This section explains how to use the In-Band Control (IBC) Messaging Application Programming Interface (API). VVR supports a special set of ioctls for accessing the IBC messaging facility. These ioctl commands allow an application to register with the facility, send and receive IBC messages, and unregister from the facility.

The IBC facility enables applications to insert application-defined control messages inband with the Primary RVG update stream being replicated to a Secondary RVG. When an IBC message arrives at the Secondary RVG, replication is frozen until directed to unfreeze by a companion application residing on the Secondary host. In this way, an application can signal a Secondary RVG that some user-defined event has occurred relative to the update stream, such as a point of application-level consistency, and enable the Secondary RVG to take some action while replication is frozen.