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Documentation: update "howto maintain git"

Browse source 
The flow described in the document is still correct, but over time I
have automated various parts of the workflow with tools and their
use was not explained at all.

Update it and outline the use of two key scripts from the 'todo'
branch, "Reintegrate" and "cook".

Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Junio C Hamano 2012-11-27 15:41:07 -08:00
parent 86ef7b37f9
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356
Documentation/howto/maintain-git.txt
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@ -8,20 +8,20 @@ Abstract: Imagine that git development is racing along as usual, when our friend
The maintainer's git time is spent on three activities.
- Communication (60%)
- Communication (45%)
Mailing list discussions on general design, fielding user
questions, diagnosing bug reports; reviewing, commenting on,
suggesting alternatives to, and rejecting patches.
- Integration (30%)
- Integration (50%)
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%)
- Own development (5%)
Scratching my own itch and sending proposed patch series out.
@ -35,6 +35,9 @@ The policy.
contain bugfixes and enhancements in any area, including
functionality, performance and usability, without regression.
- One release cycle for a feature release is expected to last for
eight to ten weeks.
- 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).
@ -58,12 +61,15 @@ The policy.
- '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.
- The tips of 'master' and 'maint' branches will not be rewound to
allow people to build their own customization on top of them.
Early in a new development cycle, 'next' is rewound to the tip of
'master' once, but otherwise it will not be rewound until the end
of the cycle.
- Usually 'master' contains all of 'maint', 'next' contains all
of 'master' and 'pu' contains all of 'next'.
- Usually 'master' contains all of 'maint' and 'next' contains all
of 'master'. 'pu' contains all the topics merged to 'next', but
is rebuilt directly on 'master'.
- The tip of 'master' is meant to be more stable than any
tagged releases, and the users are encouraged to follow it.
@ -76,11 +82,16 @@ The policy.
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).
- Scan mailing list. 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).
- Write his own patches to address issues raised on the list but
nobody has stepped up solving. Send it out just like other
contributors do, and pick them up just like patches from other
contributors (see above).
- Review the patches in the saved mailboxes. Edit proposed log
message for typofixes and clarifications, and add Acks
@ -96,40 +107,32 @@ by doing the following:
- Obviously correct fixes that pertain to the tip of 'master'
are directly applied to 'master'.
- Other topics are not handled in this step.
This step is done with "git am".
$ git checkout master ;# or "git checkout maint"
$ git am -3 -s mailbox
$ git am -sc3 mailbox
$ make test
- Merge downwards (maint->master):
$ git checkout master
$ git merge maint
$ make test
In practice, almost no patch directly goes to 'master' or
'maint'.
- Review the last issue of "What's cooking" message, review the
topics scheduled for merging upwards (topic->master and
topic->maint), and merge.
topics ready for merging (topic->master and topic->maint). Use
"Meta/cook -w" script (where Meta/ contains a checkout of the
'todo' branch) to aid this step.
And perform the merge. Use "Meta/Reintegrate -e" script (see
later) to aid this step.
$ Meta/cook -w last-issue-of-whats-cooking.mbox
$ git checkout master ;# or "git checkout maint"
$ git merge ai/topic ;# or "git merge ai/maint-topic"
$ echo ai/topic | Meta/Reintegrate -e ;# "git merge ai/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:
@ -138,9 +141,9 @@ by doing the following:
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").
branch is named as ai/topic where "ai" is two-letter string
named after 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
@ -158,7 +161,8 @@ by doing the following:
The above except the "replacement" are all done with:
$ git am -3 -s mailbox
$ git checkout ai/topic ;# or "git checkout -b ai/topic master"
$ git am -sc3 mailbox
while patch replacement is often done by:
@ -166,93 +170,166 @@ by doing the following:
then replace some parts with the new patch, and reapplying:
$ git checkout ai/topic
$ git reset --hard ai/topic~$n
$ git am -3 -s 000*.txt
$ git am -sc3 -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.
