Merge branch 'docs' of git://git.lwn.net/linux-2.6

* 'docs' of git://git.lwn.net/linux-2.6:
  Document panic_on_unrecovered_nmi sysctl
  Add a reference to paper to SubmittingPatches
  Add kerneldoc documentation for new printk format extensions
  Remove videobook.tmpl
  doc: Test-by?
  Add the development process document
  Documentation/block/data-integrity.txt: Fix section numbers

Documentation/00-INDEX

@@ -21,6 +21,9 @@ Changes
 	- list of changes that break older software packages.
 CodingStyle
 	- how the boss likes the C code in the kernel to look.
+development-process/
+	- An extended tutorial on how to work with the kernel development
+	  process.
 DMA-API.txt
 	- DMA API, pci_ API & extensions for non-consistent memory machines.
 DMA-ISA-LPC.txt

Documentation/DocBook/Makefile

@@ -6,7 +6,7 @@
 # To add a new book the only step required is to add the book to the
 # list of DOCBOOKS.
 
-DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml videobook.xml \
+DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml \
 	    kernel-hacking.xml kernel-locking.xml deviceiobook.xml \
 	    procfs-guide.xml writing_usb_driver.xml networking.xml \
 	    kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \

Documentation/SubmittingPatches

@@ -405,7 +405,7 @@ person it names.  This tag documents that potentially interested parties
 have been included in the discussion
 
 
-14) Using Test-by: and Reviewed-by:
+14) Using Tested-by: and Reviewed-by:
 
 A Tested-by: tag indicates that the patch has been successfully tested (in
 some environment) by the person named.  This tag informs maintainers that

Documentation/block/data-integrity.txt

@@ -246,7 +246,7 @@ will require extra work due to the application tag.
       retrieve the tag buffer using bio_integrity_get_tag().
 
 
-6.3 PASSING EXISTING INTEGRITY METADATA
+5.3 PASSING EXISTING INTEGRITY METADATA
 
     Filesystems that either generate their own integrity metadata or
     are capable of transferring IMD from user space can use the
@@ -283,7 +283,7 @@ will require extra work due to the application tag.
       integrity upon completion.
 
 
-6.4 REGISTERING A BLOCK DEVICE AS CAPABLE OF EXCHANGING INTEGRITY
+5.4 REGISTERING A BLOCK DEVICE AS CAPABLE OF EXCHANGING INTEGRITY
     METADATA
 
     To enable integrity exchange on a block device the gendisk must be

Documentation/development-process/1.Intro

@@ -0,0 +1,274 @@
+1: A GUIDE TO THE KERNEL DEVELOPMENT PROCESS
+
+The purpose of this document is to help developers (and their managers)
+work with the development community with a minimum of frustration.  It is
+an attempt to document how this community works in a way which is
+accessible to those who are not intimately familiar with Linux kernel
+development (or, indeed, free software development in general).  While
+there is some technical material here, this is very much a process-oriented
+discussion which does not require a deep knowledge of kernel programming to
+understand.
+
+
+1.1: EXECUTIVE SUMMARY
+
+The rest of this section covers the scope of the kernel development process
+and the kinds of frustrations that developers and their employers can
+encounter there.  There are a great many reasons why kernel code should be
+merged into the official ("mainline") kernel, including automatic
+availability to users, community support in many forms, and the ability to
+influence the direction of kernel development.  Code contributed to the
+Linux kernel must be made available under a GPL-compatible license.
+
+Section 2 introduces the development process, the kernel release cycle, and
+the mechanics of the merge window.  The various phases in the patch
+development, review, and merging cycle are covered.  There is some
+discussion of tools and mailing lists.  Developers wanting to get started
+with kernel development are encouraged to track down and fix bugs as an
+initial exercise.
+
+Section 3 covers early-stage project planning, with an emphasis on
+involving the development community as soon as possible.
+
+Section 4 is about the coding process; several pitfalls which have been
+encountered by other developers are discussed.  Some requirements for
+patches are covered, and there is an introduction to some of the tools
+which can help to ensure that kernel patches are correct.
+
+Section 5 talks about the process of posting patches for review.  To be
+taken seriously by the development community, patches must be properly
+formatted and described, and they must be sent to the right place.
+Following the advice in this section should help to ensure the best
+possible reception for your work.
+
+Section 6 covers what happens after posting patches; the job is far from
+done at that point.  Working with reviewers is a crucial part of the
+development process; this section offers a number of tips on how to avoid
+problems at this important stage.  Developers are cautioned against
+assuming that the job is done when a patch is merged into the mainline.
+
+Section 7 introduces a couple of "advanced" topics: managing patches with
+git and reviewing patches posted by others.
+
+Section 8 concludes the document with pointers to sources for more
+information on kernel development.
+
+
+1.2: WHAT THIS DOCUMENT IS ABOUT
+
+The Linux kernel, at over 6 million lines of code and well over 1000 active
+contributors, is one of the largest and most active free software projects
+in existence.  Since its humble beginning in 1991, this kernel has evolved
+into a best-of-breed operating system component which runs on pocket-sized
+digital music players, desktop PCs, the largest supercomputers in
+existence, and all types of systems in between.  It is a robust, efficient,
+and scalable solution for almost any situation.
+
+With the growth of Linux has come an increase in the number of developers
+(and companies) wishing to participate in its development.  Hardware
+vendors want to ensure that Linux supports their products well, making
+those products attractive to Linux users.  Embedded systems vendors, who
+use Linux as a component in an integrated product, want Linux to be as
+capable and well-suited to the task at hand as possible.  Distributors and
+other software vendors who base their products on Linux have a clear
+interest in the capabilities, performance, and reliability of the Linux
+kernel.  And end users, too, will often wish to change Linux to make it
+better suit their needs.
+
+One of the most compelling features of Linux is that it is accessible to
+these developers; anybody with the requisite skills can improve Linux and
+influence the direction of its development.  Proprietary products cannot
+offer this kind of openness, which is a characteristic of the free software
+process.  But, if anything, the kernel is even more open than most other
+free software projects.  A typical three-month kernel development cycle can
+involve over 1000 developers working for more than 100 different companies
+(or for no company at all).
+
+Working with the kernel development community is not especially hard.  But,
+that notwithstanding, many potential contributors have experienced
+difficulties when trying to do kernel work.  The kernel community has
+evolved its own distinct ways of operating which allow it to function
+smoothly (and produce a high-quality product) in an environment where
+thousands of lines of code are being changed every day.  So it is not
+surprising that Linux kernel development process differs greatly from
+proprietary development methods.
+
+The kernel's development process may come across as strange and
+intimidating to new developers, but there are good reasons and solid
+experience behind it.  A developer who does not understand the kernel
+community's ways (or, worse, who tries to flout or circumvent them) will
+have a frustrating experience in store.  The development community, while
+being helpful to those who are trying to learn, has little time for those
+who will not listen or who do not care about the development process.
+
+It is hoped that those who read this document will be able to avoid that
+frustrating experience.  There is a lot of material here, but the effort
+involved in reading it will be repaid in short order.  The development
+community is always in need of developers who will help to make the kernel
+better; the following text should help you - or those who work for you -
+join our community.
+
+
+1.3: CREDITS
+
+This document was written by Jonathan Corbet, corbet@lwn.net.  It has been
+improved by comments from Johannes Berg, James Berry, Alex Chiang, Roland
+Dreier, Randy Dunlap, Jake Edge, Jiri Kosina, Matt Mackall, Arthur Marsh,
+Amanda McPherson, Andrew Morton, Andrew Price, Tsugikazu Shibata, and
+Jochen Voß. 
+
+This work was supported by the Linux Foundation; thanks especially to
+Amanda McPherson, who saw the value of this effort and made it all happen.
+
+
+1.4: THE IMPORTANCE OF GETTING CODE INTO THE MAINLINE
+
+Some companies and developers occasionally wonder why they should bother
+learning how to work with the kernel community and get their code into the
+mainline kernel (the "mainline" being the kernel maintained by Linus
+Torvalds and used as a base by Linux distributors).  In the short term,
+contributing code can look like an avoidable expense; it seems easier to
+just keep the code separate and support users directly.  The truth of the
+matter is that keeping code separate ("out of tree") is a false economy.
+
+As a way of illustrating the costs of out-of-tree code, here are a few
+relevant aspects of the kernel development process; most of these will be
+discussed in greater detail later in this document.  Consider:
+
+- Code which has been merged into the mainline kernel is available to all
+  Linux users.  It will automatically be present on all distributions which
+  enable it.  There is no need for driver disks, downloads, or the hassles
+  of supporting multiple versions of multiple distributions; it all just
+  works, for the developer and for the user.  Incorporation into the
+  mainline solves a large number of distribution and support problems.
+
+- While kernel developers strive to maintain a stable interface to user
+  space, the internal kernel API is in constant flux.  The lack of a stable
+  internal interface is a deliberate design decision; it allows fundamental
+  improvements to be made at any time and results in higher-quality code.
+  But one result of that policy is that any out-of-tree code requires
+  constant upkeep if it is to work with new kernels.  Maintaining
+  out-of-tree code requires significant amounts of work just to keep that
+  code working.
+
+  Code which is in the mainline, instead, does not require this work as the
+  result of a simple rule requiring any developer who makes an API change
+  to also fix any code that breaks as the result of that change.  So code
+  which has been merged into the mainline has significantly lower
+  maintenance costs.
+
+- Beyond that, code which is in the kernel will often be improved by other
+  developers.  Surprising results can come from empowering your user
+  community and customers to improve your product.
+
+- Kernel code is subjected to review, both before and after merging into
+  the mainline.  No matter how strong the original developer's skills are,
+  this review process invariably finds ways in which the code can be
+  improved.  Often review finds severe bugs and security problems.  This is
+  especially true for code which has been developed in a closed
+  environment; such code benefits strongly from review by outside
+  developers.  Out-of-tree code is lower-quality code.
+
+- Participation in the development process is your way to influence the
+  direction of kernel development.  Users who complain from the sidelines
+  are heard, but active developers have a stronger voice - and the ability
+  to implement changes which make the kernel work better for their needs.
+
+- When code is maintained separately, the possibility that a third party
+  will contribute a different implementation of a similar feature always
+  exists.  Should that happen, getting your code merged will become much
+  harder - to the point of impossibility.  Then you will be faced with the
+  unpleasant alternatives of either (1) maintaining a nonstandard feature
+  out of tree indefinitely, or (2) abandoning your code and migrating your
+  users over to the in-tree version.
+
+- Contribution of code is the fundamental action which makes the whole
+  process work.  By contributing your code you can add new functionality to
+  the kernel and provide capabilities and examples which are of use to
+  other kernel developers.  If you have developed code for Linux (or are
+  thinking about doing so), you clearly have an interest in the continued
+  success of this platform; contributing code is one of the best ways to
+  help ensure that success.
+
+All of the reasoning above applies to any out-of-tree kernel code,
+including code which is distributed in proprietary, binary-only form.
+There are, however, additional factors which should be taken into account
+before considering any sort of binary-only kernel code distribution.  These
+include:
+
+- The legal issues around the distribution of proprietary kernel modules
+  are cloudy at best; quite a few kernel copyright holders believe that
+  most binary-only modules are derived products of the kernel and that, as
+  a result, their distribution is a violation of the GNU General Public
+  license (about which more will be said below).  Your author is not a
+  lawyer, and nothing in this document can possibly be considered to be
+  legal advice.  The true legal status of closed-source modules can only be
+  determined by the courts.  But the uncertainty which haunts those modules
+  is there regardless.
+
+- Binary modules greatly increase the difficulty of debugging kernel
+  problems, to the point that most kernel developers will not even try.  So
+  the distribution of binary-only modules will make it harder for your
+  users to get support from the community.
+
+- Support is also harder for distributors of binary-only modules, who must
+  provide a version of the module for every distribution and every kernel
+  version they wish to support.  Dozens of builds of a single module can
+  be required to provide reasonably comprehensive coverage, and your users
+  will have to upgrade your module separately every time they upgrade their
+  kernel.
+
+- Everything that was said above about code review applies doubly to
+  closed-source code.  Since this code is not available at all, it cannot
+  have been reviewed by the community and will, beyond doubt, have serious
+  problems. 
+
+Makers of embedded systems, in particular, may be tempted to disregard much
+of what has been said in this section in the belief that they are shipping
+a self-contained product which uses a frozen kernel version and requires no
+more development after its release.  This argument misses the value of
+widespread code review and the value of allowing your users to add
+capabilities to your product.  But these products, too, have a limited
+commercial life, after which a new version must be released.  At that
+point, vendors whose code is in the mainline and well maintained will be
+much better positioned to get the new product ready for market quickly.
+
+
+1.5: LICENSING
+
+Code is contributed to the Linux kernel under a number of licenses, but all
+code must be compatible with version 2 of the GNU General Public License
+(GPLv2), which is the license covering the kernel distribution as a whole.
+In practice, that means that all code contributions are covered either by
+GPLv2 (with, optionally, language allowing distribution under later
+versions of the GPL) or the three-clause BSD license.  Any contributions
+which are not covered by a compatible license will not be accepted into the
+kernel.
+
+Copyright assignments are not required (or requested) for code contributed
+to the kernel.  All code merged into the mainline kernel retains its
+original ownership; as a result, the kernel now has thousands of owners.
+
+One implication of this ownership structure is that any attempt to change
+the licensing of the kernel is doomed to almost certain failure.  There are
+few practical scenarios where the agreement of all copyright holders could
+be obtained (or their code removed from the kernel).  So, in particular,
+there is no prospect of a migration to version 3 of the GPL in the
+foreseeable future.
+
+It is imperative that all code contributed to the kernel be legitimately
+free software.  For that reason, code from anonymous (or pseudonymous)
+contributors will not be accepted.  All contributors are required to "sign
+off" on their code, stating that the code can be distributed with the
+kernel under the GPL.  Code which has not been licensed as free software by
+its owner, or which risks creating copyright-related problems for the
+kernel (such as code which derives from reverse-engineering efforts lacking
+proper safeguards) cannot be contributed.
+
+Questions about copyright-related issues are common on Linux development
+mailing lists.  Such questions will normally receive no shortage of
+answers, but one should bear in mind that the people answering those
+questions are not lawyers and cannot provide legal advice.  If you have
+legal questions relating to Linux source code, there is no substitute for
+talking with a lawyer who understands this field.  Relying on answers
+obtained on technical mailing lists is a risky affair.

