We currently do overlayfs for /etc in composefs-rs.

This has two major downsides:

• no official API to reset state (i.e. reset a file to the default from the image) without manually doing changes in the upper layer of overlayfs
• there is only one copy of /etc (instead of one copy of /etc per deployment in the current ostree case), thus you can not easily rollback to a previous deployment with the previous config

We touched a little bit on this in:

• Suggested layout for sysroot for bootc integration containers/composefs-rs#38
• bootc composefs-native backend #1190

Thus we would like to implement in bootc support for an ostree-like 3 way merge for the composefs native case that mirrors how ostree works today: https://ostreedev.github.io/ostree/deployment/#contents-of-a-deployment