1 2 How to Get Your Change Into the Linux Kernel 3 or 4 Care And Operation Of Your Linus Torvalds 5 6 7 8For a person or company who wishes to submit a change to the Linux 9kernel, the process can sometimes be daunting if you're not familiar 10with "the system." This text is a collection of suggestions which 11can greatly increase the chances of your change being accepted. 12 13This document contains a large number of suggestions in a relatively terse 14format. For detailed information on how the kernel development process 15works, see Documentation/development-process. Also, read 16Documentation/SubmitChecklist for a list of items to check before 17submitting code. If you are submitting a driver, also read 18Documentation/SubmittingDrivers; for device tree binding patches, read 19Documentation/devicetree/bindings/submitting-patches.txt. 20 21Many of these steps describe the default behavior of the git version 22control system; if you use git to prepare your patches, you'll find much 23of the mechanical work done for you, though you'll still need to prepare 24and document a sensible set of patches. In general, use of git will make 25your life as a kernel developer easier. 26 27-------------------------------------------- 28SECTION 1 - CREATING AND SENDING YOUR CHANGE 29-------------------------------------------- 30 31 320) Obtain a current source tree 33------------------------------- 34 35If you do not have a repository with the current kernel source handy, use 36git to obtain one. You'll want to start with the mainline repository, 37which can be grabbed with: 38 39 git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 40 41Note, however, that you may not want to develop against the mainline tree 42directly. Most subsystem maintainers run their own trees and want to see 43patches prepared against those trees. See the "T:" entry for the subsystem 44in the MAINTAINERS file to find that tree, or simply ask the maintainer if 45the tree is not listed there. 46 47It is still possible to download kernel releases via tarballs (as described 48in the next section), but that is the hard way to do kernel development. 49 501) "diff -up" 51------------ 52 53If you must generate your patches by hand, use "diff -up" or "diff -uprN" 54to create patches. Git generates patches in this form by default; if 55you're using git, you can skip this section entirely. 56 57All changes to the Linux kernel occur in the form of patches, as 58generated by diff(1). When creating your patch, make sure to create it 59in "unified diff" format, as supplied by the '-u' argument to diff(1). 60Also, please use the '-p' argument which shows which C function each 61change is in - that makes the resultant diff a lot easier to read. 62Patches should be based in the root kernel source directory, 63not in any lower subdirectory. 64 65To create a patch for a single file, it is often sufficient to do: 66 67 SRCTREE= linux 68 MYFILE= drivers/net/mydriver.c 69 70 cd $SRCTREE 71 cp $MYFILE $MYFILE.orig 72 vi $MYFILE # make your change 73 cd .. 74 diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch 75 76To create a patch for multiple files, you should unpack a "vanilla", 77or unmodified kernel source tree, and generate a diff against your 78own source tree. For example: 79 80 MYSRC= /devel/linux 81 82 tar xvfz linux-3.19.tar.gz 83 mv linux-3.19 linux-3.19-vanilla 84 diff -uprN -X linux-3.19-vanilla/Documentation/dontdiff \ 85 linux-3.19-vanilla $MYSRC > /tmp/patch 86 87"dontdiff" is a list of files which are generated by the kernel during 88the build process, and should be ignored in any diff(1)-generated 89patch. 90 91Make sure your patch does not include any extra files which do not 92belong in a patch submission. Make sure to review your patch -after- 93generated it with diff(1), to ensure accuracy. 94 95If your changes produce a lot of deltas, you need to split them into 96individual patches which modify things in logical stages; see section 97#3. This will facilitate easier reviewing by other kernel developers, 98very important if you want your patch accepted. 99 100If you're using git, "git rebase -i" can help you with this process. If 101you're not using git, quilt <http://savannah.nongnu.org/projects/quilt> 102is another popular alternative. 103 104 105 1062) Describe your changes. 107------------------------- 108 109Describe your problem. Whether your patch is a one-line bug fix or 1105000 lines of a new feature, there must be an underlying problem that 111motivated you to do this work. Convince the reviewer that there is a 112problem worth fixing and that it makes sense for them to read past the 113first paragraph. 