A structure describing a system capability change.
A system capability change is a system level transition from a set of system capabilities to a new set of system capabilities. Power management sends a kIOMessageSystemCapabilityChange message and provides this structure as the message data (by reference) to gIOPriorityPowerStateInterest clients when system capability changes.
An identifier for this message notification. Clients with pending I/O can signal completion by calling allowPowerChange() with this value as the argument. Clients that are able to process the notification synchronously should ignore this field.
A return value to the caller indicating the maximum time in microseconds to wait for the allowPowerChange() call. The default value is zero, which indicates the client processing has finished, and power management should not wait for an allowPowerChange() call.