- Merge maint to master as needed:
$ git checkout master
$ git merge maint
$ make test
- Merge master to next as needed:
$ git checkout next
$ git merge master
$ make test
- Review the last issue of "What's cooking" again and see if topics
that are ready to be merged to 'next' are still in good shape
(e.g. has there any new issue identified on the list with the
series?)
- Prepare 'jch' branch, which is used to represent somewhere
between 'master' and 'pu' and often is slightly ahead of 'next'.
$ Meta/Reintegrate master..pu >Meta/redo-jch.sh
The result is a script that lists topics to be merged in order to
rebuild 'pu' as the input to Meta/Reintegrate script. Remove
later topics that should not be in 'jch' yet. Add a line that
consists of '###' before the name of the first topic in the output
that should be in 'jch' but not in 'next' yet.
- Now we are ready to start merging 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;
- The new parts are of mixed quality, but earlier ones are
next-worthy; merge the early parts to next;
- Nothing is next-worthy; do not do anything.
This step is aided with Meta/redo-jch.sh script created earlier.
If a topic that was already in 'next' gained a patch, the script
would list it as "ai/topic~1". To include the new patch to the
updated 'next', drop the "~1" part; to keep it excluded, do not
touch the line. If a topic that was not in 'next' should be
merged to 'next', add it at the end of the list. Then:
$ git checkout -B jch master
$ Meta/redo-jch.sh -c1
to rebuild the 'jch' branch from scratch. "-c1" tells the script
to stop merging at the '###' line you added earlier.
At this point, build-test the result. It may reveal semantic
conflicts (e.g. a topic renamed a variable, another added a new
reference to the variable under its old name), in which case
prepare an appropriate merge-fix first (see appendix), and
rebuild the 'jch' branch from scratch, starting at the tip of
'master'.
Then do the same to 'next'
$ git checkout next
$ sh Meta/redo-jch.sh -c1 -e
The "-e" option allows the merge message that comes from the
history of the topic and the comments in the "What's cooking" to
be edited. The resulting tree should match 'jch' as the same set
of topics are merged on 'master'; otherwise there is a mismerge.
Investigate why and do not proceed until the mismerge is found
and rectified.
$ git diff jch next
When all is well, clean up the redo-jch.sh script with
$ sh Meta/redo-jch.sh -u
This removes topics listed in the script that have already been
merged to 'master'. This unfortunately loses the "###" marker,
so add it again to the appropriate place.
- Rebuild 'pu'.
$ Meta/Reintegrate master..pu >Meta/redo-pu.sh
Edit the result by adding new topics that are not still in 'pu'
in the script. Then
$ git checkout -B pu jch
$ sh Meta/redo-pu.sh
When all is well, clean up the redo-pu.sh script with
$ sh Meta/redo-pu.sh -u
Double check by running
$ git branch --no-merged pu
to see there is no unexpected leftover topics.
At this point, build-test the result for semantic conflicts, and
if there are, prepare an appropriate merge-fix first (see
appendix), and rebuild the 'pu' branch from scratch, starting at
the tip of 'jch'.
- Update "What's cooking" message to review the updates to
existing topics, newly added topics and graduated topics.
This step is helped with Meta/cook script (where Meta/ contains
a checkout of the 'todo' branch).
This step is helped with Meta/cook script.
- Merge topics to 'next'. For each branch whose tip is not
merged to 'next', one of three things can happen:
$ Meta/cook
- The commits are all next-worthy; merge the topic to next:
This script inspects the history between master..pu, finds tips
of topic branches, compares what it found with the current
contents in Meta/whats-cooking.txt, and updates that file.
Topics not listed in the file but are found in master..pu are
added to the "New topics" section, topics listed in the file that
are no longer found in master..pu are moved to the "Graduated to
master" section, and topics whose commits changed their states
(e.g. used to be only in 'pu', now merged to 'next') are updated
with change markers "<<" and ">>".
