linux/Documentation/SubmittingPatches
<<
>>
Prefs
   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
  13Read Documentation/SubmitChecklist for a list of items to check
  14before submitting code.  If you are submitting a driver, also read
  15Documentation/SubmittingDrivers.
  16
  17
  18
  19--------------------------------------------
  20SECTION 1 - CREATING AND SENDING YOUR CHANGE
  21--------------------------------------------
  22
  23
  24
  251) "diff -up"
  26------------
  27
  28Use "diff -up" or "diff -uprN" to create patches.
  29
  30All changes to the Linux kernel occur in the form of patches, as
  31generated by diff(1).  When creating your patch, make sure to create it
  32in "unified diff" format, as supplied by the '-u' argument to diff(1).
  33Also, please use the '-p' argument which shows which C function each
  34change is in - that makes the resultant diff a lot easier to read.
  35Patches should be based in the root kernel source directory,
  36not in any lower subdirectory.
  37
  38To create a patch for a single file, it is often sufficient to do:
  39
  40        SRCTREE= linux-2.6
  41        MYFILE=  drivers/net/mydriver.c
  42
  43        cd $SRCTREE
  44        cp $MYFILE $MYFILE.orig
  45        vi $MYFILE      # make your change
  46        cd ..
  47        diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
  48
  49To create a patch for multiple files, you should unpack a "vanilla",
  50or unmodified kernel source tree, and generate a diff against your
  51own source tree.  For example:
  52
  53        MYSRC= /devel/linux-2.6
  54
  55        tar xvfz linux-2.6.12.tar.gz
  56        mv linux-2.6.12 linux-2.6.12-vanilla
  57        diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \
  58                linux-2.6.12-vanilla $MYSRC > /tmp/patch
  59
  60"dontdiff" is a list of files which are generated by the kernel during
  61the build process, and should be ignored in any diff(1)-generated
  62patch.  The "dontdiff" file is included in the kernel tree in
  632.6.12 and later.
  64
  65Make sure your patch does not include any extra files which do not
  66belong in a patch submission.  Make sure to review your patch -after-
  67generated it with diff(1), to ensure accuracy.
  68
  69If your changes produce a lot of deltas, you may want to look into
  70splitting them into individual patches which modify things in
  71logical stages.  This will facilitate easier reviewing by other
  72kernel developers, very important if you want your patch accepted.
  73There are a number of scripts which can aid in this:
  74
  75Quilt:
  76http://savannah.nongnu.org/projects/quilt
  77
  78Andrew Morton's patch scripts:
  79http://userweb.kernel.org/~akpm/stuff/patch-scripts.tar.gz
  80Instead of these scripts, quilt is the recommended patch management
  81tool (see above).
  82
  83
  84
  852) Describe your changes.
  86
  87Describe the technical detail of the change(s) your patch includes.
  88
  89Be as specific as possible.  The WORST descriptions possible include
  90things like "update driver X", "bug fix for driver X", or "this patch
  91includes updates for subsystem X.  Please apply."
  92
  93The maintainer will thank you if you write your patch description in a
  94form which can be easily pulled into Linux's source code management
  95system, git, as a "commit log".  See #15, below.
  96
  97If your description starts to get long, that's a sign that you probably
  98need to split up your patch.  See #3, next.
  99
 100When you submit or resubmit a patch or patch series, include the
 101complete patch description and justification for it.  Don't just
 102say that this is version N of the patch (series).  Don't expect the
 103patch merger to refer back to earlier patch versions or referenced
 104URLs to find the patch description and put that into the patch.
 105I.e., the patch (series) and its description should be self-contained.
 106This benefits both the patch merger(s) and reviewers.  Some reviewers
 107probably didn't even receive earlier versions of the patch.
 108
 109If the patch fixes a logged bug entry, refer to that bug entry by
 110number and URL.
 111
 112If you want to refer to a specific commit, don't just refer to the
 113SHA-1 ID of the commit. Please also include the oneline summary of
 114the commit, to make it easier for reviewers to know what it is about.
