Linux Cross Reference
Linux/Documentation/SubmittingPatches

   
           How to Get Your Change Into the Linux Kernel
                   or
           Care And Operation Of Your Linus Torvalds
   
   
   
   For a person or company who wishes to submit a change to the Linux
   kernel, the process can sometimes be daunting if you're not familiar
  with "the system."  This text is a collection of suggestions which
  can greatly increase the chances of your change being accepted.
  
  Read Documentation/SubmitChecklist for a list of items to check
  before submitting code.  If you are submitting a driver, also read
  Documentation/SubmittingDrivers.
  
  
  
  --------------------------------------------
  SECTION 1 - CREATING AND SENDING YOUR CHANGE
  --------------------------------------------
  
  
  
  1) "diff -up"
  ------------
  
  Use "diff -up" or "diff -uprN" to create patches.
  
  All changes to the Linux kernel occur in the form of patches, as
  generated by diff(1).  When creating your patch, make sure to create it
  in "unified diff" format, as supplied by the '-u' argument to diff(1).
  Also, please use the '-p' argument which shows which C function each
  change is in - that makes the resultant diff a lot easier to read.
  Patches should be based in the root kernel source directory,
  not in any lower subdirectory.
  
  To create a patch for a single file, it is often sufficient to do:
  
          SRCTREE= linux-2.6
          MYFILE=  drivers/net/mydriver.c
  
          cd $SRCTREE
          cp $MYFILE $MYFILE.orig
          vi $MYFILE      # make your change
          cd ..
          diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
  
  To create a patch for multiple files, you should unpack a "vanilla",
  or unmodified kernel source tree, and generate a diff against your
  own source tree.  For example:
  
          MYSRC= /devel/linux-2.6
  
          tar xvfz linux-2.6.12.tar.gz
          mv linux-2.6.12 linux-2.6.12-vanilla
          diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \
                  linux-2.6.12-vanilla $MYSRC > /tmp/patch
  
  "dontdiff" is a list of files which are generated by the kernel during
  the build process, and should be ignored in any diff(1)-generated
  patch.  The "dontdiff" file is included in the kernel tree in
  2.6.12 and later.  For earlier kernel versions, you can get it
  from <http://www.xenotime.net/linux/doc/dontdiff>.
  
  Make sure your patch does not include any extra files which do not
  belong in a patch submission.  Make sure to review your patch -after-
  generated it with diff(1), to ensure accuracy.
  
  If your changes produce a lot of deltas, you may want to look into
  splitting them into individual patches which modify things in
  logical stages.  This will facilitate easier reviewing by other
  kernel developers, very important if you want your patch accepted.
  There are a number of scripts which can aid in this:
  
  Quilt:
  http://savannah.nongnu.org/projects/quilt
  
  Andrew Morton's patch scripts:
  http://www.zip.com.au/~akpm/linux/patches/
  Instead of these scripts, quilt is the recommended patch management
  tool (see above).
  
  
  
  2) Describe your changes.
  
  Describe the technical detail of the change(s) your patch includes.
  
  Be as specific as possible.  The WORST descriptions possible include
  things like "update driver X", "bug fix for driver X", or "this patch
  includes updates for subsystem X.  Please apply."
  
  If your description starts to get long, that's a sign that you probably
  need to split up your patch.  See #3, next.
  
  
  
  3) Separate your changes.
 
 Separate _logical changes_ into a single patch file.
 
 For example, if your changes include both bug fixes and performance
 enhancements for a single driver, separate those changes into two
 or more patches.  If your changes include an API update, and a new
 driver which uses that new API, separate those into two patches.
 
 On the other hand, if you make a single change to numerous files,
 group those changes into a single patch.  Thus a single logical change
 is contained within a single patch.
 
 If one patch depends on another patch in order for a change to be
 complete, that is OK.  Simply note "this patch depends on patch X"
 in your patch description.
 
 If you cannot condense your patch set into a smaller set of patches,
 then only post say 15 or so at a time and wait for review and integration.
 
 
 
 4) Style check your changes.
 
 Check your patch for basic style violations, details of which can be
 found in Documentation/CodingStyle.  Failure to do so simply wastes
 the reviewers time and will get your patch rejected, probably
 without even being read.
 
 At a minimum you should check your patches with the patch style
 checker prior to submission (scripts/checkpatch.pl).  You should
 be able to justify all violations that remain in your patch.
 
 
 
 5) Select e-mail destination.
 
 Look through the MAINTAINERS file and the source code, and determine
 if your change applies to a specific subsystem of the kernel, with
 an assigned maintainer.  If so, e-mail that person.
 
 If no maintainer is listed, or the maintainer does not respond, send
 your patch to the primary Linux kernel developer's mailing list,
 linux-kernel@vger.kernel.org.  Most kernel developers monitor this
 e-mail list, and can comment on your changes.
 
