HACKING: Updates that have some initial consensus, for further iteration.

HACKING

@@ -8,10 +8,9 @@ Contents:
 * COMMIT MESSAGE
 * HACKING THE BUILD SYSTEM
 * RELEASE PROCEDURE
-* SHARED LIBRARY VERSIONING
-* RELEASE PROCEDURE
 * TOOL VERSIONS
 * SHARED LIBRARY VERSIONING
+* GIT COMMIT SUBSMISSION
 * PATCH SUBMISSION
 * PATCH APPLICATION
 * STABLE PLATFORMS AND DAEMONS
@@ -29,7 +28,7 @@ assumes that tabs are every 8 columns.  Do not attempt to redefine the
 location of tab stops.  Note also that some indentation does not
 follow GNU style.  This is a historical accident, and we generally
 only clean up whitespace when code is unmaintainable due to whitespace
-issues, as fewer changes from zebra lead to easier merges.
+issues, to minimise merging conflicts.
 
 For GNU emacs, use indentation style "gnu".
 
@@ -44,9 +43,10 @@ set noexpandtab
 Be particularly careful not to break platforms/protocols that you
 cannot test.
 
-New code should have good comments, and changes to existing code
-should in many cases upgrade the comments when necessary for a
-reviewer to conclude that the change has no unintended consequences.
+New code should have good comments, which explain why the code is correct.
+Changes to existing code should in many cases upgrade the comments when
+necessary for a reviewer to conclude that the change has no unintended
+consequences.
 
 Each file in the Git repository should have a git format-placeholder (like
 an RCS Id keyword), somewhere very near the top, commented out appropriately
@@ -109,7 +109,8 @@ typically code should be good enough to be in Quagga, or it shouldn't be
 there at all.
 
 When code must be compile-time conditional, try have the compiler make it
-conditional rather than the C pre-processor. I.e. this:
+conditional rather than the C pre-processor - so that it will still be
+checked by the compiler, even if disabled. I.e.  this:
 
     if (SOME_SYMBOL)
       frobnicate();
@@ -126,7 +127,7 @@ defined (watch your AC_DEFINEs).
 
 COMMIT MESSAGES
 
-The commit message should provide:
+The commit message MUST provide:
 
 * A suitable one-line summary followed by a blank line as the very
   first line of the message, in the form:
@@ -137,36 +138,54 @@ The commit message should provide:
   there's a more suitable topic (e.g. 'build').  This topic is used to
   organise change summaries in release announcements.
 
-* An optional introduction, discussing the general intent of the change.
-* A short description of each change made, preferably:
-  * file by file
-    * function by function (use of "ditto", or globs is allowed)
+The remainder of the commit message - its "body" - should ideally try to
+address the following areas, so as to help reviewers and future browsers of
+the code-base understand why the change is correct (note also the code
+comment requirements):
 
-to provide a short description of the general intent of the patch, in terms
-of the problem it solves and how it achieves it, to help reviewers
-understand.
+* The motivation for the change (does it fix a bug, if so which? 
+  add a feature?)
+* The general approach taken, and trade-offs versus any other approaches.
+* Any testing undertaken or other information affecting the confidence
+  that can be had in the change.
+* Information to allow reviewers to be able to tell which specific changes
+  to the code are intended (and hence be able to spot any accidental
+  unintended changes).
 
 The one-line summary must be limited to 54 characters, and all other
 lines to 72 characters.
 
-The reason for such itemised commit messages is to encourage the author to
-self-review every line of the patch, as well as provide reviewers an index
-of which changes are intended, along with a short description for each.
-Some discretion is obviously required.  A C-to-english description is not
-desireable.  For short patches, a per-function/file break-down may be
-redundant.  For longer patches, such a break-down may be essential.
+Commit message bodies in the Quagga project have typically taken the
+following form:
 
