linux/Documentation/SubmittingPatches
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   2        How to Get Your Change Into the Linux Kernel
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   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.  For earlier kernel versions, you can get it
  64from <http://www.xenotime.net/linux/doc/dontdiff>.
  65
  66Make sure your patch does not include any extra files which do not
  67belong in a patch submission.  Make sure to review your patch -after-
  68generated it with diff(1), to ensure accuracy.
  69
  70If your changes produce a lot of deltas, you may want to look into
  71splitting them into individual patches which modify things in
  72logical stages.  This will facilitate easier reviewing by other
  73kernel developers, very important if you want your patch accepted.
  74There are a number of scripts which can aid in this:
  75
  76Quilt:
  77http://savannah.nongnu.org/projects/quilt
  78
  79Andrew Morton's patch scripts:
  80http://userweb.kernel.org/~akpm/stuff/patch-scripts.tar.gz
  81Instead of these scripts, quilt is the recommended patch management
  82tool (see above).
  83
  84
  85
  862) Describe your changes.
  87
  88Describe the technical detail of the change(s) your patch includes.
  89
  90Be as specific as possible.  The WORST descriptions possible include
  91things like "update driver X", "bug fix for driver X", or "this patch
  92includes updates for subsystem X.  Please apply."
  93
  94The maintainer will thank you if you write your patch description in a
  95form which can be easily pulled into Linux's source code management
  96system, git, as a "commit log".  See #15, below.
  97
  98If your description starts to get long, that's a sign that you probably
  99need to split up your patch.  See #3, next.
 100
 101When you submit or resubmit a patch or patch series, include the
 102complete patch description and justification for it.  Don't just
 103say that this is version N of the patch (series).  Don't expect the
 104patch merger to refer back to earlier patch versions or referenced
 105URLs to find the patch description and put that into the patch.
 106I.e., the patch (series) and its description should be self-contained.
 107This benefits both the patch merger(s) and reviewers.  Some reviewers
 108probably didn't even receive earlier versions of the patch.
 109
 110If the patch fixes a logged bug entry, refer to that bug entry by
 111number and URL.
 112
 113
 1143) Separate your changes.
 115
 116Separate _logical changes_ into a single patch file.
 117
 118For example, if your changes include both bug fixes and performance
 119enhancements for a single driver, separate those changes into two
 120or more patches.  If your changes include an API update, and a new
 121driver which uses that new API, separate those into two patches.
 122
 123On the other hand, if you make a single change to numerous files,
 124group those changes into a single patch.  Thus a single logical change
 125is contained within a single patch.
 126
 127If one patch depends on another patch in order for a change to be
 128complete, that is OK.  Simply note "this patch depends on patch X"
 129in your patch description.
 130
 131If you cannot condense your patch set into a smaller set of patches,
 132then only post say 15 or so at a time and wait for review and integration.
 133
 134
 135
 1364) Style check your changes.
 137
 138Check your patch for basic style violations, details of which can be
 139found in Documentation/CodingStyle.  Failure to do so simply wastes
 140the reviewers time and will get your patch rejected, probably
 141without even being read.
 142
 143At a minimum you should check your patches with the patch style
 144checker prior to submission (scripts/checkpatch.pl).  You should
 145be able to justify all violations that remain in your patch.
 146
 147
 148
 1495) Select e-mail destination.
 150
 151Look through the MAINTAINERS file and the source code, and determine
 152if your change applies to a specific subsystem of the kernel, with
 153an assigned maintainer.  If so, e-mail that person.
 154
 155If no maintainer is listed, or the maintainer does not respond, send
 156your patch to the primary Linux kernel developer's mailing list,
 157linux-kernel@vger.kernel.org.  Most kernel developers monitor this
 158e-mail list, and can comment on your changes.
 159
 160
 161Do not send more than 15 patches at once to the vger mailing lists!!!
 162
 163
 164Linus Torvalds is the final arbiter of all changes accepted into the
 165Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>. 
 166He gets a lot of e-mail, so typically you should do your best to -avoid-
 167sending him e-mail. 
 168
 169Patches which are bug fixes, are "obvious" changes, or similarly
 170require little discussion should be sent or CC'd to Linus.  Patches
 171which require discussion or do not have a clear advantage should
 172usually be sent first to linux-kernel.  Only after the patch is
 173discussed should the patch then be submitted to Linus.