114 115Describe user-visible impact. Straight up crashes and lockups are 116pretty convincing, but not all bugs are that blatant. Even if the 117problem was spotted during code review, describe the impact you think 118it can have on users. Keep in mind that the majority of Linux 119installations run kernels from secondary stable trees or 120vendor/product-specific trees that cherry-pick only specific patches 121from upstream, so include anything that could help route your change 122downstream: provoking circumstances, excerpts from dmesg, crash 123descriptions, performance regressions, latency spikes, lockups, etc. 124 125Quantify optimizations and trade-offs. If you claim improvements in 126performance, memory consumption, stack footprint, or binary size, 127include numbers that back them up. But also describe non-obvious 128costs. Optimizations usually aren't free but trade-offs between CPU, 129memory, and readability; or, when it comes to heuristics, between 130different workloads. Describe the expected downsides of your 131optimization so that the reviewer can weigh costs against benefits. 132 133Once the problem is established, describe what you are actually doing 134about it in technical detail. It's important to describe the change 135in plain English for the reviewer to verify that the code is behaving 136as you intend it to. 137 138The maintainer will thank you if you write your patch description in a 139form which can be easily pulled into Linux's source code management 140system, git, as a "commit log". See #15, below. 141 142Solve only one problem per patch. If your description starts to get 143long, that's a sign that you probably need to split up your patch. 144See #3, next. 145 146When you submit or resubmit a patch or patch series, include the 147complete patch description and justification for it. Don't just 148say that this is version N of the patch (series). Don't expect the 149subsystem maintainer to refer back to earlier patch versions or referenced 150URLs to find the patch description and put that into the patch. 151I.e., the patch (series) and its description should be self-contained. 152This benefits both the maintainers and reviewers. Some reviewers 153probably didn't even receive earlier versions of the patch. 154 155Describe your changes in imperative mood, e.g. "make xyzzy do frotz" 156instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy 157to do frotz", as if you are giving orders to the codebase to change 158its behaviour. 159 160If the patch fixes a logged bug entry, refer to that bug entry by 161number and URL. If the patch follows from a mailing list discussion, 162give a URL to the mailing list archive; use the https://lkml.kernel.org/ 163redirector with a Message-Id, to ensure that the links cannot become 164stale. 165 166However, try to make your explanation understandable without external 167resources. In addition to giving a URL to a mailing list archive or 168bug, summarize the relevant points of the discussion that led to the 169patch as submitted. 170 171If you want to refer to a specific commit, don't just refer to the 172SHA-1 ID of the commit. Please also include the oneline summary of 173the commit, to make it easier for reviewers to know what it is about. 174Example: 175 176 Commit e21d2170f36602ae2708 ("video: remove unnecessary 177 platform_set_drvdata()") removed the unnecessary 178 platform_set_drvdata(), but left the variable "dev" unused, 179 delete it. 180 181You should also be sure to use at least the first twelve characters of the 182SHA-1 ID. The kernel repository holds a *lot* of objects, making 183collisions with shorter IDs a real possibility. Bear in mind that, even if 184there is no collision with your six-character ID now, that condition may 185change five years from now. 186 187If your patch fixes a bug in a specific commit, e.g. you found an issue using 188git-bisect, please use the 'Fixes:' tag with the first 12 characters of the 189SHA-1 ID, and the one line summary. For example: 190 191 Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()") 192 193The following git-config settings can be used to add a pretty format for 194outputting the above style in the git log or git show commands 195 196 [core] 197 abbrev = 12 198 [pretty] 199 fixes = Fixes: %h (\"%s\") 200 2013) Separate your changes. 202------------------------- 203 204Separate each _logical change_ into a separate patch. 205 206For example, if your changes include both bug fixes and performance 207enhancements for a single driver, separate those changes into two 208or more patches. If your changes include an API update, and a new 209driver which uses that new API, separate those into two patches. 