Documentation/development-process/2.Process

@@ -0,0 +1,459 @@
+2: HOW THE DEVELOPMENT PROCESS WORKS
+
+Linux kernel development in the early 1990's was a pretty loose affair,
+with relatively small numbers of users and developers involved.  With a
+user base in the millions and with some 2,000 developers involved over the
+course of one year, the kernel has since had to evolve a number of
+processes to keep development happening smoothly.  A solid understanding of
+how the process works is required in order to be an effective part of it.
+
+
+2.1: THE BIG PICTURE
+
+The kernel developers use a loosely time-based release process, with a new
+major kernel release happening every two or three months.  The recent
+release history looks like this:
+
+	2.6.26	July 13, 2008
+	2.6.25	April 16, 2008
+	2.6.24	January 24, 2008
+	2.6.23	October 9, 2007
+	2.6.22	July 8, 2007
+	2.6.21	April 25, 2007
+	2.6.20	February 4, 2007
+
+Every 2.6.x release is a major kernel release with new features, internal
+API changes, and more.  A typical 2.6 release can contain over 10,000
+changesets with changes to several hundred thousand lines of code.  2.6 is
+thus the leading edge of Linux kernel development; the kernel uses a
+rolling development model which is continually integrating major changes.
+
+A relatively straightforward discipline is followed with regard to the
+merging of patches for each release.  At the beginning of each development
+cycle, the "merge window" is said to be open.  At that time, code which is
+deemed to be sufficiently stable (and which is accepted by the development
+community) is merged into the mainline kernel.  The bulk of changes for a
+new development cycle (and all of the major changes) will be merged during
+this time, at a rate approaching 1,000 changes ("patches," or "changesets")
+per day.
+
+(As an aside, it is worth noting that the changes integrated during the
+merge window do not come out of thin air; they have been collected, tested,
+and staged ahead of time.  How that process works will be described in
+detail later on).
+
+The merge window lasts for two weeks.  At the end of this time, Linus
+Torvalds will declare that the window is closed and release the first of
+the "rc" kernels.  For the kernel which is destined to be 2.6.26, for
+example, the release which happens at the end of the merge window will be
+called 2.6.26-rc1.  The -rc1 release is the signal that the time to merge
+new features has passed, and that the time to stabilize the next kernel has
+begun.
+
+Over the next six to ten weeks, only patches which fix problems should be
+submitted to the mainline.  On occasion a more significant change will be
+allowed, but such occasions are rare; developers who try to merge new
+features outside of the merge window tend to get an unfriendly reception.
+As a general rule, if you miss the merge window for a given feature, the
+best thing to do is to wait for the next development cycle.  (An occasional
+exception is made for drivers for previously-unsupported hardware; if they
+touch no in-tree code, they cannot cause regressions and should be safe to
+add at any time).
+
+As fixes make their way into the mainline, the patch rate will slow over
+time.  Linus releases new -rc kernels about once a week; a normal series
+will get up to somewhere between -rc6 and -rc9 before the kernel is
+considered to be sufficiently stable and the final 2.6.x release is made.
+At that point the whole process starts over again.
+
+As an example, here is how the 2.6.25 development cycle went (all dates in
+2008): 
+
+	January 24	2.6.24 stable release
+	February 10	2.6.25-rc1, merge window closes
+	February 15	2.6.25-rc2
+	February 24	2.6.25-rc3
+	March 4	 	2.6.25-rc4
+	March 9		2.6.25-rc5
+	March 16	2.6.25-rc6
+	March 25	2.6.25-rc7
+	April 1		2.6.25-rc8
+	April 11	2.6.25-rc9
+	April 16	2.6.25 stable release
+
+How do the developers decide when to close the development cycle and create
+the stable release?  The most significant metric used is the list of
+regressions from previous releases.  No bugs are welcome, but those which
+break systems which worked in the past are considered to be especially
+serious.  For this reason, patches which cause regressions are looked upon
+unfavorably and are quite likely to be reverted during the stabilization
+period. 
+
+The developers' goal is to fix all known regressions before the stable
+release is made.  In the real world, this kind of perfection is hard to
+achieve; there are just too many variables in a project of this size.
+There comes a point where delaying the final release just makes the problem
+worse; the pile of changes waiting for the next merge window will grow
+larger, creating even more regressions the next time around.  So most 2.6.x
+kernels go out with a handful of known regressions though, hopefully, none
+of them are serious.
+
+Once a stable release is made, its ongoing maintenance is passed off to the
+"stable team," currently comprised of Greg Kroah-Hartman and Chris Wright.
+The stable team will release occasional updates to the stable release using
+the 2.6.x.y numbering scheme.  To be considered for an update release, a
+patch must (1) fix a significant bug, and (2) already be merged into the
+mainline for the next development kernel.  Continuing our 2.6.25 example,
+the history (as of this writing) is:
+
+	May 1		2.6.25.1
+	May 6		2.6.25.2 
+	May 9		2.6.25.3 
+	May 15		2.6.25.4
+	June 7		2.6.25.5
+	June 9		2.6.25.6
+	June 16		2.6.25.7
+	June 21		2.6.25.8
+	June 24		2.6.25.9
+
+Stable updates for a given kernel are made for approximately six months;
+after that, the maintenance of stable releases is solely the responsibility
+of the distributors which have shipped that particular kernel.
+
+
+2.2: THE LIFECYCLE OF A PATCH
+
+Patches do not go directly from the developer's keyboard into the mainline
+kernel.  There is, instead, a somewhat involved (if somewhat informal)
+process designed to ensure that each patch is reviewed for quality and that
+each patch implements a change which is desirable to have in the mainline.
+This process can happen quickly for minor fixes, or, in the case of large
+and controversial changes, go on for years.  Much developer frustration
+comes from a lack of understanding of this process or from attempts to
+circumvent it.  
+
+In the hopes of reducing that frustration, this document will describe how
+a patch gets into the kernel.  What follows below is an introduction which
+describes the process in a somewhat idealized way.  A much more detailed
+treatment will come in later sections.
+
+The stages that a patch goes through are, generally:
+
+ - Design.  This is where the real requirements for the patch - and the way
+   those requirements will be met - are laid out.  Design work is often
+   done without involving the community, but it is better to do this work
+   in the open if at all possible; it can save a lot of time redesigning
+   things later.
+
+ - Early review.  Patches are posted to the relevant mailing list, and
+   developers on that list reply with any comments they may have.  This
+   process should turn up any major problems with a patch if all goes
+   well.
+
+ - Wider review.  When the patch is getting close to ready for mainline
+   inclusion, it will be accepted by a relevant subsystem maintainer -
+   though this acceptance is not a guarantee that the patch will make it
+   all the way to the mainline.  The patch will show up in the maintainer's
+   subsystem tree and into the staging trees (described below).  When the
+   process works, this step leads to more extensive review of the patch and
+   the discovery of any problems resulting from the integration of this
+   patch with work being done by others.
+
+ - Merging into the mainline.  Eventually, a successful patch will be
+   merged into the mainline repository managed by Linus Torvalds.  More
+   comments and/or problems may surface at this time; it is important that
+   the developer be responsive to these and fix any issues which arise.
+
+ - Stable release.  The number of users potentially affected by the patch
+   is now large, so, once again, new problems may arise.
+
+ - Long-term maintenance.  While it is certainly possible for a developer
+   to forget about code after merging it, that sort of behavior tends to
+   leave a poor impression in the development community.  Merging code
+   eliminates some of the maintenance burden, in that others will fix
+   problems caused by API changes.  But the original developer should
+   continue to take responsibility for the code if it is to remain useful
+   in the longer term.
+
+One of the largest mistakes made by kernel developers (or their employers)
+is to try to cut the process down to a single "merging into the mainline"
+step.  This approach invariably leads to frustration for everybody
+involved.
+
+
+2.3: HOW PATCHES GET INTO THE KERNEL
+
+There is exactly one person who can merge patches into the mainline kernel
+repository: Linus Torvalds.  But, of the over 12,000 patches which went
+into the 2.6.25 kernel, only 250 (around 2%) were directly chosen by Linus
+himself.  The kernel project has long since grown to a size where no single
+developer could possibly inspect and select every patch unassisted.  The
+way the kernel developers have addressed this growth is through the use of
+a lieutenant system built around a chain of trust.
+
+The kernel code base is logically broken down into a set of subsystems:
+networking, specific architecture support, memory management, video
+devices, etc.  Most subsystems have a designated maintainer, a developer
+who has overall responsibility for the code within that subsystem.  These
+subsystem maintainers are the gatekeepers (in a loose way) for the portion
+of the kernel they manage; they are the ones who will (usually) accept a
+patch for inclusion into the mainline kernel.
+
+Subsystem maintainers each manage their own version of the kernel source
+tree, usually (but certainly not always) using the git source management
+tool.  Tools like git (and related tools like quilt or mercurial) allow
+maintainers to track a list of patches, including authorship information
+and other metadata.  At any given time, the maintainer can identify which
+patches in his or her repository are not found in the mainline.
+
+When the merge window opens, top-level maintainers will ask Linus to "pull"
+the patches they have selected for merging from their repositories.  If
+Linus agrees, the stream of patches will flow up into his repository,
+becoming part of the mainline kernel.  The amount of attention that Linus
+pays to specific patches received in a pull operation varies.  It is clear
+that, sometimes, he looks quite closely.  But, as a general rule, Linus
+trusts the subsystem maintainers to not send bad patches upstream.
+
+Subsystem maintainers, in turn, can pull patches from other maintainers.
+For example, the networking tree is built from patches which accumulated
+first in trees dedicated to network device drivers, wireless networking,
+etc.  This chain of repositories can be arbitrarily long, though it rarely
+exceeds two or three links.  Since each maintainer in the chain trusts
+those managing lower-level trees, this process is known as the "chain of
+trust." 
+
+Clearly, in a system like this, getting patches into the kernel depends on
