A computer detects a request by a process for access to a shadow control page, wherein the shadow control page allows the process access to one or more devices. The computer assigns the shadow control page and a key to the process associated with the request. The computer detects a request by the process via the assigned shadow control page for creation of a subset of devices from the one or more devices. The computer inputs information detailing an association between the subset of devices and the assigned key into a subset definition table, wherein the subset definition table includes one or more keys and one or more corresponding subsets.