<?xml version="1.0" encoding="iso-8859-1" ?> <!DOCTYPE erlref SYSTEM "erlref.dtd"> <erlref> <header> <copyright> <year>1996</year><year>2012</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> 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. </legalnotice> <title>snmp_generic</title> <prepared></prepared> <responsible></responsible> <docno></docno> <approved></approved> <checked></checked> <date></date> <rev></rev> <file>snmp_generic.xml</file> </header> <module>snmp_generic</module> <modulesummary>Generic Functions for Implementing SNMP Objects in a Database</modulesummary> <description> <marker id="description"></marker> <p>The module <c>snmp_generic</c> contains generic functions for implementing tables (and variables) using the SNMP built-in database or Mnesia. These default functions are used if no instrumentation function is provided for a managed object in a MIB. Sometimes, it might be necessary to customize the behaviour of the default functions. For example, in some situations a trap should be sent if a row is deleted or modified, or some hardware is to be informed, when information is changed. </p> <p>The overall structure is shown in the following figure:</p> <pre> +---------------+ | SNMP Agent | +- - - - - - - -+ | MIB | +---------------+ | Association file (associates a MIB object with | snmp_generic:table_funct | snmp_generic:variable_func) +--------------------------------------+ | snmp_generic | Support for get-next, | | RowStatus operations +----------------------+---------------+ | snmpa_local_db | Mnesia | Database +--------------+-------+---------------+ | dets | ets | | (persistent) | | +--------------+-------+ </pre> <p>Each function takes the argument <c>NameDb</c>, which is a tuple <c>{Name, Db}</c>, to identify which database the functions should use. <c>Name</c> is the symbolic name of the managed object as defined in the MIB, and <c>Db</c> is either <c>volatile</c>, <c>persistent</c>, or <c>mnesia</c>. If it is <c>mnesia</c>, all variables are stored in the Mnesia table <c>snmp_variables</c> which must be a table with two attributes (not a Mnesia SNMP table). The SNMP tables are stored in Mnesia tables with the same names as the SNMP tables. All functions assume that a Mnesia table exists with the correct name and attributes. It is the programmer's responsibility to ensure this. Specifically, if variables are stored in Mnesia, the table <c>snmp_variables</c> must be created by the programmer. The record definition for this table is defined in the file <c>snmp/include/snmp_types.hrl</c>. </p> <p>If an instrumentation function in the association file for a variable <c>myVar</c> does not have a name when compiling an MIB, the compiler generates an entry. </p> <pre> {myVar, {snmp_generic, variable_func, [{myVar, Db]}}. </pre> <p>And for a table:</p> <pre> {myTable, {snmp_generic, table_func, [{myTable, Db]}}. </pre> </description> <section> <marker id="data_types"></marker> <title>DATA TYPES</title> <p>In the functions defined below, the following types are used:</p> <code type="none"> name_db() = {name(), db()} name() = atom() db() = volatile | persistent | mnesia row_index() = [int()] columns() = [column()] | [{column(), value()}] column() = int() value() = term() </code> <taglist> <tag><c>row_index()</c></tag> <item> <p>Denotes the last part of the OID which specifies the index of the row in the table (see RFC1212, 4.1.6 for more information about INDEX). </p> </item> <tag><c>columns()</c></tag> <item> <p>Is a list of column numbers in the case of a <c>get</c> operation, and a list of column numbers and values in the case of a <c>set</c> operation. </p> </item> </taglist> <marker id="get_status_col2"></marker> </section> <funcs> <func> <name>get_status_col(Name, Cols)</name> <name>get_status_col(NameDb, Cols) -> {ok, StatusVal} | false</name> <fsummary>Get the value of the status column from <c>Cols</c></fsummary> <type> <v>Name = name()</v> <v>NameDb = name_db()</v> <v>Cols = columns()</v> <v>StatusVal = term()</v> </type> <desc> <p>Gets the value of the status column from <c>Cols</c>. </p> <p>This function can be used in instrumentation functions for <c>is_set_ok</c>, <c>undo</c> or <c>set</c> to check if the status column of a table is modified.