I am running CentOS 7 and was following a chapter in a book dealing with virtualization and creating storage pools. I successfully ran the following command, but I'm not sure what setting - - - - as the sourcepath actually does.

virsh pool-define-as rhpol_virsh dir - - - - /var/lib/libvirt/rhpol_virsh 

Description of command: Define the storage pool as type "dir" with the source path "----" and target /var/lib/libvirt/rhpol_virsh directory

I read the man pages and googled this topic, but I didn't find an explanation. Can someone point me in the right direction?