The Utilities/cmlibarchive directory contains a reduced distribution of the libarchive source tree with only the library source code and CMake build system. It is not a submodule; the actual content is part of our source tree and changes can be made and committed directly. We update from upstream using Git's "subtree" merge strategy. A special branch contains commits of upstream libarchive snapshots and nothing else. No Git ref points explicitly to the head of this branch, but it is merged into our history. Update libarchive from upstream as follows. Create a local branch to explicitly reference the upstream snapshot branch head: git branch libarchive-upstream 37f225b7 Use a temporary directory to checkout the branch: mkdir libarchive-tmp cd libarchive-tmp git init git pull .. libarchive-upstream rm -rf * Now place the (reduced) libarchive content in this directory. See instructions shown by git log 37f225b7 for help extracting the content from the upstream svn repo. Then run the following commands to commit the new version. Substitute the appropriate date and version number: git add --all GIT_AUTHOR_NAME='LibArchive Upstream' \ GIT_AUTHOR_EMAIL='libarchive-discuss@googlegroups.com' \ GIT_AUTHOR_DATE='Mon Apr 14 19:19:05 2014 -0700' \ git commit -m 'libarchive 3.1.2-246-ga5a5d28b (reduced)' && git commit --amend Edit the commit message to describe the procedure used to obtain the content. Then push the changes back up to the main local repository: git push .. HEAD:libarchive-upstream cd .. rm -rf libarchive-tmp Create a topic in the main repository on which to perform the update: git checkout -b update-libarchive master Merge the libarchive-upstream branch as a subtree: git merge -s recursive -X subtree=Utilities/cmlibarchive \ libarchive-upstream If there are conflicts, resolve them and commit. Build and test the tree. Commit any additional changes needed to succeed. Finally, run git rev-parse --short=8 libarchive-upstream to get the commit from which the libarchive-upstream branch must be started on the next update. Edit the "git branch libarchive-upstream" line above to record it, and commit this file.