 115Example:
 116
 117        Commit e21d2170f36602ae2708 ("video: remove unnecessary
 118        platform_set_drvdata()") removed the unnecessary
 119        platform_set_drvdata(), but left the variable "dev" unused,
 120        delete it.
 121
 122
 1233) Separate your changes.
 124
 125Separate _logical changes_ into a single patch file.
 126
 127For example, if your changes include both bug fixes and performance
 128enhancements for a single driver, separate those changes into two
 129or more patches.  If your changes include an API update, and a new
 130driver which uses that new API, separate those into two patches.
 131
 132On the other hand, if you make a single change to numerous files,
 133group those changes into a single patch.  Thus a single logical change
 134is contained within a single patch.
 135
 136If one patch depends on another patch in order for a change to be
 137complete, that is OK.  Simply note "this patch depends on patch X"
 138in your patch description.
 139
 140If you cannot condense your patch set into a smaller set of patches,
 141then only post say 15 or so at a time and wait for review and integration.
 142
 143
 144
 1454) Style check your changes.
 146
 147Check your patch for basic style violations, details of which can be
 148found in Documentation/CodingStyle.  Failure to do so simply wastes
 149the reviewers time and will get your patch rejected, probably
 150without even being read.
 151
 152At a minimum you should check your patches with the patch style
 153checker prior to submission (scripts/checkpatch.pl).  You should
 154be able to justify all violations that remain in your patch.
 155
 156
 157
 1585) Select e-mail destination.
 159
 160Look through the MAINTAINERS file and the source code, and determine
 161if your change applies to a specific subsystem of the kernel, with
 162an assigned maintainer.  If so, e-mail that person.  The script
 163scripts/get_maintainer.pl can be very useful at this step.
 164
 165If no maintainer is listed, or the maintainer does not respond, send
 166your patch to the primary Linux kernel developer's mailing list,
 167linux-kernel@vger.kernel.org.  Most kernel developers monitor this
 168e-mail list, and can comment on your changes.
 169
 170
 171Do not send more than 15 patches at once to the vger mailing lists!!!
 172
 173
 174Linus Torvalds is the final arbiter of all changes accepted into the
 175Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>. 
 176He gets a lot of e-mail, so typically you should do your best to -avoid-
 177sending him e-mail. 
 178
 179Patches which are bug fixes, are "obvious" changes, or similarly
 180require little discussion should be sent or CC'd to Linus.  Patches
 181which require discussion or do not have a clear advantage should
 182usually be sent first to linux-kernel.  Only after the patch is
 183discussed should the patch then be submitted to Linus.
 184
 185
 186
 1876) Select your CC (e-mail carbon copy) list.
 188
 189Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
 190
 191Other kernel developers besides Linus need to be aware of your change,
 192so that they may comment on it and offer code review and suggestions.
 193linux-kernel is the primary Linux kernel developer mailing list.
 194Other mailing lists are available for specific subsystems, such as
 195USB, framebuffer devices, the VFS, the SCSI subsystem, etc.  See the
 196MAINTAINERS file for a mailing list that relates specifically to
 197your change.
 198
 199Majordomo lists of VGER.KERNEL.ORG at:
 200        <http://vger.kernel.org/vger-lists.html>
 201
 202If changes affect userland-kernel interfaces, please send
 203the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
 204a man-pages patch, or at least a notification of the change,
 205so that some information makes its way into the manual pages.
 206
 207Even if the maintainer did not respond in step #5, make sure to ALWAYS
 208copy the maintainer when you change their code.
 209
 210For small patches you may want to CC the Trivial Patch Monkey
 211trivial@kernel.org which collects "trivial" patches. Have a look
 212into the MAINTAINERS file for its current manager.
 213Trivial patches must qualify for one of the following rules:
 214 Spelling fixes in documentation
 215 Spelling fixes which could break grep(1)
 216 Warning fixes (cluttering with useless warnings is bad)
 217 Compilation fixes (only if they are actually correct)
 218 Runtime fixes (only if they actually fix things)
 219 Removing use of deprecated functions/macros (eg. check_region)
 220 Contact detail and documentation fixes
 221 Non-portable code replaced by portable code (even in arch-specific,
 222 since people copy, as long as it's trivial)
 223 Any fix by the author/maintainer of the file (ie. patch monkey
 224 in re-transmission mode)
 225
 226
 227
 2287) No MIME, no links, no compression, no attachments.  Just plain text.
