Complex codebases could benefit from git submodule feature. Here’s a quick tutorial.

Clone the repo locally:

git clone git://<master_repo>/
cd <master_repo>

Initialize submodules, and update them:

git submodule init
git submodule update --remote

When a submodule changes:

git add -p
git commit -m 'comment'
git tag -a <release> -m "<release code>"
git submodule foreach git tag -a <release> -m "<release code>"
git push
git push --tags
git submodule foreach git push --tags

get release name from git:

git tag -n9