linux/Documentation/SubmittingPatches
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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.  The script
 154scripts/get_maintainer.pl can be very useful at this step.
 155
 156If no maintainer is listed, or the maintainer does not respond, send
 157your patch to the primary Linux kernel developer's mailing list,
 158linux-kernel@vger.kernel.org.  Most kernel developers monitor this
 159e-mail list, and can comment on your changes.
 160
 161
 162Do not send more than 15 patches at once to the vger mailing lists!!!
 163
 164
 165Linus Torvalds is the final arbiter of all changes accepted into the
 166Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>. 
 167He gets a lot of e-mail, so typically you should do your best to -avoid-
 168sending him e-mail. 
 169
 170Patches which are bug fixes, are "obvious" changes, or similarly
 171require little discussion should be sent or CC'd to Linus.  Patches
 172which require discussion or do not have a clear advantage should
 173usually be sent first to linux-kernel.  Only after the patch is
 174discussed should the patch then be submitted to Linus.
 175
 176
 177
 1786) Select your CC (e-mail carbon copy) list.
 179
 180Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
 181
 182Other kernel developers besides Linus need to be aware of your change,
 183so that they may comment on it and offer code review and suggestions.
 184linux-kernel is the primary Linux kernel developer mailing list.
 185Other mailing lists are available for specific subsystems, such as
 186USB, framebuffer devices, the VFS, the SCSI subsystem, etc.  See the
 187MAINTAINERS file for a mailing list that relates specifically to
 188your change.
 189
 190Majordomo lists of VGER.KERNEL.ORG at:
 191        <http://vger.kernel.org/vger-lists.html>
 192
 193If changes affect userland-kernel interfaces, please send
 194the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
 195a man-pages patch, or at least a notification of the change,
 196so that some information makes its way into the manual pages.
 197
 198Even if the maintainer did not respond in step #5, make sure to ALWAYS
 199copy the maintainer when you change their code.
 200
 201For small patches you may want to CC the Trivial Patch Monkey
 202trivial@kernel.org which collects "trivial" patches. Have a look
 203into the MAINTAINERS file for its current manager.
 204Trivial patches must qualify for one of the following rules:
 205 Spelling fixes in documentation
 206 Spelling fixes which could break grep(1)
 207 Warning fixes (cluttering with useless warnings is bad)
 208 Compilation fixes (only if they are actually correct)
 209 Runtime fixes (only if they actually fix things)
 210 Removing use of deprecated functions/macros (eg. check_region)
 211 Contact detail and documentation fixes
 212 Non-portable code replaced by portable code (even in arch-specific,
 213 since people copy, as long as it's trivial)
 214 Any fix by the author/maintainer of the file (ie. patch monkey
 215 in re-transmission mode)
 216
 217
 218
 2197) No MIME, no links, no compression, no attachments.  Just plain text.
 220
 221Linus and other kernel developers need to be able to read and comment
 222on the changes you are submitting.  It is important for a kernel
 223developer to be able to "quote" your changes, using standard e-mail
 224tools, so that they may comment on specific portions of your code.
 225
 226For this reason, all patches should be submitting e-mail "inline".
 227WARNING:  Be wary of your editor's word-wrap corrupting your patch,
 228if you choose to cut-n-paste your patch.
 229
 230Do not attach the patch as a MIME attachment, compressed or not.
 231Many popular e-mail applications will not always transmit a MIME
 232attachment as plain text, making it impossible to comment on your
 233code.  A MIME attachment also takes Linus a bit more time to process,
 234decreasing the likelihood of your MIME-attached change being accepted.
 235
 236Exception:  If your mailer is mangling patches then someone may ask
 237you to re-send them using MIME.
 238
 239See Documentation/email-clients.txt for hints about configuring
 240your e-mail client so that it sends your patches untouched.
 241
 2428) E-mail size.
 243
 244When sending patches to Linus, always follow step #7.
 245
 246Large changes are not appropriate for mailing lists, and some
 247maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
 248it is preferred that you store your patch on an Internet-accessible
 249server, and provide instead a URL (link) pointing to your patch.
 250
 251
 252
 2539) Name your kernel version.
 254
 255It is important to note, either in the subject line or in the patch
 256description, the kernel version to which this patch applies.
 257
 258If the patch does not apply cleanly to the latest kernel version,
 259Linus will not apply it.
 260
 261
 262
 26310) Don't get discouraged.  Re-submit.
 264
 265After you have submitted your change, be patient and wait.  If Linus
 266likes your change and applies it, it will appear in the next version
 267of the kernel that he releases.