 229
 230Linus and other kernel developers need to be able to read and comment
 231on the changes you are submitting.  It is important for a kernel
 232developer to be able to "quote" your changes, using standard e-mail
 233tools, so that they may comment on specific portions of your code.
 234
 235For this reason, all patches should be submitting e-mail "inline".
 236WARNING:  Be wary of your editor's word-wrap corrupting your patch,
 237if you choose to cut-n-paste your patch.
 238
 239Do not attach the patch as a MIME attachment, compressed or not.
 240Many popular e-mail applications will not always transmit a MIME
 241attachment as plain text, making it impossible to comment on your
 242code.  A MIME attachment also takes Linus a bit more time to process,
 243decreasing the likelihood of your MIME-attached change being accepted.
 244
 245Exception:  If your mailer is mangling patches then someone may ask
 246you to re-send them using MIME.
 247
 248See Documentation/email-clients.txt for hints about configuring
 249your e-mail client so that it sends your patches untouched.
 250
 2518) E-mail size.
 252
 253When sending patches to Linus, always follow step #7.
 254
 255Large changes are not appropriate for mailing lists, and some
 256maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
 257it is preferred that you store your patch on an Internet-accessible
 258server, and provide instead a URL (link) pointing to your patch.
 259
 260
 261
 2629) Name your kernel version.
 263
 264It is important to note, either in the subject line or in the patch
 265description, the kernel version to which this patch applies.
 266
 267If the patch does not apply cleanly to the latest kernel version,
 268Linus will not apply it.
 269
 270
 271
 27210) Don't get discouraged.  Re-submit.
 273
 274After you have submitted your change, be patient and wait.  If Linus
 275likes your change and applies it, it will appear in the next version
 276of the kernel that he releases.
 277
 278However, if your change doesn't appear in the next version of the
 279kernel, there could be any number of reasons.  It's YOUR job to
 280narrow down those reasons, correct what was wrong, and submit your
 281updated change.
 282
 283It is quite common for Linus to "drop" your patch without comment.
 284That's the nature of the system.  If he drops your patch, it could be
 285due to
 286* Your patch did not apply cleanly to the latest kernel version.
 287* Your patch was not sufficiently discussed on linux-kernel.
 288* A style issue (see section 2).
 289* An e-mail formatting issue (re-read this section).
 290* A technical problem with your change.
 291* He gets tons of e-mail, and yours got lost in the shuffle.
 292* You are being annoying.
 293
 294When in doubt, solicit comments on linux-kernel mailing list.
 295
 296
 297
 29811) Include PATCH in the subject
 299
 300Due to high e-mail traffic to Linus, and to linux-kernel, it is common
 301convention to prefix your subject line with [PATCH].  This lets Linus
 302and other kernel developers more easily distinguish patches from other
 303e-mail discussions.
 304
 305
 306
 30712) Sign your work
 308
 309To improve tracking of who did what, especially with patches that can
 310percolate to their final resting place in the kernel through several
 311layers of maintainers, we've introduced a "sign-off" procedure on
 312patches that are being emailed around.
 313
 314The sign-off is a simple line at the end of the explanation for the
 315patch, which certifies that you wrote it or otherwise have the right to
 316pass it on as an open-source patch.  The rules are pretty simple: if you
 317can certify the below:
 318
 319        Developer's Certificate of Origin 1.1
 320
 321        By making a contribution to this project, I certify that:
 322
 323        (a) The contribution was created in whole or in part by me and I
 324            have the right to submit it under the open source license
 325            indicated in the file; or
 326
 327        (b) The contribution is based upon previous work that, to the best
 328            of my knowledge, is covered under an appropriate open source
 329            license and I have the right under that license to submit that
 330            work with modifications, whether created in whole or in part
 331            by me, under the same open source license (unless I am
 332            permitted to submit under a different license), as indicated
 333            in the file; or
 334
 335        (c) The contribution was provided directly to me by some other
 336            person who certified (a), (b) or (c) and I have not modified
 337            it.
