fixes a bug, use the 'Closes:' tag with a URL referencing
136 the report in the mailing list archives or a p 136 the report in the mailing list archives or a public bug tracker. For example::
137 137
138 Closes: https://example.com/issues/123 138 Closes: https://example.com/issues/1234
139 139
140 Some bug trackers have the ability to close is 140 Some bug trackers have the ability to close issues automatically when a
141 commit with such a tag is applied. Some bots m 141 commit with such a tag is applied. Some bots monitoring mailing lists can
142 also track such tags and take certain actions. 142 also track such tags and take certain actions. Private bug trackers and
143 invalid URLs are forbidden. 143 invalid URLs are forbidden.
144 144
145 If your patch fixes a bug in a specific commit 145 If your patch fixes a bug in a specific commit, e.g. you found an issue using
146 ``git bisect``, please use the 'Fixes:' tag wi 146 ``git bisect``, please use the 'Fixes:' tag with the first 12 characters of
147 the SHA-1 ID, and the one line summary. Do no 147 the SHA-1 ID, and the one line summary. Do not split the tag across multiple
148 lines, tags are exempt from the "wrap at 75 co 148 lines, tags are exempt from the "wrap at 75 columns" rule in order to simplify
149 parsing scripts. For example:: 149 parsing scripts. For example::
150 150
151 Fixes: 54a4f0239f2e ("KVM: MMU: make k 151 Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed")
152 152
153 The following ``git config`` settings can be u 153 The following ``git config`` settings can be used to add a pretty format for
154 outputting the above style in the ``git log`` 154 outputting the above style in the ``git log`` or ``git show`` commands::
155 155
156 [core] 156 [core]
157 abbrev = 12 157 abbrev = 12
158 [pretty] 158 [pretty]
159 fixes = Fixes: %h (\"%s\") 159 fixes = Fixes: %h (\"%s\")
160 160
161 An example call:: 161 An example call::
162 162
163 $ git log -1 --pretty=fixes 54a4f0239f 163 $ git log -1 --pretty=fixes 54a4f0239f2e
164 Fixes: 54a4f0239f2e ("KVM: MMU: make k 164 Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed")
165 165
166 .. _split_changes: 166 .. _split_changes:
167 167
168 Separate your changes 168 Separate your changes
169 --------------------- 169 ---------------------
170 170
171 Separate each **logical change** into a separa 171 Separate each **logical change** into a separate patch.
172 172
173 For example, if your changes include both bug 173 For example, if your changes include both bug fixes and performance
174 enhancements for a single driver, separate tho 174 enhancements for a single driver, separate those changes into two
175 or more patches. If your changes include an A 175 or more patches. If your changes include an API update, and a new
176 driver which uses that new API, separate those 176 driver which uses that new API, separate those into two patches.
177 177
178 On the other hand, if you make a single change 178 On the other hand, if you make a single change to numerous files,
179 group those changes into a single patch. Thus 179 group those changes into a single patch. Thus a single logical change
180 is contained within a single patch. 180 is contained within a single patch.
181 181
182 The point to remember is that each patch shoul 182 The point to remember is that each patch should make an easily understood
183 change that can be verified by reviewers. Eac 183 change that can be verified by reviewers. Each patch should be justifiable
184 on its own merits. 184 on its own merits.
185 185
186 If one patch depends on another patch in order 186 If one patch depends on another patch in order for a change to be
187 complete, that is OK. Simply note **"this pat 187 complete, that is OK. Simply note **"this patch depends on patch X"**
188 in your patch description. 188 in your patch description.
189 189
190 When dividing your change into a series of pat 190 When dividing your change into a series of patches, take special care to
191 ensure that the kernel builds and runs properl 191 ensure that the kernel builds and runs properly after each patch in the
192 series. Developers using ``git bisect`` to tr 192 series. Developers using ``git bisect`` to track down a problem can end up
193 splitting your patch series at any point; they 193 splitting your patch series at any point; they will not thank you if you
194 introduce bugs in the middle. 194 introduce bugs in the middle.
195 195
196 If you cannot condense your patch set into a s 196 If you cannot condense your patch set into a smaller set of patches,
197 then only post say 15 or so at a time and wait 197 then only post say 15 or so at a time and wait for review and integration.
198 198
199 199
200 200
201 Style-check your changes 201 Style-check your changes
202 ------------------------ 202 ------------------------
203 203
204 Check your patch for basic style violations, d 204 Check your patch for basic style violations, details of which can be
205 found in Documentation/process/coding-style.rs 205 found in Documentation/process/coding-style.rst.
206 Failure to do so simply wastes 206 Failure to do so simply wastes
207 the reviewers time and will get your patch rej 207 the reviewers time and will get your patch rejected, probably
208 without even being read. 208 without even being read.
209 209
210 One significant exception is when moving code 210 One significant exception is when moving code from one file to
211 another -- in this case you should not modify 211 another -- in this case you should not modify the moved code at all in
212 the same patch which moves it. This clearly d 212 the same patch which moves it. This clearly delineates the act of
213 moving the code and your changes. This greatl 213 moving the code and your changes. This greatly aids review of the
214 actual differences and allows tools to better 214 actual differences and allows tools to better track the history of
215 the code itself. 215 the code itself.
216 216
217 Check your patches with the patch style checke 217 Check your patches with the patch style checker prior to submission
218 (scripts/checkpatch.pl). Note, though, that t 218 (scripts/checkpatch.pl). Note, though, that the style checker should be
219 viewed as a guide, not as a replacement for hu 219 viewed as a guide, not as a replacement for human judgment. If your code
220 looks better with a violation then its probabl 220 looks better with a violation then its probably best left alone.
221 221
222 The checker reports at three levels: 222 The checker reports at three levels:
223 - ERROR: things that are very likely to be wr 223 - ERROR: things that are very likely to be wrong
224 - WARNING: things requiring careful review 224 - WARNING: things requiring careful review
225 - CHECK: things requiring thought 225 - CHECK: things requiring thought
226 226
227 You should be able to justify all violations t 227 You should be able to justify all violations that remain in your
228 patch. 228 patch.
229 229
230 230
231 Select the recipients for your patch 231 Select the recipients for your patch
232 ------------------------------------ 232 ------------------------------------
233 233
234 You should always copy the appropriate subsyst 234 You should always copy the appropriate subsystem maintainer(s) and list(s) on
235 any patch to code that they maintain; look thr 235 any patch to code that they maintain; look through the MAINTAINERS file and the
236 source code revision history to see who those 236 source code revision history to see who those maintainers are. The script
237 scripts/get_maintainer.pl can be very useful a 237 scripts/get_maintainer.pl can be very useful at this step (pass paths to your
238 patches as arguments to scripts/get_maintainer 238 patches as arguments to scripts/get_maintainer.pl). If you cannot find a
239 maintainer for the subsystem you are working o 239 maintainer for the subsystem you are working on, Andrew Morton
240 (akpm@linux-foundation.org) serves as a mainta 240 (akpm@linux-foundation.org) serves as a maintainer of last resort.
