Jan: Efficient RAUC Updates using composefs

Traditionally, RAUC focused on A/B updates for whole partitions, either by using filesystem images or tar archives. While the image-based OS approach has many benefits, there are scenarios where more loosely coupled components need to be handle in addition to the root filesystem. In RAUC, these can be handled with using the new "artifact updates" support.

As a system might have many artifacts installed in parallel, such as for containers (systemd-nspawn or otherwise) and systemd-sysexts, efficient storage is important. In many cases, these are updated often, so download efficiency is important as well.

After evaluating multiple alternatives, we've now decided to integrate composefs. Besides solving the requirements above, it additionally provides the same level of integrity protection as a dm-verity root filesystem, which is important in systems using secure boot.

This talk will show how RAUC uses libcomposefs and the new use-cases supported by having an efficient content-addressed backing store with full authentication.