 268
 269However, if your change doesn't appear in the next version of the
 270kernel, there could be any number of reasons.  It's YOUR job to
 271narrow down those reasons, correct what was wrong, and submit your
 272updated change.
 273
 274It is quite common for Linus to "drop" your patch without comment.
 275That's the nature of the system.  If he drops your patch, it could be
 276due to
 277* Your patch did not apply cleanly to the latest kernel version.
 278* Your patch was not sufficiently discussed on linux-kernel.
 279* A style issue (see section 2).
 280* An e-mail formatting issue (re-read this section).
 281* A technical problem with your change.
 282* He gets tons of e-mail, and yours got lost in the shuffle.
 283* You are being annoying.
 284
 285When in doubt, solicit comments on linux-kernel mailing list.
 286
 287
 288
 28911) Include PATCH in the subject
 290
 291Due to high e-mail traffic to Linus, and to linux-kernel, it is common
 292convention to prefix your subject line with [PATCH].  This lets Linus
 293and other kernel developers more easily distinguish patches from other
 294e-mail discussions.
 295
 296
 297
 29812) Sign your work
 299
 300To improve tracking of who did what, especially with patches that can
 301percolate to their final resting place in the kernel through several
 302layers of maintainers, we've introduced a "sign-off" procedure on
 303patches that are being emailed around.
 304
 305The sign-off is a simple line at the end of the explanation for the
 306patch, which certifies that you wrote it or otherwise have the right to
 307pass it on as an open-source patch.  The rules are pretty simple: if you
 308can certify the below:
 309
 310        Developer's Certificate of Origin 1.1
 311
 312        By making a contribution to this project, I certify that:
 313
 314        (a) The contribution was created in whole or in part by me and I
 315            have the right to submit it under the open source license
 316            indicated in the file; or
 317
 318        (b) The contribution is based upon previous work that, to the best
 319            of my knowledge, is covered under an appropriate open source
 320            license and I have the right under that license to submit that
 321            work with modifications, whether created in whole or in part
 322            by me, under the same open source license (unless I am
 323            permitted to submit under a different license), as indicated
 324            in the file; or
 325
 326        (c) The contribution was provided directly to me by some other
 327            person who certified (a), (b) or (c) and I have not modified
 328            it.
 329
 330        (d) I understand and agree that this project and the contribution
 331            are public and that a record of the contribution (including all
 332            personal information I submit with it, including my sign-off) is
 333            maintained indefinitely and may be redistributed consistent with
 334            this project or the open source license(s) involved.
 335
 336then you just add a line saying
 337
 338        Signed-off-by: Random J Developer <random@developer.example.org>
 339
 340using your real name (sorry, no pseudonyms or anonymous contributions.)
 341
 342Some people also put extra tags at the end.  They'll just be ignored for
 343now, but you can do this to mark internal company procedures or just
 344point out some special detail about the sign-off. 
 345
 346If you are a subsystem or branch maintainer, sometimes you need to slightly
 347modify patches you receive in order to merge them, because the code is not
 348exactly the same in your tree and the submitters'. If you stick strictly to
 349rule (c), you should ask the submitter to rediff, but this is a totally
 350counter-productive waste of time and energy. Rule (b) allows you to adjust
 351the code, but then it is very impolite to change one submitter's code and
 352make him endorse your bugs. To solve this problem, it is recommended that
 353you add a line between the last Signed-off-by header and yours, indicating
 354the nature of your changes. While there is nothing mandatory about this, it
 355seems like prepending the description with your mail and/or name, all
 356enclosed in square brackets, is noticeable enough to make it obvious that
 357you are responsible for last-minute changes. Example :
 358
 359        Signed-off-by: Random J Developer <random@developer.example.org>
 360        [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
 361        Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
 362
 363This practise is particularly helpful if you maintain a stable branch and
 364want at the same time to credit the author, track changes, merge the fix,
 365and protect the submitter from complaints. Note that under no circumstances
 366can you change the author's identity (the From header), as it is the one
 367which appears in the changelog.
 368
 369Special note to back-porters: It seems to be a common and useful practise
 370to insert an indication of the origin of a patch at the top of the commit
 371message (just after the subject line) to facilitate tracking. For instance,
 372here's what we see in 2.6-stable :
 373
 374    Date:   Tue May 13 19:10:30 2008 +0000
 375
 376        SCSI: libiscsi regression in 2.6.25: fix nop timer handling
 377
 378        commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
 379
 380And here's what appears in 2.4 :
 381
 382    Date:   Tue May 13 22:12:27 2008 +0200
 383
 384        wireless, airo: waitbusy() won't delay
 385
 386        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
 387
 388Whatever the format, this information provides a valuable help to people
 389tracking your trees, and to people trying to trouble-shoot bugs in your
 390tree.