241 241
242 linux-kernel@vger.kernel.org should be used by 242 linux-kernel@vger.kernel.org should be used by default for all patches, but the
243 volume on that list has caused a number of dev 243 volume on that list has caused a number of developers to tune it out. Please
244 do not spam unrelated lists and unrelated peop 244 do not spam unrelated lists and unrelated people, though.
245 245
246 Many kernel-related lists are hosted at kernel 246 Many kernel-related lists are hosted at kernel.org; you can find a list
247 of them at https://subspace.kernel.org. There 247 of them at https://subspace.kernel.org. There are kernel-related lists
248 hosted elsewhere as well, though. 248 hosted elsewhere as well, though.
249 249
250 Linus Torvalds is the final arbiter of all cha 250 Linus Torvalds is the final arbiter of all changes accepted into the
251 Linux kernel. His e-mail address is <torvalds@ 251 Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
252 He gets a lot of e-mail, and, at this point, v 252 He gets a lot of e-mail, and, at this point, very few patches go through
253 Linus directly, so typically you should do you 253 Linus directly, so typically you should do your best to -avoid-
254 sending him e-mail. 254 sending him e-mail.
255 255
256 If you have a patch that fixes an exploitable 256 If you have a patch that fixes an exploitable security bug, send that patch
257 to security@kernel.org. For severe bugs, a sh 257 to security@kernel.org. For severe bugs, a short embargo may be considered
258 to allow distributors to get the patch out to 258 to allow distributors to get the patch out to users; in such cases,
259 obviously, the patch should not be sent to any 259 obviously, the patch should not be sent to any public lists. See also
260 Documentation/process/security-bugs.rst. 260 Documentation/process/security-bugs.rst.
261 261
262 Patches that fix a severe bug in a released ke 262 Patches that fix a severe bug in a released kernel should be directed
263 toward the stable maintainers by putting a lin 263 toward the stable maintainers by putting a line like this::
264 264
265 Cc: stable@vger.kernel.org 265 Cc: stable@vger.kernel.org
266 266
267 into the sign-off area of your patch (note, NO 267 into the sign-off area of your patch (note, NOT an email recipient). You
268 should also read Documentation/process/stable- 268 should also read Documentation/process/stable-kernel-rules.rst
269 in addition to this document. 269 in addition to this document.
270 270
271 If changes affect userland-kernel interfaces, 271 If changes affect userland-kernel interfaces, please send the MAN-PAGES
272 maintainer (as listed in the MAINTAINERS file) 272 maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at
273 least a notification of the change, so that so 273 least a notification of the change, so that some information makes its way
274 into the manual pages. User-space API changes 274 into the manual pages. User-space API changes should also be copied to
275 linux-api@vger.kernel.org. 275 linux-api@vger.kernel.org.
276 276
277 277
278 No MIME, no links, no compression, no attachme 278 No MIME, no links, no compression, no attachments. Just plain text
279 ---------------------------------------------- 279 -------------------------------------------------------------------
280 280
281 Linus and other kernel developers need to be a 281 Linus and other kernel developers need to be able to read and comment
282 on the changes you are submitting. It is impo 282 on the changes you are submitting. It is important for a kernel
283 developer to be able to "quote" your changes, 283 developer to be able to "quote" your changes, using standard e-mail
284 tools, so that they may comment on specific po 284 tools, so that they may comment on specific portions of your code.
285 285
286 For this reason, all patches should be submitt 286 For this reason, all patches should be submitted by e-mail "inline". The
287 easiest way to do this is with ``git send-emai 287 easiest way to do this is with ``git send-email``, which is strongly
288 recommended. An interactive tutorial for ``gi 288 recommended. An interactive tutorial for ``git send-email`` is available at
289 https://git-send-email.io. 289 https://git-send-email.io.
290 290
291 If you choose not to use ``git send-email``: 291 If you choose not to use ``git send-email``:
292 292
293 .. warning:: 293 .. warning::
294 294
295 Be wary of your editor's word-wrap corruptin 295 Be wary of your editor's word-wrap corrupting your patch,
296 if you choose to cut-n-paste your patch. 296 if you choose to cut-n-paste your patch.
297 297
298 Do not attach the patch as a MIME attachment, 298 Do not attach the patch as a MIME attachment, compressed or not.
299 Many popular e-mail applications will not alwa 299 Many popular e-mail applications will not always transmit a MIME
300 attachment as plain text, making it impossible 300 attachment as plain text, making it impossible to comment on your
301 code. A MIME attachment also takes Linus a bi 301 code. A MIME attachment also takes Linus a bit more time to process,
302 decreasing the likelihood of your MIME-attache 302 decreasing the likelihood of your MIME-attached change being accepted.
303 303
304 Exception: If your mailer is mangling patches 304 Exception: If your mailer is mangling patches then someone may ask
305 you to re-send them using MIME. 305 you to re-send them using MIME.
306 306
307 See Documentation/process/email-clients.rst fo 307 See Documentation/process/email-clients.rst for hints about configuring
308 your e-mail client so that it sends your patch 308 your e-mail client so that it sends your patches untouched.
309 309
310 Respond to review comments 310 Respond to review comments
311 -------------------------- 311 --------------------------
312 312
313 Your patch will almost certainly get comments 313 Your patch will almost certainly get comments from reviewers on ways in
314 which the patch can be improved, in the form o 314 which the patch can be improved, in the form of a reply to your email. You must
315 respond to those comments; ignoring reviewers 315 respond to those comments; ignoring reviewers is a good way to get ignored in
316 return. You can simply reply to their emails t 316 return. You can simply reply to their emails to answer their comments. Review
317 comments or questions that do not lead to a co 317 comments or questions that do not lead to a code change should almost certainly
318 bring about a comment or changelog entry so th 318 bring about a comment or changelog entry so that the next reviewer better
319 understands what is going on. 319 understands what is going on.
320 320
321 Be sure to tell the reviewers what changes you 321 Be sure to tell the reviewers what changes you are making and to thank them
322 for their time. Code review is a tiring and t 322 for their time. Code review is a tiring and time-consuming process, and
323 reviewers sometimes get grumpy. Even in that 323 reviewers sometimes get grumpy. Even in that case, though, respond
324 politely and address the problems they have po 324 politely and address the problems they have pointed out. When sending a next
325 version, add a ``patch changelog`` to the cove 325 version, add a ``patch changelog`` to the cover letter or to individual patches
326 explaining difference against previous submiss 326 explaining difference against previous submission (see
327 :ref:`the_canonical_patch_format`). 327 :ref:`the_canonical_patch_format`).
