compose postprocess not handling rpm db in /usr/lib/sysimage

[alexlarsson]

In automotive, we're using the "traditional" osbuild approach to building an ostree image, similar to say fedora-ostree-image.mpp.yaml. This does basically a dnf install $rpms, and then rpm-ostree compose postprocess to create the tree which is made the ostree commit.

In cs9, after the dnf install the rpm db is in /var/lib/rpm, and all works fine. In the postprocess stage, this is moved to /usr/share/rpm and the rpm config is updated to read from ther.

However, in cs10, the rpm db is in /usr/lib/sysimage/rpm, and /var/lib/rpm is a symlink to that.
When we reach rpmostree_rootfs_postprocess_common() and try to move /var/lib/rpm it sees its a symlink and not a directory, so it does nothing, but then it changes the rpm config anyway, even though /usr/share/rpm doesn't even exist.

Long term i think we want to just keep using /usr/lib/sysimage/rpm (as in #5455), but for now this should probably be fixed to detect this case and move from /usr/lib/sysimage/rpm to /var/lib/rpm.

[cgwalters]

but for now this should probably be fixed to detect this case and move from /usr/lib/sysimage/rpm to /var/lib/rpm.

In the immediate term it should also be possible to do the move in the osbuild pipeline before invoking rpm-ostree. But yes, happy to take a patch here too.

[alexlarsson]

For now that is what I'm doing, as we want to get onto cs10 asap: https://gitlab.com/CentOS/automotive/src/automotive-image-builder/-/merge_requests/376

However, it feels like it would be better if rpm-ostree did this correctly in the first place. I'll have a look at that later.