cvs2git

Index

• Introduction
• Development status
• Documentation
• Usage

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Introduction

cvs2svn is a tool that was originally developed to migrate CVS repositories to Subversion. The current development version of cvs2svn can also output the converted repository directly to git, a distributed version control system most famous for being used for Linux kernel development. When talking about converting from CVS to git, I will refer to the program as cvs2git, even though the project and the main executable are still called "cvs2svn".

Please note that conversion to git was added in release 2.1 of cvs2svn. Please make sure you are using cvs2svn release 2.1 or newer.

Development status

Most of the work of converting a repository from CVS to a more modern version control system is inferring the most likely history given the incomplete information that CVS records. cvs2svn has a long history of making sense of even the most convoluted CVS repositories, and cvs2git uses this same machinery. Therefore, cvs2git inherits the robustness and many of the features of cvs2svn. cvs2svn can convert just about every CVS repository we have ever seen, and includes a plethora of options for customizing your conversion. See the cvs2svn documentation for a summary of cvs2svn's features.

However, the git output of cvs2git is still rather new and rough around the edges. The main cvs2svn developer is not a git user, so help would be much appreciated! Some of these missing features would be pretty easy to program, and I'd be happy to help you get started.

But thanks to the excellent git-fast-import tool, the code needed to output to git is relatively straightforward, and it is believed that cvs2git can (cautiously) be used for production conversions.

cvs2git still has the following limitations:

• The cvs2git documentation is still rather thin. See below for more references.
• CVS allows a branch to be created from arbitrary combinations of source revisions and/or source branches. cvs2git tries to create a branch from a single source, but if it can't figure out how to, it creates the branch using "merge" from multiple sources. In pathological situations, the number of merge sources for a branch can be arbitrarily large.

• It is not very intelligent about creating tags. When asked to create a tag, it unconditionally creates a tag fixup branch named TAG.FIXUP, then tags this branch. The TAG.FIXUP branch is cleared at the end of the conversion, but not deleted.

  Some CVS tags can be created from a single parent, in which case the tag fixup branch would be superfluous. It would be possible to teach cvs2git to determine when single-source tags can be created, at a considerable cost in runtime and temporary workspace. Alternatively, it is possible to delete uninteresting branches after the conversion.

• There are no checks that CVS branch and tag names are legal git names. There are probably other git constraints that should also be checked.
• The data that should be fed to git-fast-input is written to two files, which have to be loaded into git-fast-import manually. These files might grow to very large size. It would be nice to add an option to invoke git-fast-import automatically and pipe the output directly into git-fast-import; this should also speed up the conversion.
• Only single projects can be converted at a time. Given the way git is typically used, I don't think that this is a significant limitation.
• cvs2git is not especially fast. Among other things, it still uses RCS or CVS to extract the contents of the CVS revisions. Reconstructing the revision contents within cvs2git (using code that already exists in cvs2svn) might improve the conversion speed.
• The cvs2svn test suite does not include meaningful tests of git output.
• cvs2git makes no attempt to convert .cvsignore files into .gitignore files.

Documentation

There is not a lot of documentation specific to cvs2git, but much of the cvs2svn documentation applies fairly straightforwardly to cvs2git. See the following sources:

• This document.
• The cvs2svn documentation and the cvs2svn FAQ contain much general discussion and describe many features that can also be used for cvs2git.
• test-data/main-cvsrepos/cvs2svn-git.options in the cvs2svn source tree is an example of an options file that can be used to configure a cvs2git conversion. It includes from cvs2svn-example.options many settings that apply to both cvs2svn and cvs2git. Both files are extensively documented.
• The cvs2svn mailing lists, IRC channel, etc., as described in the cvs2svn FAQ.

Usage

This section outlines the steps needed to convert a CVS repository to git using cvs2git.

1. Be sure that you have the cvs2svn requirements, including either RCS or CVS (used to read revision contents from the CVS repository).
2. Obtain a copy of cvs2svn version 2.1 or newer.
   • To install cvs2svn from a tarball, simply unpack the tarball into a directory on your conversion computer (cvs2svn can be run directly from this directory).

   • To Check out the current trunk version of cvs2svn, make sure that you have Subversion installed and then run:

     svn co http://guest@cvs2svn.tigris.org/svn/cvs2svn/trunk cvs2svn-trunk
     # The password is empty; i.e., just press return.
     cd cvs2svn-trunk
     make check # ...optional
     

     Please note that the test suite includes tests that are marked "XFAIL" (expected failure); these are known and are not considered serious problems. In fact, the test for git output is marked XFAIL because the cvs2svn test suite doesn't know how to verify the contents of the git repository.

3. Configure cvs2svn for your conversion. This has to be done via the options-file method. See test-data/main-cvsrepos/cvs2svn-git.options and cvs2svn-example.options in the cvs2svn source tree as examples; both files contain lots of documentation.
4. Run cvs2svn. This creates two output files in git-fast-import format. The names of these files are specified by your options file. In the example, these files are named cvs2svn-tmp/git-blob.dat and cvs2svn-tmp/git-dump.dat.

5. Initialize a git repository, and load the dump files using git-fast-import:

   git-init
   cat cvs2svn-tmp/git-blob.dat | git-fast-import --export-marks=cvs2svn-tmp/git-marks.dat
   cat cvs2svn-tmp/git-dump.dat | git-fast-import --import-marks=cvs2svn-tmp/git-marks.dat
   

   This can, of course, be shortened to:

   git-init
   cat cvs2svn-tmp/git-blob.dat cvs2svn-tmp/git-dump.dat | git-fast-import
   

Feedback would be much appreciated, as I am a git newbie. Please send comments, bug reports, and patches to the cvs2svn mailing lists.