328 Notify people that commented on your patch abo 328 Notify people that commented on your patch about new versions by adding them to
329 the patches CC list. 329 the patches CC list.
330 330
331 See Documentation/process/email-clients.rst fo 331 See Documentation/process/email-clients.rst for recommendations on email
332 clients and mailing list etiquette. 332 clients and mailing list etiquette.
333 333
334 .. _interleaved_replies: 334 .. _interleaved_replies:
335 335
336 Use trimmed interleaved replies in email discu 336 Use trimmed interleaved replies in email discussions
337 ---------------------------------------------- 337 ----------------------------------------------------
338 Top-posting is strongly discouraged in Linux k 338 Top-posting is strongly discouraged in Linux kernel development
339 discussions. Interleaved (or "inline") replies 339 discussions. Interleaved (or "inline") replies make conversations much
340 easier to follow. For more details see: 340 easier to follow. For more details see:
341 https://en.wikipedia.org/wiki/Posting_style#In 341 https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
342 342
343 As is frequently quoted on the mailing list:: 343 As is frequently quoted on the mailing list::
344 344
345 A: http://en.wikipedia.org/wiki/Top_post 345 A: http://en.wikipedia.org/wiki/Top_post
346 Q: Were do I find info about this thing call 346 Q: Were do I find info about this thing called top-posting?
347 A: Because it messes up the order in which p 347 A: Because it messes up the order in which people normally read text.
348 Q: Why is top-posting such a bad thing? 348 Q: Why is top-posting such a bad thing?
349 A: Top-posting. 349 A: Top-posting.
350 Q: What is the most annoying thing in e-mail 350 Q: What is the most annoying thing in e-mail?
351 351
352 Similarly, please trim all unneeded quotations 352 Similarly, please trim all unneeded quotations that aren't relevant
353 to your reply. This makes responses easier to 353 to your reply. This makes responses easier to find, and saves time and
354 space. For more details see: http://daringfire 354 space. For more details see: http://daringfireball.net/2007/07/on_top ::
355 355
356 A: No. 356 A: No.
357 Q: Should I include quotations after my repl 357 Q: Should I include quotations after my reply?
358 358
359 .. _resend_reminders: 359 .. _resend_reminders:
360 360
361 Don't get discouraged - or impatient 361 Don't get discouraged - or impatient
362 ------------------------------------ 362 ------------------------------------
363 363
364 After you have submitted your change, be patie 364 After you have submitted your change, be patient and wait. Reviewers are
365 busy people and may not get to your patch righ 365 busy people and may not get to your patch right away.
366 366
367 Once upon a time, patches used to disappear in 367 Once upon a time, patches used to disappear into the void without comment,
368 but the development process works more smoothl 368 but the development process works more smoothly than that now. You should
369 receive comments within a few weeks (typically 369 receive comments within a few weeks (typically 2-3); if that does not
370 happen, make sure that you have sent your patc 370 happen, make sure that you have sent your patches to the right place.
371 Wait for a minimum of one week before resubmit 371 Wait for a minimum of one week before resubmitting or pinging reviewers
372 - possibly longer during busy times like merge 372 - possibly longer during busy times like merge windows.
373 373
374 It's also ok to resend the patch or the patch 374 It's also ok to resend the patch or the patch series after a couple of
375 weeks with the word "RESEND" added to the subj 375 weeks with the word "RESEND" added to the subject line::
376 376
377 [PATCH Vx RESEND] sub/sys: Condensed patch 377 [PATCH Vx RESEND] sub/sys: Condensed patch summary
378 378
379 Don't add "RESEND" when you are submitting a m 379 Don't add "RESEND" when you are submitting a modified version of your
380 patch or patch series - "RESEND" only applies 380 patch or patch series - "RESEND" only applies to resubmission of a
381 patch or patch series which have not been modi 381 patch or patch series which have not been modified in any way from the
382 previous submission. 382 previous submission.
383 383
384 384
385 Include PATCH in the subject 385 Include PATCH in the subject
386 ----------------------------- 386 -----------------------------
387 387
388 Due to high e-mail traffic to Linus, and to li 388 Due to high e-mail traffic to Linus, and to linux-kernel, it is common
389 convention to prefix your subject line with [P 389 convention to prefix your subject line with [PATCH]. This lets Linus
390 and other kernel developers more easily distin 390 and other kernel developers more easily distinguish patches from other
391 e-mail discussions. 391 e-mail discussions.
392 392
393 ``git send-email`` will do this for you automa 393 ``git send-email`` will do this for you automatically.
394 394
395 395
396 Sign your work - the Developer's Certificate o 396 Sign your work - the Developer's Certificate of Origin
397 ---------------------------------------------- 397 ------------------------------------------------------
398 398
399 To improve tracking of who did what, especiall 399 To improve tracking of who did what, especially with patches that can
400 percolate to their final resting place in the 400 percolate to their final resting place in the kernel through several
401 layers of maintainers, we've introduced a "sig 401 layers of maintainers, we've introduced a "sign-off" procedure on
402 patches that are being emailed around. 402 patches that are being emailed around.
403 403
404 The sign-off is a simple line at the end of th 404 The sign-off is a simple line at the end of the explanation for the
405 patch, which certifies that you wrote it or ot 405 patch, which certifies that you wrote it or otherwise have the right to
406 pass it on as an open-source patch. The rules 406 pass it on as an open-source patch. The rules are pretty simple: if you
407 can certify the below: 407 can certify the below:
408 408
409 Developer's Certificate of Origin 1.1 409 Developer's Certificate of Origin 1.1
410 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 410 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
411 411
412 By making a contribution to this project, I ce 412 By making a contribution to this project, I certify that:
413 413
414 (a) The contribution was created in wh 414 (a) The contribution was created in whole or in part by me and I
415 have the right to submit it under 415 have the right to submit it under the open source license
416 indicated in the file; or 416 indicated in the file; or
417 417
418 (b) The contribution is based upon pre 418 (b) The contribution is based upon previous work that, to the best
419 of my knowledge, is covered under 419 of my knowledge, is covered under an appropriate open source
420 license and I have the right under 420 license and I have the right under that license to submit that
421 work with modifications, whether c 421 work with modifications, whether created in whole or in part
422 by me, under the same open source 422 by me, under the same open source license (unless I am
423 permitted to submit under a differ 423 permitted to submit under a different license), as indicated
424 in the file; or 424 in the file; or
425 425
426 (c) The contribution was provided dire 426 (c) The contribution was provided directly to me by some other
427 person who certified (a), (b) or ( 427 person who certified (a), (b) or (c) and I have not modified
428 it. 428 it.
