F36: Complete adaption to https://fedoraproject.org/wiki/Changes/RelocateRPMToUsr

[lucab]

As part of F36 changes, there is this rpmdb move to /usr: https://fedoraproject.org/wiki/Changes/RelocateRPMToUsr

It just landed in rawhide with this commit: https://src.fedoraproject.org/rpms/rpm/c/0b9f813cd529a1fc7c1336e62d82b90c81f517f1?branch=rawhide

So starting with rpm-4.17.0-7 the package is shipping an empty directory at /usr/lib/sysimage/rpm.

FCOS composes are now failing with:

Finalizing rootfs: Hardlinking rpmdb to base location: File exists (os error 17)

This is because we currently try to create a symlink there to our rpmdb:

rpm-ostree/rust/src/composepost.rs

Lines 982 to 984 in ce954e8

	// And write a symlink from the proposed standard /usr/lib/sysimage/rpm
	// to our /usr/share/rpm - eventually we will invert this.
	rootfs.symlink(RPMOSTREE_SYSIMAGE_RPMDB, "../../share/rpm")?;

[lucab]

I started looking into this, and then realized it has further implications on other parts of the codebase.

As a transitory measure, perhaps we can try starting to hardlink the content of /usr/share/rpm/ under /usr/lib/sysimage/rpm.
Then complete the migration by using /usr/lib/sysimage/rpm directly, but that would involve further %_dbpath friction.

[jlebon]

As a transitory measure, perhaps we can try starting to hardlink the content of /usr/share/rpm/ under /usr/lib/sysimage/rpm.

Could we also just replace the directory back to a symlink? That way we don't have to think about whether rpm or other things do tempfile & replace or in-place modifications.

Doing what's in the comment in the code snippet above is what we should do eventually, but we should think through it carefully, esp. around upgrades now that we ship a macro dropin to set it even on client systems.

[cgwalters]

OK, retitling this issue; let's keep it open to track:

• inverting things so that /usr/share/rpm is a symlink to /usr/lib/sysimage/rpm
• Stop changing %_dbpath if it's already what we want (but we need to handle cross-builds i.e. targeting rhel8 from a fedora container)

[cgwalters]

Yeah at some point we will have to address this tech debt, it keeps coming up and is really painful when it does. Right now I'm working on https://gitlab.com/fedora/bootc/tracker/-/issues/32 and we're creating a pattern of doing this in an nutshell:

FROM quay.io/fedora/fedora:rawhide as repos
# See https://github.com/coreos/rpm-ostree/issues/3397
RUN ln -sr /usr/lib/sysimage/rpm /usr/share/rpm

# BOOTSTRAPPING: This can be any image that has the following packages.
FROM fedora as builder
RUN dnf -y install rpm-ostree selinux-policy-targeted sqlite
... # copy sources
RUN rpm-ostree experimental compose rootfs --source-root=/repos base/manifest.yaml /target-rootfs

But notice I had to add that symlink in the repos container.

It's because rpmostree-core.cxx overrides _dbpath to /usr/share/rpm before we init libdnf.