tempfiles.rs: remove duplicate tmpfiles entries

[HuijingHei]

rpm-ostree should scan the tmpfiles.d snippets at install time
and skip synthesizing entries if they are already specified.

As we may have confilicted tmpfile entries, like it will prevent
to cleanup of /var/tmp by systemd-tmpfiles-clean.service:
pkg-filesystem.conf has d /var/tmp 1777 root root - -
systemd's tmp.conf has q /var/tmp 1777 root root 30d

It is not as simple because the auto-conversion we do at package
import time may be duplicating a tmpfiles.d dropin that lives
in a separate package.

With Jonathan's suggestion:

• the importer code puts the generated tmpfiles.d dropins in e.g.
  /usr/lib/rpm-ostree/tmpfiles.d instead of the canonical place
• deduplicate_tmpfiles_entries() builds one hashmap from
  /usr/lib/rpm-ostree/tmpfiles.d and another from /usr/lib/tmpfiles.d
  and generates rpm-ostree-autovar.conf from the difference
• delete_package_from_root() is updated to remove from
  /usr/lib/rpm-ostree/tmpfiles.d

See #26 (comment)

Fixes #26

[openshift-ci]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[HuijingHei]

/holdon

[jlebon]

Thanks for working on this!

[HuijingHei]

The build always get error, but none error on local container, need more investigation.

error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in closure return types
  --> rust/src/tmpfiles.rs:77:66
   |
77 | pub(crate) fn save_tmpfile_entries(tmpfiles_dir: &Dir) -> Result<impl Iterator<Item = String>> {
   |                                                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[HuijingHei]

error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in closure return types
  --> rust/src/tmpfiles.rs:77:66
   |
77 | pub(crate) fn save_tmpfile_entries(tmpfiles_dir: &Dir) -> Result<impl Iterator<Item = String>> {
   |                                                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Thanks a lot for @jlebon 's pointer:
make sure that you're not missing a closing parenthesis or bracket somewhere before that line (line 77)

Create issue rust-lang/impl-trait-initiative#18 to track and remove the context for workaround.

[cgwalters]

One thing that will be confusing (and slightly problematic) is that today we don't invalidate the cache when the importer logic changes. And so previously imported packages will still have the old path until they stop being cached.

I've been bitten by this in coreos-assembler builds.

Maybe in this case it's OK because we still handle the old semantics.

[HuijingHei]

Yes, that is a problem, how about checking if there is old path like usr/lib/tmpfiles.d/pkg-{pkg_name}.conf, then move it to usr/lib/rpm-ostree/tmpfiles.d/{pkg_name}.conf in earlier of deduplicate_tmpfiles_entries()?

[cgwalters]

This is looking pretty good! I had one thing I'd like to fix but it can come later.

While looking at this I ended up writing a unit test because it's way faster to test out changes that way.

[jlebon]

Nice work @HuijingHei!

[HuijingHei]

Thanks @cgwalters @jlebon a lot for the pointer and guidance, also learn a lot about rust closure.

[travier]

This is potentially breaking updates on Silverblue:

• Broken update since rpm-ostree-2023.12-1.fc39.x86_64 fedora-silverblue/issue-tracker#523
• https://bodhi.fedoraproject.org/updates/FEDORA-2023-b147ec959a