This plugin mounts /var/cache/yum of your machine to chroot. It mount directory config_opts['plugin_conf']['root_cache_opts']['dir'], which is be default /var/cache/mock/NAME_OF_CHROOT/yum_cache/ and mount it as /var/cache/yum in chroot. It is enabled by default.

This plugin is enabled by default and has the following values built-in:

config_opts['plugin_conf']['yum_cache_enable'] = True
config_opts['plugin_conf']['yum_cache_opts'] = {}
config_opts['plugin_conf']['yum_cache_opts']['max_age_days'] = 30
config_opts['plugin_conf']['yum_cache_opts']['max_metadata_age_days'] = 30
config_opts['plugin_conf']['yum_cache_opts']['dir'] = "%(cache_topdir)s/%(root)s/yum_cache/"

• max_age_days - when files in cache directory is older than this number of days, then such files are removed
• max_metadata_age_days - when metadata (everything with suffix: ".sqlite", ".xml", ".bz2", ".gz") in cache directory is older than this number of days, then such files are removed.
• dir - where to put cached files