+finding the right maintainer.  Sending patches directly to Linus is not
+normally the right way to go.
+
+
+2.4: STAGING TREES
+
+The chain of subsystem trees guides the flow of patches into the kernel,
+but it also raises an interesting question: what if somebody wants to look
+at all of the patches which are being prepared for the next merge window?
+Developers will be interested in what other changes are pending to see
+whether there are any conflicts to worry about; a patch which changes a
+core kernel function prototype, for example, will conflict with any other
+patches which use the older form of that function.  Reviewers and testers
+want access to the changes in their integrated form before all of those
+changes land in the mainline kernel.  One could pull changes from all of
+the interesting subsystem trees, but that would be a big and error-prone
+job.
+
+The answer comes in the form of staging trees, where subsystem trees are
+collected for testing and review.  The older of these trees, maintained by
+Andrew Morton, is called "-mm" (for memory management, which is how it got
+started).  The -mm tree integrates patches from a long list of subsystem
+trees; it also has some patches aimed at helping with debugging.  
+
+Beyond that, -mm contains a significant collection of patches which have
+been selected by Andrew directly.  These patches may have been posted on a
+mailing list, or they may apply to a part of the kernel for which there is
+no designated subsystem tree.  As a result, -mm operates as a sort of
+subsystem tree of last resort; if there is no other obvious path for a
+patch into the mainline, it is likely to end up in -mm.  Miscellaneous
+patches which accumulate in -mm will eventually either be forwarded on to
+an appropriate subsystem tree or be sent directly to Linus.  In a typical
+development cycle, approximately 10% of the patches going into the mainline
+get there via -mm.
+
+The current -mm patch can always be found from the front page of
+
+	http://kernel.org/
+
+Those who want to see the current state of -mm can get the "-mm of the
+moment" tree, found at:
+
+	http://userweb.kernel.org/~akpm/mmotm/
+
+Use of the MMOTM tree is likely to be a frustrating experience, though;
+there is a definite chance that it will not even compile.
+
+The other staging tree, started more recently, is linux-next, maintained by
+Stephen Rothwell.  The linux-next tree is, by design, a snapshot of what
+the mainline is expected to look like after the next merge window closes.
+Linux-next trees are announced on the linux-kernel and linux-next mailing
+lists when they are assembled; they can be downloaded from:
+
+	http://www.kernel.org/pub/linux/kernel/people/sfr/linux-next/
+
+Some information about linux-next has been gathered at:
+
+	http://linux.f-seidel.de/linux-next/pmwiki/
+
+How the linux-next tree will fit into the development process is still
+changing.  As of this writing, the first full development cycle involving
+linux-next (2.6.26) is coming to an end; thus far, it has proved to be a
+valuable resource for finding and fixing integration problems before the
+beginning of the merge window.  See http://lwn.net/Articles/287155/ for
+more information on how linux-next has worked to set up the 2.6.27 merge
+window.
+
+Some developers have begun to suggest that linux-next should be used as the
+target for future development as well.  The linux-next tree does tend to be
+far ahead of the mainline and is more representative of the tree into which
+any new work will be merged.  The downside to this idea is that the
+volatility of linux-next tends to make it a difficult development target.
+See http://lwn.net/Articles/289013/ for more information on this topic, and
+stay tuned; much is still in flux where linux-next is involved.
+
+
+2.5: TOOLS
+
+As can be seen from the above text, the kernel development process depends
+heavily on the ability to herd collections of patches in various
+directions.  The whole thing would not work anywhere near as well as it
+does without suitably powerful tools.  Tutorials on how to use these tools
+are well beyond the scope of this document, but there is space for a few
+pointers.
+
+By far the dominant source code management system used by the kernel
+community is git.  Git is one of a number of distributed version control
+systems being developed in the free software community.  It is well tuned
+for kernel development, in that it performs quite well when dealing with
+large repositories and large numbers of patches.  It also has a reputation
+for being difficult to learn and use, though it has gotten better over
+time.  Some sort of familiarity with git is almost a requirement for kernel
+developers; even if they do not use it for their own work, they'll need git
+to keep up with what other developers (and the mainline) are doing.
+
+Git is now packaged by almost all Linux distributions.  There is a home
+page at 
+
+	http://git.or.cz/
+
+That page has pointers to documentation and tutorials.  One should be
+aware, in particular, of the Kernel Hacker's Guide to git, which has
+information specific to kernel development:
+
+	http://linux.yyz.us/git-howto.html
+
+Among the kernel developers who do not use git, the most popular choice is
+almost certainly Mercurial:
+
+	http://www.selenic.com/mercurial/
+
+Mercurial shares many features with git, but it provides an interface which
+many find easier to use.
+
+The other tool worth knowing about is Quilt:
+
+	http://savannah.nongnu.org/projects/quilt/
+
+Quilt is a patch management system, rather than a source code management
+system.  It does not track history over time; it is, instead, oriented
+toward tracking a specific set of changes against an evolving code base.
+Some major subsystem maintainers use quilt to manage patches intended to go
+upstream.  For the management of certain kinds of trees (-mm, for example),
+quilt is the best tool for the job.
+
+
+2.6: MAILING LISTS
+
+A great deal of Linux kernel development work is done by way of mailing
+lists.  It is hard to be a fully-functioning member of the community
+without joining at least one list somewhere.  But Linux mailing lists also
+represent a potential hazard to developers, who risk getting buried under a
+load of electronic mail, running afoul of the conventions used on the Linux
+lists, or both.
+
+Most kernel mailing lists are run on vger.kernel.org; the master list can
+be found at:
+
+	http://vger.kernel.org/vger-lists.html
+
+There are lists hosted elsewhere, though; a number of them are at
+lists.redhat.com.
+
+The core mailing list for kernel development is, of course, linux-kernel.
+This list is an intimidating place to be; volume can reach 500 messages per
+day, the amount of noise is high, the conversation can be severely
+technical, and participants are not always concerned with showing a high
+degree of politeness.  But there is no other place where the kernel
+development community comes together as a whole; developers who avoid this
+list will miss important information.
+
+There are a few hints which can help with linux-kernel survival:
+
+- Have the list delivered to a separate folder, rather than your main
+  mailbox.  One must be able to ignore the stream for sustained periods of
+  time.
+
+- Do not try to follow every conversation - nobody else does.  It is
+  important to filter on both the topic of interest (though note that
+  long-running conversations can drift away from the original subject
+  without changing the email subject line) and the people who are
+  participating.  
+
+- Do not feed the trolls.  If somebody is trying to stir up an angry
+  response, ignore them.
+
+- When responding to linux-kernel email (or that on other lists) preserve
+  the Cc: header for all involved.  In the absence of a strong reason (such
+  as an explicit request), you should never remove recipients.  Always make
+  sure that the person you are responding to is in the Cc: list.  This
+  convention also makes it unnecessary to explicitly ask to be copied on
+  replies to your postings.
+
+- Search the list archives (and the net as a whole) before asking
+  questions.  Some developers can get impatient with people who clearly
+  have not done their homework.
+
+- Avoid top-posting (the practice of putting your answer above the quoted
+  text you are responding to).  It makes your response harder to read and
+  makes a poor impression.
+
+- Ask on the correct mailing list.  Linux-kernel may be the general meeting
+  point, but it is not the best place to find developers from all
+  subsystems.
+
+The last point - finding the correct mailing list - is a common place for
+beginning developers to go wrong.  Somebody who asks a networking-related
+question on linux-kernel will almost certainly receive a polite suggestion
+to ask on the netdev list instead, as that is the list frequented by most
+networking developers.  Other lists exist for the SCSI, video4linux, IDE,
+filesystem, etc. subsystems.  The best place to look for mailing lists is
+in the MAINTAINERS file packaged with the kernel source.
+
+
+2.7: GETTING STARTED WITH KERNEL DEVELOPMENT
+
+Questions about how to get started with the kernel development process are
+common - from both individuals and companies.  Equally common are missteps
+which make the beginning of the relationship harder than it has to be.
+
+Companies often look to hire well-known developers to get a development
+group started.  This can, in fact, be an effective technique.  But it also
+tends to be expensive and does not do much to grow the pool of experienced
+kernel developers.  It is possible to bring in-house developers up to speed
+on Linux kernel development, given the investment of a bit of time.  Taking
+this time can endow an employer with a group of developers who understand
+the kernel and the company both, and who can help to train others as well.
+Over the medium term, this is often the more profitable approach.
+
+Individual developers are often, understandably, at a loss for a place to
+start.  Beginning with a large project can be intimidating; one often wants
+to test the waters with something smaller first.  This is the point where
+some developers jump into the creation of patches fixing spelling errors or
+minor coding style issues.  Unfortunately, such patches create a level of
+noise which is distracting for the development community as a whole, so,
+increasingly, they are looked down upon.  New developers wishing to
+introduce themselves to the community will not get the sort of reception
+they wish for by these means.
+
+Andrew Morton gives this advice for aspiring kernel developers
+
+	The #1 project for all kernel beginners should surely be "make sure
+	that the kernel runs perfectly at all times on all machines which
+	you can lay your hands on".  Usually the way to do this is to work
+	with others on getting things fixed up (this can require
+	persistence!) but that's fine - it's a part of kernel development.
+
+(http://lwn.net/Articles/283982/).
+
+In the absence of obvious problems to fix, developers are advised to look
+at the current lists of regressions and open bugs in general.  There is
+never any shortage of issues in need of fixing; by addressing these issues,
+developers will gain experience with the process while, at the same time,
+building respect with the rest of the development community.

