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diff --git a/Documentation/gitworkflows.txt b/Documentation/gitworkflows.txt new file mode 100644 index 0000000000..1ef55fffcf --- /dev/null +++ b/Documentation/gitworkflows.txt @@ -0,0 +1,479 @@ +gitworkflows(7) +=============== + +NAME +---- +gitworkflows - An overview of recommended workflows with git + +SYNOPSIS +-------- +git * + + +DESCRIPTION +----------- + +This document attempts to write down and motivate some of the workflow +elements used for `git.git` itself. Many ideas apply in general, +though the full workflow is rarely required for smaller projects with +fewer people involved. + +We formulate a set of 'rules' for quick reference, while the prose +tries to motivate each of them. Do not always take them literally; +you should value good reasons for your actions higher than manpages +such as this one. + + +SEPARATE CHANGES +---------------- + +As a general rule, you should try to split your changes into small +logical steps, and commit each of them. They should be consistent, +working independently of any later commits, pass the test suite, etc. +This makes the review process much easier, and the history much more +useful for later inspection and analysis, for example with +linkgit:git-blame[1] and linkgit:git-bisect[1]. + +To achieve this, try to split your work into small steps from the very +beginning. It is always easier to squash a few commits together than +to split one big commit into several. Don't be afraid of making too +small or imperfect steps along the way. You can always go back later +and edit the commits with `git rebase \--interactive` before you +publish them. You can use `git stash save \--keep-index` to run the +test suite independent of other uncommitted changes; see the EXAMPLES +section of linkgit:git-stash[1]. + + +MANAGING BRANCHES +----------------- + +There are two main tools that can be used to include changes from one +branch on another: linkgit:git-merge[1] and +linkgit:git-cherry-pick[1]. + +Merges have many advantages, so we try to solve as many problems as +possible with merges alone. Cherry-picking is still occasionally +useful; see "Merging upwards" below for an example. + +Most importantly, merging works at the branch level, while +cherry-picking works at the commit level. This means that a merge can +carry over the changes from 1, 10, or 1000 commits with equal ease, +which in turn means the workflow scales much better to a large number +of contributors (and contributions). Merges are also easier to +understand because a merge commit is a "promise" that all changes from +all its parents are now included. + +There is a tradeoff of course: merges require a more careful branch +management. The following subsections discuss the important points. + + +Graduation +~~~~~~~~~~ + +As a given feature goes from experimental to stable, it also +"graduates" between the corresponding branches of the software. +`git.git` uses the following 'integration branches': + +* 'maint' tracks the commits that should go into the next "maintenance + release", i.e., update of the last released stable version; + +* 'master' tracks the commits that should go into the next release; + +* 'next' is intended as a testing branch for topics being tested for + stability for master. + +There is a fourth official branch that is used slightly differently: + +* 'pu' (proposed updates) is an integration branch for things that are + not quite ready for inclusion yet (see "Integration Branches" + below). + +Each of the four branches is usually a direct descendant of the one +above it. + +Conceptually, the feature enters at an unstable branch (usually 'next' +or 'pu'), and "graduates" to 'master' for the next release once it is +considered stable enough. + + +Merging upwards +~~~~~~~~~~~~~~~ + +The "downwards graduation" discussed above cannot be done by actually +merging downwards, however, since that would merge 'all' changes on +the unstable branch into the stable one. Hence the following: + +.Merge upwards +[caption="Rule: "] +===================================== +Always commit your fixes to the oldest supported branch that require +them. Then (periodically) merge the integration branches upwards into each +other. +===================================== + +This gives a very controlled flow of fixes. If you notice that you +have applied a fix to e.g. 'master' that is also required in 'maint', +you will need to cherry-pick it (using linkgit:git-cherry-pick[1]) +downwards. This will happen a few times and is nothing to worry about +unless you do it very frequently. + + +Topic branches +~~~~~~~~~~~~~~ + +Any nontrivial feature will require several patches to implement, and +may get extra bugfixes or improvements during its lifetime. + +Committing everything directly on the integration branches leads to many +problems: Bad commits cannot be undone, so they must be reverted one +by one, which creates confusing histories and further error potential +when you forget to revert part of a group of changes. Working in +parallel mixes up the changes, creating further confusion. + +Use of "topic branches" solves these problems. The name is pretty +self explanatory, with a caveat that comes from the "merge upwards" +rule above: + +.Topic branches +[caption="Rule: "] +===================================== +Make a side branch for every topic (feature, bugfix, ...). Fork it off +at the oldest integration branch that you will eventually want to merge it +into. +===================================== + +Many things can then be done very naturally: + +* To get the feature/bugfix into an integration branch, simply merge + it. If the topic has evolved further in the meantime, merge again. + (Note that you do not necessarily have to merge it to the oldest + integration branch first. For example, you can first merge a bugfix + to 'next', give it some testing time, and merge to 'maint' when you + know it is stable.) + +* If you find you need new features from the branch 'other' to