429 429
430 (d) I understand and agree that this p 430 (d) I understand and agree that this project and the contribution
431 are public and that a record of th 431 are public and that a record of the contribution (including all
432 personal information I submit with 432 personal information I submit with it, including my sign-off) is
433 maintained indefinitely and may be 433 maintained indefinitely and may be redistributed consistent with
434 this project or the open source li 434 this project or the open source license(s) involved.
435 435
436 then you just add a line saying:: 436 then you just add a line saying::
437 437
438 Signed-off-by: Random J Developer <rand 438 Signed-off-by: Random J Developer <random@developer.example.org>
439 439
440 using a known identity (sorry, no anonymous co 440 using a known identity (sorry, no anonymous contributions.)
441 This will be done for you automatically if you 441 This will be done for you automatically if you use ``git commit -s``.
442 Reverts should also include "Signed-off-by". ` 442 Reverts should also include "Signed-off-by". ``git revert -s`` does that
443 for you. 443 for you.
444 444
445 Some people also put extra tags at the end. T 445 Some people also put extra tags at the end. They'll just be ignored for
446 now, but you can do this to mark internal comp 446 now, but you can do this to mark internal company procedures or just
447 point out some special detail about the sign-o 447 point out some special detail about the sign-off.
448 448
449 Any further SoBs (Signed-off-by:'s) following 449 Any further SoBs (Signed-off-by:'s) following the author's SoB are from
450 people handling and transporting the patch, bu 450 people handling and transporting the patch, but were not involved in its
451 development. SoB chains should reflect the **r 451 development. SoB chains should reflect the **real** route a patch took
452 as it was propagated to the maintainers and ul 452 as it was propagated to the maintainers and ultimately to Linus, with
453 the first SoB entry signalling primary authors 453 the first SoB entry signalling primary authorship of a single author.
454 454
455 455
456 When to use Acked-by:, Cc:, and Co-developed-b 456 When to use Acked-by:, Cc:, and Co-developed-by:
457 ---------------------------------------------- 457 ------------------------------------------------
458 458
459 The Signed-off-by: tag indicates that the sign 459 The Signed-off-by: tag indicates that the signer was involved in the
460 development of the patch, or that he/she was i 460 development of the patch, or that he/she was in the patch's delivery path.
461 461
462 If a person was not directly involved in the p 462 If a person was not directly involved in the preparation or handling of a
463 patch but wishes to signify and record their a 463 patch but wishes to signify and record their approval of it then they can
464 ask to have an Acked-by: line added to the pat 464 ask to have an Acked-by: line added to the patch's changelog.
465 465
466 Acked-by: is often used by the maintainer of t 466 Acked-by: is often used by the maintainer of the affected code when that
467 maintainer neither contributed to nor forwarde 467 maintainer neither contributed to nor forwarded the patch.
468 468
469 Acked-by: is not as formal as Signed-off-by:. 469 Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
470 has at least reviewed the patch and has indica 470 has at least reviewed the patch and has indicated acceptance. Hence patch
471 mergers will sometimes manually convert an ack 471 mergers will sometimes manually convert an acker's "yep, looks good to me"
472 into an Acked-by: (but note that it is usually 472 into an Acked-by: (but note that it is usually better to ask for an
473 explicit ack). 473 explicit ack).
474 474
475 Acked-by: does not necessarily indicate acknow 475 Acked-by: does not necessarily indicate acknowledgement of the entire patch.
476 For example, if a patch affects multiple subsy 476 For example, if a patch affects multiple subsystems and has an Acked-by: from
477 one subsystem maintainer then this usually ind 477 one subsystem maintainer then this usually indicates acknowledgement of just
478 the part which affects that maintainer's code. 478 the part which affects that maintainer's code. Judgement should be used here.
479 When in doubt people should refer to the origi 479 When in doubt people should refer to the original discussion in the mailing
480 list archives. 480 list archives.
481 481
482 If a person has had the opportunity to comment 482 If a person has had the opportunity to comment on a patch, but has not
483 provided such comments, you may optionally add 483 provided such comments, you may optionally add a ``Cc:`` tag to the patch.
484 This is the only tag which might be added with 484 This is the only tag which might be added without an explicit action by the
485 person it names - but it should indicate that 485 person it names - but it should indicate that this person was copied on the
486 patch. This tag documents that potentially in 486 patch. This tag documents that potentially interested parties
487 have been included in the discussion. 487 have been included in the discussion.
488 488
489 Co-developed-by: states that the patch was co- 489 Co-developed-by: states that the patch was co-created by multiple developers;
490 it is used to give attribution to co-authors ( 490 it is used to give attribution to co-authors (in addition to the author
491 attributed by the From: tag) when several peop 491 attributed by the From: tag) when several people work on a single patch. Since
492 Co-developed-by: denotes authorship, every Co- 492 Co-developed-by: denotes authorship, every Co-developed-by: must be immediately
493 followed by a Signed-off-by: of the associated 493 followed by a Signed-off-by: of the associated co-author. Standard sign-off
494 procedure applies, i.e. the ordering of Signed 494 procedure applies, i.e. the ordering of Signed-off-by: tags should reflect the
495 chronological history of the patch insofar as 495 chronological history of the patch insofar as possible, regardless of whether
496 the author is attributed via From: or Co-devel 496 the author is attributed via From: or Co-developed-by:. Notably, the last
497 Signed-off-by: must always be that of the deve 497 Signed-off-by: must always be that of the developer submitting the patch.
498 498
499 Note, the From: tag is optional when the From: 499 Note, the From: tag is optional when the From: author is also the person (and
500 email) listed in the From: line of the email h 500 email) listed in the From: line of the email header.