Documentation/development-process/3.Early-stage

@@ -0,0 +1,195 @@
+3: EARLY-STAGE PLANNING
+
+When contemplating a Linux kernel development project, it can be tempting
+to jump right in and start coding.  As with any significant project,
+though, much of the groundwork for success is best laid before the first
+line of code is written.  Some time spent in early planning and
+communication can save far more time later on.
+
+
+3.1: SPECIFYING THE PROBLEM
+
+Like any engineering project, a successful kernel enhancement starts with a
+clear description of the problem to be solved.  In some cases, this step is
+easy: when a driver is needed for a specific piece of hardware, for
+example.  In others, though, it is tempting to confuse the real problem
+with the proposed solution, and that can lead to difficulties.
+
+Consider an example: some years ago, developers working with Linux audio
+sought a way to run applications without dropouts or other artifacts caused
+by excessive latency in the system.  The solution they arrived at was a
+kernel module intended to hook into the Linux Security Module (LSM)
+framework; this module could be configured to give specific applications
+access to the realtime scheduler.  This module was implemented and sent to
+the linux-kernel mailing list, where it immediately ran into problems.
+
+To the audio developers, this security module was sufficient to solve their
+immediate problem.  To the wider kernel community, though, it was seen as a
+misuse of the LSM framework (which is not intended to confer privileges
+onto processes which they would not otherwise have) and a risk to system
+stability.  Their preferred solutions involved realtime scheduling access
+via the rlimit mechanism for the short term, and ongoing latency reduction
+work in the long term.
+
+The audio community, however, could not see past the particular solution
+they had implemented; they were unwilling to accept alternatives.  The
+resulting disagreement left those developers feeling disillusioned with the
+entire kernel development process; one of them went back to an audio list
+and posted this:
+
+	There are a number of very good Linux kernel developers, but they
+	tend to get outshouted by a large crowd of arrogant fools. Trying
+	to communicate user requirements to these people is a waste of
+	time. They are much too "intelligent" to listen to lesser mortals.
+
+(http://lwn.net/Articles/131776/).
+
+The reality of the situation was different; the kernel developers were far
+more concerned about system stability, long-term maintenance, and finding
+the right solution to the problem than they were with a specific module.
+The moral of the story is to focus on the problem - not a specific solution
+- and to discuss it with the development community before investing in the
+creation of a body of code.
+
+So, when contemplating a kernel development project, one should obtain
+answers to a short set of questions:
+
+ - What, exactly, is the problem which needs to be solved?
+
+ - Who are the users affected by this problem?  Which use cases should the
+   solution address?
+
+ - How does the kernel fall short in addressing that problem now?
+
+Only then does it make sense to start considering possible solutions.
+
+
+3.2: EARLY DISCUSSION
+
+When planning a kernel development project, it makes great sense to hold
+discussions with the community before launching into implementation.  Early
+communication can save time and trouble in a number of ways:
+
+ - It may well be that the problem is addressed by the kernel in ways which
+   you have not understood.  The Linux kernel is large and has a number of
+   features and capabilities which are not immediately obvious.  Not all
+   kernel capabilities are documented as well as one might like, and it is
+   easy to miss things.  Your author has seen the posting of a complete
+   driver which duplicated an existing driver that the new author had been
+   unaware of.  Code which reinvents existing wheels is not only wasteful;
+   it will also not be accepted into the mainline kernel.
+
+ - There may be elements of the proposed solution which will not be
+   acceptable for mainline merging.  It is better to find out about
+   problems like this before writing the code.
+
+ - It's entirely possible that other developers have thought about the
+   problem; they may have ideas for a better solution, and may be willing
+   to help in the creation of that solution.
+
+Years of experience with the kernel development community have taught a
+clear lesson: kernel code which is designed and developed behind closed
+doors invariably has problems which are only revealed when the code is
+released into the community.  Sometimes these problems are severe,
+requiring months or years of effort before the code can be brought up to
+the kernel community's standards.  Some examples include:
+
+ - The Devicescape network stack was designed and implemented for
+   single-processor systems.  It could not be merged into the mainline
+   until it was made suitable for multiprocessor systems.  Retrofitting
+   locking and such into code is a difficult task; as a result, the merging
+   of this code (now called mac80211) was delayed for over a year.
+
+ - The Reiser4 filesystem included a number of capabilities which, in the
+   core kernel developers' opinion, should have been implemented in the
+   virtual filesystem layer instead.  It also included features which could
+   not easily be implemented without exposing the system to user-caused
+   deadlocks.  The late revelation of these problems - and refusal to
+   address some of them - has caused Reiser4 to stay out of the mainline
+   kernel.
+
+ - The AppArmor security module made use of internal virtual filesystem
+   data structures in ways which were considered to be unsafe and
+   unreliable.  This code has since been significantly reworked, but
+   remains outside of the mainline.
+
+In each of these cases, a great deal of pain and extra work could have been
+avoided with some early discussion with the kernel developers.
+
+
+3.3: WHO DO YOU TALK TO?
+
+When developers decide to take their plans public, the next question will
+be: where do we start?  The answer is to find the right mailing list(s) and
+the right maintainer.  For mailing lists, the best approach is to look in
+the MAINTAINERS file for a relevant place to post.  If there is a suitable
+subsystem list, posting there is often preferable to posting on
+linux-kernel; you are more likely to reach developers with expertise in the
+relevant subsystem and the environment may be more supportive.
+
+Finding maintainers can be a bit harder.  Again, the MAINTAINERS file is
+the place to start.  That file tends to not always be up to date, though,
+and not all subsystems are represented there.  The person listed in the
+MAINTAINERS file may, in fact, not be the person who is actually acting in
+that role currently.  So, when there is doubt about who to contact, a
+useful trick is to use git (and "git log" in particular) to see who is
+currently active within the subsystem of interest.  Look at who is writing
+patches, and who, if anybody, is attaching Signed-off-by lines to those
+patches.  Those are the people who will be best placed to help with a new
+development project.
+
+If all else fails, talking to Andrew Morton can be an effective way to
+track down a maintainer for a specific piece of code.
+
+
+3.4: WHEN TO POST?
+
+If possible, posting your plans during the early stages can only be
+helpful.  Describe the problem being solved and any plans that have been
+made on how the implementation will be done.  Any information you can
+provide can help the development community provide useful input on the
+project.
+
+One discouraging thing which can happen at this stage is not a hostile
+reaction, but, instead, little or no reaction at all.  The sad truth of the
+matter is (1) kernel developers tend to be busy, (2) there is no shortage
+of people with grand plans and little code (or even prospect of code) to
+back them up, and (3) nobody is obligated to review or comment on ideas
+posted by others.  If a request-for-comments posting yields little in the
+way of comments, do not assume that it means there is no interest in the
+project.  Unfortunately, you also cannot assume that there are no problems
+with your idea.  The best thing to do in this situation is to proceed,
+keeping the community informed as you go.
+
+
+3.5: GETTING OFFICIAL BUY-IN
+
+If your work is being done in a corporate environment - as most Linux
+kernel work is - you must, obviously, have permission from suitably
+empowered managers before you can post your company's plans or code to a
+public mailing list.  The posting of code which has not been cleared for
+release under a GPL-compatible license can be especially problematic; the
+sooner that a company's management and legal staff can agree on the posting
+of a kernel development project, the better off everybody involved will be.
+
+Some readers may be thinking at this point that their kernel work is
+intended to support a product which does not yet have an officially
+acknowledged existence.  Revealing their employer's plans on a public
+mailing list may not be a viable option.  In cases like this, it is worth
+considering whether the secrecy is really necessary; there is often no real
+need to keep development plans behind closed doors.
+
+That said, there are also cases where a company legitimately cannot
+disclose its plans early in the development process.  Companies with
+experienced kernel developers may choose to proceed in an open-loop manner
+on the assumption that they will be able to avoid serious integration
+problems later.  For companies without that sort of in-house expertise, the
+best option is often to hire an outside developer to review the plans under
+a non-disclosure agreement.  The Linux Foundation operates an NDA program
+designed to help with this sort of situation; more information can be found
+at:
+
+    http://www.linuxfoundation.org/en/NDA_program
+
+This kind of review is often enough to avoid serious problems later on
+without requiring public disclosure of the project.

