Any directory passed to --prefer-pkgs will be searched for a repodata
directory. If the directory does not contain a repodata directory, then
each ancestor directory is checked. This allows for the user error of
specifying an individual architecture directory (e.g. x86_64) instead of the
parent repository directory that contains the repodata:
repository/
x86_64/
*.rpm
repodata/
*.xml.gz
The use case for this feature is it allows snapshots of the OBS repositories
to be offloaded to an network-attached filesystem. repodata directories are
used as the xml.gz files are faster to read than the 100s of rpms in a given
snapshot. These snapshots are used to track older rpm sets that may be
deployed for testing.