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 concern (among others) kept AppArmor out of the
     mainline for years.

  
  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.

  The task of finding the right maintainer is sometimes challenging enough
  that the kernel developers have added a script to ease the process:
  
  	.../scripts/get_maintainer.pl
  
  This script will return the current maintainer(s) for a given file or
  directory when given the "-f" option.  If passed a patch on the
  command line, it will list the maintainers who should probably receive
  copies of the patch.  There are a number of options regulating how hard
  get_maintainer.pl will search for maintainers; please be careful about
  using the more aggressive options as you may end up including developers
  who have no real interest in the code you are modifying.

  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.  Beyond that, high-level designs often hide problems
  which are only reviewed when somebody actually tries to implement those
  designs; for that reason, kernel developers would rather see the code.
  
  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.