 338
 339        (d) I understand and agree that this project and the contribution
 340            are public and that a record of the contribution (including all
 341            personal information I submit with it, including my sign-off) is
 342            maintained indefinitely and may be redistributed consistent with
 343            this project or the open source license(s) involved.
 344
 345then you just add a line saying
 346
 347        Signed-off-by: Random J Developer <random@developer.example.org>
 348
 349using your real name (sorry, no pseudonyms or anonymous contributions.)
 350
 351Some people also put extra tags at the end.  They'll just be ignored for
 352now, but you can do this to mark internal company procedures or just
 353point out some special detail about the sign-off. 
 354
 355If you are a subsystem or branch maintainer, sometimes you need to slightly
 356modify patches you receive in order to merge them, because the code is not
 357exactly the same in your tree and the submitters'. If you stick strictly to
 358rule (c), you should ask the submitter to rediff, but this is a totally
 359counter-productive waste of time and energy. Rule (b) allows you to adjust
 360the code, but then it is very impolite to change one submitter's code and
 361make him endorse your bugs. To solve this problem, it is recommended that
 362you add a line between the last Signed-off-by header and yours, indicating
 363the nature of your changes. While there is nothing mandatory about this, it
 364seems like prepending the description with your mail and/or name, all
 365enclosed in square brackets, is noticeable enough to make it obvious that
 366you are responsible for last-minute changes. Example :
 367
 368        Signed-off-by: Random J Developer <random@developer.example.org>
 369        [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
 370        Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
 371
 372This practise is particularly helpful if you maintain a stable branch and
 373want at the same time to credit the author, track changes, merge the fix,
 374and protect the submitter from complaints. Note that under no circumstances
 375can you change the author's identity (the From header), as it is the one
 376which appears in the changelog.
 377
 378Special note to back-porters: It seems to be a common and useful practise
 379to insert an indication of the origin of a patch at the top of the commit
 380message (just after the subject line) to facilitate tracking. For instance,
 381here's what we see in 2.6-stable :
 382
 383    Date:   Tue May 13 19:10:30 2008 +0000
 384
 385        SCSI: libiscsi regression in 2.6.25: fix nop timer handling
 386
 387        commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
 388
 389And here's what appears in 2.4 :
 390
 391    Date:   Tue May 13 22:12:27 2008 +0200
 392
 393        wireless, airo: waitbusy() won't delay
 394
 395        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
 396
 397Whatever the format, this information provides a valuable help to people
 398tracking your trees, and to people trying to trouble-shoot bugs in your
 399tree.
 400
 401
 40213) When to use Acked-by: and Cc:
 403
 404The Signed-off-by: tag indicates that the signer was involved in the
 405development of the patch, or that he/she was in the patch's delivery path.
 406
 407If a person was not directly involved in the preparation or handling of a
 408patch but wishes to signify and record their approval of it then they can
 409arrange to have an Acked-by: line added to the patch's changelog.
 410
 411Acked-by: is often used by the maintainer of the affected code when that
 412maintainer neither contributed to nor forwarded the patch.
 413
 414Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
 415has at least reviewed the patch and has indicated acceptance.  Hence patch
 416mergers will sometimes manually convert an acker's "yep, looks good to me"
 417into an Acked-by:.
 418
 419Acked-by: does not necessarily indicate acknowledgement of the entire patch.
 420For example, if a patch affects multiple subsystems and has an Acked-by: from
 421one subsystem maintainer then this usually indicates acknowledgement of just
 422the part which affects that maintainer's code.  Judgement should be used here.
 423When in doubt people should refer to the original discussion in the mailing
 424list archives.
 425
 426If a person has had the opportunity to comment on a patch, but has not
 427provided such comments, you may optionally add a "Cc:" tag to the patch.
