Inverse overlay mount possibility

[Gerharddc]

The documentation at https://docs.podman.io/en/latest/markdown/podman-run.1.html#volume-v-source-volume-host-dir-container-dir-options states the following about overlay volume mounts:

The :O flag tells Podman to mount the directory from the host as a temporary storage using the overlay file system. The container processes can modify content within the mountpoint which is stored in the container storage in a separate directory. In overlay terms, the source directory is the lower, and the container storage directory is the upper. Modifications to the mount point are destroyed when the container finishes executing, similar to a tmpfs mount point being unmounted.

However, I want to have the exact opposite. I.e. I want to mount a host directory as an overlay over a read-only container directory. The reason I want this is because I want to prepare a home directory when I build a container but then I want any changes inside this home directory to be persisted to a non-volatile host directory. This is so that changes to the home directory inside the container do not get lost when the container is destroyed or rebuilt.

Is this already possible in some way or something to request a feature for?

[nalind]

Unless I'm misunderstanding what you're saying, that's how volume mounts work without the "O" flag.

[Gerharddc]

Not quite. A normal volume mount completely overrides the existing directory in my experience. So if I volume mount something to /home/user for instance, it will completely hide everything that the container has inside that directory and only show what is present in the host directory that got mounted. I am looking for something that behaves like an overlay instead (i.e. files from both directories are visible and writes get persisted to the host/upper directory).