Importing Modules With Full History Into Git

Here is how you can import a kamailio module with full history (that means all previous commits done on the svn will also be visible in git) into the sip-router git repository.

First off, make sure you have a local copy of the sip-router git repository with kamailio history merged into it. You can find a step-by-step guide here.

I suppose that the module you want to import into the git repository will be based on the sources present in the kamailio svn trunk, so as the next step create a new branch based on the kamailio trunk:

$ git co -b sqlops_filtered km/trunk

The name of the new branch is sqlops_filtered because I am importing kamailio sqlops module, "_filtered" because this branch will be used to filter commits.

Like revision numbers in svn (and unlike versions in cvs), git commits, identified by those cryptic sha1 hashes, record the state of all files in the source tree at the time when the commit was made. But this is a problem because we only one to import the files in modules/sqlops directory and ignore all other files outside this directory. Even if you try to checkout an older commit which changed only files within modules/sqlops, you always get a full source tree, including files of all other modules. There is no way you can get a particular revision of selected files only–like you can do it with cvs.

But there is a solution: git-filter-branch. This is a handy git command which (among other things) can walk through all commits in the history of the current branch and tranform the commits into new commits with selected files only. To include only files in modules/sqlops we can do the following:

$ git-filter-branch --subdirectory-filter modules/sqlops

The command rewrite the history of the current branch, your current branch should be "sqlops_filtered" if you followed this guide from the beginning. If you investigate the history of the branch with git log, you should see only commits that are related to files in modules/sqlops. (The module contained only one commit at the time of writing of this memo so don't be surprised if you only see one commit in the history).

If you examine your current working directory now, you'll notice that the directory contains files from modules/sqlops in the top level directory. We need to put them back into modules/sqlopts before we can merge the branch into sip-router tree, this can be done with git-filter-branch again. But before we can run the command second time, we need to remove some residual files from the previous run:

$ rm -rf .git/refs/original

And the following command will move all the files back to modules/sqlops subdirectory:

$ git-filter-branch --index-filter 'git ls-files -s |
   sed "s-\t-&modules/sqlopt/-" |
   GIT_INDEX_FILE=$GIT_INDEX_FILE.new git update-index --index-info &&
   mv $GIT_INDEX_FILE.new $GIT_INDEX_FILE' HEAD

The previous command might look a little scary, but it is documented in man git-filter-branch if you are interested in details.

If you examine your current working directory now, it should contain modules directory with sqlops subdirectory and all the module files there. This branch is now ready to be merged into the sip-router tree, so create a new branch, for example sqlops, based on the sip-router master branch:

$ git co -b sqlops sr/master

And now you can merge branch sqlops_filtered into the newly created branch:

$ git merge sqlops_filtered

And if everything went well, congratulations, you successfully imported your first kamailio module into the sip-router git repository. Branch "sqlops_filtered" is no more needed so you can safely delete it.