Git export with hardlinks

This package implements a git export command that can be given a list of already exported worktrees and the tree SHAs these worktrees correspond too. For every file to export it then looks in the existing worktrees whether an identical file is already present and in that case hardlinks to the new export location instead of writing the same file again.

Use Case: A git based web deployment system that exports git trees to be served by a web server. Every new deployment is written to a new folder. After the export, the web server should start serving new requests from the new folder.

Usage

usage: git_export_hardlinks.py [-h] [-l [LINK [LINK ...]]] treeish target

git export that reuses already existing exports and hardlinks files from them.

positional arguments:
  treeish               treeish (ref, commit, tree) to export
  target                location where to export to

optional arguments:
  -h, --help            show this help message and exit
  -l [LINK [LINK ...]], --link [LINK [LINK ...]]
                        existing export to hardlink from: TREEISH,PATH. Newest
                        first

Be aware of the dangers of hardlinks. Hardlinks on linux do not have copy-on-
write semantics! This command also does not verify the integrity of old
exported trees. Use git reset --hard after this command to guarantee a correct
export.

Examples

Export a git tag:

./git_export_hardlinks.py v0.1 /var/lib/deployments/v0.1/export

Export a git commit:

./git_export_hardlinks.py b86a93d9ca0d272410586f18a95b41c3b9a600ab /var/lib/deployments/2012-02-05

Export a git branch and link to previous trees:

./git_export_hardlinks.py \
    -l 0b96bf5f72d2c282b31726b3fbff279a89220b14,/srv/deploy/2013-02-13_10-08-13 \
    -l aae9deb62ad0c8d1ba64c75845a0809da485f42e,/srv/deploy/2013-02-12_14-09-15 \
    -l fe2665df0df31da3098de376268d4cd25ea6a6b7,/srv/deploy/2013-02-12_12-57-55 \
    -- 2013-02-14_17-44-12 /srv/deploy/2013-02-14_17-44-12

Notes:

• The double dash (--) before the positional arguments works around a python argparse issue.
• The exported trees are listed from newest to oldest. It is assumed that the newest tree is also the most similar tree.
• You might want to generate the options for this commands with some shell scripting.
• The command can not parse git refspecs like HEAD{2}.
• You might want to limit the number of -l arguments. Otherwise git_export_hardlink will search all trees before giving up and writing the file from the git object store.

License

Apache 2.0. I don't care too much about licenses. Ask me if you'd prefer another one.