210 211On the other hand, if you make a single change to numerous files, 212group those changes into a single patch. Thus a single logical change 213is contained within a single patch. 214 215The point to remember is that each patch should make an easily understood 216change that can be verified by reviewers. Each patch should be justifiable 217on its own merits. 218 219If one patch depends on another patch in order for a change to be 220complete, that is OK. Simply note "this patch depends on patch X" 221in your patch description. 222 223When dividing your change into a series of patches, take special care to 224ensure that the kernel builds and runs properly after each patch in the 225series. Developers using "git bisect" to track down a problem can end up 226splitting your patch series at any point; they will not thank you if you 227introduce bugs in the middle. 228 229If you cannot condense your patch set into a smaller set of patches, 230then only post say 15 or so at a time and wait for review and integration. 231 232 233 2344) Style-check your changes. 235---------------------------- 236 237Check your patch for basic style violations, details of which can be 238found in Documentation/CodingStyle. Failure to do so simply wastes 239the reviewers time and will get your patch rejected, probably 240without even being read. 241 242One significant exception is when moving code from one file to 243another -- in this case you should not modify the moved code at all in 244the same patch which moves it. This clearly delineates the act of 245moving the code and your changes. This greatly aids review of the 246actual differences and allows tools to better track the history of 247the code itself. 248 249Check your patches with the patch style checker prior to submission 250(scripts/checkpatch.pl). Note, though, that the style checker should be 251viewed as a guide, not as a replacement for human judgment. If your code 252looks better with a violation then its probably best left alone. 253 254The checker reports at three levels: 255 - ERROR: things that are very likely to be wrong 256 - WARNING: things requiring careful review 257 - CHECK: things requiring thought 258 259You should be able to justify all violations that remain in your 260patch. 261 262 2635) Select the recipients for your patch. 264---------------------------------------- 265 266You should always copy the appropriate subsystem maintainer(s) on any patch 267to code that they maintain; look through the MAINTAINERS file and the 268source code revision history to see who those maintainers are. The 269script scripts/get_maintainer.pl can be very useful at this step. If you 270cannot find a maintainer for the subsystem your are working on, Andrew 271Morton (akpm@linux-foundation.org) serves as a maintainer of last resort. 272 273You should also normally choose at least one mailing list to receive a copy 274of your patch set. linux-kernel@vger.kernel.org functions as a list of 275last resort, but the volume on that list has caused a number of developers 276to tune it out. Look in the MAINTAINERS file for a subsystem-specific 277list; your patch will probably get more attention there. Please do not 278spam unrelated lists, though. 279 280Many kernel-related lists are hosted on vger.kernel.org; you can find a 281list of them at http://vger.kernel.org/vger-lists.html. There are 282kernel-related lists hosted elsewhere as well, though. 283 284Do not send more than 15 patches at once to the vger mailing lists!!! 285 286Linus Torvalds is the final arbiter of all changes accepted into the 287Linux kernel. His e-mail address is <torvalds@linux-foundation.org>. 288He gets a lot of e-mail, and, at this point, very few patches go through 289Linus directly, so typically you should do your best to -avoid- 290sending him e-mail. 291 292If you have a patch that fixes an exploitable security bug, send that patch 293to security@kernel.org. For severe bugs, a short embargo may be considered 294to allow distrbutors to get the patch out to users; in such cases, 295obviously, the patch should not be sent to any public lists. 296 297Patches that fix a severe bug in a released kernel should be directed 298toward the stable maintainers by putting a line like this: 299 300 Cc: stable@vger.kernel.org 301 302into your patch. 303 304Note, however, that some subsystem maintainers want to come to their own 305conclusions on which patches should go to the stable trees. The networking 306maintainer, in particular, would rather not see individual developers 307adding lines like the above to their patches. 