Patent ID: 7904606

Claim:
A computer program product for processing a transport control channel program with chain linked branching at a control unit configured for communication with an input/output (I/O) subsystem in an I/O processing system, the computer program product comprising: a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising: receiving a login request message; transmitting a login accept message in response to the login request message, the login accept message including a maximum linked commands field indicating a maximum count of additional command messages after a first command message that the control unit supports; receiving a command message at the control unit from the I/O subsystem to perform an I/O operation, wherein the received command message is one of the first command message and the additional command messages; reading a chain linked flag in the received command message, the chain linked flag indicating that a subsequent command message for the I/O operation follows the received command message; reading a serialization flag in the received command message, the serialization flag requesting that device status be returned to the I/O subsystem in order to select the subsequent command message; executing one or more commands in the received command message; and transmitting the device status to the I/O subsystem in response to executing the one or more commands in combination with the serialization flag.