1. A method in a data processing system for controlling data flow, the method comprising: monitoring a data flow between a host data processing system and a storage data processing system for an event requiring a control of the data flow; responsive to detecting an event requiring a control of the data flow, an initiator one of the host data processing system and the storage data processing system forming a control message for the data flow, wherein the control message includes an identified data type that is affected by the event, an identified action to be taken with respect to the identified data type, and an identified time duration for the identified action to be in effect, wherein the identified action to be taken with respect to the identified data and the identified time duration for the identified action to be in effect are specified by the initiator one of the host data processing system and the storage data processing system; the initiator one of the host data processing system and the storage data processing system sending the control message to a receiver one of the host data processing system and the storage data processing system, wherein the receiver one of the host data processing system and the storage data processing system modifies the data flow by taking the identified action with respect to the identified data type that is affected by the event for the identified time duration specified in the control message; and the receiver one of the host data processing system and the storage data processing system querying the initiator one of the host data processing system and the storage data processing system for obtaining an update on the identified time duration for coordinating the data flow, and for verifying responsiveness of the initiator one of the host data processing system and the storage data processing system.