308 309If changes affect userland-kernel interfaces, please send the MAN-PAGES 310maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at 311least a notification of the change, so that some information makes its way 312into the manual pages. User-space API changes should also be copied to 313linux-api@vger.kernel.org. 314 315For small patches you may want to CC the Trivial Patch Monkey 316trivial@kernel.org which collects "trivial" patches. Have a look 317into the MAINTAINERS file for its current manager. 318Trivial patches must qualify for one of the following rules: 319 Spelling fixes in documentation 320 Spelling fixes for errors which could break grep(1) 321 Warning fixes (cluttering with useless warnings is bad) 322 Compilation fixes (only if they are actually correct) 323 Runtime fixes (only if they actually fix things) 324 Removing use of deprecated functions/macros 325 Contact detail and documentation fixes 326 Non-portable code replaced by portable code (even in arch-specific, 327 since people copy, as long as it's trivial) 328 Any fix by the author/maintainer of the file (ie. patch monkey 329 in re-transmission mode) 330 331 332 3336) No MIME, no links, no compression, no attachments. Just plain text. 334----------------------------------------------------------------------- 335 336Linus and other kernel developers need to be able to read and comment 337on the changes you are submitting. It is important for a kernel 338developer to be able to "quote" your changes, using standard e-mail 339tools, so that they may comment on specific portions of your code. 340 341For this reason, all patches should be submitting e-mail "inline". 342WARNING: Be wary of your editor's word-wrap corrupting your patch, 343if you choose to cut-n-paste your patch. 344 345Do not attach the patch as a MIME attachment, compressed or not. 346Many popular e-mail applications will not always transmit a MIME 347attachment as plain text, making it impossible to comment on your 348code. A MIME attachment also takes Linus a bit more time to process, 349decreasing the likelihood of your MIME-attached change being accepted. 350 351Exception: If your mailer is mangling patches then someone may ask 352you to re-send them using MIME. 353 354See Documentation/email-clients.txt for hints about configuring 355your e-mail client so that it sends your patches untouched. 356 3577) E-mail size. 358--------------- 359 360Large changes are not appropriate for mailing lists, and some 361maintainers. If your patch, uncompressed, exceeds 300 kB in size, 362it is preferred that you store your patch on an Internet-accessible 363server, and provide instead a URL (link) pointing to your patch. But note 364that if your patch exceeds 300 kB, it almost certainly needs to be broken up 365anyway. 366 3678) Respond to review comments. 368------------------------------ 369 370Your patch will almost certainly get comments from reviewers on ways in 371which the patch can be improved. You must respond to those comments; 372ignoring reviewers is a good way to get ignored in return. Review comments 373or questions that do not lead to a code change should almost certainly 374bring about a comment or changelog entry so that the next reviewer better 375understands what is going on. 376 377Be sure to tell the reviewers what changes you are making and to thank them 378for their time. Code review is a tiring and time-consuming process, and 379reviewers sometimes get grumpy. Even in that case, though, respond 380politely and address the problems they have pointed out. 381 382 3839) Don't get discouraged - or impatient. 384---------------------------------------- 385 386After you have submitted your change, be patient and wait. Reviewers are 387busy people and may not get to your patch right away. 388 389Once upon a time, patches used to disappear into the void without comment, 390but the development process works more smoothly than that now. You should 391receive comments within a week or so; if that does not happen, make sure 392that you have sent your patches to the right place. Wait for a minimum of 393one week before resubmitting or pinging reviewers - possibly longer during 394busy times like merge windows. 395 396 39710) Include PATCH in the subject 398-------------------------------- 399 400Due to high e-mail traffic to Linus, and to linux-kernel, it is common 401convention to prefix your subject line with [PATCH]. This lets Linus 402and other kernel developers more easily distinguish patches from other 403e-mail discussions. 404 405 406 40711) Sign your work 408------------------ 409 410To improve tracking of who did what, especially with patches that can 411percolate to their final resting place in the kernel through several 412layers of maintainers, we've introduced a "sign-off" procedure on 413patches that are being emailed around. 