501 501
502 Example of a patch submitted by the From: auth 502 Example of a patch submitted by the From: author::
503 503
504 <changelog> 504 <changelog>
505 505
506 Co-developed-by: First Co-Author <first 506 Co-developed-by: First Co-Author <first@coauthor.example.org>
507 Signed-off-by: First Co-Author <first@c 507 Signed-off-by: First Co-Author <first@coauthor.example.org>
508 Co-developed-by: Second Co-Author <seco 508 Co-developed-by: Second Co-Author <second@coauthor.example.org>
509 Signed-off-by: Second Co-Author <second 509 Signed-off-by: Second Co-Author <second@coauthor.example.org>
510 Signed-off-by: From Author <from@author 510 Signed-off-by: From Author <from@author.example.org>
511 511
512 Example of a patch submitted by a Co-developed 512 Example of a patch submitted by a Co-developed-by: author::
513 513
514 From: From Author <from@author.example. 514 From: From Author <from@author.example.org>
515 515
516 <changelog> 516 <changelog>
517 517
518 Co-developed-by: Random Co-Author <rand 518 Co-developed-by: Random Co-Author <random@coauthor.example.org>
519 Signed-off-by: Random Co-Author <random 519 Signed-off-by: Random Co-Author <random@coauthor.example.org>
520 Signed-off-by: From Author <from@author 520 Signed-off-by: From Author <from@author.example.org>
521 Co-developed-by: Submitting Co-Author < 521 Co-developed-by: Submitting Co-Author <sub@coauthor.example.org>
522 Signed-off-by: Submitting Co-Author <su 522 Signed-off-by: Submitting Co-Author <sub@coauthor.example.org>
523 523
524 524
525 Using Reported-by:, Tested-by:, Reviewed-by:, 525 Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
526 ---------------------------------------------- 526 ----------------------------------------------------------------------
527 527
528 The Reported-by tag gives credit to people who 528 The Reported-by tag gives credit to people who find bugs and report them and it
529 hopefully inspires them to help us again in th 529 hopefully inspires them to help us again in the future. The tag is intended for
530 bugs; please do not use it to credit feature r 530 bugs; please do not use it to credit feature requests. The tag should be
531 followed by a Closes: tag pointing to the repo 531 followed by a Closes: tag pointing to the report, unless the report is not
532 available on the web. The Link: tag can be use 532 available on the web. The Link: tag can be used instead of Closes: if the patch
533 fixes a part of the issue(s) being reported. P 533 fixes a part of the issue(s) being reported. Please note that if the bug was
534 reported in private, then ask for permission f 534 reported in private, then ask for permission first before using the Reported-by
535 tag. 535 tag.
536 536
537 A Tested-by: tag indicates that the patch has 537 A Tested-by: tag indicates that the patch has been successfully tested (in
538 some environment) by the person named. This t 538 some environment) by the person named. This tag informs maintainers that
539 some testing has been performed, provides a me 539 some testing has been performed, provides a means to locate testers for
540 future patches, and ensures credit for the tes 540 future patches, and ensures credit for the testers.
541 541
542 Reviewed-by:, instead, indicates that the patc 542 Reviewed-by:, instead, indicates that the patch has been reviewed and found
543 acceptable according to the Reviewer's Stateme 543 acceptable according to the Reviewer's Statement:
544 544
545 Reviewer's statement of oversight 545 Reviewer's statement of oversight
546 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 546 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
547 547
548 By offering my Reviewed-by: tag, I state that: 548 By offering my Reviewed-by: tag, I state that:
549 549
550 (a) I have carried out a technical re 550 (a) I have carried out a technical review of this patch to
551 evaluate its appropriateness and 551 evaluate its appropriateness and readiness for inclusion into
552 the mainline kernel. 552 the mainline kernel.
553 553
554 (b) Any problems, concerns, or questi 554 (b) Any problems, concerns, or questions relating to the patch
555 have been communicated back to th 555 have been communicated back to the submitter. I am satisfied
556 with the submitter's response to 556 with the submitter's response to my comments.
557 557
558 (c) While there may be things that co 558 (c) While there may be things that could be improved with this
559 submission, I believe that it is, 559 submission, I believe that it is, at this time, (1) a
560 worthwhile modification to the ke 560 worthwhile modification to the kernel, and (2) free of known
561 issues which would argue against 561 issues which would argue against its inclusion.
562 562
563 (d) While I have reviewed the patch a 563 (d) While I have reviewed the patch and believe it to be sound, I
564 do not (unless explicitly stated 564 do not (unless explicitly stated elsewhere) make any
565 warranties or guarantees that it 565 warranties or guarantees that it will achieve its stated
566 purpose or function properly in a 566 purpose or function properly in any given situation.
567 567
568 A Reviewed-by tag is a statement of opinion th 568 A Reviewed-by tag is a statement of opinion that the patch is an
569 appropriate modification of the kernel without 569 appropriate modification of the kernel without any remaining serious
570 technical issues. Any interested reviewer (wh 570 technical issues. Any interested reviewer (who has done the work) can
571 offer a Reviewed-by tag for a patch. This tag 571 offer a Reviewed-by tag for a patch. This tag serves to give credit to
572 reviewers and to inform maintainers of the deg 572 reviewers and to inform maintainers of the degree of review which has been
573 done on the patch. Reviewed-by: tags, when su 573 done on the patch. Reviewed-by: tags, when supplied by reviewers known to
574 understand the subject area and to perform tho 574 understand the subject area and to perform thorough reviews, will normally
575 increase the likelihood of your patch getting 575 increase the likelihood of your patch getting into the kernel.
576 576
577 Both Tested-by and Reviewed-by tags, once rece 577 Both Tested-by and Reviewed-by tags, once received on mailing list from tester
578 or reviewer, should be added by author to the 578 or reviewer, should be added by author to the applicable patches when sending
579 next versions. However if the patch has chang 579 next versions. However if the patch has changed substantially in following
580 version, these tags might not be applicable an 580 version, these tags might not be applicable anymore and thus should be removed.
581 Usually removal of someone's Tested-by or Revi 581 Usually removal of someone's Tested-by or Reviewed-by tags should be mentioned
582 in the patch changelog (after the '---' separa 582 in the patch changelog (after the '---' separator).
583 583
584 A Suggested-by: tag indicates that the patch i 584 A Suggested-by: tag indicates that the patch idea is suggested by the person
585 named and ensures credit to the person for the 585 named and ensures credit to the person for the idea. Please note that this
586 tag should not be added without the reporter's 586 tag should not be added without the reporter's permission, especially if the
587 idea was not posted in a public forum. That sa 587 idea was not posted in a public forum. That said, if we diligently credit our
588 idea reporters, they will, hopefully, be inspi 588 idea reporters, they will, hopefully, be inspired to help us again in the
589 future. 589 future.
590 590
591 A Fixes: tag indicates that the patch fixes an 591 A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
592 is used to make it easy to determine where a b 592 is used to make it easy to determine where a bug originated, which can help
593 review a bug fix. This tag also assists the st 593 review a bug fix. This tag also assists the stable kernel team in determining
594 which stable kernel versions should receive yo 594 which stable kernel versions should receive your fix. This is the preferred
595 method for indicating a bug fixed by the patch 595 method for indicating a bug fixed by the patch. See :ref:`describe_changes`
596 for more details. 596 for more details.
597 597
598 Note: Attaching a Fixes: tag does not subvert 598 Note: Attaching a Fixes: tag does not subvert the stable kernel rules
599 process nor the requirement to Cc: stable@vger 599 process nor the requirement to Cc: stable@vger.kernel.org on all stable
600 patch candidates. For more information, please 600 patch candidates. For more information, please read
601 Documentation/process/stable-kernel-rules.rst. 601 Documentation/process/stable-kernel-rules.rst.
602 602
603 .. _the_canonical_patch_format: 603 .. _the_canonical_patch_format:
604 604
605 The canonical patch format 605 The canonical patch format
606 -------------------------- 606 --------------------------
607 607
608 This section describes how the patch itself sh 608 This section describes how the patch itself should be formatted. Note
609 that, if you have your patches stored in a ``g 609 that, if you have your patches stored in a ``git`` repository, proper patch
610 formatting can be had with ``git format-patch` 610 formatting can be had with ``git format-patch``. The tools cannot create
611 the necessary text, though, so read the instru 611 the necessary text, though, so read the instructions below anyway.
