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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:
log flag for the event is true.
up.
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.
Types:
Name = string()
Closes an event 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).
disk_log(3), eva(3), eva_sup(3), file(3), log(3)