 391
 392
 39313) When to use Acked-by: and Cc:
 394
 395The Signed-off-by: tag indicates that the signer was involved in the
 396development of the patch, or that he/she was in the patch's delivery path.
 397
 398If a person was not directly involved in the preparation or handling of a
 399patch but wishes to signify and record their approval of it then they can
 400arrange to have an Acked-by: line added to the patch's changelog.
 401
 402Acked-by: is often used by the maintainer of the affected code when that
 403maintainer neither contributed to nor forwarded the patch.
 404
 405Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
 406has at least reviewed the patch and has indicated acceptance.  Hence patch
 407mergers will sometimes manually convert an acker's "yep, looks good to me"
 408into an Acked-by:.
 409
 410Acked-by: does not necessarily indicate acknowledgement of the entire patch.
 411For example, if a patch affects multiple subsystems and has an Acked-by: from
 412one subsystem maintainer then this usually indicates acknowledgement of just
 413the part which affects that maintainer's code.  Judgement should be used here.
 414When in doubt people should refer to the original discussion in the mailing
 415list archives.
 416
 417If a person has had the opportunity to comment on a patch, but has not
 418provided such comments, you may optionally add a "Cc:" tag to the patch.
 419This is the only tag which might be added without an explicit action by the
 420person it names.  This tag documents that potentially interested parties
 421have been included in the discussion
 422
 423
 42414) Using Reported-by:, Tested-by: and Reviewed-by:
 425
 426If this patch fixes a problem reported by somebody else, consider adding a
 427Reported-by: tag to credit the reporter for their contribution.  Please
 428note that this tag should not be added without the reporter's permission,
 429especially if the problem was not reported in a public forum.  That said,
 430if we diligently credit our bug reporters, they will, hopefully, be
 431inspired to help us again in the future.
 432
 433A Tested-by: tag indicates that the patch has been successfully tested (in
 434some environment) by the person named.  This tag informs maintainers that
 435some testing has been performed, provides a means to locate testers for
 436future patches, and ensures credit for the testers.
 437
 438Reviewed-by:, instead, indicates that the patch has been reviewed and found
 439acceptable according to the Reviewer's Statement:
 440
 441        Reviewer's statement of oversight
 442
 443        By offering my Reviewed-by: tag, I state that:
 444
 445         (a) I have carried out a technical review of this patch to
 446             evaluate its appropriateness and readiness for inclusion into
 447             the mainline kernel.
 448
 449         (b) Any problems, concerns, or questions relating to the patch
 450             have been communicated back to the submitter.  I am satisfied
 451             with the submitter's response to my comments.
 452
 453         (c) While there may be things that could be improved with this
 454             submission, I believe that it is, at this time, (1) a
 455             worthwhile modification to the kernel, and (2) free of known
 456             issues which would argue against its inclusion.
 457
 458         (d) While I have reviewed the patch and believe it to be sound, I
 459             do not (unless explicitly stated elsewhere) make any
 460             warranties or guarantees that it will achieve its stated
 461             purpose or function properly in any given situation.
 462
 463A Reviewed-by tag is a statement of opinion that the patch is an
 464appropriate modification of the kernel without any remaining serious
 465technical issues.  Any interested reviewer (who has done the work) can
 466offer a Reviewed-by tag for a patch.  This tag serves to give credit to
 467reviewers and to inform maintainers of the degree of review which has been
 468done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
 469understand the subject area and to perform thorough reviews, will normally
 470increase the likelihood of your patch getting into the kernel.
 471
 472
 47315) The canonical patch format
 474
 475The canonical patch subject line is:
 476
 477    Subject: [PATCH 001/123] subsystem: summary phrase
 478
 479The canonical patch message body contains the following:
 480
 481  - A "from" line specifying the patch author.
 482
 483  - An empty line.
 484
 485  - The body of the explanation, which will be copied to the
 486    permanent changelog to describe this patch.
 487
 488  - The "Signed-off-by:" lines, described above, which will
 489    also go in the changelog.
 490
 491  - A marker line containing simply "---".
 492
 493  - Any additional comments not suitable for the changelog.
 494
 495  - The actual patch (diff output).
