Function read_tmpfiles_from_dir 

pub(crate) fn read_tmpfiles_from_dir(
    rootfs: &Dir,
    dir_path: &str,
    resolver: &PathResolver,
    generation: &mut BootcTmpfilesGeneration,
) -> Result<BTreeMap<PathIdentity, String>>

Read all tmpfiles.d entries from a single directory. Declared paths are canonicalized against rootfs (see PathResolver) so the returned map is keyed by physical identity.