Documentation/development-process/4.Coding

@@ -0,0 +1,384 @@
+4: GETTING THE CODE RIGHT
+
+While there is much to be said for a solid and community-oriented design
+process, the proof of any kernel development project is in the resulting
+code.  It is the code which will be examined by other developers and merged
+(or not) into the mainline tree.  So it is the quality of this code which
+will determine the ultimate success of the project.
+
+This section will examine the coding process.  We'll start with a look at a
+number of ways in which kernel developers can go wrong.  Then the focus
+will shift toward doing things right and the tools which can help in that
+quest.
+
+
+4.1: PITFALLS
+
+* Coding style
+
+The kernel has long had a standard coding style, described in
+Documentation/CodingStyle.  For much of that time, the policies described
+in that file were taken as being, at most, advisory.  As a result, there is
+a substantial amount of code in the kernel which does not meet the coding
+style guidelines.  The presence of that code leads to two independent
+hazards for kernel developers.
+
+The first of these is to believe that the kernel coding standards do not
+matter and are not enforced.  The truth of the matter is that adding new
+code to the kernel is very difficult if that code is not coded according to
+the standard; many developers will request that the code be reformatted
+before they will even review it.  A code base as large as the kernel
+requires some uniformity of code to make it possible for developers to
+quickly understand any part of it.  So there is no longer room for
+strangely-formatted code.
+
+Occasionally, the kernel's coding style will run into conflict with an
+employer's mandated style.  In such cases, the kernel's style will have to
+win before the code can be merged.  Putting code into the kernel means
+giving up a degree of control in a number of ways - including control over
+how the code is formatted.
+
+The other trap is to assume that code which is already in the kernel is
+urgently in need of coding style fixes.  Developers may start to generate
+reformatting patches as a way of gaining familiarity with the process, or
+as a way of getting their name into the kernel changelogs - or both.  But
+pure coding style fixes are seen as noise by the development community;
+they tend to get a chilly reception.  So this type of patch is best
+avoided.  It is natural to fix the style of a piece of code while working
+on it for other reasons, but coding style changes should not be made for
+their own sake.
+
+The coding style document also should not be read as an absolute law which
+can never be transgressed.  If there is a good reason to go against the
+style (a line which becomes far less readable if split to fit within the
+80-column limit, for example), just do it.
+
+
+* Abstraction layers
+
+Computer Science professors teach students to make extensive use of
+abstraction layers in the name of flexibility and information hiding.
+Certainly the kernel makes extensive use of abstraction; no project
+involving several million lines of code could do otherwise and survive.
+But experience has shown that excessive or premature abstraction can be
+just as harmful as premature optimization.  Abstraction should be used to
+the level required and no further.
+
+At a simple level, consider a function which has an argument which is
+always passed as zero by all callers.  One could retain that argument just
+in case somebody eventually needs to use the extra flexibility that it
+provides.  By that time, though, chances are good that the code which
+implements this extra argument has been broken in some subtle way which was
+never noticed - because it has never been used.  Or, when the need for
+extra flexibility arises, it does not do so in a way which matches the
+programmer's early expectation.  Kernel developers will routinely submit
+patches to remove unused arguments; they should, in general, not be added
+in the first place.
+
+Abstraction layers which hide access to hardware - often to allow the bulk
+of a driver to be used with multiple operating systems - are especially
+frowned upon.  Such layers obscure the code and may impose a performance
+penalty; they do not belong in the Linux kernel.
+
+On the other hand, if you find yourself copying significant amounts of code
+from another kernel subsystem, it is time to ask whether it would, in fact,
+make sense to pull out some of that code into a separate library or to
+implement that functionality at a higher level.  There is no value in
+replicating the same code throughout the kernel.
+
+
+* #ifdef and preprocessor use in general
+
+The C preprocessor seems to present a powerful temptation to some C
+programmers, who see it as a way to efficiently encode a great deal of
+flexibility into a source file.  But the preprocessor is not C, and heavy
+use of it results in code which is much harder for others to read and
+harder for the compiler to check for correctness.  Heavy preprocessor use
+is almost always a sign of code which needs some cleanup work.
+
+Conditional compilation with #ifdef is, indeed, a powerful feature, and it
+is used within the kernel.  But there is little desire to see code which is
+sprinkled liberally with #ifdef blocks.  As a general rule, #ifdef use
+should be confined to header files whenever possible.
+Conditionally-compiled code can be confined to functions which, if the code
+is not to be present, simply become empty.  The compiler will then quietly
+optimize out the call to the empty function.  The result is far cleaner
+code which is easier to follow.
+
+C preprocessor macros present a number of hazards, including possible
+multiple evaluation of expressions with side effects and no type safety.
+If you are tempted to define a macro, consider creating an inline function
+instead.  The code which results will be the same, but inline functions are
+easier to read, do not evaluate their arguments multiple times, and allow
+the compiler to perform type checking on the arguments and return value.
+
+
+* Inline functions
+
+Inline functions present a hazard of their own, though.  Programmers can
+become enamored of the perceived efficiency inherent in avoiding a function
+call and fill a source file with inline functions.  Those functions,
+however, can actually reduce performance.  Since their code is replicated
+at each call site, they end up bloating the size of the compiled kernel.
+That, in turn, creates pressure on the processor's memory caches, which can
+slow execution dramatically.  Inline functions, as a rule, should be quite
+small and relatively rare.  The cost of a function call, after all, is not
+that high; the creation of large numbers of inline functions is a classic
+example of premature optimization.
+
+In general, kernel programmers ignore cache effects at their peril.  The
+classic time/space tradeoff taught in beginning data structures classes
+often does not apply to contemporary hardware.  Space *is* time, in that a
+larger program will run slower than one which is more compact.
+
+
+* Locking
+
+In May, 2006, the "Devicescape" networking stack was, with great
+fanfare, released under the GPL and made available for inclusion in the
+mainline kernel.  This donation was welcome news; support for wireless
+networking in Linux was considered substandard at best, and the Devicescape
+stack offered the promise of fixing that situation.  Yet, this code did not
+actually make it into the mainline until June, 2007 (2.6.22).  What
+happened?
+
+This code showed a number of signs of having been developed behind
+corporate doors.  But one large problem in particular was that it was not
+designed to work on multiprocessor systems.  Before this networking stack
+(now called mac80211) could be merged, a locking scheme needed to be
+retrofitted onto it.  
+
+Once upon a time, Linux kernel code could be developed without thinking
+about the concurrency issues presented by multiprocessor systems.  Now,
+however, this document is being written on a dual-core laptop.  Even on
+single-processor systems, work being done to improve responsiveness will
+raise the level of concurrency within the kernel.  The days when kernel
+code could be written without thinking about locking are long past.
+
+Any resource (data structures, hardware registers, etc.) which could be
+accessed concurrently by more than one thread must be protected by a lock.
+New code should be written with this requirement in mind; retrofitting
+locking after the fact is a rather more difficult task.  Kernel developers
+should take the time to understand the available locking primitives well
+enough to pick the right tool for the job.  Code which shows a lack of
+attention to concurrency will have a difficult path into the mainline.
+
+
+* Regressions
+
+One final hazard worth mentioning is this: it can be tempting to make a
+change (which may bring big improvements) which causes something to break
+for existing users.  This kind of change is called a "regression," and
+regressions have become most unwelcome in the mainline kernel.  With few
+exceptions, changes which cause regressions will be backed out if the
+regression cannot be fixed in a timely manner.  Far better to avoid the
+regression in the first place.
+
+It is often argued that a regression can be justified if it causes things
+to work for more people than it creates problems for.  Why not make a
+change if it brings new functionality to ten systems for each one it
+breaks?  The best answer to this question was expressed by Linus in July,
+2007:
+
+	So we don't fix bugs by introducing new problems.  That way lies
+	madness, and nobody ever knows if you actually make any real
+	progress at all. Is it two steps forwards, one step back, or one
+	step forward and two steps back?
+
+(http://lwn.net/Articles/243460/).
+
+An especially unwelcome type of regression is any sort of change to the
+user-space ABI.  Once an interface has been exported to user space, it must
+be supported indefinitely.  This fact makes the creation of user-space
+interfaces particularly challenging: since they cannot be changed in
+incompatible ways, they must be done right the first time.  For this
+reason, a great deal of thought, clear documentation, and wide review for
+user-space interfaces is always required.
+
+
+
+4.2: CODE CHECKING TOOLS
+
+For now, at least, the writing of error-free code remains an ideal that few
+of us can reach.  What we can hope to do, though, is to catch and fix as
+many of those errors as possible before our code goes into the mainline
+kernel.  To that end, the kernel developers have put together an impressive
+array of tools which can catch a wide variety of obscure problems in an
+automated way.  Any problem caught by the computer is a problem which will
+not afflict a user later on, so it stands to reason that the automated
+tools should be used whenever possible.
+
+The first step is simply to heed the warnings produced by the compiler.
+Contemporary versions of gcc can detect (and warn about) a large number of
+potential errors.  Quite often, these warnings point to real problems.
+Code submitted for review should, as a rule, not produce any compiler
+warnings.  When silencing warnings, take care to understand the real cause
+and try to avoid "fixes" which make the warning go away without addressing
+its cause.
+
+Note that not all compiler warnings are enabled by default.  Build the
+kernel with "make EXTRA_CFLAGS=-W" to get the full set.
+
+The kernel provides several configuration options which turn on debugging
+features; most of these are found in the "kernel hacking" submenu.  Several
+of these options should be turned on for any kernel used for development or
+testing purposes.  In particular, you should turn on:
+
+ - ENABLE_WARN_DEPRECATED, ENABLE_MUST_CHECK, and FRAME_WARN to get an
+   extra set of warnings for problems like the use of deprecated interfaces
+   or ignoring an important return value from a function.  The output
+   generated by these warnings can be verbose, but one need not worry about
+   warnings from other parts of the kernel.
+
+ - DEBUG_OBJECTS will add code to track the lifetime of various objects
+   created by the kernel and warn when things are done out of order.  If
+   you are adding a subsystem which creates (and exports) complex objects
+   of its own, consider adding support for the object debugging
+   infrastructure.
+
+ - DEBUG_SLAB can find a variety of memory allocation and use errors; it
+   should be used on most development kernels.
+
+ - DEBUG_SPINLOCK, DEBUG_SPINLOCK_SLEEP, and DEBUG_MUTEXES will find a
+   number of common locking errors.
+
+There are quite a few other debugging options, some of which will be
+discussed below.  Some of them have a significant performance impact and
+should not be used all of the time.  But some time spent learning the
+available options will likely be paid back many times over in short order. 
+
+One of the heavier debugging tools is the locking checker, or "lockdep."
+This tool will track the acquisition and release of every lock (spinlock or
+mutex) in the system, the order in which locks are acquired relative to
+each other, the current interrupt environment, and more.  It can then
+ensure that locks are always acquired in the same order, that the same
+interrupt assumptions apply in all situations, and so on.  In other words,
+lockdep can find a number of scenarios in which the system could, on rare
+occasion, deadlock.  This kind of problem can be painful (for both
+developers and users) in a deployed system; lockdep allows them to be found
+in an automated manner ahead of time.  Code with any sort of non-trivial
+locking should be run with lockdep enabled before being submitted for
+inclusion. 
+
+As a diligent kernel programmer, you will, beyond doubt, check the return
+status of any operation (such as a memory allocation) which can fail.  The
+fact of the matter, though, is that the resulting failure recovery paths
+are, probably, completely untested.  Untested code tends to be broken code;
+you could be much more confident of your code if all those error-handling
+paths had been exercised a few times.
+
+The kernel provides a fault injection framework which can do exactly that,
+especially where memory allocations are involved.  With fault injection
+enabled, a configurable percentage of memory allocations will be made to
+fail; these failures can be restricted to a specific range of code.
+Running with fault injection enabled allows the programmer to see how the
+code responds when things go badly.  See
+Documentation/fault-injection/fault-injection.text for more information on
+how to use this facility.
+
+Other kinds of errors can be found with the "sparse" static analysis tool.
+With sparse, the programmer can be warned about confusion between
+user-space and kernel-space addresses, mixture of big-endian and
+small-endian quantities, the passing of integer values where a set of bit
+flags is expected, and so on.  Sparse must be installed separately (it can
+be found at http://www.kernel.org/pub/software/devel/sparse/ if your
+distributor does not package it); it can then be run on the code by adding
+"C=1" to your make command.
+
+Other kinds of portability errors are best found by compiling your code for
+other architectures.  If you do not happen to have an S/390 system or a
+Blackfin development board handy, you can still perform the compilation
+step.  A large set of cross compilers for x86 systems can be found at 
+
+	http://www.kernel.org/pub/tools/crosstool/
+
+Some time spent installing and using these compilers will help avoid
+embarrassment later.
+
+
+4.3: DOCUMENTATION
+
+Documentation has often been more the exception than the rule with kernel
+development.  Even so, adequate documentation will help to ease the merging
+of new code into the kernel, make life easier for other developers, and
+will be helpful for your users.  In many cases, the addition of
+documentation has become essentially mandatory.
+
+The first piece of documentation for any patch is its associated
+changelog.  Log entries should describe the problem being solved, the form
+of the solution, the people who worked on the patch, any relevant
+effects on performance, and anything else that might be needed to
+understand the patch.
+
+Any code which adds a new user-space interface - including new sysfs or
+/proc files - should include documentation of that interface which enables
+user-space developers to know what they are working with.  See
+Documentation/ABI/README for a description of how this documentation should
+be formatted and what information needs to be provided.
+
+The file Documentation/kernel-parameters.txt describes all of the kernel's
+boot-time parameters.  Any patch which adds new parameters should add the
+appropriate entries to this file.
+
+Any new configuration options must be accompanied by help text which
+clearly explains the options and when the user might want to select them. 
+
+Internal API information for many subsystems is documented by way of
+specially-formatted comments; these comments can be extracted and formatted
+in a number of ways by the "kernel-doc" script.  If you are working within
+a subsystem which has kerneldoc comments, you should maintain them and add
+them, as appropriate, for externally-available functions.  Even in areas
+which have not been so documented, there is no harm in adding kerneldoc
+comments for the future; indeed, this can be a useful activity for
+beginning kernel developers.  The format of these comments, along with some
+information on how to create kerneldoc templates can be found in the file
+Documentation/kernel-doc-nano-HOWTO.txt.
+
+Anybody who reads through a significant amount of existing kernel code will
+note that, often, comments are most notable by their absence.  Once again,
+the expectations for new code are higher than they were in the past;
+merging uncommented code will be harder.  That said, there is little desire
+for verbosely-commented code.  The code should, itself, be readable, with
+comments explaining the more subtle aspects.
+
+Certain things should always be commented.  Uses of memory barriers should
+be accompanied by a line explaining why the barrier is necessary.  The
+locking rules for data structures generally need to be explained somewhere.
+Major data structures need comprehensive documentation in general.
+Non-obvious dependencies between separate bits of code should be pointed
+out.  Anything which might tempt a code janitor to make an incorrect
+"cleanup" needs a comment saying why it is done the way it is.  And so on.
+
+
+4.4: INTERNAL API CHANGES
+
+The binary interface provided by the kernel to user space cannot be broken
+except under the most severe circumstances.  The kernel's internal
+programming interfaces, instead, are highly fluid and can be changed when
+the need arises.  If you find yourself having to work around a kernel API,
+or simply not using a specific functionality because it does not meet your
+needs, that may be a sign that the API needs to change.  As a kernel
+developer, you are empowered to make such changes.
+
+There are, of course, some catches.  API changes can be made, but they need
+to be well justified.  So any patch making an internal API change should be
+accompanied by a description of what the change is and why it is
+necessary.  This kind of change should also be broken out into a separate
+patch, rather than buried within a larger patch.
+
+The other catch is that a developer who changes an internal API is
+generally charged with the task of fixing any code within the kernel tree
+which is broken by the change.  For a widely-used function, this duty can
+lead to literally hundreds or thousands of changes - many of which are
+likely to conflict with work being done by other developers.  Needless to
+say, this can be a large job, so it is best to be sure that the
+justification is solid.
+
+When making an incompatible API change, one should, whenever possible,
+ensure that code which has not been updated is caught by the compiler.  
+This will help you to be sure that you have found all in-tree uses of that
+interface.  It will also alert developers of out-of-tree code that there is
+a change that they need to respond to.  Supporting out-of-tree code is not
+something that kernel developers need to be worried about, but we also do
+not have to make life harder for out-of-tree developers than it it needs to
+be. 