 
 Do not send more than 15 patches at once to the vger mailing lists!!!
 
 
 Linus Torvalds is the final arbiter of all changes accepted into the
 Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>. 
 He gets a lot of e-mail, so typically you should do your best to -avoid-
 sending him e-mail. 
 
 Patches which are bug fixes, are "obvious" changes, or similarly
 require little discussion should be sent or CC'd to Linus.  Patches
 which require discussion or do not have a clear advantage should
 usually be sent first to linux-kernel.  Only after the patch is
 discussed should the patch then be submitted to Linus.
 
 
 
 6) Select your CC (e-mail carbon copy) list.
 
 Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
 
 Other kernel developers besides Linus need to be aware of your change,
 so that they may comment on it and offer code review and suggestions.
 linux-kernel is the primary Linux kernel developer mailing list.
 Other mailing lists are available for specific subsystems, such as
 USB, framebuffer devices, the VFS, the SCSI subsystem, etc.  See the
 MAINTAINERS file for a mailing list that relates specifically to
 your change.
 
 Majordomo lists of VGER.KERNEL.ORG at:
         <http://vger.kernel.org/vger-lists.html>
 
 If changes affect userland-kernel interfaces, please send
 the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
 a man-pages patch, or at least a notification of the change,
 so that some information makes its way into the manual pages.
 
 Even if the maintainer did not respond in step #4, make sure to ALWAYS
 copy the maintainer when you change their code.
 
 For small patches you may want to CC the Trivial Patch Monkey
 trivial@kernel.org managed by Adrian Bunk; which collects "trivial"
 patches. Trivial patches must qualify for one of the following rules:
  Spelling fixes in documentation
  Spelling fixes which could break grep(1)
  Warning fixes (cluttering with useless warnings is bad)
  Compilation fixes (only if they are actually correct)
  Runtime fixes (only if they actually fix things)
  Removing use of deprecated functions/macros (eg. check_region)
  Contact detail and documentation fixes
  Non-portable code replaced by portable code (even in arch-specific,
  since people copy, as long as it's trivial)
  Any fix by the author/maintainer of the file (ie. patch monkey
  in re-transmission mode)
 URL: <http://www.kernel.org/pub/linux/kernel/people/bunk/trivial/>
 
 
 
 7) No MIME, no links, no compression, no attachments.  Just plain text.
 
 Linus and other kernel developers need to be able to read and comment
 on the changes you are submitting.  It is important for a kernel
 developer to be able to "quote" your changes, using standard e-mail
 tools, so that they may comment on specific portions of your code.
 
 For this reason, all patches should be submitting e-mail "inline".
 WARNING:  Be wary of your editor's word-wrap corrupting your patch,
 if you choose to cut-n-paste your patch.
 
 Do not attach the patch as a MIME attachment, compressed or not.
 Many popular e-mail applications will not always transmit a MIME
 attachment as plain text, making it impossible to comment on your
 code.  A MIME attachment also takes Linus a bit more time to process,
 decreasing the likelihood of your MIME-attached change being accepted.
 
 Exception:  If your mailer is mangling patches then someone may ask
 you to re-send them using MIME.
 
 
 WARNING: Some mailers like Mozilla send your messages with
 ---- message header ----
 Content-Type: text/plain; charset=us-ascii; format=flowed
 ---- message header ----
 The problem is that "format=flowed" makes some of the mailers
 on receiving side to replace TABs with spaces and do similar
 changes. Thus the patches from you can look corrupted.
 
 To fix this just make your mozilla defaults/pref/mailnews.js file to look like:
 pref("mailnews.send_plaintext_flowed", false); // RFC 2646=======
 pref("mailnews.display.disable_format_flowed_support", true);
 
 
 
 8) E-mail size.
 
 When sending patches to Linus, always follow step #7.
 
 Large changes are not appropriate for mailing lists, and some
 maintainers.  If your patch, uncompressed, exceeds 40 kB in size,
 it is preferred that you store your patch on an Internet-accessible
 server, and provide instead a URL (link) pointing to your patch.
 
 
 
 9) Name your kernel version.
 
 It is important to note, either in the subject line or in the patch
 description, the kernel version to which this patch applies.
 
 If the patch does not apply cleanly to the latest kernel version,
 Linus will not apply it.
 
 
 
 10) Don't get discouraged.  Re-submit.
 
 After you have submitted your change, be patient and wait.  If Linus
 likes your change and applies it, it will appear in the next version
 of the kernel that he releases.
 
 However, if your change doesn't appear in the next version of the
 kernel, there could be any number of reasons.  It's YOUR job to
 narrow down those reasons, correct what was wrong, and submit your
 updated change.
 
