Static deltas for offline updates

OSTree supports generating “self-contained” static delta files, via an invocation similar to the following:

$ ostree --repo=/path/to/repo static-delta generate --min-fallback-size=0 --filename=delta-update-file --from=<from> <to>

Note the usage of --min-fallback-size=0 to ensure that the delta is self-contained.

Then, you can copy delta-update-file to a USB key or similar, and a target system can apply it via e.g.:

$ ostree --repo=/ostree/repo static-delta apply-offline /path/to/delta-update-file

The above invocation will merely apply the content into the repository. To make it bootable, this will then need to be further followed up by e.g. ostree admin deploy <to> or with a higher level tool such as rpm-ostree, via rpm-ostree deploy :<to>.