Patent ID: 8990439
Filing Date: 2015-03-24
Classification: G06F

Abstract:
1. A computer program product for performing an input/output (I/O) operation initiated by an I/O operation instruction at a host computer system configured for communication with a control unit, 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: sending a transport mode command message from a channel subsystem in the host computer system to the control unit to initiate the I/O operation, the command message including a command for data to be transferred from the host computer system to an I/O device controlled by the control unit; and sending a data transfer message to the control unit, the data transfer message having an amount of the data to be transferred, the amount of the data to be transferred to be less than or equal to a maximum amount of data, the maximum amount of data corresponding to a number of buffers associated with the control unit and a size of each of the number of buffers, the number of buffers indicated by a buffer credit value maintained in the host computer system, and the size indicated by a buffer size value maintained in the host computer system, the buffer size value received from the control unit during initialization of a link between the control unit and the channel subsystem.