snmp_generic - Generic Functions for Implementing SNMP Objects in a Database
Please see following description for synopsis
snmp_generic(3) Erlang Module Definition snmp_generic(3)
NAME
snmp_generic - Generic Functions for Implementing SNMP Objects in a
Database
DESCRIPTION
The module snmp_generic 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 pro-
vided 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.
The overall structure is shown in the following figure:
+---------------+
| 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) | |
+--------------+-------+
Each function takes the argument NameDb, which is a tuple {Name, Db},
to identify which database the functions should use. Name is the sym-
bolic name of the managed object as defined in the MIB, and Db is
either volatile, persistent, or mnesia. If it is mnesia, all variables
are stored in the Mnesia table snmp_variables 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 snmp_vari-
ables must be created by the programmer. The record definition for this
table is defined in the file snmp/include/snmp_types.hrl.
If an instrumentation function in the association file for a variable
myVar does not have a name when compiling an MIB, the compiler gener-
ates an entry.
{myVar, {snmp_generic, variable_func, [{myVar, Db]}}.
And for a table:
{myTable, {snmp_generic, table_func, [{myTable, Db]}}.
DATA TYPES
In the functions defined below, the following types are used:
name_db() = {name(), db()}
name() = atom()
db() = volatile | persistent | mnesia
row_index() = [int()]
columns() = [column()] | [{column(), value()}]
column() = int()
value() = term()
row_index():
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).
columns():
Is a list of column numbers in the case of a get operation, and a
list of column numbers and values in the case of a set operation.
EXPORTS
get_status_col(Name, Cols)
get_status_col(NameDb, Cols) -> {ok, StatusVal} | false
Types:
Name = name()
NameDb = name_db()
Cols = columns()
StatusVal = term()
Gets the value of the status column from Cols.
This function can be used in instrumentation functions for
is_set_ok, undo or set to check if the status column of a table
is modified.
get_index_types(Name)
Types:
Name = name()
Gets the index types of Name
This function can be used in instrumentation functions to
retrieve the index types part of the table info.
get_table_info(Name, Item) -> table_info_result()
Types:
Name = name()
Item = table_item() | all
table_item() = nbr_of_cols | defvals | status_col |
not_accessible | index_types | first_accessible |
first_own_index
table_info_result() = Value | [{table_item(), Value}]
Value = term()
Get a specific table info item or, if Item has the value all, a
two tuple list (property list) is instead returned with all the
items and their respctive values of the given table.
This function can be used in instrumentation functions to
retrieve a given part of the table info.
table_func(Op1, NameDb)
table_func(Op2, RowIndex, Cols, NameDb) -> Ret
Types:
Op1 = new | delete
Op2 = get | next | is_set_ok | set | undo
NameDb = name_db()
RowIndex = row_index()
Cols = columns()
Ret = term()
This is the default instrumentation function for tables.
* The new function creates the table if it does not exist, but
only if the database is the SNMP internal db.
* The delete function does not delete the table from the data-
base since unloading an MIB does not necessarily mean that
the table should be destroyed.
* The is_set_ok function checks that a row which is to be mod-
ified or deleted exists, and that a row which is to be cre-
ated does not exist.
* The undo function does nothing.
* The set function checks if it has enough information to make
the row change its status from notReady to notInService
(when a row has been been set to createAndWait). If a row is
set to createAndWait, columns without a value are set to
noinit. If Mnesia is used, the set functionality is handled
within a transaction.
If it is possible for a manager to create or delete rows in the
table, there must be a RowStatus column for is_set_ok, set and
undo to work properly.
The function returns according to the specification of an
instrumentation function.
table_get_elements(NameDb, RowIndex, Cols) -> Values
Types:
NameDb = name_db()
RowIndex = row_index()
Cols = columns()
Values = [value() | noinit]
Returns a list with values for all columns in Cols. If a column
is undefined, its value is noinit.
table_next(NameDb, RestOid) -> RowIndex | endOfTable
Types:
NameDb = name_db()
RestOid = [int()]
RowIndex = row_index()
Finds the indices of the next row in the table. RestOid does not
have to specify an existing row.
table_row_exists(NameDb, RowIndex) -> bool()
Types:
NameDb = name_db()
RowIndex = row_index()
Checks if a row in a table exists.
table_set_elements(NameDb, RowIndex, Cols) -> bool()
Types:
NameDb = name_db()
RowIndex = row_index()
Cols = columns()
Sets the elements in Cols to the row specified by RowIndex. No
checks are performed on the new values.
If the Mnesia database is used, this function calls mnesia:write
to store the values. This means that this function must be
called from within a transaction (mnesia:transaction/1 or mne-
sia:dirty/1).
variable_func(Op1, NameDb)
variable_func(Op2, Val, NameDb) -> Ret
Types:
Op1 = new | delete | get
Op2 = is_set_ok | set | undo
NameDb = name_db()
Val = value()
Ret = term()
This is the default instrumentation function for variables.
The new 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).
The delete function does not delete the variable from the data-
base.
The function returns according to the specification of an
instrumentation function.
variable_get(NameDb) -> {value, Value} | undefined
Types:
NameDb = name_db()
Value = value()
Gets the value of a variable.
variable_set(NameDb, NewVal) -> true | false
Types:
NameDb = name_db()
NewVal = value()
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.
Returns false if the NameDb argument is incorrectly specified,
otherwise true.
EXAMPLE
The following example shows an implementation of a table which is
stored in Mnesia, but with some checks performed at set-request opera-
tions.
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).
The .funcs file would look like:
{myTable, {myModule, myTable_func, [{myTable, mnesia}]}}.
Ericsson AB snmp 5.11 snmp_generic(3)