414 415The sign-off is a simple line at the end of the explanation for the 416patch, which certifies that you wrote it or otherwise have the right to 417pass it on as an open-source patch. The rules are pretty simple: if you 418can certify the below: 419 420 Developer's Certificate of Origin 1.1 421 422 By making a contribution to this project, I certify that: 423 424 (a) The contribution was created in whole or in part by me and I 425 have the right to submit it under the open source license 426 indicated in the file; or 427 428 (b) The contribution is based upon previous work that, to the best 429 of my knowledge, is covered under an appropriate open source 430 license and I have the right under that license to submit that 431 work with modifications, whether created in whole or in part 432 by me, under the same open source license (unless I am 433 permitted to submit under a different license), as indicated 434 in the file; or 435 436 (c) The contribution was provided directly to me by some other 437 person who certified (a), (b) or (c) and I have not modified 438 it. 439 440 (d) I understand and agree that this project and the contribution 441 are public and that a record of the contribution (including all 442 personal information I submit with it, including my sign-off) is 443 maintained indefinitely and may be redistributed consistent with 444 this project or the open source license(s) involved. 445 446then you just add a line saying 447 448 Signed-off-by: Random J Developer <random@developer.example.org> 449 450using your real name (sorry, no pseudonyms or anonymous contributions.) 451 452Some people also put extra tags at the end. They'll just be ignored for 453now, but you can do this to mark internal company procedures or just 454point out some special detail about the sign-off. 455 456If you are a subsystem or branch maintainer, sometimes you need to slightly 457modify patches you receive in order to merge them, because the code is not 458exactly the same in your tree and the submitters'. If you stick strictly to 459rule (c), you should ask the submitter to rediff, but this is a totally 460counter-productive waste of time and energy. Rule (b) allows you to adjust 461the code, but then it is very impolite to change one submitter's code and 462make him endorse your bugs. To solve this problem, it is recommended that 463you add a line between the last Signed-off-by header and yours, indicating 464the nature of your changes. While there is nothing mandatory about this, it 465seems like prepending the description with your mail and/or name, all 466enclosed in square brackets, is noticeable enough to make it obvious that 467you are responsible for last-minute changes. Example : 468 469 Signed-off-by: Random J Developer <random@developer.example.org> 470 [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h] 471 Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org> 472 473This practice is particularly helpful if you maintain a stable branch and 474want at the same time to credit the author, track changes, merge the fix, 475and protect the submitter from complaints. Note that under no circumstances 476can you change the author's identity (the From header), as it is the one 477which appears in the changelog. 478 479Special note to back-porters: It seems to be a common and useful practice 480to insert an indication of the origin of a patch at the top of the commit 481message (just after the subject line) to facilitate tracking. For instance, 482here's what we see in a 3.x-stable release: 483 484Date: Tue Oct 7 07:26:38 2014 -0400 485 486 libata: Un-break ATA blacklist 487 488 commit 1c40279960bcd7d52dbdf1d466b20d24b99176c8 upstream. 489 490And here's what might appear in an older kernel once a patch is backported: 491 492 Date: Tue May 13 22:12:27 2008 +0200 493 494 wireless, airo: waitbusy() won't delay 495 496 [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a] 497 498Whatever the format, this information provides a valuable help to people 499tracking your trees, and to people trying to troubleshoot bugs in your 500tree. 501 502 50312) When to use Acked-by: and Cc: 504--------------------------------- 505 506The Signed-off-by: tag indicates that the signer was involved in the 507development of the patch, or that he/she was in the patch's delivery path. 508 509If a person was not directly involved in the preparation or handling of a 510patch but wishes to signify and record their approval of it then they can 511ask to have an Acked-by: line added to the patch's changelog. 