Patent ID: 8392619

Claim:
A non-transitory computer program product for providing indirect data addressing at an input/output (I/O) subsystem of an I/O processing system, the computer program product comprising: a non-transitory tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising: receiving a control word for an I/O operation, the control word including an indirect data address for data associated with the I/O operation, the indirect data address including a starting location of a list of storage addresses that collectively specify the data; forwarding a transport command control block (TCCB) from the channel subsystem to a control unit controlling an I/O device for executing the I/O operation, the TCCB including at least one device control word (DCW) and the TCCB being obtained by a location identified by a transport control word (TCW); gathering the data, wherein gathering comprises accessing entries of the list until a last entry is accessed, wherein accessing includes 1) and 2): 1) based on an entry of the list comprising a not-set first flag and a corresponding first storage address, gathering data from a corresponding storage location; and 2) based on an entry of the list comprising a set first flag and a corresponding second storage address, obtaining a next entry of the list from a second storage location, wherein the second storage address is located contiguously to the first storage address when an entry of the list comprises the not-set first flag, and the second storage address is located non-contiguously to the first storage address when an entry of the list comprises the set first flag; and transmitting the gathered data to the control unit in the I/O processing system.