612 612
613 The canonical patch subject line is:: 613 The canonical patch subject line is::
614 614
615 Subject: [PATCH 001/123] subsystem: summar 615 Subject: [PATCH 001/123] subsystem: summary phrase
616 616
617 The canonical patch message body contains the 617 The canonical patch message body contains the following:
618 618
619 - A ``from`` line specifying the patch autho 619 - A ``from`` line specifying the patch author, followed by an empty
620 line (only needed if the person sending th 620 line (only needed if the person sending the patch is not the author).
621 621
622 - The body of the explanation, line wrapped 622 - The body of the explanation, line wrapped at 75 columns, which will
623 be copied to the permanent changelog to de 623 be copied to the permanent changelog to describe this patch.
624 624
625 - An empty line. 625 - An empty line.
626 626
627 - The ``Signed-off-by:`` lines, described ab 627 - The ``Signed-off-by:`` lines, described above, which will
628 also go in the changelog. 628 also go in the changelog.
629 629
630 - A marker line containing simply ``---``. 630 - A marker line containing simply ``---``.
631 631
632 - Any additional comments not suitable for t 632 - Any additional comments not suitable for the changelog.
633 633
634 - The actual patch (``diff`` output). 634 - The actual patch (``diff`` output).
635 635
636 The Subject line format makes it very easy to 636 The Subject line format makes it very easy to sort the emails
637 alphabetically by subject line - pretty much a 637 alphabetically by subject line - pretty much any email reader will
638 support that - since because the sequence numb 638 support that - since because the sequence number is zero-padded,
639 the numerical and alphabetic sort is the same. 639 the numerical and alphabetic sort is the same.
640 640
641 The ``subsystem`` in the email's Subject shoul 641 The ``subsystem`` in the email's Subject should identify which
642 area or subsystem of the kernel is being patch 642 area or subsystem of the kernel is being patched.
643 643
644 The ``summary phrase`` in the email's Subject 644 The ``summary phrase`` in the email's Subject should concisely
645 describe the patch which that email contains. 645 describe the patch which that email contains. The ``summary
646 phrase`` should not be a filename. Do not use 646 phrase`` should not be a filename. Do not use the same ``summary
647 phrase`` for every patch in a whole patch seri 647 phrase`` for every patch in a whole patch series (where a ``patch
648 series`` is an ordered sequence of multiple, r 648 series`` is an ordered sequence of multiple, related patches).
649 649
650 Bear in mind that the ``summary phrase`` of yo 650 Bear in mind that the ``summary phrase`` of your email becomes a
651 globally-unique identifier for that patch. It 651 globally-unique identifier for that patch. It propagates all the way
652 into the ``git`` changelog. The ``summary phr 652 into the ``git`` changelog. The ``summary phrase`` may later be used in
653 developer discussions which refer to the patch 653 developer discussions which refer to the patch. People will want to
654 google for the ``summary phrase`` to read disc 654 google for the ``summary phrase`` to read discussion regarding that
655 patch. It will also be the only thing that pe 655 patch. It will also be the only thing that people may quickly see
656 when, two or three months later, they are goin 656 when, two or three months later, they are going through perhaps
657 thousands of patches using tools such as ``git 657 thousands of patches using tools such as ``gitk`` or ``git log
658 --oneline``. 658 --oneline``.
659 659
660 For these reasons, the ``summary`` must be no 660 For these reasons, the ``summary`` must be no more than 70-75
661 characters, and it must describe both what the 661 characters, and it must describe both what the patch changes, as well
662 as why the patch might be necessary. It is ch 662 as why the patch might be necessary. It is challenging to be both
663 succinct and descriptive, but that is what a w 663 succinct and descriptive, but that is what a well-written summary
664 should do. 664 should do.
665 665
666 The ``summary phrase`` may be prefixed by tags 666 The ``summary phrase`` may be prefixed by tags enclosed in square
667 brackets: "Subject: [PATCH <tag>...] <summary 667 brackets: "Subject: [PATCH <tag>...] <summary phrase>". The tags are
668 not considered part of the summary phrase, but 668 not considered part of the summary phrase, but describe how the patch
669 should be treated. Common tags might include 669 should be treated. Common tags might include a version descriptor if
670 the multiple versions of the patch have been s 670 the multiple versions of the patch have been sent out in response to
671 comments (i.e., "v1, v2, v3"), or "RFC" to ind 671 comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
672 comments. 672 comments.
673 673
674 If there are four patches in a patch series th 674 If there are four patches in a patch series the individual patches may
675 be numbered like this: 1/4, 2/4, 3/4, 4/4. Thi 675 be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures that developers
676 understand the order in which the patches shou 676 understand the order in which the patches should be applied and that
677 they have reviewed or applied all of the patch 677 they have reviewed or applied all of the patches in the patch series.
678 678
679 Here are some good example Subjects:: 679 Here are some good example Subjects::
680 680
681 Subject: [PATCH 2/5] ext2: improve scalabi 681 Subject: [PATCH 2/5] ext2: improve scalability of bitmap searching
682 Subject: [PATCH v2 01/27] x86: fix eflags 682 Subject: [PATCH v2 01/27] x86: fix eflags tracking
683 Subject: [PATCH v2] sub/sys: Condensed pat 683 Subject: [PATCH v2] sub/sys: Condensed patch summary
684 Subject: [PATCH v2 M/N] sub/sys: Condensed 684 Subject: [PATCH v2 M/N] sub/sys: Condensed patch summary
685 685
686 The ``from`` line must be the very first line 686 The ``from`` line must be the very first line in the message body,
687 and has the form: 687 and has the form:
688 688
689 From: Patch Author <author@example.com> 689 From: Patch Author <author@example.com>
690 690
691 The ``from`` line specifies who will be credit 691 The ``from`` line specifies who will be credited as the author of the
692 patch in the permanent changelog. If the ``fr 692 patch in the permanent changelog. If the ``from`` line is missing,
693 then the ``From:`` line from the email header 693 then the ``From:`` line from the email header will be used to determine
694 the patch author in the changelog. 694 the patch author in the changelog.
