eva_log

MODULE

eva_log

MODULE SUMMARY

Log functionality for events and alarms in EVA

DESCRIPTION

The EVA log service uses the generic Log Control service to implement log functionality for events and alarms defined in EVA.

In the rest of this description, the term event refers to both events and alarms as defined in EVA.

This log functionality supports logging of events from EVA. It uses the module disk_log for logging of events, using the internal log format defined by disk_log. There can be several logs active at the same time. Each log uses a filter function to decide whether an event should be stored in the log or not.

There are several ways to control whether an event should be stored in a log or not. First of all, eva_log checks if the log flag in eventTable is set (see eva(3)). If it is set to false, the event is not stored in any log, even if there are logs that are configured to log the event. In this way, logging of individual events can be turned on/off by a manager. If the log flag is true, eva_log checks the operational status of the log. If it is down, the event is not stored. If it is up, the associated filter function is called. If this function returns true, the event is stored, otherwise it is discarded. To summarize, all these conditions must be true for an event to be stored:

• The log flag for the event is true.
  


• The operational status for the log is up.
  


• The filter function for the log returns true, when applied to the event.
  



There is a concept of a default log. The default log is used to log any event that has the log flag in eventTable set to true, but no log is currently able to store the event (or there is no other log defined to log the event). The usage of the default log is optional.

EXPORTS

close(Name) -> ok

Types:
Name = string()

Closes an event log.

get_logs() -> [#eva_log]

Returns all event logs known to eva_log. The record #eva_log is defined in the file eva_log.hrl.

open(Name, FilterFunction, WrapTime) -> ok | {error, Reason}

Types:
Name = string()
FilterFunction = {M, F, A}
M = F = atom()
A = list()
WrapTime = integer()

Makes eva_log aware of the log Name. The log must be an open disk_log log, with log format internal. This function will call log:open(Name, eva_log, WrapTime) in order to register the log in the generic Log Control service.

The FilterFunction is used when an event is received from EVA. It is then called as M:F(Event ++ A), and supposed to return true if the event should be stored in the log. All other return values makes the event be discarded. The filter function can be exchanged during runtime, by using set_filter/2.

set_filter(Name, FilterFunction)

Types:
Name = string()
FilterFunction = {M, F, A}
M = F = atom()
A = list()

Changes the filter function for the event log.

start_link()
start_link(DefaultLog) -> {ok, Pid} | {error, Reason}

Types:
DefaultLog = {Name, WrapTime} | false
Name = string()
WrapTime = integer()

Starts the eva log service. This function can be used to include the service in a supervisor. Normally, functions in the supervisor eva_sup can be used instead.

DefaultLog is either the name and wrap time of the default log to use, or false. If it is not false, the log must have been created with disk_log, just as any other log (see open/3). The default log is used to log any event that has the log flag set to true in eventTable, but no log has actually logged the event, either because there was no such log, or the log had operational status down. If the DefaultLog argument is omitted, it defaults to false. If the default log is used, it will be made known to the generic Log Control service as log:open(Name, eva_log, WrapTime).

SEE ALSO

disk_log(3), eva(3), eva_sup(3), file(3), log(3)

AUTHORS

Martin Björklund - support@erlang.ericsson.se