 428This is the only tag which might be added without an explicit action by the
 429person it names.  This tag documents that potentially interested parties
 430have been included in the discussion
 431
 432
 43314) Using Reported-by:, Tested-by:, Reviewed-by: and Suggested-by:
 434
 435If this patch fixes a problem reported by somebody else, consider adding a
 436Reported-by: tag to credit the reporter for their contribution.  Please
 437note that this tag should not be added without the reporter's permission,
 438especially if the problem was not reported in a public forum.  That said,
 439if we diligently credit our bug reporters, they will, hopefully, be
 440inspired to help us again in the future.
 441
 442A Tested-by: tag indicates that the patch has been successfully tested (in
 443some environment) by the person named.  This tag informs maintainers that
 444some testing has been performed, provides a means to locate testers for
 445future patches, and ensures credit for the testers.
 446
 447Reviewed-by:, instead, indicates that the patch has been reviewed and found
 448acceptable according to the Reviewer's Statement:
 449
 450        Reviewer's statement of oversight
 451
 452        By offering my Reviewed-by: tag, I state that:
 453
 454         (a) I have carried out a technical review of this patch to
 455             evaluate its appropriateness and readiness for inclusion into
 456             the mainline kernel.
 457
 458         (b) Any problems, concerns, or questions relating to the patch
 459             have been communicated back to the submitter.  I am satisfied
 460             with the submitter's response to my comments.
 461
 462         (c) While there may be things that could be improved with this
 463             submission, I believe that it is, at this time, (1) a
 464             worthwhile modification to the kernel, and (2) free of known
 465             issues which would argue against its inclusion.
 466
 467         (d) While I have reviewed the patch and believe it to be sound, I
 468             do not (unless explicitly stated elsewhere) make any
 469             warranties or guarantees that it will achieve its stated
 470             purpose or function properly in any given situation.
 471
 472A Reviewed-by tag is a statement of opinion that the patch is an
 473appropriate modification of the kernel without any remaining serious
 474technical issues.  Any interested reviewer (who has done the work) can
 475offer a Reviewed-by tag for a patch.  This tag serves to give credit to
 476reviewers and to inform maintainers of the degree of review which has been
 477done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
 478understand the subject area and to perform thorough reviews, will normally
 479increase the likelihood of your patch getting into the kernel.
 480
 481A Suggested-by: tag indicates that the patch idea is suggested by the person
 482named and ensures credit to the person for the idea. Please note that this
 483tag should not be added without the reporter's permission, especially if the
 484idea was not posted in a public forum. That said, if we diligently credit our
 485idea reporters, they will, hopefully, be inspired to help us again in the
 486future.
 487
 488
 48915) The canonical patch format
 490
 491The canonical patch subject line is:
 492
 493    Subject: [PATCH 001/123] subsystem: summary phrase
 494
 495The canonical patch message body contains the following:
 496
 497  - A "from" line specifying the patch author.
 498
 499  - An empty line.
 500
 501  - The body of the explanation, which will be copied to the
 502    permanent changelog to describe this patch.
 503
 504  - The "Signed-off-by:" lines, described above, which will
 505    also go in the changelog.
 506
 507  - A marker line containing simply "---".
 508
 509  - Any additional comments not suitable for the changelog.
 510
 511  - The actual patch (diff output).
 512
 513The Subject line format makes it very easy to sort the emails
 514alphabetically by subject line - pretty much any email reader will
 515support that - since because the sequence number is zero-padded,
 516the numerical and alphabetic sort is the same.
 517
 518The "subsystem" in the email's Subject should identify which
 519area or subsystem of the kernel is being patched.
 520
 521The "summary phrase" in the email's Subject should concisely
 522describe the patch which that email contains.  The "summary
 523phrase" should not be a filename.  Do not use the same "summary
 524phrase" for every patch in a whole patch series (where a "patch
 525series" is an ordered sequence of multiple, related patches).
 526
 527Bear in mind that the "summary phrase" of your email becomes a
 528globally-unique identifier for that patch.  It propagates all the way
 529into the git changelog.  The "summary phrase" may later be used in
 530developer discussions which refer to the patch.  People will want to
 531google for the "summary phrase" to read discussion regarding that
 532patch.  It will also be the only thing that people may quickly see
 533when, two or three months later, they are going through perhaps
 534thousands of patches using tools such as "gitk" or "git log
 535--oneline".
