%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1996-2009. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%
-module(snmp_shadow_table).
-export([table_func/2, table_func/4]).
-include("snmpa_internal.hrl").
-record(time_stamp, {key, data}).
-define(verify(Expr, Error), verify(catch Expr, Error, ?FILE, ?LINE)).
verify(Res, Error, File, Line) ->
case Res of
{atomic, _} ->
Res;
ok ->
Res;
_ ->
error_msg("~s(~w): crashed ~p -> ~p ~p~n",
[File, Line, Error, Res, process_info(self())]),
Res
end.
%%%-----------------------------------------------------------------
%%% This module contains generic functions for implementing an SNMP
%%% table as a 'shadow'-table in Mnesia. This means that for the
%%% SNMP table, there exists one Mnesia table with all information
%%% of the table.
%%% The Mnesia table is updated whenever an SNMP request is issued
%%% for the table and a specified amount of time has past since the
%%% last update.
%%% This is implemented as instrumentation functions to be used
%%% for the table.
%%%-----------------------------------------------------------------
create_time_stamp_table() ->
Props = [{type, set},
{attributes, record_info(fields, time_stamp)}],
create_table(time_stamp, Props, ram_copies, false),
NRef =
case mnesia:dirty_read({time_stamp, ref_count}) of
[] -> 1;
[#time_stamp{data = Ref}] -> Ref + 1
end,
ok = mnesia:dirty_write(#time_stamp{key = ref_count, data = NRef}).
delete_time_stamp_table() ->
Tab = time_stamp,
case catch mnesia:dirty_read({Tab, ref_count}) of
{'EXIT', _Reason} ->
delete_table(Tab);
[] ->
delete_table(Tab);
[#time_stamp{data = 1}] ->
delete_table(Tab);
[#time_stamp{data = Ref}] ->
ok = mnesia:dirty_write(#time_stamp{key = ref_count, data = Ref - 1})
end.
update(Name, UpdateFunc, Interval) ->
CurrentTime = get_time(),
case mnesia:dirty_read({time_stamp, Name}) of
[#time_stamp{data = Expire}] when CurrentTime =< Expire -> ok;
_ ->
UpdateFunc(),
ok = mnesia:dirty_write(#time_stamp{key = Name,
data = CurrentTime + Interval})
end.
%%-----------------------------------------------------------------
%% Func: table_func(Op, Extra)
%% table_func(Op, RowIndex, Cols, Extra)
%% Args: Extra = {Name, SnmpKey, Attributes, Interval, UpdateFunc}
%% Purpose: Instrumentation function for the table.
%% Name is the name of the table
%% SnmpKey is the snmpkey as it should be specifed in order
%% to create the Mnesia table as an SNMP table
%% Attributes is the attributes as it should be specifed in order
%% to create the Mnesia table as an SNMP table
%% Interval is the minimum time in milliseconds between two
%% updates of the table
%% UpdateFunc is a function with no arguments that is called
%% whenever the table must be updated
%% Returns: As specified for an SNMP table instrumentation function.
%%-----------------------------------------------------------------
table_func(new, {Name, SnmpKey, Attribs, _Interval, _UpdateFunc}) ->
create_time_stamp_table(),
Props = [{type, set},
{snmp, [{key, SnmpKey}]},
{attributes, Attribs}],
create_table(Name, Props, ram_copies, true);
table_func(delete, {Name, _SnmpKey, _Attribs, _Interval, _UpdateFunc}) ->
delete_time_stamp_table(),
delete_table(Name).
table_func(Op, RowIndex, Cols,
{Name, _SnmpKey, _Attribs, Interval, UpdateFunc}) ->
update(Name, UpdateFunc, Interval),
snmp_generic:table_func(Op, RowIndex, Cols, {Name, mnesia}).
get_time() ->
{M,S,U} = erlang:now(),
1000000000 * M + 1000 * S + (U div 1000).
%%-----------------------------------------------------------------
%% Urrk.
%% We want named tables, without schema info; the tables should
%% be locally named, but if the node crashes, info about the
%% table shouldn't be kept. We could use ets tables for this.
%% BUT, we also want the snmp functionality, therefore we must
%% use mnesia.
%% The problem arises when the node that implements these tables
%% crashes, and another node takes over the MIB-implementations.
%% That node cannot create the shadow tables again, because they
%% already exist (according to mnesia...). Therefore, we must
%% check if we maybe must delete the table first, and then create
%% it again.
%%-----------------------------------------------------------------
create_table(Tab, Props, Storage, DeleteAll) ->
case lists:member(Tab, mnesia:system_info(tables)) of
true ->
case mnesia:table_info(Tab, storage_type) of
unknown ->
?verify(mnesia:add_table_copy(Tab, node(), Storage),
[add_table_copy, Tab, node(), Storage]);
Storage when DeleteAll == true ->
delete_all(Tab);
_ ->
ignore
end;
false ->
Nodes = [node()],
Props2 = [{local_content, true}, {Storage, Nodes}] ++ Props,
?verify(mnesia:create_table(Tab, Props2),
[create_table, Tab, Props2])
end.
delete_all(Tab) ->
delete_all(mnesia:dirty_first(Tab), Tab).
delete_all('$end_of_table', _Tab) ->
ok;
delete_all(Key, Tab) ->
ok = mnesia:dirty_delete({Tab, Key}),
delete_all(mnesia:dirty_next(Tab, Key), Tab).
delete_table(Tab) ->
case lists:member(Tab, mnesia:system_info(tables)) of
true ->
case ?verify(mnesia:del_table_copy(Tab, node()),
[del_table_copy, Tab, node()]) of
{atomic, ok} ->
ok;
{aborted, _Reason} ->
catch delete_all(Tab),
ok
end;
false ->
ok
end.
%%-----------------------------------------------------------------
error_msg(F, A) ->
?snmpa_error(F, A).