 174
 175
 176
 1776) Select your CC (e-mail carbon copy) list.
 178
 179Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
 180
 181Other kernel developers besides Linus need to be aware of your change,
 182so that they may comment on it and offer code review and suggestions.
 183linux-kernel is the primary Linux kernel developer mailing list.
 184Other mailing lists are available for specific subsystems, such as
 185USB, framebuffer devices, the VFS, the SCSI subsystem, etc.  See the
 186MAINTAINERS file for a mailing list that relates specifically to
 187your change.
 188
 189Majordomo lists of VGER.KERNEL.ORG at:
 190        <http://vger.kernel.org/vger-lists.html>
 191
 192If changes affect userland-kernel interfaces, please send
 193the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
 194a man-pages patch, or at least a notification of the change,
 195so that some information makes its way into the manual pages.
 196
 197Even if the maintainer did not respond in step #5, make sure to ALWAYS
 198copy the maintainer when you change their code.
 199
 200For small patches you may want to CC the Trivial Patch Monkey
 201trivial@kernel.org which collects "trivial" patches. Have a look
 202into the MAINTAINERS file for its current manager.
 203Trivial patches must qualify for one of the following rules:
 204 Spelling fixes in documentation
 205 Spelling fixes which could break grep(1)
 206 Warning fixes (cluttering with useless warnings is bad)
 207 Compilation fixes (only if they are actually correct)
 208 Runtime fixes (only if they actually fix things)
 209 Removing use of deprecated functions/macros (eg. check_region)
 210 Contact detail and documentation fixes
 211 Non-portable code replaced by portable code (even in arch-specific,
 212 since people copy, as long as it's trivial)
 213 Any fix by the author/maintainer of the file (ie. patch monkey
 214 in re-transmission mode)
 215
 216
 217
 2187) No MIME, no links, no compression, no attachments.  Just plain text.
 219
 220Linus and other kernel developers need to be able to read and comment
 221on the changes you are submitting.  It is important for a kernel
 222developer to be able to "quote" your changes, using standard e-mail
 223tools, so that they may comment on specific portions of your code.
 224
 225For this reason, all patches should be submitting e-mail "inline".
 226WARNING:  Be wary of your editor's word-wrap corrupting your patch,
 227if you choose to cut-n-paste your patch.
 228
 229Do not attach the patch as a MIME attachment, compressed or not.
 230Many popular e-mail applications will not always transmit a MIME
 231attachment as plain text, making it impossible to comment on your
 232code.  A MIME attachment also takes Linus a bit more time to process,
 233decreasing the likelihood of your MIME-attached change being accepted.
 234
 235Exception:  If your mailer is mangling patches then someone may ask
 236you to re-send them using MIME.
 237
 238See Documentation/email-clients.txt for hints about configuring
 239your e-mail client so that it sends your patches untouched.
 240
 2418) E-mail size.
 242
 243When sending patches to Linus, always follow step #7.
 244
 245Large changes are not appropriate for mailing lists, and some
 246maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
 247it is preferred that you store your patch on an Internet-accessible
 248server, and provide instead a URL (link) pointing to your patch.
 249
 250
 251
 2529) Name your kernel version.
 253
 254It is important to note, either in the subject line or in the patch
 255description, the kernel version to which this patch applies.
 256
 257If the patch does not apply cleanly to the latest kernel version,
 258Linus will not apply it.
 259
 260
 261
 26210) Don't get discouraged.  Re-submit.
 263
 264After you have submitted your change, be patient and wait.  If Linus
 265likes your change and applies it, it will appear in the next version
 266of the kernel that he releases.
 267
 268However, if your change doesn't appear in the next version of the
 269kernel, there could be any number of reasons.  It's YOUR job to
 270narrow down those reasons, correct what was wrong, and submit your
 271updated change.
 272
 273It is quite common for Linus to "drop" your patch without comment.
 274That's the nature of the system.  If he drops your patch, it could be
 275due to
 276* Your patch did not apply cleanly to the latest kernel version.
 277* Your patch was not sufficiently discussed on linux-kernel.
 278* A style issue (see section 2).
 279* An e-mail formatting issue (re-read this section).
 280* A technical problem with your change.
 281* He gets tons of e-mail, and yours got lost in the shuffle.
 282* You are being annoying.
 283
 284When in doubt, solicit comments on linux-kernel mailing list.