512 513Acked-by: is often used by the maintainer of the affected code when that 514maintainer neither contributed to nor forwarded the patch. 515 516Acked-by: is not as formal as Signed-off-by:. It is a record that the acker 517has at least reviewed the patch and has indicated acceptance. Hence patch 518mergers will sometimes manually convert an acker's "yep, looks good to me" 519into an Acked-by: (but note that it is usually better to ask for an 520explicit ack). 521 522Acked-by: does not necessarily indicate acknowledgement of the entire patch. 523For example, if a patch affects multiple subsystems and has an Acked-by: from 524one subsystem maintainer then this usually indicates acknowledgement of just 525the part which affects that maintainer's code. Judgement should be used here. 526When in doubt people should refer to the original discussion in the mailing 527list archives. 528 529If a person has had the opportunity to comment on a patch, but has not 530provided such comments, you may optionally add a "Cc:" tag to the patch. 531This is the only tag which might be added without an explicit action by the 532person it names - but it should indicate that this person was copied on the 533patch. This tag documents that potentially interested parties 534have been included in the discussion. 535 536 53713) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes: 538-------------------------------------------------------------------------- 539 540The Reported-by tag gives credit to people who find bugs and report them and it 541hopefully inspires them to help us again in the future. Please note that if 542the bug was reported in private, then ask for permission first before using the 543Reported-by tag. 544 545A Tested-by: tag indicates that the patch has been successfully tested (in 546some environment) by the person named. This tag informs maintainers that 547some testing has been performed, provides a means to locate testers for 548future patches, and ensures credit for the testers. 549 550Reviewed-by:, instead, indicates that the patch has been reviewed and found 551acceptable according to the Reviewer's Statement: 552 553 Reviewer's statement of oversight 554 555 By offering my Reviewed-by: tag, I state that: 556 557 (a) I have carried out a technical review of this patch to 558 evaluate its appropriateness and readiness for inclusion into 559 the mainline kernel. 560 561 (b) Any problems, concerns, or questions relating to the patch 562 have been communicated back to the submitter. I am satisfied 563 with the submitter's response to my comments. 564 565 (c) While there may be things that could be improved with this 566 submission, I believe that it is, at this time, (1) a 567 worthwhile modification to the kernel, and (2) free of known 568 issues which would argue against its inclusion. 569 570 (d) While I have reviewed the patch and believe it to be sound, I 571 do not (unless explicitly stated elsewhere) make any 572 warranties or guarantees that it will achieve its stated 573 purpose or function properly in any given situation. 574 575A Reviewed-by tag is a statement of opinion that the patch is an 576appropriate modification of the kernel without any remaining serious 577technical issues. Any interested reviewer (who has done the work) can 578offer a Reviewed-by tag for a patch. This tag serves to give credit to 579reviewers and to inform maintainers of the degree of review which has been 580done on the patch. Reviewed-by: tags, when supplied by reviewers known to 581understand the subject area and to perform thorough reviews, will normally 582increase the likelihood of your patch getting into the kernel. 583 584A Suggested-by: tag indicates that the patch idea is suggested by the person 585named and ensures credit to the person for the idea. Please note that this 586tag should not be added without the reporter's permission, especially if the 587idea was not posted in a public forum. That said, if we diligently credit our 588idea reporters, they will, hopefully, be inspired to help us again in the 589future. 590 591A Fixes: tag indicates that the patch fixes an issue in a previous commit. It 592is used to make it easy to determine where a bug originated, which can help 593review a bug fix. This tag also assists the stable kernel team in determining 594which stable kernel versions should receive your fix. This is the preferred 595method for indicating a bug fixed by the patch. See #2 above for more details. 596 597 59814) The canonical patch format 599------------------------------ 600 601This section describes how the patch itself should be formatted. Note 602that, if you have your patches stored in a git repository, proper patch 603formatting can be had with "git format-patch". The tools cannot create 604the necessary text, though, so read the instructions below anyway. 