Documentation/development-process/5.Posting

@@ -0,0 +1,278 @@
+5: POSTING PATCHES
+
+Sooner or later, the time comes when your work is ready to be presented to
+the community for review and, eventually, inclusion into the mainline
+kernel.  Unsurprisingly, the kernel development community has evolved a set
+of conventions and procedures which are used in the posting of patches;
+following them will make life much easier for everybody involved.  This
+document will attempt to cover these expectations in reasonable detail;
+more information can also be found in the files SubmittingPatches,
+SubmittingDrivers, and SubmitChecklist in the kernel documentation
+directory.
+
+
+5.1: WHEN TO POST
+
+There is a constant temptation to avoid posting patches before they are
+completely "ready."  For simple patches, that is not a problem.  If the
+work being done is complex, though, there is a lot to be gained by getting
+feedback from the community before the work is complete.  So you should
+consider posting in-progress work, or even making a git tree available so
+that interested developers can catch up with your work at any time.
+
+When posting code which is not yet considered ready for inclusion, it is a
+good idea to say so in the posting itself.  Also mention any major work
+which remains to be done and any known problems.  Fewer people will look at
+patches which are known to be half-baked, but those who do will come in
+with the idea that they can help you drive the work in the right direction.
+
+
+5.2: BEFORE CREATING PATCHES
+
+There are a number of things which should be done before you consider
+sending patches to the development community.  These include:
+
+ - Test the code to the extent that you can.  Make use of the kernel's
+   debugging tools, ensure that the kernel will build with all reasonable
+   combinations of configuration options, use cross-compilers to build for
+   different architectures, etc.
+
+ - Make sure your code is compliant with the kernel coding style
+   guidelines.
+
+ - Does your change have performance implications?  If so, you should run
+   benchmarks showing what the impact (or benefit) of your change is; a
+   summary of the results should be included with the patch.
+
+ - Be sure that you have the right to post the code.  If this work was done
+   for an employer, the employer likely has a right to the work and must be
+   agreeable with its release under the GPL.
+
+As a general rule, putting in some extra thought before posting code almost
+always pays back the effort in short order.
+
+
+5.3: PATCH PREPARATION
+
+The preparation of patches for posting can be a surprising amount of work,
+but, once again, attempting to save time here is not generally advisable
+even in the short term.
+
+Patches must be prepared against a specific version of the kernel.  As a
+general rule, a patch should be based on the current mainline as found in
+Linus's git tree.  It may become necessary to make versions against -mm,
+linux-next, or a subsystem tree, though, to facilitate wider testing and
+review.  Depending on the area of your patch and what is going on
+elsewhere, basing a patch against these other trees can require a
+significant amount of work resolving conflicts and dealing with API
+changes.
+
+Only the most simple changes should be formatted as a single patch;
+everything else should be made as a logical series of changes.  Splitting
+up patches is a bit of an art; some developers spend a long time figuring
+out how to do it in the way that the community expects.  There are a few
+rules of thumb, however, which can help considerably:
+
+ - The patch series you post will almost certainly not be the series of
+   changes found in your working revision control system.  Instead, the
+   changes you have made need to be considered in their final form, then
+   split apart in ways which make sense.  The developers are interested in
+   discrete, self-contained changes, not the path you took to get to those
+   changes.
+
+ - Each logically independent change should be formatted as a separate
+   patch.  These changes can be small ("add a field to this structure") or
+   large (adding a significant new driver, for example), but they should be
+   conceptually small and amenable to a one-line description.  Each patch
+   should make a specific change which can be reviewed on its own and
+   verified to do what it says it does.
+
+ - As a way of restating the guideline above: do not mix different types of
+   changes in the same patch.  If a single patch fixes a critical security
+   bug, rearranges a few structures, and reformats the code, there is a
+   good chance that it will be passed over and the important fix will be
+   lost.
+
+ - Each patch should yield a kernel which builds and runs properly; if your
+   patch series is interrupted in the middle, the result should still be a
+   working kernel.  Partial application of a patch series is a common
+   scenario when the "git bisect" tool is used to find regressions; if the
+   result is a broken kernel, you will make life harder for developers and
+   users who are engaging in the noble work of tracking down problems.
+
+ - Do not overdo it, though.  One developer recently posted a set of edits
+   to a single file as 500 separate patches - an act which did not make him
+   the most popular person on the kernel mailing list.  A single patch can
+   be reasonably large as long as it still contains a single *logical*
+   change. 
+
+ - It can be tempting to add a whole new infrastructure with a series of
+   patches, but to leave that infrastructure unused until the final patch
+   in the series enables the whole thing.  This temptation should be
+   avoided if possible; if that series adds regressions, bisection will
+   finger the last patch as the one which caused the problem, even though
+   the real bug is elsewhere.  Whenever possible, a patch which adds new
+   code should make that code active immediately.
+
+Working to create the perfect patch series can be a frustrating process
+which takes quite a bit of time and thought after the "real work" has been
+done.  When done properly, though, it is time well spent.
+
+
+5.4: PATCH FORMATTING
+
+So now you have a perfect series of patches for posting, but the work is
+not done quite yet.  Each patch needs to be formatted into a message which
+quickly and clearly communicates its purpose to the rest of the world.  To
+that end, each patch will be composed of the following:
+
+ - An optional "From" line naming the author of the patch.  This line is
+   only necessary if you are passing on somebody else's patch via email,
+   but it never hurts to add it when in doubt.
+
+ - A one-line description of what the patch does.  This message should be
+   enough for a reader who sees it with no other context to figure out the
+   scope of the patch; it is the line that will show up in the "short form"
+   changelogs.  This message is usually formatted with the relevant
+   subsystem name first, followed by the purpose of the patch.  For
+   example:
+
+	gpio: fix build on CONFIG_GPIO_SYSFS=n
+
+ - A blank line followed by a detailed description of the contents of the
+   patch.  This description can be as long as is required; it should say
+   what the patch does and why it should be applied to the kernel.
+
+ - One or more tag lines, with, at a minimum, one Signed-off-by: line from
+   the author of the patch.  Tags will be described in more detail below.
+
+The above three items should, normally, be the text used when committing
+the change to a revision control system.  They are followed by:
+
+ - The patch itself, in the unified ("-u") patch format.  Using the "-p"
+   option to diff will associate function names with changes, making the
+   resulting patch easier for others to read.
+
+You should avoid including changes to irrelevant files (those generated by
+the build process, for example, or editor backup files) in the patch.  The
+file "dontdiff" in the Documentation directory can help in this regard;
+pass it to diff with the "-X" option.
+
+The tags mentioned above are used to describe how various developers have
+been associated with the development of this patch.  They are described in
+detail in the SubmittingPatches document; what follows here is a brief
+summary.  Each of these lines has the format:
+
+	tag: Full Name <email address>  optional-other-stuff
+
+The tags in common use are:
+
+ - Signed-off-by: this is a developer's certification that he or she has
+   the right to submit the patch for inclusion into the kernel.  It is an
+   agreement to the Developer's Certificate of Origin, the full text of
+   which can be found in Documentation/SubmittingPatches.  Code without a
+   proper signoff cannot be merged into the mainline.
+
+ - Acked-by: indicates an agreement by another developer (often a
+   maintainer of the relevant code) that the patch is appropriate for
+   inclusion into the kernel.
+
+ - Tested-by: states that the named person has tested the patch and found
+   it to work.
+
+ - Reviewed-by: the named developer has reviewed the patch for correctness;
+   see the reviewer's statement in Documentation/SubmittingPatches for more
+   detail.
+
+ - Reported-by: names a user who reported a problem which is fixed by this
+   patch; this tag is used to give credit to the (often underappreciated)
+   people who test our code and let us know when things do not work
+   correctly.
+
+ - Cc: the named person received a copy of the patch and had the
+   opportunity to comment on it.
+
+Be careful in the addition of tags to your patches: only Cc: is appropriate
+for addition without the explicit permission of the person named.
+
+
+5.5: SENDING THE PATCH
+
+Before you mail your patches, there are a couple of other things you should
+take care of:
+
+ - Are you sure that your mailer will not corrupt the patches?  Patches
+   which have had gratuitous white-space changes or line wrapping performed
+   by the mail client will not apply at the other end, and often will not
+   be examined in any detail.  If there is any doubt at all, mail the patch
+   to yourself and convince yourself that it shows up intact.  
+
+   Documentation/email-clients.txt has some helpful hints on making
+   specific mail clients work for sending patches.
+
+ - Are you sure your patch is free of silly mistakes?  You should always
+   run patches through scripts/checkpatch.pl and address the complaints it
+   comes up with.  Please bear in mind that checkpatch.pl, while being the
+   embodiment of a fair amount of thought about what kernel patches should
+   look like, is not smarter than you.  If fixing a checkpatch.pl complaint
+   would make the code worse, don't do it.
+
+Patches should always be sent as plain text.  Please do not send them as
+attachments; that makes it much harder for reviewers to quote sections of
+the patch in their replies.  Instead, just put the patch directly into your
+message.
+
+When mailing patches, it is important to send copies to anybody who might
+be interested in it.  Unlike some other projects, the kernel encourages
+people to err on the side of sending too many copies; don't assume that the
+relevant people will see your posting on the mailing lists.  In particular,
+copies should go to:
+
+ - The maintainer(s) of the affected subsystem(s).  As described earlier,
+   the MAINTAINERS file is the first place to look for these people.
+
+ - Other developers who have been working in the same area - especially
+   those who might be working there now.  Using git to see who else has
+   modified the files you are working on can be helpful.
+
+ - If you are responding to a bug report or a feature request, copy the
+   original poster as well.
+
+ - Send a copy to the relevant mailing list, or, if nothing else applies,
+   the linux-kernel list.
+
+ - If you are fixing a bug, think about whether the fix should go into the
+   next stable update.  If so, stable@kernel.org should get a copy of the
+   patch.  Also add a "Cc: stable@kernel.org" to the tags within the patch
+   itself; that will cause the stable team to get a notification when your
+   fix goes into the mainline.
+
+When selecting recipients for a patch, it is good to have an idea of who
+you think will eventually accept the patch and get it merged.  While it
+is possible to send patches directly to Linus Torvalds and have him merge
+them, things are not normally done that way.  Linus is busy, and there are
+subsystem maintainers who watch over specific parts of the kernel.  Usually
+you will be wanting that maintainer to merge your patches.  If there is no
+obvious maintainer, Andrew Morton is often the patch target of last resort.
+
+Patches need good subject lines.  The canonical format for a patch line is
+something like:
+
+	[PATCH nn/mm] subsys: one-line description of the patch
+
+where "nn" is the ordinal number of the patch, "mm" is the total number of
+patches in the series, and "subsys" is the name of the affected subsystem.
+Clearly, nn/mm can be omitted for a single, standalone patch.  
+
+If you have a significant series of patches, it is customary to send an
+introductory description as part zero.  This convention is not universally
+followed though; if you use it, remember that information in the
+introduction does not make it into the kernel changelogs.  So please ensure
+that the patches, themselves, have complete changelog information.
+
+In general, the second and following parts of a multi-part patch should be
+sent as a reply to the first part so that they all thread together at the
+receiving end.  Tools like git and quilt have commands to mail out a set of
+patches with the proper threading.  If you have a long series, though, and
+are using git, please provide the --no-chain-reply-to option to avoid
+creating exceptionally deep nesting.