 496
 497The Subject line format makes it very easy to sort the emails
 498alphabetically by subject line - pretty much any email reader will
 499support that - since because the sequence number is zero-padded,
 500the numerical and alphabetic sort is the same.
 501
 502The "subsystem" in the email's Subject should identify which
 503area or subsystem of the kernel is being patched.
 504
 505The "summary phrase" in the email's Subject should concisely
 506describe the patch which that email contains.  The "summary
 507phrase" should not be a filename.  Do not use the same "summary
 508phrase" for every patch in a whole patch series (where a "patch
 509series" is an ordered sequence of multiple, related patches).
 510
 511Bear in mind that the "summary phrase" of your email becomes a
 512globally-unique identifier for that patch.  It propagates all the way
 513into the git changelog.  The "summary phrase" may later be used in
 514developer discussions which refer to the patch.  People will want to
 515google for the "summary phrase" to read discussion regarding that
 516patch.  It will also be the only thing that people may quickly see
 517when, two or three months later, they are going through perhaps
 518thousands of patches using tools such as "gitk" or "git log
 519--oneline".
 520
 521For these reasons, the "summary" must be no more than 70-75
 522characters, and it must describe both what the patch changes, as well
 523as why the patch might be necessary.  It is challenging to be both
 524succinct and descriptive, but that is what a well-written summary
 525should do.
 526
 527The "summary phrase" may be prefixed by tags enclosed in square
 528brackets: "Subject: [PATCH tag] <summary phrase>".  The tags are not
 529considered part of the summary phrase, but describe how the patch
 530should be treated.  Common tags might include a version descriptor if
 531the multiple versions of the patch have been sent out in response to
 532comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
 533comments.  If there are four patches in a patch series the individual
 534patches may be numbered like this: 1/4, 2/4, 3/4, 4/4.  This assures
 535that developers understand the order in which the patches should be
 536applied and that they have reviewed or applied all of the patches in
 537the patch series.
 538
 539A couple of example Subjects:
 540
 541    Subject: [patch 2/5] ext2: improve scalability of bitmap searching
 542    Subject: [PATCHv2 001/207] x86: fix eflags tracking
 543
 544The "from" line must be the very first line in the message body,
 545and has the form:
 546
 547        From: Original Author <author@example.com>
 548
 549The "from" line specifies who will be credited as the author of the
 550patch in the permanent changelog.  If the "from" line is missing,
 551then the "From:" line from the email header will be used to determine
 552the patch author in the changelog.
 553
 554The explanation body will be committed to the permanent source
 555changelog, so should make sense to a competent reader who has long
 556since forgotten the immediate details of the discussion that might
 557have led to this patch.  Including symptoms of the failure which the
 558patch addresses (kernel log messages, oops messages, etc.) is
 559especially useful for people who might be searching the commit logs
 560looking for the applicable patch.  If a patch fixes a compile failure,
 561it may not be necessary to include _all_ of the compile failures; just
 562enough that it is likely that someone searching for the patch can find
 563it.  As in the "summary phrase", it is important to be both succinct as
 564well as descriptive.
 565
 566The "---" marker line serves the essential purpose of marking for patch
 567handling tools where the changelog message ends.
 568
 569One good use for the additional comments after the "---" marker is for
 570a diffstat, to show what files have changed, and the number of
 571inserted and deleted lines per file.  A diffstat is especially useful
 572on bigger patches.  Other comments relevant only to the moment or the
 573maintainer, not suitable for the permanent changelog, should also go
 574here.  A good example of such comments might be "patch changelogs"
 575which describe what has changed between the v1 and v2 version of the
 576patch.
 577
 578If you are going to include a diffstat after the "---" marker, please
 579use diffstat options "-p 1 -w 70" so that filenames are listed from
 580the top of the kernel source tree and don't use too much horizontal
 581space (easily fit in 80 columns, maybe with some indentation).
 582
 583See more details on the proper patch format in the following
 584references.
 585
 586
 58716) Sending "git pull" requests  (from Linus emails)
 588
 589Please write the git repo address and branch name alone on the same line
 590so that I can't even by mistake pull from the wrong branch, and so
 591that a triple-click just selects the whole thing.
 592
 593So the proper format is something along the lines of:
 594
 595        "Please pull from
 596
 597                git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
 598
 599         to get these changes:"
 600
 601so that I don't have to hunt-and-peck for the address and inevitably
 602get it wrong (actually, I've only gotten it wrong a few times, and
 603checking against the diffstat tells me when I get it wrong, but I'm
 604just a lot more comfortable when I don't have to "look for" the right
 605thing to pull, and double-check that I have the right branch-name).
