Dirac SVN Repository


SVN Repository Organization


In a subversion repository, the organization of the paths is of fundamental importance for the everyday work and usability. We want to follow the standard (but not enforced) basic hierarchy of a project hosted on SVN, which consists of the 3 directories:
  • trunk: the main trunk of development
  • tags: fixed versions of the project identified by symbolic names
  • branches: branches of evolution of the project parallel to the trunk

Out development model requires the necessity to have package level tags and branches. At the same time, we need something that can be used as a tag on the whole project. Moreover, LHCb unique CVS repository is hosting many CMT projects and a global tag is pointless, but we can profit from the possibility of check out a complete tagged project in one command.

Version 2.0


Even though the previous structure is valid, it makes working with whole projects more problematic that what it could be. Mainly because of the usage of svn:externals, which is more powerful than the CVS aliases, but it is not flexible enough for our use case (URL pointing to the repository may change).

For Gaudi the package tags and the project tags have more or less the same importance (LHCb uses local tags while Atlas and other experiments use only the project tags), and for Dirac (which is being migrated to SVN too) the local tags were never used. This, essentially, means that the projects tags are more important than what was thought when devising the first structure of the repository.

The current structure makes also problematic to work with RADs like eclipse.


A structure that allows good integration between project-level and package-level tags can be achieved with something like:

One directory per project (all capital letters, by convention) is visible at the top level of the repository. Inside that directory the three standard directories: trunk, tags and branches. The trunk directory contains the structure of the project as it should be checked out: a cmt directory and one directory per package (with or without a "hat" level).

The tags and branches directories sport the same structure. A directory with the same name of the project will contain the project-level tags/branches, while a directory per package will contain the package-level tags/branches. User tags (or branches) could be stored in further subdirectories in the normal package tags (or branches) directory, for example PROJECT/tags/Package/username/tag.

Not all the foreseen directories are needed for a working repository. A repository can be fully functional without project-level tags or without package-level tags.

In case the grouping of the packages on a per project basis (like in the LHCb repository) is not wanted, a fake project can be used to host all (or part) of the packages (for example called packages). Of course, in this case it is possible to check out a project only using some dedicated tool, like the "getpack" utility used in LHCb.

The special project packages can also be used to host the packages the do not belong (yet/anymore) to a project.

Note that to simplify the maintenance of the repository, when a package needs to be moved from a project to another (or to the special project packages), also the tags and branches directories must be moved.

Meta-data (and getpack)

To make it possible for tools to work with both version 1.0 or version 2.0 of the repository and to take into account the fact that the packages are distributed between various projects (and not grouped in a single directory) some properties of the top-level directory have to be set:
must be set to "2.0" to declare the version of the structure of the repository
newline-separated list of projects in the repository, the correct case can should be used
newline-separated list of known packages in the repository
Empty lines or lines starting with # should be ignored.

A line of the packages property must be a space-separated list containing the name of the package (with hat), the name of the project owning it. Optionally it can contain tag specifications (a string representing a path in the repository where %v stands for the version id), to be used to locate special tags (useful if the package has been moved from one project to another). For example:

Hat/PackageA Project   OLDPROJECT/tags/OLDPROJECT/%v/Hat/PackageA
in this case, the tags for Hat/PackageA should be found with the patterns
  • PROJECT/tags/PROJECT/%v/Hat/PackageA
  • PROJECT/tags/Hat/PackageA/%v
  • PROJECT/branches/PROJECT/%v/Hat/PackageA
  • PROJECT/branches/Hat/PackageA/%v
  • OLDPROJECT/tags/OLDPROJECT/%v/Hat/PackageA


svn Quick Reference for cvs Users

Environment variables for the repositories:
  • DIRACCVS=:kserver:isscvs.cern.ch/local/reps/Dirac
    anonymous read-only access
    read-write access