695 695
696 The explanation body will be committed to the 696 The explanation body will be committed to the permanent source
697 changelog, so should make sense to a competent 697 changelog, so should make sense to a competent reader who has long since
698 forgotten the immediate details of the discuss 698 forgotten the immediate details of the discussion that might have led to
699 this patch. Including symptoms of the failure 699 this patch. Including symptoms of the failure which the patch addresses
700 (kernel log messages, oops messages, etc.) are 700 (kernel log messages, oops messages, etc.) are especially useful for
701 people who might be searching the commit logs 701 people who might be searching the commit logs looking for the applicable
702 patch. The text should be written in such deta 702 patch. The text should be written in such detail so that when read
703 weeks, months or even years later, it can give 703 weeks, months or even years later, it can give the reader the needed
704 details to grasp the reasoning for **why** the 704 details to grasp the reasoning for **why** the patch was created.
705 705
706 If a patch fixes a compile failure, it may not 706 If a patch fixes a compile failure, it may not be necessary to include
707 _all_ of the compile failures; just enough tha 707 _all_ of the compile failures; just enough that it is likely that
708 someone searching for the patch can find it. A 708 someone searching for the patch can find it. As in the ``summary
709 phrase``, it is important to be both succinct 709 phrase``, it is important to be both succinct as well as descriptive.
710 710
711 The ``---`` marker line serves the essential p 711 The ``---`` marker line serves the essential purpose of marking for
712 patch handling tools where the changelog messa 712 patch handling tools where the changelog message ends.
713 713
714 One good use for the additional comments after 714 One good use for the additional comments after the ``---`` marker is
715 for a ``diffstat``, to show what files have ch 715 for a ``diffstat``, to show what files have changed, and the number of
716 inserted and deleted lines per file. A ``diffs 716 inserted and deleted lines per file. A ``diffstat`` is especially useful
717 on bigger patches. If you are going to include 717 on bigger patches. If you are going to include a ``diffstat`` after the
718 ``---`` marker, please use ``diffstat`` option 718 ``---`` marker, please use ``diffstat`` options ``-p 1 -w 70`` so that
719 filenames are listed from the top of the kerne 719 filenames are listed from the top of the kernel source tree and don't
720 use too much horizontal space (easily fit in 8 720 use too much horizontal space (easily fit in 80 columns, maybe with some
721 indentation). (``git`` generates appropriate d 721 indentation). (``git`` generates appropriate diffstats by default.)
722 722
723 Other comments relevant only to the moment or 723 Other comments relevant only to the moment or the maintainer, not
724 suitable for the permanent changelog, should a 724 suitable for the permanent changelog, should also go here. A good
725 example of such comments might be ``patch chan 725 example of such comments might be ``patch changelogs`` which describe
726 what has changed between the v1 and v2 version 726 what has changed between the v1 and v2 version of the patch.
727 727
728 Please put this information **after** the ``-- 728 Please put this information **after** the ``---`` line which separates
729 the changelog from the rest of the patch. The 729 the changelog from the rest of the patch. The version information is
730 not part of the changelog which gets committed 730 not part of the changelog which gets committed to the git tree. It is
731 additional information for the reviewers. If i 731 additional information for the reviewers. If it's placed above the
732 commit tags, it needs manual interaction to re 732 commit tags, it needs manual interaction to remove it. If it is below
733 the separator line, it gets automatically stri 733 the separator line, it gets automatically stripped off when applying the
734 patch:: 734 patch::
735 735
736 <commit message> 736 <commit message>
737 ... 737 ...
738 Signed-off-by: Author <author@mail> 738 Signed-off-by: Author <author@mail>
739 --- 739 ---
740 V2 -> V3: Removed redundant helper function 740 V2 -> V3: Removed redundant helper function
741 V1 -> V2: Cleaned up coding style and addres 741 V1 -> V2: Cleaned up coding style and addressed review comments
742 742
743 path/to/file | 5+++-- 743 path/to/file | 5+++--
744 ... 744 ...
745 745
746 See more details on the proper patch format in 746 See more details on the proper patch format in the following
747 references. 747 references.
748 748
749 .. _backtraces: 749 .. _backtraces:
750 750
751 Backtraces in commit messages 751 Backtraces in commit messages
752 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 752 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
753 753
754 Backtraces help document the call chain leadin 754 Backtraces help document the call chain leading to a problem. However,
755 not all backtraces are helpful. For example, e 755 not all backtraces are helpful. For example, early boot call chains are
756 unique and obvious. Copying the full dmesg out 756 unique and obvious. Copying the full dmesg output verbatim, however,
757 adds distracting information like timestamps, 757 adds distracting information like timestamps, module lists, register and
758 stack dumps. 758 stack dumps.
759 759
760 Therefore, the most useful backtraces should d 760 Therefore, the most useful backtraces should distill the relevant
761 information from the dump, which makes it easi 761 information from the dump, which makes it easier to focus on the real
762 issue. Here is an example of a well-trimmed ba 762 issue. Here is an example of a well-trimmed backtrace::
763 763
764 unchecked MSR access error: WRMSR to 0xd51 ( 764 unchecked MSR access error: WRMSR to 0xd51 (tried to write 0x0000000000000064)
765 at rIP: 0xffffffffae059994 (native_write_msr 765 at rIP: 0xffffffffae059994 (native_write_msr+0x4/0x20)
766 Call Trace: 766 Call Trace:
767 mba_wrmsr 767 mba_wrmsr
768 update_domains 768 update_domains
769 rdtgroup_mkdir 769 rdtgroup_mkdir
770 770
771 .. _explicit_in_reply_to: 771 .. _explicit_in_reply_to:
772 772
773 Explicit In-Reply-To headers 773 Explicit In-Reply-To headers
774 ---------------------------- 774 ----------------------------
775 775
776 It can be helpful to manually add In-Reply-To: 776 It can be helpful to manually add In-Reply-To: headers to a patch
777 (e.g., when using ``git send-email``) to assoc 777 (e.g., when using ``git send-email``) to associate the patch with
778 previous relevant discussion, e.g. to link a b 778 previous relevant discussion, e.g. to link a bug fix to the email with
779 the bug report. However, for a multi-patch se 779 the bug report. However, for a multi-patch series, it is generally
780 best to avoid using In-Reply-To: to link to ol 780 best to avoid using In-Reply-To: to link to older versions of the
781 series. This way multiple versions of the pat 781 series. This way multiple versions of the patch don't become an
782 unmanageable forest of references in email cli 782 unmanageable forest of references in email clients. If a link is
783 helpful, you can use the https://lore.kernel.o 783 helpful, you can use the https://lore.kernel.org/ redirector (e.g., in
784 the cover email text) to link to an earlier ve 784 the cover email text) to link to an earlier version of the patch series.