-An example (where the general discussion is obviously somewhat redundant,
-given the one-line summary):
+* An optional introduction, describing the change generally.
+* A short description of each specific change made, preferably:
+  * file by file
+    * function by function (use of "ditto", or globs is allowed)
+
+Contributors are strongly encouraged to follow this form.
+
+This itemised commit messages allows reviewers to have confidence that the
+author has self-reviewed every line of the patch, as well as providing
+reviewers a clear index of which changes are intended, and descriptions for
+them (C-to-english descriptions are not desireable - some discretion is
+useful).  For short patches, a per-function/file break-down may be
+redundant.  For longer patches, such a break-down may be essential.  A
+contrived example (where the general discussion is obviously somewhat
+redundant, given the one-line summary):
 
 zebra: Enhance frob FSM to detect loss of frob
 
-* (general) Add a new DOWN state to the frob state machine
-   to allow the barinator to detect loss of frob.
+Add a new DOWN state to the frob state machine to allow the barinator to
+detect loss of frob.
+
 * frob.h: (struct frob) Add DOWN state flag.
 * frob.c: (frob_change) set/clear DOWN appropriately on state change.
 * bar.c: (barinate) Check frob for DOWN state.
 
+Please have a look at the git commit logs to get a feel for what the norms
+are.
+
 Note that the commit message format follows git norms, so that "git
 log --oneline" will have useful output.
 
@@ -249,14 +268,30 @@ installed together.
 
 GIT COMMIT SUBSMISSION
 
-The preferred method for changes is to provide git commits via a
-publically-accessible git repository.
+The preferred method for submitting changes is to provide git commits via a
+publically-accessible git repository, which the maintainers can easily pull.
+
+The commits should be in a branch based off the Quagga.net master - a
+"feature branch".  Ideally there should be no commits to this branch other
+than those in master, and those intended to be submitted.  However, merge
+commits to this branch from the Quagga master are permitted, though strongly
+discouraged - use another (potentially local and throw-away) branch to test
+merge with the latest Quagga master.
+
+Recommended practice is to keep different logical sets of changes on
+separate branches - "topic" or "feature" branches.  This allows you to still
+merge them together to one branch (potentially local and/or "throw-away")
+for testing or use, while retaining smaller, independent branches that are
+easier to merge.
 
 All content guidelines in PATCH SUBMISSION apply.
 
 
 PATCH SUBMISSION
 
+* For complex changes, contributors are strongly encouraged to first start a
+  design discussion on the quagga-dev list before starting any coding.
+
 * Send a clean diff against the 'master' branch of the quagga.git
   repository, in unified diff format, preferably with the '-p' argument to
   show C function affected by any chunk, and with the -w and -b arguments to
@@ -265,7 +300,7 @@ PATCH SUBMISSION
     git diff -up mybranch..remotes/quagga.net/master
 
   It is preferable to use git format-patch, and even more preferred to
-  publish a git repostory.
+  publish a git repostory (see GIT COMMIT SUBSMISSION).
 
   If not using git format-patch, Include the commit message in the email.
 
@@ -280,6 +315,20 @@ PATCH SUBMISSION
 * Do not make gratuitous changes to whitespace. See the w and b arguments
   to diff.
 
+* Changes should be arranged so that the least contraversial and most
+  trivial are first, and the most complex or more contraversial are last. 
+  This will maximise how many the Quagga maintainers can merge, even if some
+  other commits need further work.
+
+* Providing a unit-test is strongly encouraged. Doing so will make it
+  much easier for maintainers to have confidence that they will be able
+  to support your change.
+
+* New code should be arranged so that it easy to verify and test. E.g. 
+  stateful logic should be separated out from functional logic as much as
+  possible: wherever possible, move complex logic out to smaller helper
+  functions which access no state other than their arguments.
+
 * State on which platforms and with what daemons the patch has been
   tested.  Understand that if the set of testing locations is small,
   and the patch might have unforeseen or hard to fix consequences that
@@ -305,9 +354,9 @@ PATCH APPLICATION
 * Immediately after commiting, double-check (with git-log and/or gitk). If
   there's a small mistake you can easily fix it with 'git commit --amend ..'
 
-* By committing a patch, you are responsible for fixing problems
-  resulting from it (or backing it out).
-
+* When merging a branch, always use an explicit merge commit. Giving --no-ff
+  ensures a merge commit is created which documents "this human decided to
+  merge this branch at this time".
 
 STABLE PLATFORMS AND DAEMONS