Group Services Programming Guide and Reference

Dealing with adapter events with multiple aliases

The representation of adapters in subscription notifications is to use the provider_id and use the instance number to represent the physical adapter name. This allows the subscriber to associate the list of adapters from the notification with the physical adapters to which the events relate. However, this support is not sufficient in certain cases, where a single adapter is represented multiple times due to the use of IP alias addresses.

To allow subscribers to differentiate among the different aliases, if a subscription notification includes one or more adapters with multiple aliases, a ha_gs_special_block_t will be included that has an array of the IP alias address associated with the adapter listed in the changing membership. The ordering of the array entries will match that in the gs_current_membership and gs_changing_membership fields.

If the network is not defined as supporting multiple aliases:

The HA_GS_SUBSCRIPTION_SPECIAL_DATA will not be set into the gs_subscription_type field in the subscription notification.

• The client should simply act as it currently does, and use the instance number to associate the listed adapter with the physical adapter.
• The gs_subscription_special_data field will be NULL.

If the network is defined as supporting multiple aliases:

• HA_GS_SUBSCRIPTION_SPECIAL_DATA will be OR'ed into the gs_subscription_type field in the subscription notification.
• The gs_subscription_special_data field in the subscription notification will point to an ha_gs_special_data block.
  • The gs_special_block_count field will contain the count of ha_gs_special_block_t elements.
  • The gs_special_block_flags field will contain one or both of the following: HA_GS_CURRENT_ADAPTER_ALIAS_ARRAY and HA_GS_CHANGING_ADAPTER_ALIAS_ARRAY.
• The gs_subscription_special_data field in the subscription notification will point to one or more ha_gs_special_block_t elements.
  • If the subscription notification contains a list of providers in the gs_current_membership field, there will be a ha_gs_special_block_t with its gs_special_flag field containing HA_GS_CURRENT_ADAPTER_ALIAS_ARRAY.
  • If the subscription notification contains a list of providers in the gs_changing_membership field, there will be a ha_gs_special_block_t with its gs_special_flag field containing HA_GS_CHANGING_ADAPTER_ALIAS_ARRAY.
• For each ha_gs_special_block_t, the following will be true:
  • The gs_special_num_entries field will contain the same number of entries as the number of adapters that were listed in the gs_changing_membership field.
  • The gs_special_length field will contain 4.
  • The gs_special field will point to the array of entries, listed in the order matching the order of adapters in the gs_current_membership and gs_changing_membership fields. Each entry will contain the IP address of the adapter's alias affected by the notification (death or join).