continue + working on your topic, merge 'other' to 'topic'. (However, do not + do this "just habitually", see below.) + +* If you find you forked off the wrong branch and want to move it + "back in time", use linkgit:git-rebase[1]. + +Note that the last point clashes with the other two: a topic that has +been merged elsewhere should not be rebased. See the section on +RECOVERING FROM UPSTREAM REBASE in linkgit:git-rebase[1]. + +We should point out that "habitually" (regularly for no real reason) +merging an integration branch into your topics -- and by extension, +merging anything upstream into anything downstream on a regular basis +-- is frowned upon: + +.Merge to downstream only at well-defined points +[caption="Rule: "] +===================================== +Do not merge to downstream except with a good reason: upstream API +changes affect your branch; your branch no longer merges to upstream +cleanly; etc. +===================================== + +Otherwise, the topic that was merged to suddenly contains more than a +single (well-separated) change. The many resulting small merges will +greatly clutter up history. Anyone who later investigates the history +of a file will have to find out whether that merge affected the topic +in development. An upstream might even inadvertently be merged into a +"more stable" branch. And so on. + + +Throw-away integration +~~~~~~~~~~~~~~~~~~~~~~ + +If you followed the last paragraph, you will now have many small topic +branches, and occasionally wonder how they interact. Perhaps the +result of merging them does not even work? But on the other hand, we +want to avoid merging them anywhere "stable" because such merges +cannot easily be undone. + +The solution, of course, is to make a merge that we can undo: merge +into a throw-away branch. + +.Throw-away integration branches +[caption="Rule: "] +===================================== +To test the interaction of several topics, merge them into a +throw-away branch. You must never base any work on such a branch! +===================================== + +If you make it (very) clear that this branch is going to be deleted +right after the testing, you can even publish this branch, for example +to give the testers a chance to work with it, or other developers a +chance to see if their in-progress work will be compatible. `git.git` +has such an official throw-away integration branch called 'pu'. + + +Branch management for a release +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Assuming you are using the merge approach discussed above, when you +are releasing your project you will need to do some additional branch +management work. + +A feature release is created from the 'master' branch, since 'master' +tracks the commits that should go into the next feature release. + +The 'master' branch is supposed to be a superset of 'maint'. If this +condition does not hold, then 'maint' contains some commits that +are not included on 'master'. The fixes represented by those commits +will therefore not be included in your feature release. + +To verify that 'master' is indeed a superset of 'maint', use git log: + +.Verify 'master' is a superset of 'maint' +[caption="Recipe: "] +===================================== +`git log master..maint` +===================================== + +This command should not list any commits. Otherwise, check out +'master' and merge 'maint' into it. + +Now you can proceed with the creation of the feature release. Apply a +tag to the tip of 'master' indicating the release version: + +.Release tagging +[caption="Recipe: "] +===================================== +`git tag -s -m "GIT X.Y.Z" vX.Y.Z master` +===================================== + +You need to push the new tag to a public git server (see +"DISTRIBUTED WORKFLOWS" below). This makes the tag available to +others tracking your project. The push could also trigger a +post-update hook to perform release-related items such as building +release tarballs and preformatted documentation pages. + +Similarly, for a maintenance release, 'maint' is tracking the commits +to be released. Therefore, in the steps above simply tag and push +'maint' rather than 'master'. + + +Maintenance branch management after a feature release +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +After a feature release, you need to manage your maintenance branches. + +First, if you wish to continue to release maintenance fixes for the +feature release made before the recent one, then you must create +another branch to track commits for that previous release. + +To do this, the current maintenance branch is copied to another branch +named with the previous release version number (e.g. maint-X.Y.(Z-1) +where X.Y.Z is the current release). + +.Copy maint +[caption="Recipe: "] +===================================== +`git branch maint-X.Y.(Z-1) maint` +===================================== + +The 'maint' branch should now be fast-forwarded to the newly released +code so that maintenance fixes can be tracked for the current release: + +.Update maint to new release +[caption="Recipe: "] +===================================== +* `git checkout maint` +* `git merge --ff-only master` +===================================== + +If the merge fails because it is not a fast-forward, then it is +possible some fixes on 'maint' were missed in the feature release. +This will not happen if the content of the branches was verified as +described in the previous section. + + +Branch management for next and pu after a feature release +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +After a feature release, the integration branch 'next' may optionally be +rewound and rebuilt from the tip of 'master' using the surviving +topics on 'next': + +.Rewind and rebuild next +[caption="Recipe: "] +===================================== +* `git checkout next` +* `git reset --hard master` +* `git merge ai/topic_in_next1` +* `git merge ai/topic_in_next2` +* ... +===================================== + +The advantage