  • Checkout head version of a package
    • cvs
      cvs -d $DIRACCVS checkout LHCbDIRACConfig
    • svn
      svn checkout $DIRACSVN/LHCbDIRAC/trunk/LHCBDIRACConfig
  • Checkout tagged version of a package
    • cvs
      cvs -d $DIRACCVS checkout -r v20r0 DiracConfig
    • svn
      svn checkout $DIRACSVN/DIRAC/tags/LHCbDIRACConfig/v1r0 LHCbDIRACConfig
  • Checkout a complete project head version
    • cvs (Dirac only)
      mkdir DIRAC
      cd DIRAC
      cvs -d $DIRACCVS checkout all
    • svn
      svn checkout $DIRACSVN/LHCbDIRAC/trunk LHCbDIRAC
  • Checkout tagged version of a complete project
    • cvs (Dirac only)
      mkdir -p DIRAC/DIRAC_v20r0
      cd DIRAC/DIRAC_v20r0
      cvs -d $DIRACCVS checkout -r DIRAC_v1r0 all
    • svn
      mkdir DIRAC
      cd DIRAC
      svn checkout $DIRACSVN/LHCbDIRAC/tags/LHCBDIRAC/LHCBDIRAC_v1r0


The commit is identical in CVS and Subversion
  • Commit the changes in the current directory (and subdirectories)
    • cvs
      cvs commit 
    • svn
      svn commit
  • Commit the changes of a single file
    • cvs
      cvs commit "myfile"
    • svn
      svn commit "myfile"


I want to distinguish between two use cases:
  • simple update: synchronize the local copy with the latest (or a specific) revision of the repository
  • update with tags: move from a tagged local version to the head one or to a branch

Simple Update

Nothing really special:
  • cvs
    cvs update
  • svn
    svn update
The way to select a revision or a moment in time a slightly different, but easy to sort out using the help.

Update with Tags

This is the complex part, since tags do not exists (as such) in Subversion. With SVN, tags are represented by copies of the trunk directory, so moving the working copy from a tag to another (or trunk or branch) means changing the path of the origin of the working copy.
  • Move the working copy from the current tag to the trunk/HEAD (assuming you are in the top directory of the package)
    • cvs
      cvs update -APd
    • svn
      svn switch $DIRACSVN/LHCbDIRAC/trunk/MyPackage
  • Move the working copy from the current tag to the another tag (assuming you are in the top directory of the package)
    • cvs
      cvs update -Pd -r other_tag
    • svn
      svn switch $DIRACSVN/LHCbDIRAC/tags/MyPackage/other_tag

Check for updates in the repository

To just check if there are changes in the repository that you didn't get yet, you can do a "dry-run" update with cvs. That does not exist in svn, you have to ask the status of the repository.
  • cvs
    cvs update -n
  • svn
    svn status -u
    svn status --show-updates

Comparison (diff)

  • Comparison between the base of the working copy and the working copy
    • cvs
      cvs diff -u
    • svn
      svn diff
  • Comparison between two tags (or branch, or trunk)
    • cvs
      cvs diff -u -r tag1 -r tag2
    • svn
      svn diff $DIRACSVN/LHCbDIRAC/tags/MyPackage/tag1 $DIRACSVN/LHCbDIRAC/tags/MyPackage/tag2

Tagging and Branching

  • Tag the working copy (assuming you are in the top directory of the package)
    • cvs
      cvs tag the_tag
    • svn
      svn cp .  $DIRACSVN/LHCbDIRAC/tags/MyPackage/the_tag
  • Tag the head version in the repository
    • cvs
      cvs rtag the_tag MyPackage
    • svn
      svn cp $DIRACSVN/LHCbDIRAC/trunk/MyPackage $DIRACSVN/LHCbDIRAC/tags/MyPackage/the_tag
Branching is done in CVS addind the option '-b' to the command 'tag', while in Subversion it is enough to replace tags with branches.


Help desk reported problems

These are just to remember them.

-- Main.JoelClosier - 08 Jun 2009

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Topic revision: r3 - 2009-12-07 - JoelClosier
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