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A NOF application can use the REGISTER_INDICATION_SINK verb to request information about changes to the SNAP-IX configuration or to the status of its resources. SNAP-IX then sends an indication message to the application each time a change occurs.
For a complete list of indications that an application can request, see NOF Indications.
Except for CONFIG_INDICATION, NOF_STATUS_INDICATION, and SNA_NET_INDICATION, each indication is returned when a resource of the specified type changes its status. For example, if the application registers for DLC indications, SNAP-IX sends a DLC_INDICATION message to the application each time a DLC becomes active or inactive.
An indication returns summary information about the change that has occurred. If necessary, the application can then issue the appropriate QUERY_* verb to obtain more detailed information.
If the local node is short of resources, it can temporarily suppress indications and not send them to applications. When the resource shortage condition clears, and the local node subsequently generates an indication of a type that it has previously suppressed, it then sets a parameter on the indication to inform the application that one or more previous indications of this type have been lost. The application should then issue QUERY_* verbs for the appropriate resource type to determine the current state of resources.
For more information about registering to receive indications, see REGISTER_INDICATION_SINK. For more information about individual indications, see NOF Indications.
An application can register to receive information about changes to the configuration of a particular target (the domain configuration file, a running node, or an inactive node). This enables it to keep track of changes that can be made by other NOF applications or by the administration programs. To do this, the application registers as for other indications, specifying CONFIG_INDICATION as the requested indication type.
No specific VCB structure is associated with this indication type. Instead, when a change to the configuration occurs, SNAP-IX indicates this change to the application by sending a copy of the completed VCB from the NOF verb that made the change.
For more information about configuration indications, see CONFIG_INDICATION.
An application can register to receive information about changes to the SNA network file sna.net on the master server. This enables the application to keep track of changes to this file that can be made by other NOF applications or by the command-line administration program. To do this, the application registers as for other indications, specifying SNA_NET_INDICATION as the requested indication type.
Two VCB structures are associated with this indication type:
ADD_BACKUP (indicating that a backup server has been added to the end of the file)
DELETE_BACKUP (indicating that an unused backup server has been removed from the file)
Registering with a type of SNA_NET_INDICATION will return an ADD_BACKUP indication when a backup server is added or a DELETE_BACKUP indication when a server is deleted; the application does not need to register separately for each of these indications. In each case, the format of the indication is a copy of the completed VCB from the NOF verb that made the change.
For more information about SNA network file indications, see SNA_NET_INDICATION.
SNAP-IX sends a NOF status indication to a registered NOF application when the application can no longer access its target node or file (because the SNAP-IX software on the target computer has been stopped or because the communications path to this computer has been lost). If the application is registered to receive indications from the master configuration file, this indication is also returned if another server takes over as master (and therefore the target file is no longer the master configuration file).
The application does not need to register explicitly to receive this indication; SNAP-IX returns it to any application that has registered for any type of NOF indications on the appropriate target. The indication is returned on the callback routine that the application supplied to the REGISTER_INDICATION_SINK verb (or to the first REGISTER_INDICATION_SINK verb, if the application has issued more than one).
After the application receives an indication that the target has failed, all subsequent verbs using the relevant target handle will be rejected, except for DISCONNECT_NODE or CLOSE_FILE (to free the target handle). In addition, any registrations for indications on this target handle will be lost; in order to continue receiving indications when the target becomes available, the application must connect again to the target and register again for the required indications.
For more information about NOF status indications, see NOF Indications.
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