$ git checkout next
$ git merge ai/topic ;# or "git merge ai/maint-topic"
$ make test
Look for lines enclosed in "<<" and ">>"; they hold contents from
old file that are replaced by this integration round. After
verifying them, remove the old part. Review the description for
each topic and update its doneness and plan as needed. To review
the updated plan, run
- The new parts are of mixed quality, but earlier ones are
next-worthy; merge the early parts to next:
$ Meta/cook -w
$ git checkout next
$ git merge ai/topic~2 ;# the tip two are dubious
$ make test
which will pick up comments given to the topics, such as "Will
merge to 'next'", etc. (see Meta/cook script to learn what kind
of phrases are supported).
- Nothing is next-worthy; do not do anything.
- Compile, test and install all four (five) integration branches;
Meta/Dothem script may aid this step.
- [** OBSOLETE **] Optionally rebase topics that do not have any commit
in next yet, when they 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.
- [** OBSOLETE **] 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 and other mirrors.
- Format documentation if the 'master' branch was updated;
Meta/dodoc.sh script may aid this step.
- Push the integration branches out to public places; Meta/pushall
script may aid this step.
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'.
* Each topic is tested individually, and also together with other
topics cooking first in 'pu', then in 'jch' and then in 'next'.
Until it matures, no 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.
"Merge branch '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
@ -274,3 +351,78 @@ Some observations to be made.
* 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.
[Appendix]
Preparing a "merge-fix"
A merge of two topics may not textually conflict but still have
conflict at the semantic level. A classic example is for one topic
to rename an variable and all its uses, while another topic adds a
new use of the variable under its old name. When these two topics
are merged together, the reference to the variable newly added by
the latter topic will still use the old name in the result.
The Meta/Reintegrate script that is used by redo-jch and redo-pu
scripts implements a crude but usable way to work this issue around.
When the script merges branch $X, it checks if "refs/merge-fix/$X"
exists, and if so, the effect of it is squashed into the result of
the mechanical merge. In other words,
$ echo $X | Meta/Reintegrate
is roughly equivalent to this sequence:
$ git merge --rerere-autoupdate $X
$ git commit
$ git cherry-pick -n refs/merge-fix/$X
$ git commit --amend
The goal of this "prepare a merge-fix" step is to come up with a
commit that can be squashed into a result of mechanical merge to
correct semantic conflicts.
After finding that the result of merging branch "ai/topic" to an
integration branch had such a semantic conflict, say pu~4, check the
problematic merge out on a detached HEAD, edit the working tree to
fix the semantic conflict, and make a separate commit to record the
fix-up:
$ git checkout pu~4
$ git show -s --pretty=%s ;# double check
Merge branch 'ai/topic' to pu
$ edit
$ git commit -m 'merge-fix/ai/topic' -a
Then make a reference "refs/merge-fix/ai/topic" to point at this
result:
$ git update-ref refs/merge-fix/ai/topic HEAD
Then double check the result by asking Meta/Reintegrate to redo the
merge:
$ git checkout pu~5 ;# the parent of the problem merge
$ echo ai/topic | Meta/Reintegrate
$ git diff pu~4
This time, because you prepared refs/merge-fix/ai/topic, the
resulting merge should have been tweaked to include the fix for the
semantic conflict.
Note that this assumes that the order in which conflicting branches
are merged does not change. If the reason why merging ai/topic
branch needs this merge-fix is because another branch merged earlier
to the integration branch changed the underlying assumption ai/topic
branch made (e.g. ai/topic branch added a site to refer to a
variable, while the other branch renamed that variable and adjusted
existing use sites), and if you changed redo-jch (or redo-pu) script
to merge ai/topic branch before the other branch, then the above
merge-fix should not be applied while merging ai/topic, but should
instead be applied while merging the other branch. You would need
to move the fix to apply to the other branch, perhaps like this:
$ mf=refs/merge-fix
$ git update-ref $mf/$the_other_branch $mf/ai/topic
$ git update-ref -d $mf/ai/topic