 536
 537For these reasons, the "summary" must be no more than 70-75
 538characters, and it must describe both what the patch changes, as well
 539as why the patch might be necessary.  It is challenging to be both
 540succinct and descriptive, but that is what a well-written summary
 541should do.
 542
 543The "summary phrase" may be prefixed by tags enclosed in square
 544brackets: "Subject: [PATCH tag] <summary phrase>".  The tags are not
 545considered part of the summary phrase, but describe how the patch
 546should be treated.  Common tags might include a version descriptor if
 547the multiple versions of the patch have been sent out in response to
 548comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
 549comments.  If there are four patches in a patch series the individual
 550patches may be numbered like this: 1/4, 2/4, 3/4, 4/4.  This assures
 551that developers understand the order in which the patches should be
 552applied and that they have reviewed or applied all of the patches in
 553the patch series.
 554
 555A couple of example Subjects:
 556
 557    Subject: [patch 2/5] ext2: improve scalability of bitmap searching
 558    Subject: [PATCHv2 001/207] x86: fix eflags tracking
 559
 560The "from" line must be the very first line in the message body,
 561and has the form:
 562
 563        From: Original Author <author@example.com>
 564
 565The "from" line specifies who will be credited as the author of the
 566patch in the permanent changelog.  If the "from" line is missing,
 567then the "From:" line from the email header will be used to determine
 568the patch author in the changelog.
 569
 570The explanation body will be committed to the permanent source
 571changelog, so should make sense to a competent reader who has long
 572since forgotten the immediate details of the discussion that might
 573have led to this patch.  Including symptoms of the failure which the
 574patch addresses (kernel log messages, oops messages, etc.) is
 575especially useful for people who might be searching the commit logs
 576looking for the applicable patch.  If a patch fixes a compile failure,
 577it may not be necessary to include _all_ of the compile failures; just
 578enough that it is likely that someone searching for the patch can find
 579it.  As in the "summary phrase", it is important to be both succinct as
 580well as descriptive.
 581
 582The "---" marker line serves the essential purpose of marking for patch
 583handling tools where the changelog message ends.
 584
 585One good use for the additional comments after the "---" marker is for
 586a diffstat, to show what files have changed, and the number of
 587inserted and deleted lines per file.  A diffstat is especially useful
 588on bigger patches.  Other comments relevant only to the moment or the
 589maintainer, not suitable for the permanent changelog, should also go
 590here.  A good example of such comments might be "patch changelogs"
 591which describe what has changed between the v1 and v2 version of the
 592patch.
 593
 594If you are going to include a diffstat after the "---" marker, please
 595use diffstat options "-p 1 -w 70" so that filenames are listed from
 596the top of the kernel source tree and don't use too much horizontal
 597space (easily fit in 80 columns, maybe with some indentation).
 598
 599See more details on the proper patch format in the following
 600references.
 601
 602
 60316) Sending "git pull" requests  (from Linus emails)
 604
 605Please write the git repo address and branch name alone on the same line
 606so that I can't even by mistake pull from the wrong branch, and so
 607that a triple-click just selects the whole thing.
 608
 609So the proper format is something along the lines of:
 610
 611        "Please pull from
 612
 613                git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
 614
 615         to get these changes:"
 616
 617so that I don't have to hunt-and-peck for the address and inevitably
 618get it wrong (actually, I've only gotten it wrong a few times, and
 619checking against the diffstat tells me when I get it wrong, but I'm
 620just a lot more comfortable when I don't have to "look for" the right
 621thing to pull, and double-check that I have the right branch-name).
 622
 623
 624Please use "git diff -M --stat --summary" to generate the diffstat:
 625the -M enables rename detection, and the summary enables a summary of
 626new/deleted or renamed files.
 627
 628With rename detection, the statistics are rather different [...]
 629because git will notice that a fair number of the changes are renames.