</p> <marker id="get_index_types"></marker> </desc> </func> <func> <name>get_index_types(Name)</name> <fsummary>Get the index types of <c>Name</c></fsummary> <type> <v>Name = name()</v> </type> <desc> <p>Gets the index types of <c>Name</c></p> <p>This function can be used in instrumentation functions to retrieve the index types part of the table info.</p> <marker id="get_table_info"></marker> </desc> </func> <func> <name>get_table_info(Name, Item) -> table_info_result()</name> <fsummary>Get table info item of MIB table <c>Name</c></fsummary> <type> <v>Name = name()</v> <v>Item = table_item() | all</v> <v>table_item() = nbr_of_cols | defvals | status_col | not_accessible | index_types | first_accessible | first_own_index</v> <v>table_info_result() = Value | [{table_item(), Value}]</v> <v>Value = term()</v> </type> <desc> <p>Get a specific table info item or, if <c>Item</c> has the value <c>all</c>, a two tuple list (property list) is instead returned with all the items and their respctive values of the given table. </p> <p>This function can be used in instrumentation functions to retrieve a given part of the table info.</p> <marker id="table_func"></marker> </desc> </func> <func> <name>table_func(Op1, NameDb)</name> <name>table_func(Op2, RowIndex, Cols, NameDb) -> Ret</name> <fsummary>Default instrumentation function for tables</fsummary> <type> <v>Op1 = new | delete </v> <v>Op2 = get | next | is_set_ok | set | undo</v> <v>NameDb = name_db()</v> <v>RowIndex = row_index()</v> <v>Cols = columns()</v> <v>Ret = term()</v> </type> <desc> <p>This is the default instrumentation function for tables. </p> <list type="bulleted"> <item>The <c>new</c> function creates the table if it does not exist, but only if the database is the SNMP internal db.</item> <item>The <c>delete</c> function does not delete the table from the database since unloading an MIB does not necessarily mean that the table should be destroyed.</item> <item>The <c>is_set_ok</c> function checks that a row which is to be modified or deleted exists, and that a row which is to be created does not exist.</item> <item>The <c>undo</c> function does nothing.</item> <item>The <c>set</c> function checks if it has enough information to make the row change its status from <c>notReady</c> to <c>notInService</c> (when a row has been been set to <c>createAndWait</c>). If a row is set to <c>createAndWait</c>, columns without a value are set to <c>noinit</c>. If Mnesia is used, the set functionality is handled within a transaction.</item> </list> <p>If it is possible for a manager to create or delete rows in the table, there must be a <c>RowStatus</c> column for <c>is_set_ok</c>, <c>set</c> and <c>undo</c> to work properly. </p> <p>The function returns according to the specification of an instrumentation function. </p> <marker id="table_get_elements"></marker> </desc> </func> <func> <name>table_get_elements(NameDb, RowIndex, Cols) -> Values</name> <fsummary>Get elements in a table row</fsummary> <type> <v>NameDb = name_db()</v> <v>RowIndex = row_index()</v> <v>Cols = columns()</v> <v>Values = [value() | noinit]</v> </type> <desc> <p>Returns a list with values for all columns in <c>Cols</c>. If a column is undefined, its value is <c>noinit</c>.