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%% ``The contents of this file are subject to the Erlang Public License,
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%% Version 1.1, (the "License"); you may not use this file except in
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%% compliance with the License. You should have received a copy of the
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%% Erlang Public License along with this software. If not, it can be
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%% retrieved via the world wide web at http://www.erlang.org/.
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%% Software distributed under the License is distributed on an "AS IS"
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%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
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%% the License for the specific language governing rights and limitations
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%% The Initial Developer of the Original Code is Ericsson Utvecklings AB.
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%% Portions created by Ericsson are Copyright 1999, Ericsson Utvecklings
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%% AB. All Rights Reserved.''
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-module(snmp_shadow_table).
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-export([table_func/2, table_func/4]).
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-include("snmpa_internal.hrl").
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-record(time_stamp, {key, data}).
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-define(verify(Expr, Error), verify(catch Expr, Error, ?FILE, ?LINE)).
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verify(Res, Error, File, Line) ->
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error_msg("~s(~w): crashed ~p -> ~p ~p~n",
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[File, Line, Error, Res, process_info(self())]),
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%%%-----------------------------------------------------------------
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%%% This module contains generic functions for implementing an SNMP
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%%% table as a 'shadow'-table in Mnesia. This means that for the
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%%% SNMP table, there exists one Mnesia table with all information
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%%% The Mnesia table is updated whenever an SNMP request is issued
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%%% for the table and a specified amount of time has past since the
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%%% This is implemented as instrumentation functions to be used
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%%%-----------------------------------------------------------------
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create_time_stamp_table() ->
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{attributes, record_info(fields, time_stamp)}],
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create_table(time_stamp, Props, ram_copies, false),
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case mnesia:dirty_read({time_stamp, ref_count}) of
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[#time_stamp{data = Ref}] -> Ref + 1
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ok = mnesia:dirty_write(#time_stamp{key = ref_count, data = NRef}).
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delete_time_stamp_table() ->
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case catch mnesia:dirty_read({Tab, ref_count}) of
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[#time_stamp{data = 1}] ->
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[#time_stamp{data = Ref}] ->
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ok = mnesia:dirty_write(#time_stamp{key = ref_count, data = Ref - 1})
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update(Name, UpdateFunc, Interval) ->
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CurrentTime = get_time(),
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case mnesia:dirty_read({time_stamp, Name}) of
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[#time_stamp{data = Expire}] when CurrentTime =< Expire -> ok;
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ok = mnesia:dirty_write(#time_stamp{key = Name,
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data = CurrentTime + Interval})
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%%-----------------------------------------------------------------
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%% Func: table_func(Op, Extra)
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%% table_func(Op, RowIndex, Cols, Extra)
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%% Args: Extra = {Name, SnmpKey, Attributes, Interval, UpdateFunc}
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%% Purpose: Instrumentation function for the table.
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%% Name is the name of the table
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%% SnmpKey is the snmpkey as it should be specifed in order
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%% to create the Mnesia table as an SNMP table
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%% Attributes is the attributes as it should be specifed in order
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%% to create the Mnesia table as an SNMP table
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%% Interval is the minimum time in milliseconds between two
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%% updates of the table
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%% UpdateFunc is a function with no arguments that is called
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%% whenever the table must be updated
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%% Returns: As specified for an SNMP table instrumentation function.
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%%-----------------------------------------------------------------
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table_func(new, {Name, SnmpKey, Attribs, _Interval, _UpdateFunc}) ->
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create_time_stamp_table(),
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Props = [{type, set},
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{snmp, [{key, SnmpKey}]},
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{attributes, Attribs}],
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create_table(Name, Props, ram_copies, true);
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table_func(delete, {Name, _SnmpKey, _Attribs, _Interval, _UpdateFunc}) ->
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delete_time_stamp_table(),
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table_func(Op, RowIndex, Cols,
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{Name, _SnmpKey, _Attribs, Interval, UpdateFunc}) ->
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update(Name, UpdateFunc, Interval),
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snmp_generic:table_func(Op, RowIndex, Cols, {Name, mnesia}).
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{M,S,U} = erlang:now(),
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1000000000 * M + 1000 * S + (U div 1000).
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%%-----------------------------------------------------------------
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%% We want named tables, without schema info; the tables should
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%% be locally named, but if the node crashes, info about the
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%% table shouldn't be kept. We could use ets tables for this.
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%% BUT, we also want the snmp functionality, therefore we must
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%% The problem arises when the node that implements these tables
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%% crashes, and another node takes over the MIB-implementations.
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%% That node cannot create the shadow tables again, because they
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%% already exist (according to mnesia...). Therefore, we must
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%% check if we maybe must delete the table first, and then create
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%%-----------------------------------------------------------------
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create_table(Tab, Props, Storage, DeleteAll) ->
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case lists:member(Tab, mnesia:system_info(tables)) of
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case mnesia:table_info(Tab, storage_type) of
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?verify(mnesia:add_table_copy(Tab, node(), Storage),
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[add_table_copy, Tab, node(), Storage]);
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Storage when DeleteAll == true ->
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Props2 = [{local_content, true}, {Storage, Nodes}] ++ Props,
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?verify(mnesia:create_table(Tab, Props2),
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[create_table, Tab, Props2])
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delete_all(mnesia:dirty_first(Tab), Tab).
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delete_all('$end_of_table', _Tab) ->
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delete_all(Key, Tab) ->
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ok = mnesia:dirty_delete({Tab, Key}),
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delete_all(mnesia:dirty_next(Tab, Key), Tab).
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case lists:member(Tab, mnesia:system_info(tables)) of
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case ?verify(mnesia:del_table_copy(Tab, node()),
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[del_table_copy, Tab, node()]) of
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{aborted, _Reason} ->
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catch delete_all(Tab),
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%%-----------------------------------------------------------------
added
removed
lib/snmp/src/agent/snmp_shadow_table.erl