 630
 631-----------------------------------
 632SECTION 2 - HINTS, TIPS, AND TRICKS
 633-----------------------------------
 634
 635This section lists many of the common "rules" associated with code
 636submitted to the kernel.  There are always exceptions... but you must
 637have a really good reason for doing so.  You could probably call this
 638section Linus Computer Science 101.
 639
 640
 641
 6421) Read Documentation/CodingStyle
 643
 644Nuff said.  If your code deviates too much from this, it is likely
 645to be rejected without further review, and without comment.
 646
 647One significant exception is when moving code from one file to
 648another -- in this case you should not modify the moved code at all in
 649the same patch which moves it.  This clearly delineates the act of
 650moving the code and your changes.  This greatly aids review of the
 651actual differences and allows tools to better track the history of
 652the code itself.
 653
 654Check your patches with the patch style checker prior to submission
 655(scripts/checkpatch.pl).  The style checker should be viewed as
 656a guide not as the final word.  If your code looks better with
 657a violation then its probably best left alone.
 658
 659The checker reports at three levels:
 660 - ERROR: things that are very likely to be wrong
 661 - WARNING: things requiring careful review
 662 - CHECK: things requiring thought
 663
 664You should be able to justify all violations that remain in your
 665patch.
 666
 667
 668
 6692) #ifdefs are ugly
 670
 671Code cluttered with ifdefs is difficult to read and maintain.  Don't do
 672it.  Instead, put your ifdefs in a header, and conditionally define
 673'static inline' functions, or macros, which are used in the code.
 674Let the compiler optimize away the "no-op" case.
 675
 676Simple example, of poor code:
 677
 678        dev = alloc_etherdev (sizeof(struct funky_private));
 679        if (!dev)
 680                return -ENODEV;
 681        #ifdef CONFIG_NET_FUNKINESS
 682        init_funky_net(dev);
 683        #endif
 684
 685Cleaned-up example:
 686
 687(in header)
 688        #ifndef CONFIG_NET_FUNKINESS
 689        static inline void init_funky_net (struct net_device *d) {}
 690        #endif
 691
 692(in the code itself)
 693        dev = alloc_etherdev (sizeof(struct funky_private));
 694        if (!dev)
 695                return -ENODEV;
 696        init_funky_net(dev);
 697
 698
 699
 7003) 'static inline' is better than a macro
 701
 702Static inline functions are greatly preferred over macros.
 703They provide type safety, have no length limitations, no formatting
 704limitations, and under gcc they are as cheap as macros.
 705
 706Macros should only be used for cases where a static inline is clearly
 707suboptimal [there are a few, isolated cases of this in fast paths],
 708or where it is impossible to use a static inline function [such as
 709string-izing].
 710
 711'static inline' is preferred over 'static __inline__', 'extern inline',
 712and 'extern __inline__'.
 713
 714
 715
 7164) Don't over-design.
 717
 718Don't try to anticipate nebulous future cases which may or may not
 719be useful:  "Make it as simple as you can, and no simpler."
 720
 721
 722
 723----------------------
 724SECTION 3 - REFERENCES
 725----------------------
 726
 727Andrew Morton, "The perfect patch" (tpp).
 728  <http://userweb.kernel.org/~akpm/stuff/tpp.txt>
 729
 730Jeff Garzik, "Linux kernel patch submission format".
 731  <http://linux.yyz.us/patch-format.html>
 732
 733Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
 734  <http://www.kroah.com/log/linux/maintainer.html>
 735  <http://www.kroah.com/log/linux/maintainer-02.html>
 736  <http://www.kroah.com/log/linux/maintainer-03.html>
 737  <http://www.kroah.com/log/linux/maintainer-04.html>
 738  <http://www.kroah.com/log/linux/maintainer-05.html>
 739
 740NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
 741  <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2>
 742
 743Kernel Documentation/CodingStyle:
 744  <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
 745
 746Linus Torvalds's mail on the canonical patch format:
 747  <http://lkml.org/lkml/2005/4/7/183>
 748
 749Andi Kleen, "On submitting kernel patches"
 750  Some strategies to get difficult or controversial changes in.
 751  http://halobates.de/on-submitting-patches.pdf
 752
 753--
 754
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.