</p> <marker id="table_next"></marker> </desc> </func> <func> <name>table_next(NameDb, RestOid) -> RowIndex | endOfTable</name> <fsummary>Find the next row in the table</fsummary> <type> <v>NameDb = name_db()</v> <v>RestOid = [int()]</v> <v>RowIndex = row_index()</v> </type> <desc> <p>Finds the indices of the next row in the table. <c>RestOid</c> does not have to specify an existing row.</p> <marker id="table_row_exists"></marker> </desc> </func> <func> <name>table_row_exists(NameDb, RowIndex) -> bool()</name> <fsummary>Check if a row in a table exists</fsummary> <type> <v>NameDb = name_db()</v> <v>RowIndex = row_index()</v> </type> <desc> <p>Checks if a row in a table exists.</p> <marker id="table_set_elements"></marker> </desc> </func> <func> <name>table_set_elements(NameDb, RowIndex, Cols) -> bool()</name> <fsummary>Set elements in a table row</fsummary> <type> <v>NameDb = name_db()</v> <v>RowIndex = row_index()</v> <v>Cols = columns()</v> </type> <desc> <p>Sets the elements in <c>Cols</c> to the row specified by <c>RowIndex</c>. No checks are performed on the new values. </p> <p>If the Mnesia database is used, this function calls <c>mnesia:write</c> to store the values. This means that this function must be called from within a transaction (<c>mnesia:transaction/1</c> or <c>mnesia:dirty/1</c>).</p> <marker id="variable_func"></marker> </desc> </func> <func> <name>variable_func(Op1, NameDb)</name> <name>variable_func(Op2, Val, NameDb) -> Ret</name> <fsummary>Default instrumentation function for tables</fsummary> <type> <v>Op1 = new | delete | get</v> <v>Op2 = is_set_ok | set | undo</v> <v>NameDb = name_db()</v> <v>Val = value()</v> <v>Ret = term()</v> </type> <desc> <p>This is the default instrumentation function for variables.</p> <p>The <c>new</c> function creates a new variable in the database with a default value as defined in the MIB, or a zero value (depending on the type). </p> <p>The <c>delete</c> function does not delete the variable from the database. </p> <p>The function returns according to the specification of an instrumentation function. </p> <marker id="variable_get"></marker> </desc> </func> <func> <name>variable_get(NameDb) -> {value, Value} | undefined</name> <fsummary>Get the value of a variable</fsummary> <type> <v>NameDb = name_db()</v> <v>Value = value()</v> </type> <desc> <p>Gets the value of a variable.</p> <marker id="variable_set"></marker> </desc> </func> <func> <name>variable_set(NameDb, NewVal) -> true | false</name> <fsummary>Set a value for a variable</fsummary> <type> <v>NameDb = name_db()</v> <v>NewVal = value()</v> </type> <desc> <p>Sets a new value to a variable. The variable is created if it does not exist. No checks are made on the type of the new value. </p> <p>Returns <c>false</c> if the <c>NameDb</c> argument is incorrectly specified, otherwise <c>true</c>.</p> </desc> </func> </funcs> <section> <marker id="example"></marker> <title>Example</title> <p>The following example shows an implementation of a table which is stored in Mnesia, but with some checks performed at set-request operations. </p> <pre> myTable_func(new, NameDb) -> % pass unchanged snmp_generic:table_func(new, NameDb). myTable_func(delete, NameDb) -> % pass unchanged snmp_generic:table_func(delete, NameDb). %% change row myTable_func(is_set_ok, RowIndex, Cols, NameDb) -> case snmp_generic:table_func(is_set_ok, RowIndex, Cols, NameDb) of {noError, 0} -> myApplication:is_set_ok(RowIndex, Cols); Err -> Err end; myTable_func(set, RowIndex, Cols, NameDb) -> case snmp_generic:table_func(set, RowIndex, Cols, NameDb), {noError, 0} -> % Now the row is updated, tell the application myApplication:update(RowIndex, Cols); Err -> Err end; myTable_func(Op, RowIndex, Cols, NameDb) -> % pass unchanged snmp_generic:table_func(Op, RowIndex, Cols, NameDb). </pre> <p>The <c>.funcs</c> file would look like: </p> <pre> {myTable, {myModule, myTable_func, [{myTable, mnesia}]}}. </pre> </section> </erlref>