 It is quite common for Linus to "drop" your patch without comment.
 That's the nature of the system.  If he drops your patch, it could be
 due to
 * Your patch did not apply cleanly to the latest kernel version.
 * Your patch was not sufficiently discussed on linux-kernel.
 * A style issue (see section 2).
 * An e-mail formatting issue (re-read this section).
 * A technical problem with your change.
 * He gets tons of e-mail, and yours got lost in the shuffle.
 * You are being annoying.
 
 When in doubt, solicit comments on linux-kernel mailing list.
 
 
 
 11) Include PATCH in the subject
 
 Due to high e-mail traffic to Linus, and to linux-kernel, it is common
 convention to prefix your subject line with [PATCH].  This lets Linus
 and other kernel developers more easily distinguish patches from other
 e-mail discussions.
 
 
 
 12) Sign your work
 
 To improve tracking of who did what, especially with patches that can
 percolate to their final resting place in the kernel through several
 layers of maintainers, we've introduced a "sign-off" procedure on
 patches that are being emailed around.
 
 The sign-off is a simple line at the end of the explanation for the
 patch, which certifies that you wrote it or otherwise have the right to
 pass it on as a open-source patch.  The rules are pretty simple: if you
 can certify the below:
 
         Developer's Certificate of Origin 1.1
 
         By making a contribution to this project, I certify that:
 
         (a) The contribution was created in whole or in part by me and I
             have the right to submit it under the open source license
             indicated in the file; or
 
         (b) The contribution is based upon previous work that, to the best
             of my knowledge, is covered under an appropriate open source
             license and I have the right under that license to submit that
             work with modifications, whether created in whole or in part
             by me, under the same open source license (unless I am
             permitted to submit under a different license), as indicated
             in the file; or
 
         (c) The contribution was provided directly to me by some other
             person who certified (a), (b) or (c) and I have not modified
             it.
 
         (d) I understand and agree that this project and the contribution
             are public and that a record of the contribution (including all
             personal information I submit with it, including my sign-off) is
             maintained indefinitely and may be redistributed consistent with
             this project or the open source license(s) involved.
 
 then you just add a line saying
 
         Signed-off-by: Random J Developer <random@developer.example.org>
 
 using your real name (sorry, no pseudonyms or anonymous contributions.)
 
 Some people also put extra tags at the end.  They'll just be ignored for
 now, but you can do this to mark internal company procedures or just
 point out some special detail about the sign-off. 
 
 
 13) When to use Acked-by:
 
 The Signed-off-by: tag indicates that the signer was involved in the
 development of the patch, or that he/she was in the patch's delivery path.
 
 If a person was not directly involved in the preparation or handling of a
 patch but wishes to signify and record their approval of it then they can
 arrange to have an Acked-by: line added to the patch's changelog.
 
 Acked-by: is often used by the maintainer of the affected code when that
 maintainer neither contributed to nor forwarded the patch.
 
 Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
 has at least reviewed the patch and has indicated acceptance.  Hence patch
 mergers will sometimes manually convert an acker's "yep, looks good to me"
 into an Acked-by:.
 
 Acked-by: does not necessarily indicate acknowledgement of the entire patch.
 For example, if a patch affects multiple subsystems and has an Acked-by: from
 one subsystem maintainer then this usually indicates acknowledgement of just
 the part which affects that maintainer's code.  Judgement should be used here.
  When in doubt people should refer to the original discussion in the mailing
 list archives.
 
 
 14) The canonical patch format
 
 The canonical patch subject line is:
 
     Subject: [PATCH 001/123] subsystem: summary phrase
 
 The canonical patch message body contains the following:
 
   - A "from" line specifying the patch author.
 
   - An empty line.
 
   - The body of the explanation, which will be copied to the
     permanent changelog to describe this patch.
 
   - The "Signed-off-by:" lines, described above, which will
     also go in the changelog.
 
   - A marker line containing simply "---".
 
   - Any additional comments not suitable for the changelog.
 
   - The actual patch (diff output).
 
 The Subject line format makes it very easy to sort the emails
 alphabetically by subject line - pretty much any email reader will
 support that - since because the sequence number is zero-padded,
 the numerical and alphabetic sort is the same.
 
 The "subsystem" in the email's Subject should identify which
 area or subsystem of the kernel is being patched.
 
 The "summary phrase" in the email's Subject should concisely
 describe the patch which that email contains.  The "summary
 phrase" should not be a filename.  Do not use the same "summary
 phrase" for every patch in a whole patch series (where a "patch
 series" is an ordered sequence of multiple, related patches).
 
 Bear in mind that the "summary phrase" of your email becomes
 a globally-unique identifier for that patch.  It propagates
 all the way into the git changelog.  The "summary phrase" may
 later be used in developer discussions which refer to the patch.
 People will want to google for the "summary phrase" to read
 discussion regarding that patch.
 