Documentation/development-process/6.Followthrough

@@ -0,0 +1,202 @@
+6: FOLLOWTHROUGH
+
+At this point, you have followed the guidelines given so far and, with the
+addition of your own engineering skills, have posted a perfect series of
+patches.  One of the biggest mistakes that even experienced kernel
+developers can make is to conclude that their work is now done.  In truth,
+posting patches indicates a transition into the next stage of the process,
+with, possibly, quite a bit of work yet to be done.
+
+It is a rare patch which is so good at its first posting that there is no
+room for improvement.  The kernel development process recognizes this fact,
+and, as a result, is heavily oriented toward the improvement of posted
+code.  You, as the author of that code, will be expected to work with the
+kernel community to ensure that your code is up to the kernel's quality
+standards.  A failure to participate in this process is quite likely to
+prevent the inclusion of your patches into the mainline.
+
+
+6.1: WORKING WITH REVIEWERS
+
+A patch of any significance will result in a number of comments from other
+developers as they review the code.  Working with reviewers can be, for
+many developers, the most intimidating part of the kernel development
+process.  Life can be made much easier, though, if you keep a few things in
+mind:
+
+ - If you have explained your patch well, reviewers will understand its
+   value and why you went to the trouble of writing it.  But that value
+   will not keep them from asking a fundamental question: what will it be
+   like to maintain a kernel with this code in it five or ten years later?
+   Many of the changes you may be asked to make - from coding style tweaks
+   to substantial rewrites - come from the understanding that Linux will
+   still be around and under development a decade from now.
+
+ - Code review is hard work, and it is a relatively thankless occupation;
+   people remember who wrote kernel code, but there is little lasting fame
+   for those who reviewed it.  So reviewers can get grumpy, especially when
+   they see the same mistakes being made over and over again.  If you get a
+   review which seems angry, insulting, or outright offensive, resist the
+   impulse to respond in kind.  Code review is about the code, not about
+   the people, and code reviewers are not attacking you personally.
+
+ - Similarly, code reviewers are not trying to promote their employers'
+   agendas at the expense of your own.  Kernel developers often expect to
+   be working on the kernel years from now, but they understand that their
+   employer could change.  They truly are, almost without exception,
+   working toward the creation of the best kernel they can; they are not
+   trying to create discomfort for their employers' competitors.
+
+What all of this comes down to is that, when reviewers send you comments,
+you need to pay attention to the technical observations that they are
+making.  Do not let their form of expression or your own pride keep that
+from happening.  When you get review comments on a patch, take the time to
+understand what the reviewer is trying to say.  If possible, fix the things
+that the reviewer is asking you to fix.  And respond back to the reviewer:
+thank them, and describe how you will answer their questions.
+
+Note that you do not have to agree with every change suggested by
+reviewers.  If you believe that the reviewer has misunderstood your code,
+explain what is really going on.  If you have a technical objection to a
+suggested change, describe it and justify your solution to the problem.  If
+your explanations make sense, the reviewer will accept them.  Should your
+explanation not prove persuasive, though, especially if others start to
+agree with the reviewer, take some time to think things over again.  It can
+be easy to become blinded by your own solution to a problem to the point
+that you don't realize that something is fundamentally wrong or, perhaps,
+you're not even solving the right problem.
+
+One fatal mistake is to ignore review comments in the hope that they will
+go away.  They will not go away.  If you repost code without having
+responded to the comments you got the time before, you're likely to find
+that your patches go nowhere.
+
+Speaking of reposting code: please bear in mind that reviewers are not
+going to remember all the details of the code you posted the last time
+around.  So it is always a good idea to remind reviewers of previously
+raised issues and how you dealt with them; the patch changelog is a good
+place for this kind of information.  Reviewers should not have to search
+through list archives to familiarize themselves with what was said last
+time; if you help them get a running start, they will be in a better mood
+when they revisit your code.
+
+What if you've tried to do everything right and things still aren't going
+anywhere?  Most technical disagreements can be resolved through discussion,
+but there are times when somebody simply has to make a decision.  If you
+honestly believe that this decision is going against you wrongly, you can
+always try appealing to a higher power.  As of this writing, that higher
+power tends to be Andrew Morton.  Andrew has a great deal of respect in the
+kernel development community; he can often unjam a situation which seems to
+be hopelessly blocked.  Appealing to Andrew should not be done lightly,
+though, and not before all other alternatives have been explored.  And bear
+in mind, of course, that he may not agree with you either.
+
+
+6.2: WHAT HAPPENS NEXT
+
+If a patch is considered to be a good thing to add to the kernel, and once
+most of the review issues have been resolved, the next step is usually
+entry into a subsystem maintainer's tree.  How that works varies from one
+subsystem to the next; each maintainer has his or her own way of doing
+things.  In particular, there may be more than one tree - one, perhaps,
+dedicated to patches planned for the next merge window, and another for
+longer-term work.  
+
+For patches applying to areas for which there is no obvious subsystem tree
+(memory management patches, for example), the default tree often ends up
+being -mm.  Patches which affect multiple subsystems can also end up going
+through the -mm tree.
+
+Inclusion into a subsystem tree can bring a higher level of visibility to a
+patch.  Now other developers working with that tree will get the patch by
+default.  Subsystem trees typically feed into -mm and linux-next as well,
+making their contents visible to the development community as a whole.  At
+this point, there's a good chance that you will get more comments from a
+new set of reviewers; these comments need to be answered as in the previous
+round.
+
+What may also happen at this point, depending on the nature of your patch,
+is that conflicts with work being done by others turn up.  In the worst
+case, heavy patch conflicts can result in some work being put on the back
+burner so that the remaining patches can be worked into shape and merged.
+Other times, conflict resolution will involve working with the other
+developers and, possibly, moving some patches between trees to ensure that
+everything applies cleanly.  This work can be a pain, but count your
+blessings: before the advent of the linux-next tree, these conflicts often
+only turned up during the merge window and had to be addressed in a hurry.
+Now they can be resolved at leisure, before the merge window opens.
+
+Some day, if all goes well, you'll log on and see that your patch has been
+merged into the mainline kernel.  Congratulations!  Once the celebration is
+complete (and you have added yourself to the MAINTAINERS file), though, it
+is worth remembering an important little fact: the job still is not done.
+Merging into the mainline brings its own challenges.
+
+To begin with, the visibility of your patch has increased yet again.  There
+may be a new round of comments from developers who had not been aware of
+the patch before.  It may be tempting to ignore them, since there is no
+longer any question of your code being merged.  Resist that temptation,
+though; you still need to be responsive to developers who have questions or
+suggestions.
+
+More importantly, though: inclusion into the mainline puts your code into
+the hands of a much larger group of testers.  Even if you have contributed
+a driver for hardware which is not yet available, you will be surprised by
+how many people will build your code into their kernels.  And, of course,
+where there are testers, there will be bug reports.
+
+The worst sort of bug reports are regressions.  If your patch causes a
+regression, you'll find an uncomfortable number of eyes upon you;
+regressions need to be fixed as soon as possible.  If you are unwilling or
+unable to fix the regression (and nobody else does it for you), your patch
+will almost certainly be removed during the stabilization period.  Beyond
+negating all of the work you have done to get your patch into the mainline,
+having a patch pulled as the result of a failure to fix a regression could
+well make it harder for you to get work merged in the future.
+
+After any regressions have been dealt with, there may be other, ordinary
+bugs to deal with.  The stabilization period is your best opportunity to
+fix these bugs and ensure that your code's debut in a mainline kernel
+release is as solid as possible.  So, please, answer bug reports, and fix
+the problems if at all possible.  That's what the stabilization period is
+for; you can start creating cool new patches once any problems with the old
+ones have been taken care of.
+
+And don't forget that there are other milestones which may also create bug
+reports: the next mainline stable release, when prominent distributors pick
+up a version of the kernel containing your patch, etc.  Continuing to
+respond to these reports is a matter of basic pride in your work.  If that
+is insufficient motivation, though, it's also worth considering that the
+development community remembers developers who lose interest in their code
+after it's merged.  The next time you post a patch, they will be evaluating
+it with the assumption that you will not be around to maintain it
+afterward.
+
+
+6.3: OTHER THINGS THAT CAN HAPPEN
+
+One day, you may open your mail client and see that somebody has mailed you
+a patch to your code.  That is one of the advantages of having your code
+out there in the open, after all.  If you agree with the patch, you can
+either forward it on to the subsystem maintainer (be sure to include a
+proper From: line so that the attribution is correct, and add a signoff of
+your own), or send an Acked-by: response back and let the original poster
+send it upward.
+
+If you disagree with the patch, send a polite response explaining why.  If
+possible, tell the author what changes need to be made to make the patch
+acceptable to you.  There is a certain resistance to merging patches which
+are opposed by the author and maintainer of the code, but it only goes so
+far.  If you are seen as needlessly blocking good work, those patches will
+eventually flow around you and get into the mainline anyway.  In the Linux
+kernel, nobody has absolute veto power over any code.  Except maybe Linus.
+
+On very rare occasion, you may see something completely different: another
+developer posts a different solution to your problem.  At that point,
+chances are that one of the two patches will not be merged, and "mine was
+here first" is not considered to be a compelling technical argument.  If
+somebody else's patch displaces yours and gets into the mainline, there is
+really only one way to respond: be pleased that your problem got solved and
+get on with your work.  Having one's work shoved aside in this manner can
+be hurtful and discouraging, but the community will remember your reaction
+long after they have forgotten whose patch actually got merged.