 285
 286
 287
 28811) Include PATCH in the subject
 289
 290Due to high e-mail traffic to Linus, and to linux-kernel, it is common
 291convention to prefix your subject line with [PATCH].  This lets Linus
 292and other kernel developers more easily distinguish patches from other
 293e-mail discussions.
 294
 295
 296
 29712) Sign your work
 298
 299To improve tracking of who did what, especially with patches that can
 300percolate to their final resting place in the kernel through several
 301layers of maintainers, we've introduced a "sign-off" procedure on
 302patches that are being emailed around.
 303
 304The sign-off is a simple line at the end of the explanation for the
 305patch, which certifies that you wrote it or otherwise have the right to
 306pass it on as an open-source patch.  The rules are pretty simple: if you
 307can certify the below:
 308
 309        Developer's Certificate of Origin 1.1
 310
 311        By making a contribution to this project, I certify that:
 312
 313        (a) The contribution was created in whole or in part by me and I
 314            have the right to submit it under the open source license
 315            indicated in the file; or
 316
 317        (b) The contribution is based upon previous work that, to the best
 318            of my knowledge, is covered under an appropriate open source
 319            license and I have the right under that license to submit that
 320            work with modifications, whether created in whole or in part
 321            by me, under the same open source license (unless I am
 322            permitted to submit under a different license), as indicated
 323            in the file; or
 324
 325        (c) The contribution was provided directly to me by some other
 326            person who certified (a), (b) or (c) and I have not modified
 327            it.
 328
 329        (d) I understand and agree that this project and the contribution
 330            are public and that a record of the contribution (including all
 331            personal information I submit with it, including my sign-off) is
 332            maintained indefinitely and may be redistributed consistent with
 333            this project or the open source license(s) involved.
 334
 335then you just add a line saying
 336
 337        Signed-off-by: Random J Developer <random@developer.example.org>
 338
 339using your real name (sorry, no pseudonyms or anonymous contributions.)
 340
 341Some people also put extra tags at the end.  They'll just be ignored for
 342now, but you can do this to mark internal company procedures or just
 343point out some special detail about the sign-off. 
 344
 345If you are a subsystem or branch maintainer, sometimes you need to slightly
 346modify patches you receive in order to merge them, because the code is not
 347exactly the same in your tree and the submitters'. If you stick strictly to
 348rule (c), you should ask the submitter to rediff, but this is a totally
 349counter-productive waste of time and energy. Rule (b) allows you to adjust
 350the code, but then it is very impolite to change one submitter's code and
 351make him endorse your bugs. To solve this problem, it is recommended that
 352you add a line between the last Signed-off-by header and yours, indicating
 353the nature of your changes. While there is nothing mandatory about this, it
 354seems like prepending the description with your mail and/or name, all
 355enclosed in square brackets, is noticeable enough to make it obvious that
 356you are responsible for last-minute changes. Example :
 357
 358        Signed-off-by: Random J Developer <random@developer.example.org>
 359        [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
 360        Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
 361
 362This practise is particularly helpful if you maintain a stable branch and
 363want at the same time to credit the author, track changes, merge the fix,
 364and protect the submitter from complaints. Note that under no circumstances
 365can you change the author's identity (the From header), as it is the one
 366which appears in the changelog.
 367
 368Special note to back-porters: It seems to be a common and useful practise
 369to insert an indication of the origin of a patch at the top of the commit
 370message (just after the subject line) to facilitate tracking. For instance,
 371here's what we see in 2.6-stable :
 372
 373    Date:   Tue May 13 19:10:30 2008 +0000
 374
 375        SCSI: libiscsi regression in 2.6.25: fix nop timer handling
 376
 377        commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
 378
 379And here's what appears in 2.4 :
 380
 381    Date:   Tue May 13 22:12:27 2008 +0200
 382
 383        wireless, airo: waitbusy() won't delay
 384
 385        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
 386
 387Whatever the format, this information provides a valuable help to people
 388tracking your trees, and to people trying to trouble-shoot bugs in your
 389tree.
 390
 391
 39213) When to use Acked-by: and Cc:
 393
 394The Signed-off-by: tag indicates that the signer was involved in the
 395development of the patch, or that he/she was in the patch's delivery path.