605 606The canonical patch subject line is: 607 608 Subject: [PATCH 001/123] subsystem: summary phrase 609 610The canonical patch message body contains the following: 611 612 - A "from" line specifying the patch author (only needed if the person 613 sending the patch is not the author). 614 615 - An empty line. 616 617 - The body of the explanation, line wrapped at 75 columns, which will 618 be copied to the permanent changelog to describe this patch. 619 620 - The "Signed-off-by:" lines, described above, which will 621 also go in the changelog. 622 623 - A marker line containing simply "---". 624 625 - Any additional comments not suitable for the changelog. 626 627 - The actual patch (diff output). 628 629The Subject line format makes it very easy to sort the emails 630alphabetically by subject line - pretty much any email reader will 631support that - since because the sequence number is zero-padded, 632the numerical and alphabetic sort is the same. 633 634The "subsystem" in the email's Subject should identify which 635area or subsystem of the kernel is being patched. 636 637The "summary phrase" in the email's Subject should concisely 638describe the patch which that email contains. The "summary 639phrase" should not be a filename. Do not use the same "summary 640phrase" for every patch in a whole patch series (where a "patch 641series" is an ordered sequence of multiple, related patches). 642 643Bear in mind that the "summary phrase" of your email becomes a 644globally-unique identifier for that patch. It propagates all the way 645into the git changelog. The "summary phrase" may later be used in 646developer discussions which refer to the patch. People will want to 647google for the "summary phrase" to read discussion regarding that 648patch. It will also be the only thing that people may quickly see 649when, two or three months later, they are going through perhaps 650thousands of patches using tools such as "gitk" or "git log 651--oneline". 652 653For these reasons, the "summary" must be no more than 70-75 654characters, and it must describe both what the patch changes, as well 655as why the patch might be necessary. It is challenging to be both 656succinct and descriptive, but that is what a well-written summary 657should do. 658 659The "summary phrase" may be prefixed by tags enclosed in square 660brackets: "Subject: [PATCH tag] <summary phrase>". The tags are not 661considered part of the summary phrase, but describe how the patch 662should be treated. Common tags might include a version descriptor if 663the multiple versions of the patch have been sent out in response to 664comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for 665comments. If there are four patches in a patch series the individual 666patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures 667that developers understand the order in which the patches should be 668applied and that they have reviewed or applied all of the patches in 669the patch series. 670 671A couple of example Subjects: 672 673 Subject: [patch 2/5] ext2: improve scalability of bitmap searching 674 Subject: [PATCHv2 001/207] x86: fix eflags tracking 675 676The "from" line must be the very first line in the message body, 677and has the form: 678 679 From: Original Author <author@example.com> 680 681The "from" line specifies who will be credited as the author of the 682patch in the permanent changelog. If the "from" line is missing, 683then the "From:" line from the email header will be used to determine 684the patch author in the changelog. 685 686The explanation body will be committed to the permanent source 687changelog, so should make sense to a competent reader who has long 688since forgotten the immediate details of the discussion that might 689have led to this patch. Including symptoms of the failure which the 690patch addresses (kernel log messages, oops messages, etc.) is 691especially useful for people who might be searching the commit logs 692looking for the applicable patch. If a patch fixes a compile failure, 693it may not be necessary to include _all_ of the compile failures; just 694enough that it is likely that someone searching for the patch can find 695it. As in the "summary phrase", it is important to be both succinct as 696well as descriptive. 