Documentation/development-process/7.AdvancedTopics

@@ -0,0 +1,173 @@
+7: ADVANCED TOPICS
+
+At this point, hopefully, you have a handle on how the development process
+works.  There is still more to learn, however!  This section will cover a
+number of topics which can be helpful for developers wanting to become a
+regular part of the Linux kernel development process.
+
+7.1: MANAGING PATCHES WITH GIT
+
+The use of distributed version control for the kernel began in early 2002,
+when Linus first started playing with the proprietary BitKeeper
+application.  While BitKeeper was controversial, the approach to software
+version management it embodied most certainly was not.  Distributed version
+control enabled an immediate acceleration of the kernel development
+project.  In current times, there are several free alternatives to
+BitKeeper.  For better or for worse, the kernel project has settled on git
+as its tool of choice.
+
+Managing patches with git can make life much easier for the developer,
+especially as the volume of those patches grows.  Git also has its rough
+edges and poses certain hazards; it is a young and powerful tool which is
+still being civilized by its developers.  This document will not attempt to
+teach the reader how to use git; that would be sufficient material for a
+long document in its own right.  Instead, the focus here will be on how git
+fits into the kernel development process in particular.  Developers who
+wish to come up to speed with git will find more information at:
+
+	http://git.or.cz/
+
+	http://www.kernel.org/pub/software/scm/git/docs/user-manual.html
+
+and on various tutorials found on the web.
+
+The first order of business is to read the above sites and get a solid
+understanding of how git works before trying to use it to make patches
+available to others.  A git-using developer should be able to obtain a copy
+of the mainline repository, explore the revision history, commit changes to
+the tree, use branches, etc.  An understanding of git's tools for the
+rewriting of history (such as rebase) is also useful.  Git comes with its
+own terminology and concepts; a new user of git should know about refs,
+remote branches, the index, fast-forward merges, pushes and pulls, detached
+heads, etc.  It can all be a little intimidating at the outset, but the
+concepts are not that hard to grasp with a bit of study.
+
+Using git to generate patches for submission by email can be a good
+exercise while coming up to speed.
+
+When you are ready to start putting up git trees for others to look at, you
+will, of course, need a server that can be pulled from.  Setting up such a
+server with git-daemon is relatively straightforward if you have a system
+which is accessible to the Internet.  Otherwise, free, public hosting sites
+(Github, for example) are starting to appear on the net.  Established
+developers can get an account on kernel.org, but those are not easy to come
+by; see http://kernel.org/faq/ for more information.
+
+The normal git workflow involves the use of a lot of branches.  Each line
+of development can be separated into a separate "topic branch" and
+maintained independently.  Branches in git are cheap, there is no reason to
+not make free use of them.  And, in any case, you should not do your
+development in any branch which you intend to ask others to pull from.
+Publicly-available branches should be created with care; merge in patches
+from development branches when they are in complete form and ready to go -
+not before.
+
+Git provides some powerful tools which can allow you to rewrite your
+development history.  An inconvenient patch (one which breaks bisection,
+say, or which has some other sort of obvious bug) can be fixed in place or
+made to disappear from the history entirely.  A patch series can be
+rewritten as if it had been written on top of today's mainline, even though
+you have been working on it for months.  Changes can be transparently
+shifted from one branch to another.  And so on.  Judicious use of git's
+ability to revise history can help in the creation of clean patch sets with
+fewer problems.
+
+Excessive use of this capability can lead to other problems, though, beyond
+a simple obsession for the creation of the perfect project history.
+Rewriting history will rewrite the changes contained in that history,
+turning a tested (hopefully) kernel tree into an untested one.  But, beyond
+that, developers cannot easily collaborate if they do not have a shared
+view of the project history; if you rewrite history which other developers
+have pulled into their repositories, you will make life much more difficult
+for those developers.  So a simple rule of thumb applies here: history
+which has been exported to others should generally be seen as immutable
+thereafter.
+
+So, once you push a set of changes to your publicly-available server, those
+changes should not be rewritten.  Git will attempt to enforce this rule if
+you try to push changes which do not result in a fast-forward merge
+(i.e. changes which do not share the same history).  It is possible to
+override this check, and there may be times when it is necessary to rewrite
+an exported tree.  Moving changesets between trees to avoid conflicts in
+linux-next is one example.  But such actions should be rare.  This is one
+of the reasons why development should be done in private branches (which
+can be rewritten if necessary) and only moved into public branches when
+it's in a reasonably advanced state.
+
+As the mainline (or other tree upon which a set of changes is based)
+advances, it is tempting to merge with that tree to stay on the leading
+edge.  For a private branch, rebasing can be an easy way to keep up with
+another tree, but rebasing is not an option once a tree is exported to the
+world.  Once that happens, a full merge must be done.  Merging occasionally
+makes good sense, but overly frequent merges can clutter the history
+needlessly.  Suggested technique in this case is to merge infrequently, and
+generally only at specific release points (such as a mainline -rc
+release).  If you are nervous about specific changes, you can always
+perform test merges in a private branch.  The git "rerere" tool can be
+useful in such situations; it remembers how merge conflicts were resolved
+so that you don't have to do the same work twice.
+
+One of the biggest recurring complaints about tools like git is this: the
+mass movement of patches from one repository to another makes it easy to
+slip in ill-advised changes which go into the mainline below the review
+radar.  Kernel developers tend to get unhappy when they see that kind of
+thing happening; putting up a git tree with unreviewed or off-topic patches
+can affect your ability to get trees pulled in the future.  Quoting Linus:
+
+	You can send me patches, but for me to pull a git patch from you, I
+	need to know that you know what you're doing, and I need to be able
+	to trust things *without* then having to go and check every
+	individual change by hand.
+
+(http://lwn.net/Articles/224135/).  
+
+To avoid this kind of situation, ensure that all patches within a given
+branch stick closely to the associated topic; a "driver fixes" branch
+should not be making changes to the core memory management code.  And, most
+importantly, do not use a git tree to bypass the review process.  Post an
+occasional summary of the tree to the relevant list, and, when the time is
+right, request that the tree be included in linux-next.
+
+If and when others start to send patches for inclusion into your tree,
+don't forget to review them.  Also ensure that you maintain the correct
+authorship information; the git "am" tool does its best in this regard, but
+you may have to add a "From:" line to the patch if it has been relayed to
+you via a third party.
+
+When requesting a pull, be sure to give all the relevant information: where
+your tree is, what branch to pull, and what changes will result from the
+pull.  The git request-pull command can be helpful in this regard; it will
+format the request as other developers expect, and will also check to be
+sure that you have remembered to push those changes to the public server. 
+
+
+7.2: REVIEWING PATCHES
+
+Some readers will certainly object to putting this section with "advanced
+topics" on the grounds that even beginning kernel developers should be
+reviewing patches.  It is certainly true that there is no better way to
+learn how to program in the kernel environment than by looking at code
+posted by others.  In addition, reviewers are forever in short supply; by
+looking at code you can make a significant contribution to the process as a
+whole.
+
+Reviewing code can be an intimidating prospect, especially for a new kernel
+developer who may well feel nervous about questioning code - in public -
+which has been posted by those with more experience.  Even code written by
+the most experienced developers can be improved, though.  Perhaps the best
+piece of advice for reviewers (all reviewers) is this: phrase review
+comments as questions rather than criticisms.  Asking "how does the lock
+get released in this path?" will always work better than stating "the
+locking here is wrong."
+
+Different developers will review code from different points of view.  Some
+are mostly concerned with coding style and whether code lines have trailing
+white space.  Others will focus primarily on whether the change implemented
+by the patch as a whole is a good thing for the kernel or not.  Yet others
+will check for problematic locking, excessive stack usage, possible
+security issues, duplication of code found elsewhere, adequate
+documentation, adverse effects on performance, user-space ABI changes, etc.
+All types of review, if they lead to better code going into the kernel, are
+welcome and worthwhile.
+
+

Documentation/development-process/8.Conclusion

@@ -0,0 +1,74 @@
+8: FOR MORE INFORMATION
+
+There are numerous sources of information on Linux kernel development and
+related topics.  First among those will always be the Documentation
+directory found in the kernel source distribution.  The top-level HOWTO
+file is an important starting point; SubmittingPatches and
+SubmittingDrivers are also something which all kernel developers should
+read.  Many internal kernel APIs are documented using the kerneldoc
+mechanism; "make htmldocs" or "make pdfdocs" can be used to generate those
+documents in HTML or PDF format (though the version of TeX shipped by some
+distributions runs into internal limits and fails to process the documents
+properly).
+
+Various web sites discuss kernel development at all levels of detail.  Your
+author would like to humbly suggest http://lwn.net/ as a source;
+information on many specific kernel topics can be found via the LWN kernel
+index at:
+
+	http://lwn.net/Kernel/Index/
+
+Beyond that, a valuable resource for kernel developers is:
+
+	http://kernelnewbies.org/
+
+Information about the linux-next tree gathers at:
+
+	http://linux.f-seidel.de/linux-next/pmwiki/
+
+And, of course, one should not forget http://kernel.org/, the definitive
+location for kernel release information.
+
+There are a number of books on kernel development:
+
+	Linux Device Drivers, 3rd Edition (Jonathan Corbet, Alessandro
+	Rubini, and Greg Kroah-Hartman).  Online at
+	http://lwn.net/Kernel/LDD3/.
+
+	Linux Kernel Development (Robert Love).
+
+	Understanding the Linux Kernel (Daniel Bovet and Marco Cesati).
+
+All of these books suffer from a common fault, though: they tend to be
+somewhat obsolete by the time they hit the shelves, and they have been on
+the shelves for a while now.  Still, there is quite a bit of good
+information to be found there.
+
+Documentation for git can be found at:
+
+	http://www.kernel.org/pub/software/scm/git/docs/
+
+	http://www.kernel.org/pub/software/scm/git/docs/user-manual.html
+
+
+9: CONCLUSION
+
+Congratulations to anybody who has made it through this long-winded
+document.  Hopefully it has provided a helpful understanding of how the
+Linux kernel is developed and how you can participate in that process.
+
+In the end, it's the participation that matters.  Any open source software
+project is no more than the sum of what its contributors put into it.  The
+Linux kernel has progressed as quickly and as well as it has because it has
+been helped by an impressively large group of developers, all of whom are
+working to make it better.  The kernel is a premier example of what can be
+done when thousands of people work together toward a common goal.
+
+The kernel can always benefit from a larger developer base, though.  There
+is always more work to do.  But, just as importantly, most other
+participants in the Linux ecosystem can benefit through contributing to the
+kernel.  Getting code into the mainline is the key to higher code quality,
+lower maintenance and distribution costs, a higher level of influence over
+the direction of kernel development, and more.  It is a situation where
+everybody involved wins.  Fire up your editor and come join us; you will be
+more than welcome.