from libarchive.googlecode.com: Add a new "archive_read_disk" API
that provides the important service of reading metadata from the
disk. In particular, this will make it possible to remove all
knowledge of extended attributes, ACLs, etc, from clients such
as bsdtar and bsdcpio.
Closely related, this API also provides pluggable uid->uname
and gid->gname lookup and caching services similar to
the uname->uid and gname->gid services provided by archive_write_disk.
Remember this is also required for correct ACL management.
Documentation is still pending...
43a8e5f098