 606
 607
 608Please use "git diff -M --stat --summary" to generate the diffstat:
 609the -M enables rename detection, and the summary enables a summary of
 610new/deleted or renamed files.
 611
 612With rename detection, the statistics are rather different [...]
 613because git will notice that a fair number of the changes are renames.
 614
 615-----------------------------------
 616SECTION 2 - HINTS, TIPS, AND TRICKS
 617-----------------------------------
 618
 619This section lists many of the common "rules" associated with code
 620submitted to the kernel.  There are always exceptions... but you must
 621have a really good reason for doing so.  You could probably call this
 622section Linus Computer Science 101.
 623
 624
 625
 6261) Read Documentation/CodingStyle
 627
 628Nuff said.  If your code deviates too much from this, it is likely
 629to be rejected without further review, and without comment.
 630
 631One significant exception is when moving code from one file to
 632another -- in this case you should not modify the moved code at all in
 633the same patch which moves it.  This clearly delineates the act of
 634moving the code and your changes.  This greatly aids review of the
 635actual differences and allows tools to better track the history of
 636the code itself.
 637
 638Check your patches with the patch style checker prior to submission
 639(scripts/checkpatch.pl).  The style checker should be viewed as
 640a guide not as the final word.  If your code looks better with
 641a violation then its probably best left alone.
 642
 643The checker reports at three levels:
 644 - ERROR: things that are very likely to be wrong
 645 - WARNING: things requiring careful review
 646 - CHECK: things requiring thought
 647
 648You should be able to justify all violations that remain in your
 649patch.
 650
 651
 652
 6532) #ifdefs are ugly
 654
 655Code cluttered with ifdefs is difficult to read and maintain.  Don't do
 656it.  Instead, put your ifdefs in a header, and conditionally define
 657'static inline' functions, or macros, which are used in the code.
 658Let the compiler optimize away the "no-op" case.
 659
 660Simple example, of poor code:
 661
 662        dev = alloc_etherdev (sizeof(struct funky_private));
 663        if (!dev)
 664                return -ENODEV;
 665        #ifdef CONFIG_NET_FUNKINESS
 666        init_funky_net(dev);
 667        #endif
 668
 669Cleaned-up example:
 670
 671(in header)
 672        #ifndef CONFIG_NET_FUNKINESS
 673        static inline void init_funky_net (struct net_device *d) {}
 674        #endif
 675
 676(in the code itself)
 677        dev = alloc_etherdev (sizeof(struct funky_private));
 678        if (!dev)
 679                return -ENODEV;
 680        init_funky_net(dev);
 681
 682
 683
 6843) 'static inline' is better than a macro
 685
 686Static inline functions are greatly preferred over macros.
 687They provide type safety, have no length limitations, no formatting
 688limitations, and under gcc they are as cheap as macros.
 689
 690Macros should only be used for cases where a static inline is clearly
 691suboptimal [there are a few, isolated cases of this in fast paths],
 692or where it is impossible to use a static inline function [such as
 693string-izing].
 694
 695'static inline' is preferred over 'static __inline__', 'extern inline',
 696and 'extern __inline__'.
 697
 698
 699
 7004) Don't over-design.
 701
 702Don't try to anticipate nebulous future cases which may or may not
 703be useful:  "Make it as simple as you can, and no simpler."
 704
 705
 706
 707----------------------
 708SECTION 3 - REFERENCES
 709----------------------
 710
 711Andrew Morton, "The perfect patch" (tpp).
 712  <http://userweb.kernel.org/~akpm/stuff/tpp.txt>
 713
 714Jeff Garzik, "Linux kernel patch submission format".
 715  <http://linux.yyz.us/patch-format.html>
 716
 717Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
 718  <http://www.kroah.com/log/linux/maintainer.html>
 719  <http://www.kroah.com/log/linux/maintainer-02.html>
 720  <http://www.kroah.com/log/linux/maintainer-03.html>
 721  <http://www.kroah.com/log/linux/maintainer-04.html>
 722  <http://www.kroah.com/log/linux/maintainer-05.html>
 723
 724NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
 725  <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2>
 726
 727Kernel Documentation/CodingStyle:
 728  <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
 729
 730Linus Torvalds's mail on the canonical patch format:
 731  <http://lkml.org/lkml/2005/4/7/183>
 732
 733Andi Kleen, "On submitting kernel patches"
 734  Some strategies to get difficult or controversial changes in.
 735  http://halobates.de/on-submitting-patches.pdf
 736
 737--
 738
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