697 698The "---" marker line serves the essential purpose of marking for patch 699handling tools where the changelog message ends. 700 701One good use for the additional comments after the "---" marker is for 702a diffstat, to show what files have changed, and the number of 703inserted and deleted lines per file. A diffstat is especially useful 704on bigger patches. Other comments relevant only to the moment or the 705maintainer, not suitable for the permanent changelog, should also go 706here. A good example of such comments might be "patch changelogs" 707which describe what has changed between the v1 and v2 version of the 708patch. 709 710If you are going to include a diffstat after the "---" marker, please 711use diffstat options "-p 1 -w 70" so that filenames are listed from 712the top of the kernel source tree and don't use too much horizontal 713space (easily fit in 80 columns, maybe with some indentation). (git 714generates appropriate diffstats by default.) 715 716See more details on the proper patch format in the following 717references. 718 719 72015) Sending "git pull" requests 721------------------------------- 722 723If you have a series of patches, it may be most convenient to have the 724maintainer pull them directly into the subsystem repository with a 725"git pull" operation. Note, however, that pulling patches from a developer 726requires a higher degree of trust than taking patches from a mailing list. 727As a result, many subsystem maintainers are reluctant to take pull 728requests, especially from new, unknown developers. If in doubt you can use 729the pull request as the cover letter for a normal posting of the patch 730series, giving the maintainer the option of using either. 731 732A pull request should have [GIT] or [PULL] in the subject line. The 733request itself should include the repository name and the branch of 734interest on a single line; it should look something like: 735 736 Please pull from 737 738 git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus 739 740 to get these changes:" 741 742A pull request should also include an overall message saying what will be 743included in the request, a "git shortlog" listing of the patches 744themselves, and a diffstat showing the overall effect of the patch series. 745The easiest way to get all this information together is, of course, to let 746git do it for you with the "git request-pull" command. 747 748Some maintainers (including Linus) want to see pull requests from signed 749commits; that increases their confidence that the request actually came 750from you. Linus, in particular, will not pull from public hosting sites 751like GitHub in the absence of a signed tag. 752 753The first step toward creating such tags is to make a GNUPG key and get it 754signed by one or more core kernel developers. This step can be hard for 755new developers, but there is no way around it. Attending conferences can 756be a good way to find developers who can sign your key. 757 758Once you have prepared a patch series in git that you wish to have somebody 759pull, create a signed tag with "git tag -s". This will create a new tag 760identifying the last commit in the series and containing a signature 761created with your private key. You will also have the opportunity to add a 762changelog-style message to the tag; this is an ideal place to describe the 763effects of the pull request as a whole. 764 765If the tree the maintainer will be pulling from is not the repository you 766are working from, don't forget to push the signed tag explicitly to the 767public tree. 768 769When generating your pull request, use the signed tag as the target. A 770command like this will do the trick: 771 772 git request-pull master git://my.public.tree/linux.git my-signed-tag 773 774 775---------------------- 776SECTION 2 - REFERENCES 777---------------------- 778 779Andrew Morton, "The perfect patch" (tpp). 780 <http://www.ozlabs.org/~akpm/stuff/tpp.txt> 781 782Jeff Garzik, "Linux kernel patch submission format". 783 <http://linux.yyz.us/patch-format.html> 784 785Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer". 786 <http://www.kroah.com/log/linux/maintainer.html> 787 <http://www.kroah.com/log/linux/maintainer-02.html> 788 <http://www.kroah.com/log/linux/maintainer-03.html> 789 <http://www.kroah.com/log/linux/maintainer-04.html> 790 <http://www.kroah.com/log/linux/maintainer-05.html> 791 <http://www.kroah.com/log/linux/maintainer-06.html> 792 793NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people! 794 <https://lkml.org/lkml/2005/7/11/336> 795 796Kernel Documentation/CodingStyle: 797 <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle> 798 799Linus Torvalds's mail on the canonical patch format: 800 <http://lkml.org/lkml/2005/4/7/183> 801 802Andi Kleen, "On submitting kernel patches" 803 Some strategies to get difficult or controversial changes in. 804 http://halobates.de/on-submitting-patches.pdf 805 806-- 807