 A couple of example Subjects:
 
     Subject: [patch 2/5] ext2: improve scalability of bitmap searching
     Subject: [PATCHv2 001/207] x86: fix eflags tracking
 
 The "from" line must be the very first line in the message body,
 and has the form:
 
         From: Original Author <author@example.com>
 
 The "from" line specifies who will be credited as the author of the
 patch in the permanent changelog.  If the "from" line is missing,
 then the "From:" line from the email header will be used to determine
 the patch author in the changelog.
 
 The explanation body will be committed to the permanent source
 changelog, so should make sense to a competent reader who has long
 since forgotten the immediate details of the discussion that might
 have led to this patch.
 
 The "---" marker line serves the essential purpose of marking for patch
 handling tools where the changelog message ends.
 
 One good use for the additional comments after the "---" marker is for
 a diffstat, to show what files have changed, and the number of inserted
 and deleted lines per file.  A diffstat is especially useful on bigger
 patches.  Other comments relevant only to the moment or the maintainer,
 not suitable for the permanent changelog, should also go here.
 Use diffstat options "-p 1 -w 70" so that filenames are listed from the
 top of the kernel source tree and don't use too much horizontal space
 (easily fit in 80 columns, maybe with some indentation).
 
 See more details on the proper patch format in the following
 references.
 
 
 
 
 -----------------------------------
 SECTION 2 - HINTS, TIPS, AND TRICKS
 -----------------------------------
 
 This section lists many of the common "rules" associated with code
 submitted to the kernel.  There are always exceptions... but you must
 have a really good reason for doing so.  You could probably call this
 section Linus Computer Science 101.
 
 
 
 1) Read Documentation/CodingStyle
 
 Nuff said.  If your code deviates too much from this, it is likely
 to be rejected without further review, and without comment.
 
 One significant exception is when moving code from one file to
 another -- in this case you should not modify the moved code at all in
 the same patch which moves it.  This clearly delineates the act of
 moving the code and your changes.  This greatly aids review of the
 actual differences and allows tools to better track the history of
 the code itself.
 
 Check your patches with the patch style checker prior to submission
 (scripts/checkpatch.pl).  The style checker should be viewed as
 a guide not as the final word.  If your code looks better with
 a violation then its probably best left alone.
 
 The checker reports at three levels:
  - ERROR: things that are very likely to be wrong
  - WARNING: things requiring careful review
  - CHECK: things requiring thought
 
 You should be able to justify all violations that remain in your
 patch.
 
 
 
 2) #ifdefs are ugly
 
 Code cluttered with ifdefs is difficult to read and maintain.  Don't do
 it.  Instead, put your ifdefs in a header, and conditionally define
 'static inline' functions, or macros, which are used in the code.
 Let the compiler optimize away the "no-op" case.
 
 Simple example, of poor code:
 
         dev = alloc_etherdev (sizeof(struct funky_private));
         if (!dev)
                 return -ENODEV;
         #ifdef CONFIG_NET_FUNKINESS
         init_funky_net(dev);
         #endif
 
 Cleaned-up example:
 
 (in header)
         #ifndef CONFIG_NET_FUNKINESS
         static inline void init_funky_net (struct net_device *d) {}
         #endif
 
 (in the code itself)
         dev = alloc_etherdev (sizeof(struct funky_private));
         if (!dev)
                 return -ENODEV;
         init_funky_net(dev);
 
 
 
 3) 'static inline' is better than a macro
 
 Static inline functions are greatly preferred over macros.
 They provide type safety, have no length limitations, no formatting
 limitations, and under gcc they are as cheap as macros.
 
 Macros should only be used for cases where a static inline is clearly
 suboptimal [there a few, isolated cases of this in fast paths],
 or where it is impossible to use a static inline function [such as
 string-izing].
 
 'static inline' is preferred over 'static __inline__', 'extern inline',
 and 'extern __inline__'.
 
 
 
 4) Don't over-design.
 
 Don't try to anticipate nebulous future cases which may or may not
 be useful:  "Make it as simple as you can, and no simpler."
 
 
 
 ----------------------
 SECTION 3 - REFERENCES
 ----------------------
 
 Andrew Morton, "The perfect patch" (tpp).
   <http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt>
 
 Jeff Garzik, "Linux kernel patch submission format".
   <http://linux.yyz.us/patch-format.html>
 
 Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
   <http://www.kroah.com/log/2005/03/31/>
   <http://www.kroah.com/log/2005/07/08/>
   <http://www.kroah.com/log/2005/10/19/>
   <http://www.kroah.com/log/2006/01/11/>
 
 NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
   <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2>
 
 Kernel Documentation/CodingStyle:
   <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
 
 Linus Torvalds's mail on the canonical patch format:
   <http://lkml.org/lkml/2005/4/7/183>
 --