 396
 397If a person was not directly involved in the preparation or handling of a
 398patch but wishes to signify and record their approval of it then they can
 399arrange to have an Acked-by: line added to the patch's changelog.
 400
 401Acked-by: is often used by the maintainer of the affected code when that
 402maintainer neither contributed to nor forwarded the patch.
 403
 404Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
 405has at least reviewed the patch and has indicated acceptance.  Hence patch
 406mergers will sometimes manually convert an acker's "yep, looks good to me"
 407into an Acked-by:.
 408
 409Acked-by: does not necessarily indicate acknowledgement of the entire patch.
 410For example, if a patch affects multiple subsystems and has an Acked-by: from
 411one subsystem maintainer then this usually indicates acknowledgement of just
 412the part which affects that maintainer's code.  Judgement should be used here.
 413When in doubt people should refer to the original discussion in the mailing
 414list archives.
 415
 416If a person has had the opportunity to comment on a patch, but has not
 417provided such comments, you may optionally add a "Cc:" tag to the patch.
 418This is the only tag which might be added without an explicit action by the
 419person it names.  This tag documents that potentially interested parties
 420have been included in the discussion
 421
 422
 42314) Using Reported-by:, Tested-by: and Reviewed-by:
 424
 425If this patch fixes a problem reported by somebody else, consider adding a
 426Reported-by: tag to credit the reporter for their contribution.  Please
 427note that this tag should not be added without the reporter's permission,
 428especially if the problem was not reported in a public forum.  That said,
 429if we diligently credit our bug reporters, they will, hopefully, be
 430inspired to help us again in the future.
 431
 432A Tested-by: tag indicates that the patch has been successfully tested (in
 433some environment) by the person named.  This tag informs maintainers that
 434some testing has been performed, provides a means to locate testers for
 435future patches, and ensures credit for the testers.
 436
 437Reviewed-by:, instead, indicates that the patch has been reviewed and found
 438acceptable according to the Reviewer's Statement:
 439
 440        Reviewer's statement of oversight
 441
 442        By offering my Reviewed-by: tag, I state that:
 443
 444         (a) I have carried out a technical review of this patch to
 445             evaluate its appropriateness and readiness for inclusion into
 446             the mainline kernel.
 447
 448         (b) Any problems, concerns, or questions relating to the patch
 449             have been communicated back to the submitter.  I am satisfied
 450             with the submitter's response to my comments.
 451
 452         (c) While there may be things that could be improved with this
 453             submission, I believe that it is, at this time, (1) a
 454             worthwhile modification to the kernel, and (2) free of known
 455             issues which would argue against its inclusion.
 456
 457         (d) While I have reviewed the patch and believe it to be sound, I
 458             do not (unless explicitly stated elsewhere) make any
 459             warranties or guarantees that it will achieve its stated
 460             purpose or function properly in any given situation.
 461
 462A Reviewed-by tag is a statement of opinion that the patch is an
 463appropriate modification of the kernel without any remaining serious
 464technical issues.  Any interested reviewer (who has done the work) can
 465offer a Reviewed-by tag for a patch.  This tag serves to give credit to
 466reviewers and to inform maintainers of the degree of review which has been
 467done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
 468understand the subject area and to perform thorough reviews, will normally
 469increase the likelihood of your patch getting into the kernel.
 470
 471
 47215) The canonical patch format
 473
 474The canonical patch subject line is:
 475
 476    Subject: [PATCH 001/123] subsystem: summary phrase
 477
 478The canonical patch message body contains the following:
 479
 480  - A "from" line specifying the patch author.
 481
 482  - An empty line.
 483
 484  - The body of the explanation, which will be copied to the
 485    permanent changelog to describe this patch.
 486
 487  - The "Signed-off-by:" lines, described above, which will
 488    also go in the changelog.
 489
 490  - A marker line containing simply "---".
 491
 492  - Any additional comments not suitable for the changelog.
 493
 494  - The actual patch (diff output).
 495
 496The Subject line format makes it very easy to sort the emails
 497alphabetically by subject line - pretty much any email reader will
 498support that - since because the sequence number is zero-padded,
 499the numerical and alphabetic sort is the same.
 500
 501The "subsystem" in the email's Subject should identify which
 502area or subsystem of the kernel is being patched.
 503
 504The "summary phrase" in the email's Subject should concisely
 505describe the patch which that email contains.  The "summary
 506phrase" should not be a filename.  Do not use the same "summary
 507phrase" for every patch in a whole patch series (where a "patch
 508series" is an ordered sequence of multiple, related patches).
