Introduction

There are a couple of FreeBSD git repositories that have been converted with various programs and various parameters. This page describes the "official" git-branches of the FreeBSD project that should be used as common repositories to base other work on.

The repositories are provided as a read-only mirror of the state of the Subversion src, doc and, ports repositories at http://svn.FreeBSD.org/base, http://svn.FreeBSD.org/doc, and http://svn.FreeBSD.org/ports respectively. Using git to commit changes to these repositories is not officially supported (but doable), instead it is supposed to serve as a collaboration point by using additional tools like Github, Gitorious, or Gerrit, etc.

Bear in mind that git will not replace Subversion for use in FreeBSD and the repository is only offered on a best-effort basis. The steps to redo the conversion are outlined below, so that people can move the process in-house should they see the need for it.

CAVEAT EMPTOR: The repositories might need to be re-done every once in a while due to bugs or improvements in the converter. This will result in changed commit IDs for the impacted branches. As the actual tree objects for a certain SVN revision will remain identical, it will always be possible to rebase or merge your work on these new branches and not run into any merge conflicts. Ask on the mailing lists if you need help with the required git commands.

Contents

  1. Introduction
  2. The Repositories
  3. Known Problems
  4. Quick Start
  5. Collaboration
  6. Integration
    1. Using git-svn (FreeBSD committers only)
  7. FAQ
  8. Verification
  9. Further Reading
  10. Implementation Details

The Repositories

The official repository-mirrors are updated at least hourly, should they lag the svn repository by more than that, please contact <uqs@FreeBSD.org> (monitoring still needs to be put into place, help wanted btw).

The obsolete, non-compatible repositories are:

Known Problems

Quick Start

$ git clone --config remote.origin.fetch='+refs/notes/*:refs/notes/*' git://github.com/freebsd/freebsd.git
$ cd freebsd && git pull   # For some reason, the notes will not be fetched during the clone operation ...
$ hack, hack, hack
$ git commit

Advanced, useful examples to show the diff between a subdir of a branch, or the commits that introduced these diffs. It is basically what svn mergeinfo --show-revs=eligible does. See git-log(1) for more info. 

$ git diff origin/stable/9 master -- usr.sbin/acpi
$ git log --graph --format=oneline --right-only --cherry-pick --no-merges origin/stable/9...origin/master -- usr.sbin/acpi

See any other git howto or documentation if you're stuck on the basics. A useful reference for the issue with notes is http://git-scm.com/2010/08/25/notes.html.

Collaboration

There is no endorsed way yet of how users should collaborate with developers on changes they have made. Please bear in mind that git is strictly ancillary at this point and not many committers are using it.

Having your patches/feature-branches published on github for a FreeBSD committer to comment on and pull from seems like the first sensible step. Sending a patch-bomb with git send-email might be an alternative to github or for developers that do not want to use git.

Receiving and integrating these patches can be done in various ways, see below.

Integration

Integrating the changes back into svn is not as trivial as using git-svn(1), as the current repository doesn't have the required meta-information. Instead patches can be applied to a subversion workspace just like any other regular patch.

A more sophisticated approach would be to share the svn and the git workspaces, which can be done by putting .svn in .gitignore and vice versa. This requires subversion 1.7 and you need to know how to recover from out-of-sync workspaces in both subversion and git, or be extra careful to avoid this situation.

Using git-svn (FreeBSD committers only)

The repositories on github also have a branch that is the result of a conversion using git-svn, i.e. the necessary conversion has already been made. To use this, you simply need to: 

$ git clone git://github.com/freebsd/freebsd.git
$ cd freebsd
$ git svn init -Thead svn+ssh://svn.freebsd.org/base .
# People w/o write access to SVN can use this instead: git svn init -Thead --rewrite-root=svn+ssh://svn.freebsd.org/base svn://svn.freebsd.org/base .
$ git update-ref refs/remotes/trunk `git show-ref origin/svn_head|cut -d" " -f1` # git-svn really needs this branch
$ git svn fetch  # This will now reconstruct the necessary metadata and should be pretty fast
$ git checkout trunk; git branch -D master # delete master
$ git checkout -b master trunk # and have master hang off trunk
$ git svn rebase # this will now update everything to the latest state in head

Now you can periodically sync to svn using git svn rebase and you can push small changes back to svn using git svn dcommit, but read on.

Things to keep in mind:

FAQ

Everything done is so that everybody can verify the integrity of the conversion using the tools mentioned in this article. Hence the focus on repeat-ability of the process.

Verification

Verifying that the git export is identical to the SVN tree (in content), can be done like this: 

$ svn export --ignore-keywords svn://svn.freebsd.org/base/head freebsd.svn
...
Exported revision 243246.
$ git clone --config remote.origin.fetch='+refs/notes/*:refs/notes/*' git://github.com/freebsd/freebsd.git freebsd.git
$ cd freebsd.git && git pull
$ git log
<We see that revision 243246 is git commit f9ebae3>
$ git checkout f9ebae3
$ cd ../freebsd.svn
$ git --git-dir ../freebsd.git/.git diff
<There should be no output, i.e. no diff>

Further Reading

It is *really* recommended, that you read Git for computer scientists and skim GitTalkDevSummit, although it's really outdated.

It really helps to understand the data structure of a git commit, because then you know how merging/rebasing works and can fix snafus easily.

A good visual git reference can be found at A Visual Git Reference.

Implementation Details

The software used for the conversion is a slightly modified fork of svn2git, as used by the KDE project. It can be found at https://gitorious.org/~uqs/svn2git/uqs-svn2git

It requires a rules file to map svn trees and/or revisions to git branches or tags. The current rules don't make use of tags but simply store them as branches.

See the attached freebsd.rules, freebsd-doc.rules, and freebsd-ports.rules for the current rulesets (subject to change). The command line parameters used for the continuous conversion are: 

svn2git/svn-all-fast-export --rules freebsd.rules --add-metadata-notes --identity-domain FreeBSD.org http://svn.freebsd.org/base
svn2git/svn-all-fast-export --rules freebsd-doc.rules --add-metadata-notes --identity-domain FreeBSD.org http://svn.freebsd.org/doc
svn2git/svn-all-fast-export --rules freebsd-ports.rules --add-metadata-notes --identity-domain FreeBSD.org http://svn.freebsd.org/ports