From: Junio C Hamano <gitster@pobox.com> Date: Wed, 21 Nov 2007 16:32:55 -0800 Subject: Addendum to "MaintNotes" Abstract: Imagine that git development is racing along as usual, when our friendly neighborhood maintainer is struck down by a wayward bus. Out of the hordes of suckers (loyal developers), you have been tricked (chosen) to step up as the new maintainer. This howto will show you "how to" do it. The maintainer's git time is spent on three activities. - Communication (60%) Mailing list discussions on general design, fielding user questions, diagnosing bug reports; reviewing, commenting on, suggesting alternatives to, and rejecting patches. - Integration (30%) Applying new patches from the contributors while spotting and correcting minor mistakes, shuffling the integration and testing branches, pushing the results out, cutting the releases, and making announcements. - Own development (10%) Scratching my own itch and sending proposed patch series out. The policy on Integration is informally mentioned in "A Note from the maintainer" message, which is periodically posted to this mailing list after each feature release is made. The policy. - Feature releases are numbered as vX.Y.Z and are meant to contain bugfixes and enhancements in any area, including functionality, performance and usability, without regression. - Maintenance releases are numbered as vX.Y.Z.W and are meant to contain only bugfixes for the corresponding vX.Y.Z feature release and earlier maintenance releases vX.Y.Z.V (V < W). - 'master' branch is used to prepare for the next feature release. In other words, at some point, the tip of 'master' branch is tagged with vX.Y.Z. - 'maint' branch is used to prepare for the next maintenance release. After the feature release vX.Y.Z is made, the tip of 'maint' branch is set to that release, and bugfixes will accumulate on the branch, and at some point, the tip of the branch is tagged with vX.Y.Z.1, vX.Y.Z.2, and so on. - 'next' branch is used to publish changes (both enhancements and fixes) that (1) have worthwhile goal, (2) are in a fairly good shape suitable for everyday use, (3) but have not yet demonstrated to be regression free. New changes are tested in 'next' before merged to 'master'. - 'pu' branch is used to publish other proposed changes that do not yet pass the criteria set for 'next'. - The tips of 'master', 'maint' and 'next' branches will always fast forward, to allow people to build their own customization on top of them. - Usually 'master' contains all of 'maint', 'next' contains all of 'master' and 'pu' contains all of 'next'. - The tip of 'master' is meant to be more stable than any tagged releases, and the users are encouraged to follow it. - The 'next' branch is where new action takes place, and the users are encouraged to test it so that regressions and bugs are found before new topics are merged to 'master'. A typical git day for the maintainer implements the above policy by doing the following: - Scan mailing list and #git channel log. Respond with review comments, suggestions etc. Kibitz. Collect potentially usable patches from the mailing list. Patches about a single topic go to one mailbox (I read my mail in Gnus, and type \C-o to save/append messages in files in mbox format). - Review the patches in the saved mailboxes. Edit proposed log message for typofixes and clarifications, and add Acks collected from the list. Edit patch to incorporate "Oops, that should have been like this" fixes from the discussion. - Classify the collected patches and handle 'master' and 'maint' updates: - Obviously correct fixes that pertain to the tip of 'maint' are directly applied to 'maint'. - Obviously correct fixes that pertain to the tip of 'master' are directly applied to 'master'. This step is done with "git am". $ git checkout master ;# or "git checkout maint" $ git am -3 -s mailbox $ make test - Merge downwards (maint->master): $ git checkout master $ git merge maint $ make test - Review the last issue of "What's cooking" message, review the topics scheduled for merging upwards (topic->master and topic->maint), and merge. $ git checkout master ;# or "git checkout maint" $ git merge ai/topic ;# or "git merge ai/maint-topic" $ git log -p ORIG_HEAD.. ;# final review $ git diff ORIG_HEAD.. ;# final review $ make test ;# final review $ git branch -d ai/topic ;# or "git branch -d ai/maint-topic" - Merge downwards (maint->master) if needed: $ git checkout master $ git merge maint $ make test - Merge downwards (master->next) if needed: $ git checkout next $ git merge master $ make test - Handle the remaining patches: - Anything unobvious that is applicable to 'master' (in