 509
 510Bear in mind that the "summary phrase" of your email becomes a
 511globally-unique identifier for that patch.  It propagates all the way
 512into the git changelog.  The "summary phrase" may later be used in
 513developer discussions which refer to the patch.  People will want to
 514google for the "summary phrase" to read discussion regarding that
 515patch.  It will also be the only thing that people may quickly see
 516when, two or three months later, they are going through perhaps
 517thousands of patches using tools such as "gitk" or "git log
 518--oneline".
 519
 520For these reasons, the "summary" must be no more than 70-75
 521characters, and it must describe both what the patch changes, as well
 522as why the patch might be necessary.  It is challenging to be both
 523succinct and descriptive, but that is what a well-written summary
 524should do.
 525
 526The "summary phrase" may be prefixed by tags enclosed in square
 527brackets: "Subject: [PATCH tag] <summary phrase>".  The tags are not
 528considered part of the summary phrase, but describe how the patch
 529should be treated.  Common tags might include a version descriptor if
 530the multiple versions of the patch have been sent out in response to
 531comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
 532comments.  If there are four patches in a patch series the individual
 533patches may be numbered like this: 1/4, 2/4, 3/4, 4/4.  This assures
 534that developers understand the order in which the patches should be
 535applied and that they have reviewed or applied all of the patches in
 536the patch series.
 537
 538A couple of example Subjects:
 539
 540    Subject: [patch 2/5] ext2: improve scalability of bitmap searching
 541    Subject: [PATCHv2 001/207] x86: fix eflags tracking
 542
 543The "from" line must be the very first line in the message body,
 544and has the form:
 545
 546        From: Original Author <author@example.com>
 547
 548The "from" line specifies who will be credited as the author of the
 549patch in the permanent changelog.  If the "from" line is missing,
 550then the "From:" line from the email header will be used to determine
 551the patch author in the changelog.
 552
 553The explanation body will be committed to the permanent source
 554changelog, so should make sense to a competent reader who has long
 555since forgotten the immediate details of the discussion that might
 556have led to this patch.  Including symptoms of the failure which the
 557patch addresses (kernel log messages, oops messages, etc.) is
 558especially useful for people who might be searching the commit logs
 559looking for the applicable patch.  If a patch fixes a compile failure,
 560it may not be necessary to include _all_ of the compile failures; just
 561enough that it is likely that someone searching for the patch can find
 562it.  As in the "summary phrase", it is important to be both succinct as
 563well as descriptive.
 564
 565The "---" marker line serves the essential purpose of marking for patch
 566handling tools where the changelog message ends.
 567
 568One good use for the additional comments after the "---" marker is for
 569a diffstat, to show what files have changed, and the number of
 570inserted and deleted lines per file.  A diffstat is especially useful
 571on bigger patches.  Other comments relevant only to the moment or the
 572maintainer, not suitable for the permanent changelog, should also go
 573here.  A good example of such comments might be "patch changelogs"
 574which describe what has changed between the v1 and v2 version of the
 575patch.
 576
 577If you are going to include a diffstat after the "---" marker, please
 578use diffstat options "-p 1 -w 70" so that filenames are listed from
 579the top of the kernel source tree and don't use too much horizontal
 580space (easily fit in 80 columns, maybe with some indentation).
 581
 582See more details on the proper patch format in the following
 583references.
 584
 585
 58616) Sending "git pull" requests  (from Linus emails)
 587
 588Please write the git repo address and branch name alone on the same line
 589so that I can't even by mistake pull from the wrong branch, and so
 590that a triple-click just selects the whole thing.
 591
 592So the proper format is something along the lines of:
 593
 594        "Please pull from
 595
 596                git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
 597
 598         to get these changes:"
 599
 600so that I don't have to hunt-and-peck for the address and inevitably
 601get it wrong (actually, I've only gotten it wrong a few times, and
 602checking against the diffstat tells me when I get it wrong, but I'm
 603just a lot more comfortable when I don't have to "look for" the right
 604thing to pull, and double-check that I have the right branch-name).
 605
 606
 607Please use "git diff -M --stat --summary" to generate the diffstat:
 608the -M enables rename detection, and the summary enables a summary of
 609new/deleted or renamed files.
