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diff --git a/Documentation/cvs-migration.txt b/Documentation/cvs-migration.txt new file mode 100644 index 0000000000..fa94efde8d --- /dev/null +++ b/Documentation/cvs-migration.txt @@ -0,0 +1,304 @@ +git for CVS users +================= + +So you're a CVS user. That's ok, it's a treatable condition. The job of +this document is to put you on the road to recovery, by helping you +convert an existing cvs repository to git, and by showing you how to use a +git repository in a cvs-like fashion. + +Some basic familiarity with git is required. This +link:tutorial.html[tutorial introduction to git] should be sufficient. + +First, note some ways that git differs from CVS: + + * Commits are atomic and project-wide, not per-file as in CVS. + + * Offline work is supported: you can make multiple commits locally, + then submit them when you're ready. + + * Branching is fast and easy. + + * Every working tree contains a repository with a full copy of the + project history, and no repository is inherently more important than + any other. However, you can emulate the CVS model by designating a + single shared repository which people can synchronize with; see below + for details. + +Importing a CVS archive +----------------------- + +First, install version 2.1 or higher of cvsps from +link:http://www.cobite.com/cvsps/[http://www.cobite.com/cvsps/] and make +sure it is in your path. The magic command line is then + +------------------------------------------- +$ git cvsimport -v -d <cvsroot> -C <destination> <module> +------------------------------------------- + +This puts a git archive of the named CVS module in the directory +<destination>, which will be created if necessary. The -v option makes +the conversion script very chatty. + +The import checks out from CVS every revision of every file. Reportedly +cvsimport can average some twenty revisions per second, so for a +medium-sized project this should not take more than a couple of minutes. +Larger projects or remote repositories may take longer. + +The main trunk is stored in the git branch named `origin`, and additional +CVS branches are stored in git branches with the same names. The most +recent version of the main trunk is also left checked out on the `master` +branch, so you can start adding your own changes right away. + +The import is incremental, so if you call it again next month it will +fetch any CVS updates that have been made in the meantime. For this to +work, you must not modify the imported branches; instead, create new +branches for your own changes, and merge in the imported branches as +necessary. + +Development Models +------------------ + +CVS users are accustomed to giving a group of developers commit access to +a common repository. In the next section we'll explain how to do this +with git. However, the distributed nature of git allows other development +models, and you may want to first consider whether one of them might be a +better fit for your project. + +For example, you can choose a single person to maintain the project's +primary public repository. Other developers then clone this repository +and each work in their own clone. When they have a series of changes that +they're happy with, they ask the maintainer to pull from the branch +containing the changes. The maintainer reviews their changes and pulls +them into the primary repository, which other developers pull from as +necessary to stay coordinated. The Linux kernel and other projects use +variants of this model. + +With a small group, developers may just pull changes from each other's +repositories without the need for a central maintainer. + +Emulating the CVS Development Model +----------------------------------- + +Start with an ordinary git working directory containing the project, and +remove the checked-out files, keeping just the bare .git directory: + +------------------------------------------------ +$ mv project/.git /pub/repo.git +$ rm -r project/ +------------------------------------------------ + +Next, give every team member read/write access to this repository. One +easy way to do this is to give all the team members ssh access to the +machine where the repository is hosted. If you don't want to give them a +full shell on the machine, there is a restricted shell which only allows +users to do git pushes and pulls; see gitlink:git-shell[1]. + +Put all the committers should in the same group, and make the repository +writable by that group: + +------------------------------------------------ +$ chgrp -R $group repo.git +$ find repo.git -mindepth 1 -type d |xargs chmod ug+rwx,g+s +$ GIT_DIR=repo.git git repo-config core.sharedrepository true +------------------------------------------------ + +Make sure committers have a umask of at most 027, so that the directories +they create are writable and searchable by other group members. + +Suppose this repository is now set up in /pub/repo.git on the host +foo.com. Then as an individual commiter you can clone the shared +repository: + +------------------------------------------------ +$ git clone foo.com:/pub/repo.git/ my-project +$ cd my-project +------------------------------------------------ + +and hack away. The equivalent of `cvs update` is + +------------------------------------------------ +$ git pull origin +------------------------------------------------ + +which merges in any work that others might have done since the clone +operation. + +[NOTE] +================================ +The first `git clone` places the following in the +`my-project/.git/remotes/origin` file, and that's why the previous step +and the next step both work. +------------ +URL: foo.com:/pub/project.git/ my-project +Pull: master:origin +------------ +================================ + +You can update the shared repository with your changes using: + +------------------------------------------------ +$ git push origin master +------------------------------------------------ + +If someone else has updated the repository more recently, `git push`, like +`cvs commit`, will complain, in which case you must pull any changes +before attempting the push again. + +In the `git push` command above we specify the name of the remote branch +to update (`master`). If we leave that out, `git push` tries to update +any branches in the remote repository that have the same name as a branch +in the local repository. So