Use the following configuration file (also stored in fs.1.conf):

fs/	file	fs/

Mount the portal.  By default, every path will be based off of /.

% mkdir portal
% mount_portal /usr/share/examples/mount_portal/fs.1.conf `pwd`/portal
% cksum /etc/rc
1896381655 10514 /etc/rc
% cksum portal/fs/etc/rc
1896381655 10514 portal/fs/etc/rc

As it currently stands, the fs option is of limited usefulness.
The man page mentions that it can be used to "provide a
controlled escape path from a chrooted environment".