of doing this is that the history of 'next' will be +clean. For example, some topics merged into 'next' may have initially +looked promising, but were later found to be undesirable or premature. +In such a case, the topic is reverted out of 'next' but the fact +remains in the history that it was once merged and reverted. By +recreating 'next', you give another incarnation of such topics a clean +slate to retry, and a feature release is a good point in history to do +so. + +If you do this, then you should make a public announcement indicating +that 'next' was rewound and rebuilt. + +The same rewind and rebuild process may be followed for 'pu'. A public +announcement is not necessary since 'pu' is a throw-away branch, as +described above. + + +DISTRIBUTED WORKFLOWS +--------------------- + +After the last section, you should know how to manage topics. In +general, you will not be the only person working on the project, so +you will have to share your work. + +Roughly speaking, there are two important workflows: merge and patch. +The important difference is that the merge workflow can propagate full +history, including merges, while patches cannot. Both workflows can +be used in parallel: in `git.git`, only subsystem maintainers use +the merge workflow, while everyone else sends patches. + +Note that the maintainer(s) may impose restrictions, such as +"Signed-off-by" requirements, that all commits/patches submitted for +inclusion must adhere to. Consult your project's documentation for +more information. + + +Merge workflow +~~~~~~~~~~~~~~ + +The merge workflow works by copying branches between upstream and +downstream. Upstream can merge contributions into the official +history; downstream base their work on the official history. + +There are three main tools that can be used for this: + +* linkgit:git-push[1] copies your branches to a remote repository, + usually to one that can be read by all involved parties; + +* linkgit:git-fetch[1] that copies remote branches to your repository; + and + +* linkgit:git-pull[1] that does fetch and merge in one go. + +Note the last point. Do 'not' use 'git pull' unless you actually want +to merge the remote branch. + +Getting changes out is easy: + +.Push/pull: Publishing branches/topics +[caption="Recipe: "] +===================================== +`git push <remote> <branch>` and tell everyone where they can fetch +from. +===================================== + +You will still have to tell people by other means, such as mail. (Git +provides the linkgit:git-request-pull[1] to send preformatted pull +requests to upstream maintainers to simplify this task.) + +If you just want to get the newest copies of the integration branches, +staying up to date is easy too: + +.Push/pull: Staying up to date +[caption="Recipe: "] +===================================== +Use `git fetch <remote>` or `git remote update` to stay up to date. +===================================== + +Then simply fork your topic branches from the stable remotes as +explained earlier. + +If you are a maintainer and would like to merge other people's topic +branches to the integration branches, they will typically send a +request to do so by mail. Such a request looks like + +------------------------------------- +Please pull from + <url> <branch> +------------------------------------- + +In that case, 'git pull' can do the fetch and merge in one go, as +follows. + +.Push/pull: Merging remote topics +[caption="Recipe: "] +===================================== +`git pull <url> <branch>` +===================================== + +Occasionally, the maintainer may get merge conflicts when he tries to +pull changes from downstream. In this case, he can ask downstream to +do the merge and resolve the conflicts themselves (perhaps they will +know better how to resolve them). It is one of the rare cases where +downstream 'should' merge from upstream. + + +Patch workflow +~~~~~~~~~~~~~~ + +If you are a contributor that sends changes upstream in the form of +emails, you should use topic branches as usual (see above). Then use +linkgit:git-format-patch[1] to generate the corresponding emails +(highly recommended over manually formatting them because it makes the +maintainer's life easier). + +.format-patch/am: Publishing branches/topics +[caption="Recipe: "] +===================================== +* `git format-patch -M upstream..topic` to turn them into preformatted + patch files +* `git send-email --to=<recipient> <patches>` +===================================== + +See the linkgit:git-format-patch[1] and linkgit:git-send-email[1] +manpages for further usage notes. + +If the maintainer tells you that your patch no longer applies to the +current upstream, you will have to rebase your topic (you cannot use a +merge because you cannot format-patch merges): + +.format-patch/am: Keeping topics up to date +[caption="Recipe: "] +===================================== +`git pull --rebase <url> <branch>` +===================================== + +You can then fix the conflicts during the rebase. Presumably you have +not published your topic other than by mail, so rebasing it is not a +problem. + +If you receive such a patch series (as maintainer, or perhaps as a +reader of the mailing list it was sent to), save the mails to files, +create a new topic branch and use 'git am' to import the commits: + +.format-patch/am: Importing patches +[caption="Recipe: "] +===================================== +`git am < patch` +===================================== + +One feature worth pointing out is the three-way merge, which can help +if you get conflicts: `git am -3` will use index information contained +in patches to figure out the merge base. See linkgit:git-am[1] for +other options. + + +SEE ALSO +-------- +linkgit:gittutorial[7], +linkgit:git-push[1], +linkgit:git-pull[1], +linkgit:git-merge[1], +linkgit:git-rebase[1], +linkgit:git-format-patch[1], +linkgit:git-send-email[1], +linkgit:git-am[1] + +GIT +--- +Part of the linkgit:git[1] suite. |