 610
 611With rename detection, the statistics are rather different [...]
 612because git will notice that a fair number of the changes are renames.
 613
 614-----------------------------------
 615SECTION 2 - HINTS, TIPS, AND TRICKS
 616-----------------------------------
 617
 618This section lists many of the common "rules" associated with code
 619submitted to the kernel.  There are always exceptions... but you must
 620have a really good reason for doing so.  You could probably call this
 621section Linus Computer Science 101.
 622
 623
 624
 6251) Read Documentation/CodingStyle
 626
 627Nuff said.  If your code deviates too much from this, it is likely
 628to be rejected without further review, and without comment.
 629
 630One significant exception is when moving code from one file to
 631another -- in this case you should not modify the moved code at all in
 632the same patch which moves it.  This clearly delineates the act of
 633moving the code and your changes.  This greatly aids review of the
 634actual differences and allows tools to better track the history of
 635the code itself.
 636
 637Check your patches with the patch style checker prior to submission
 638(scripts/checkpatch.pl).  The style checker should be viewed as
 639a guide not as the final word.  If your code looks better with
 640a violation then its probably best left alone.
 641
 642The checker reports at three levels:
 643 - ERROR: things that are very likely to be wrong
 644 - WARNING: things requiring careful review
 645 - CHECK: things requiring thought
 646
 647You should be able to justify all violations that remain in your
 648patch.
 649
 650
 651
 6522) #ifdefs are ugly
 653
 654Code cluttered with ifdefs is difficult to read and maintain.  Don't do
 655it.  Instead, put your ifdefs in a header, and conditionally define
 656'static inline' functions, or macros, which are used in the code.
 657Let the compiler optimize away the "no-op" case.
 658
 659Simple example, of poor code:
 660
 661        dev = alloc_etherdev (sizeof(struct funky_private));
 662        if (!dev)
 663                return -ENODEV;
 664        #ifdef CONFIG_NET_FUNKINESS
 665        init_funky_net(dev);
 666        #endif
 667
 668Cleaned-up example:
 669
 670(in header)
 671        #ifndef CONFIG_NET_FUNKINESS
 672        static inline void init_funky_net (struct net_device *d) {}
 673        #endif
 674
 675(in the code itself)
 676        dev = alloc_etherdev (sizeof(struct funky_private));
 677        if (!dev)
 678                return -ENODEV;
 679        init_funky_net(dev);
 680
 681
 682
 6833) 'static inline' is better than a macro
 684
 685Static inline functions are greatly preferred over macros.
 686They provide type safety, have no length limitations, no formatting
 687limitations, and under gcc they are as cheap as macros.
 688
 689Macros should only be used for cases where a static inline is clearly
 690suboptimal [there are a few, isolated cases of this in fast paths],
 691or where it is impossible to use a static inline function [such as
 692string-izing].
 693
 694'static inline' is preferred over 'static __inline__', 'extern inline',
 695and 'extern __inline__'.
 696
 697
 698
 6994) Don't over-design.
 700
 701Don't try to anticipate nebulous future cases which may or may not
 702be useful:  "Make it as simple as you can, and no simpler."
 703
 704
 705
 706----------------------
 707SECTION 3 - REFERENCES
 708----------------------
 709
 710Andrew Morton, "The perfect patch" (tpp).
 711  <http://userweb.kernel.org/~akpm/stuff/tpp.txt>
 712
 713Jeff Garzik, "Linux kernel patch submission format".
 714  <http://linux.yyz.us/patch-format.html>
 715
 716Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
 717  <http://www.kroah.com/log/linux/maintainer.html>
 718  <http://www.kroah.com/log/linux/maintainer-02.html>
 719  <http://www.kroah.com/log/linux/maintainer-03.html>
 720  <http://www.kroah.com/log/linux/maintainer-04.html>
 721  <http://www.kroah.com/log/linux/maintainer-05.html>
 722
 723NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
 724  <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2>
 725
 726Kernel Documentation/CodingStyle:
 727  <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
 728
 729Linus Torvalds's mail on the canonical patch format:
 730  <http://lkml.org/lkml/2005/4/7/183>
 731
 732Andi Kleen, "On submitting kernel patches"
 733  Some strategies to get difficult or controversial changes in.
 734  http://halobates.de/on-submitting-patches.pdf
 735
 736--
 737
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