Doc/SubmittingPatches

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The content of doc/SubmittingPatches.txt (release 3.72):


I don't have specific submission guidelines for SYSLINUX, but the ones that appropriate to the Linux kernel are certainly good enough for SYSLINUX.

In particular, however, I appreciate if patches sent follow the standard Linux submission format, as I can automatically import them into git, retaining description and author information. Thus, this file from the Linux kernel might be useful.




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.


Contents

SECTION 1 - CREATING AND SENDING YOUR CHANGE

"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).


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.


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.


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.


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.


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/>


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.

See Documentation/email-clients.txt for hints about configuring your e-mail client so that it sends your patches untouched.

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.


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.


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.


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.


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.


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.


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.


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.


#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);


'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__'.


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>
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