the last `push` can be done with either of: + +------------ +$ git push origin +$ git push repo.shared.xz:/pub/scm/project.git/ +------------ + +as long as the shared repository does not have any branches +other than `master`. + +[NOTE] +============ +Because of this behaviour, if the shared repository and the developer's +repository both have branches named `origin`, then a push like the above +attempts to update the `origin` branch in the shared repository from the +developer's `origin` branch. The results may be unexpected, so it's +usually best to remove any branch named `origin` from the shared +repository. +============ + +Advanced Shared Repository Management +------------------------------------- + +Git allows you to specify scripts called "hooks" to be run at certain +points. You can use these, for example, to send all commits to the shared +repository to a mailing list. See link:hooks.txt[Hooks used by git]. + +You can enforce finer grained permissions using update hooks. See +link:howto/update-hook-example.txt[Controlling access to branches using +update hooks]. + +CVS annotate +------------ + +So, something has gone wrong, and you don't know whom to blame, and +you're an ex-CVS user and used to do "cvs annotate" to see who caused +the breakage. You're looking for the "git annotate", and it's just +claiming not to find such a script. You're annoyed. + +Yes, that's right. Core git doesn't do "annotate", although it's +technically possible, and there are at least two specialized scripts out +there that can be used to get equivalent information (see the git +mailing list archives for details). + +git has a couple of alternatives, though, that you may find sufficient +or even superior depending on your use. One is called "git-whatchanged" +(for obvious reasons) and the other one is called "pickaxe" ("a tool for +the software archaeologist"). + +The "git-whatchanged" script is a truly trivial script that can give you +a good overview of what has changed in a file or a directory (or an +arbitrary list of files or directories). The "pickaxe" support is an +additional layer that can be used to further specify exactly what you're +looking for, if you already know the specific area that changed. + +Let's step back a bit and think about the reason why you would +want to do "cvs annotate a-file.c" to begin with. + +You would use "cvs annotate" on a file when you have trouble +with a function (or even a single "if" statement in a function) +that happens to be defined in the file, which does not do what +you want it to do. And you would want to find out why it was +written that way, because you are about to modify it to suit +your needs, and at the same time you do not want to break its +current callers. For that, you are trying to find out why the +original author did things that way in the original context. + +Many times, it may be enough to see the commit log messages of +commits that touch the file in question, possibly along with the +patches themselves, like this: + + $ git-whatchanged -p a-file.c + +This will show log messages and patches for each commit that +touches a-file. + +This, however, may not be very useful when this file has many +modifications that are not related to the piece of code you are +interested in. You would see many log messages and patches that +do not have anything to do with the piece of code you are +interested in. As an example, assuming that you have this piece +of code that you are interested in in the HEAD version: + + if (frotz) { + nitfol(); + } + +you would use git-rev-list and git-diff-tree like this: + + $ git-rev-list HEAD | + git-diff-tree --stdin -v -p -S'if (frotz) { + nitfol(); + }' + +We have already talked about the "\--stdin" form of git-diff-tree +command that reads the list of commits and compares each commit +with its parents (otherwise you should go back and read the tutorial). +The git-whatchanged command internally runs +the equivalent of the above command, and can be used like this: + + $ git-whatchanged -p -S'if (frotz) { + nitfol(); + }' + +When the -S option is used, git-diff-tree command outputs +differences between two commits only if one tree has the +specified string in a file and the corresponding file in the +other tree does not. The above example looks for a commit that +has the "if" statement in it in a file, but its parent commit +does not have it in the same shape in the corresponding file (or +the other way around, where the parent has it and the commit +does not), and the differences between them are shown, along +with the commit message (thanks to the -v flag). It does not +show anything for commits that do not touch this "if" statement. + +Also, in the original context, the same statement might have +appeared at first in a different file and later the file was +renamed to "a-file.c". CVS annotate would not help you to go +back across such a rename, but git would still help you in such +a situation. For that, you can give the -C flag to +git-diff-tree, like this: + + $ git-whatchanged -p -C -S'if (frotz) { + nitfol(); + }' + +When the -C flag is used, file renames and copies are followed. +So if the "if" statement in question happens to be in "a-file.c" +in the current HEAD commit, even if the file was originally +called "o-file.c" and then renamed in an earlier commit, or if +the file was created by copying an existing "o-file.c" in an +earlier commit, you will not lose track. If the "if" statement +did not change across such a rename or copy, then the commit that +does rename or copy would not show in the output, and if the +"if" statement was modified while the file was still called +"o-file.c", it would find the commit that changed the statement +when it was in "o-file.c". + +NOTE: The current version of "git-diff-tree -C" is not eager + enough to find copies, and it will miss the fact that a-file.c + was created by copying o-file.c unless o-file.c was somehow + changed in the same commit. + +You can use the --pickaxe-all flag in addition to the -S flag. +This causes the differences from all the files contained in +those two commits, not just the differences between the files +that contain this changed "if" statement: + + $ git-whatchanged -p -C -S'if (frotz) { + nitfol(); + }' --pickaxe-all + +NOTE: This option is called "--pickaxe-all" because -S + option is internally called "pickaxe", a tool for software + archaeologists. |