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diff --git a/Documentation/cvs-migration.txt b/Documentation/cvs-migration.txt index 6812683a1..b657f4589 100644 --- a/Documentation/cvs-migration.txt +++ b/Documentation/cvs-migration.txt @@ -1,113 +1,21 @@ 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. +Git differs from CVS in that 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; +this document explains how to do that. 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: +Developing against a shared repository +-------------------------------------- - * 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 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 +Suppose a shared repository is set up in /pub/repo.git on the host foo.com. Then as an individual committer you can clone the shared -repository: +repository over ssh with: ------------------------------------------------ $ git clone foo.com:/pub/repo.git/ my-project @@ -121,7 +29,8 @@ $ git pull origin ------------------------------------------------ which merges in any work that others might have done since the clone -operation. +operation. If there are uncommitted changes in your working tree, commit +them first before running git pull. [NOTE] ================================ @@ -129,20 +38,22 @@ 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 +URL: foo.com:/pub/project.git/ +Pull: refs/heads/master:refs/remotes/origin/master ------------ ================================ -You can update the shared repository with your changes using: +You can update the shared repository with your changes by first committing +your changes, and then using the gitlink:git-push[1] command: ------------------------------------------------ $ 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. +to "push" those commits to the shared repository. 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 @@ -151,21 +62,77 @@ 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/ +$ git push foo.com:/pub/project.git/ ------------ as long as the shared repository does not have any branches other than `master`. -[NOTE] -============ -Because of this behavior, 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. -============ +Setting Up a Shared Repository +------------------------------ + +We assume you have already created a git repository for your project, +possibly created from scratch or from a tarball (see the +link:tutorial.html[tutorial]), or imported from an already existing CVS +repository (see the next section). + +Assume your existing repo is at /home/alice/myproject. Create a new "bare" +repository (a repository without a working tree) and fetch your project into +it: + +------------------------------------------------ +$ mkdir /pub/my-repo.git +$ cd /pub/my-repo.git +$ git --bare init-db --shared +$ git --bare fetch /home/alice/myproject master:master +------------------------------------------------ + +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 in the same group, and make the repository +writable by that group: + +------------------------------------------------ +$ chgrp -R $group /pub/my-repo.git +------------------------------------------------ + +Make sure committers have a umask of at most 027, so that the directories +they create are writable and searchable by other group members. + +Importing a CVS archive +----------------------- + +First, install version 2.1 or higher of cvsps from +link:http://www.cobite.com/cvsps/[http://www.cobite.com/cvsps/] and make +sure it is in your path. Then cd to a checked out CVS working directory +of the project you are interested in and run gitlink:git-cvsimport[1]: + +------------------------------------------- +$ git cvsimport -C <destination> +------------------------------------------- + +This puts a git archive of the named CVS module in the directory +<destination>, which will be created if necessary. + +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. Advanced Shared Repository Management ------------------------------------- @@ -178,127 +145,30 @@ 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 ------------- +Providing CVS Access to a git Repository +---------------------------------------- + +It is also possible to provide true CVS access to a git repository, so +that developers can still use CVS; see gitlink:git-cvsserver[1] for +details. + +Alternative Development Models +------------------------------ + +CVS users are accustomed to giving a group of developers commit access to +a common repository. As we've seen, this is also possible 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. -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. +With a small group, developers may just pull changes from each other's +repositories without the need for a central maintainer. |