other words, does not depend on anything that is still in 'next' and not in 'master') is applied to a new topic branch that is forked from the tip of 'master'. This includes both enhancements and unobvious fixes to 'master'. A topic branch is named as ai/topic where "ai" is typically author's initial and "topic" is a descriptive name of the topic (in other words, "what's the series is about"). - An unobvious fix meant for 'maint' is applied to a new topic branch that is forked from the tip of 'maint'. The topic is named as ai/maint-topic. - Changes that pertain to an existing topic are applied to the branch, but: - obviously correct ones are applied first; - questionable ones are discarded or applied to near the tip; - Replacement patches to an existing topic are accepted only for commits not in 'next'. The above except the "replacement" are all done with: $ git am -3 -s mailbox while patch replacement is often done by: $ git format-patch ai/topic~$n..ai/topic ;# export existing then replace some parts with the new patch, and reapplying: $ git reset --hard ai/topic~$n $ git am -3 -s 000*.txt The full test suite is always run for 'maint' and 'master' after patch application; for topic branches the tests are run as time permits. - Update "What's cooking" message to review the updates to existing topics, newly added topics and graduated topics. This step is helped with Meta/UWC script (where Meta/ contains a checkout of the 'todo' branch). - Merge topics to 'next'. For each branch whose tip is not merged to 'next', one of three things can happen: - The commits are all next-worthy; merge the topic to next: $ git checkout next $ git merge ai/topic ;# or "git merge ai/maint-topic" $ make test - The new parts are of mixed quality, but earlier ones are next-worthy; merge the early parts to next: $ git checkout next $ git merge ai/topic~2 ;# the tip two are dubious $ make test - Nothing is next-worthy; do not do anything. - Rebase topics that do not have any commit in next yet. This step is optional but sometimes is worth doing when an old series that is not in next can take advantage of low-level framework change that is merged to 'master' already. $ git rebase master ai/topic This step is helped with Meta/git-topic.perl script to identify which topic is rebaseable. There also is a pre-rebase hook to make sure that topics that are already in 'next' are not rebased beyond the merged commit. - Rebuild "pu" to merge the tips of topics not in 'next'. $ git checkout pu $ git reset --hard next $ git merge ai/topic ;# repeat for all remaining topics $ make test This step is helped with Meta/PU script - Push four integration branches to a private repository at k.org and run "make test" on all of them. - Push four integration branches to /pub/scm/git/git.git at k.org. This triggers its post-update hook which: (1) runs "git pull" in $HOME/git-doc/ repository to pull 'master' just pushed out; (2) runs "make doc" in $HOME/git-doc/, install the generated documentation in staging areas, which are separate repositories that have html and man branches checked out. (3) runs "git commit" in the staging areas, and run "git push" back to /pub/scm/git/git.git/ to update the html and man branches. (4) installs generated documentation to /pub/software/scm/git/docs/ to be viewed from http://www.kernel.org/ - Fetch html and man branches back from k.org, and push four integration branches and the two documentation branches to repo.or.cz Some observations to be made. * Each topic is tested individually, and also together with other topics cooking in 'next'. Until it matures, none part of it is merged to 'master'. * A topic already in 'next' can get fixes while still in 'next'. Such a topic will have many merges to 'next' (in other words, "git log --first-parent next" will show many "Merge ai/topic to next" for the same topic. * An unobvious fix for 'maint' is cooked in 'next' and then merged to 'master' to make extra sure it is Ok and then merged to 'maint'. * Even when 'next' becomes empty (in other words, all topics prove stable and are merged to 'master' and "git diff master next" shows empty), it has tons of merge commits that will never be in 'master'. * In principle, "git log --first-parent master..next" should show nothing but merges (in practice, there are fixup commits and reverts that are not merges). * Commits near the tip of a topic branch that are not in 'next' are fair game to be discarded, replaced or rewritten. Commits already merged to 'next' will not be. * Being in the 'next' branch is not a guarantee for a topic to be included in the next feature release. Being in the 'master' branch typically is.