785 785
786 786
787 Providing base tree information 787 Providing base tree information
788 ------------------------------- 788 -------------------------------
789 789
790 When other developers receive your patches and 790 When other developers receive your patches and start the review process,
791 it is absolutely necessary for them to know wh 791 it is absolutely necessary for them to know what is the base
792 commit/branch your work applies on, considerin 792 commit/branch your work applies on, considering the sheer amount of
793 maintainer trees present nowadays. Note again 793 maintainer trees present nowadays. Note again the **T:** entry in the
794 MAINTAINERS file explained above. 794 MAINTAINERS file explained above.
795 795
796 This is even more important for automated CI p 796 This is even more important for automated CI processes that attempt to
797 run a series of tests in order to establish th 797 run a series of tests in order to establish the quality of your
798 submission before the maintainer starts the re 798 submission before the maintainer starts the review.
799 799
800 If you are using ``git format-patch`` to gener 800 If you are using ``git format-patch`` to generate your patches, you can
801 automatically include the base tree informatio 801 automatically include the base tree information in your submission by
802 using the ``--base`` flag. The easiest and mos 802 using the ``--base`` flag. The easiest and most convenient way to use
803 this option is with topical branches:: 803 this option is with topical branches::
804 804
805 $ git checkout -t -b my-topical-branch mas 805 $ git checkout -t -b my-topical-branch master
806 Branch 'my-topical-branch' set up to track 806 Branch 'my-topical-branch' set up to track local branch 'master'.
807 Switched to a new branch 'my-topical-branc 807 Switched to a new branch 'my-topical-branch'
808 808
809 [perform your edits and commits] 809 [perform your edits and commits]
810 810
811 $ git format-patch --base=auto --cover-let 811 $ git format-patch --base=auto --cover-letter -o outgoing/ master
812 outgoing/0000-cover-letter.patch 812 outgoing/0000-cover-letter.patch
813 outgoing/0001-First-Commit.patch 813 outgoing/0001-First-Commit.patch
814 outgoing/... 814 outgoing/...
815 815
816 When you open ``outgoing/0000-cover-letter.pat 816 When you open ``outgoing/0000-cover-letter.patch`` for editing, you will
817 notice that it will have the ``base-commit:`` 817 notice that it will have the ``base-commit:`` trailer at the very
818 bottom, which provides the reviewer and the CI 818 bottom, which provides the reviewer and the CI tools enough information
819 to properly perform ``git am`` without worryin 819 to properly perform ``git am`` without worrying about conflicts::
820 820
821 $ git checkout -b patch-review [base-commi 821 $ git checkout -b patch-review [base-commit-id]
822 Switched to a new branch 'patch-review' 822 Switched to a new branch 'patch-review'
823 $ git am patches.mbox 823 $ git am patches.mbox
824 Applying: First Commit 824 Applying: First Commit
825 Applying: ... 825 Applying: ...
826 826
827 Please see ``man git-format-patch`` for more i 827 Please see ``man git-format-patch`` for more information about this
828 option. 828 option.
829 829
830 .. note:: 830 .. note::
831 831
832 The ``--base`` feature was introduced in g 832 The ``--base`` feature was introduced in git version 2.9.0.
833 833
834 If you are not using git to format your patche 834 If you are not using git to format your patches, you can still include
835 the same ``base-commit`` trailer to indicate t 835 the same ``base-commit`` trailer to indicate the commit hash of the tree
836 on which your work is based. You should add it 836 on which your work is based. You should add it either in the cover
837 letter or in the first patch of the series and 837 letter or in the first patch of the series and it should be placed
838 either below the ``---`` line or at the very b 838 either below the ``---`` line or at the very bottom of all other
839 content, right before your email signature. 839 content, right before your email signature.
840 840
841 Make sure that base commit is in an official m 841 Make sure that base commit is in an official maintainer/mainline tree
842 and not in some internal, accessible only to y 842 and not in some internal, accessible only to you tree - otherwise it
843 would be worthless. 843 would be worthless.
844 844
845 Tooling 845 Tooling
846 ------- 846 -------
847 847
848 Many of the technical aspects of this process 848 Many of the technical aspects of this process can be automated using
849 b4, documented at <https://b4.docs.kernel.org/ 849 b4, documented at <https://b4.docs.kernel.org/en/latest/>. This can
850 help with things like tracking dependencies, r 850 help with things like tracking dependencies, running checkpatch and
851 with formatting and sending mails. 851 with formatting and sending mails.
852 852
853 References 853 References
854 ---------- 854 ----------
855 855
856 Andrew Morton, "The perfect patch" (tpp). 856 Andrew Morton, "The perfect patch" (tpp).
857 <https://www.ozlabs.org/~akpm/stuff/tpp.txt> 857 <https://www.ozlabs.org/~akpm/stuff/tpp.txt>
858 858
859 Jeff Garzik, "Linux kernel patch submission fo 859 Jeff Garzik, "Linux kernel patch submission format".
860 <https://web.archive.org/web/20180829112450/ 860 <https://web.archive.org/web/20180829112450/http://linux.yyz.us/patch-format.html>
861 861
862 Greg Kroah-Hartman, "How to piss off a kernel 862 Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
863 <http://www.kroah.com/log/linux/maintainer.h 863 <http://www.kroah.com/log/linux/maintainer.html>
864 864
865 <http://www.kroah.com/log/linux/maintainer-0 865 <http://www.kroah.com/log/linux/maintainer-02.html>
866 866
867 <http://www.kroah.com/log/linux/maintainer-0 867 <http://www.kroah.com/log/linux/maintainer-03.html>
868 868
869 <http://www.kroah.com/log/linux/maintainer-0 869 <http://www.kroah.com/log/linux/maintainer-04.html>
870 870
871 <http://www.kroah.com/log/linux/maintainer-0 871 <http://www.kroah.com/log/linux/maintainer-05.html>
872 872
873 <http://www.kroah.com/log/linux/maintainer-0 873 <http://www.kroah.com/log/linux/maintainer-06.html>
874 874
875 Kernel Documentation/process/coding-style.rst 875 Kernel Documentation/process/coding-style.rst
876 876
877 Linus Torvalds's mail on the canonical patch f 877 Linus Torvalds's mail on the canonical patch format:
878 <https://lore.kernel.org/r/Pine.LNX.4.58.0504 878 <https://lore.kernel.org/r/Pine.LNX.4.58.0504071023190.28951@ppc970.osdl.org">https://lore.kernel.org/r/Pine.LNX.4.58.0504071023190.28951@ppc970.osdl.org>
879 879
880 Andi Kleen, "On submitting kernel patches" 880 Andi Kleen, "On submitting kernel patches"
881 Some strategies to get difficult or controve 881 Some strategies to get difficult or controversial changes in.
882 882
883 http://halobates.de/on-submitting-patches.pd 883 http://halobates.de/on-submitting-patches.pdf
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
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