table of contents
other versions
- jessie 1:17.3-dfsg-4+deb8u2
- jessie-backports 1:19.2.1+dfsg-2+deb9u1~bpo8+1
- stretch 1:19.2.1+dfsg-2+deb9u2
- testing 1:21.2.5+dfsg-1
- unstable 1:21.2.6+dfsg-1
- experimental 1:22.0~rc1+dfsg-1
snmp_index(3erl) | Erlang Module Definition | snmp_index(3erl) |
NAME¶
snmp_index - Abstract Data Type for SNMP IndexingDESCRIPTION¶
The module snmp_index implements an Abstract Data Type (ADT) for an SNMP index structure for SNMP tables. It is implemented as an ets table of the ordered_set data-type, which means that all operations are O(log n). In the table, the key is an ASN.1 OBJECT IDENTIFIER. This index is used to separate the implementation of the SNMP ordering from the actual implementation of the table. The SNMP ordering, that is implementation of GET NEXT, is implemented in this module. For example, suppose there is an SNMP table, which is best implemented in Erlang as one process per SNMP table row. Suppose further that the INDEX in the SNMP table is an OCTET STRING. The index structure would be created as follows:snmp_index:new(string)For each new process we create, we insert an item in an snmp_index structure:
new_process(Name, SnmpIndex) -> Pid = start_process(), NewSnmpIndex = snmp_index:insert(SnmpIndex, Name, Pid), <...>With this structure, we can now map an OBJECT IDENTIFIER in e.g. a GET NEXT request, to the correct process:
get_next_pid(Oid, SnmpIndex) -> {ok, {_, Pid}} = snmp_index:get_next(SnmpIndex, Oid), Pid.
COMMON DATA TYPES¶
The following data types are used in the functions below:- *
- index()
- *
- oid() = [byte()]
- *
- key_types = type_spec() | {type_spec(), type_spec(), ...}
- *
- type_spec() = fix_string | string | integer
- *
- key() = key_spec() | {key_spec(), key_spec(), ...}
- *
- key_spec() = string() | integer()
Warning:
All API functions that update the index return a NewIndex term. This is
for backward compatibility with a previous implementation that used a B+ tree
written purely in Erlang for the index. The NewIndex return value can
now be ignored. The return value is now the unchanged table identifier for the
ets table.
The implementation using ets tables introduces a semantic incompatibility with
older implementations. In those older implementations, using pure Erlang
terms, the index was garbage collected like any other Erlang term and did not
have to be deleted when discarded. An ets table is deleted only when the
process creating it explicitly deletes it or when the creating process
terminates.
A new interface delete/1 is now added to handle the case when a process
wants to discard an index table (i.e. to build a completely new). Any
application using transient snmp indexes has to be modified to handle this.
As an snmp adaption usually keeps the index for the whole of the systems
lifetime, this is rarely a problem.
EXPORTS¶
delete(Index) -> true
Types:
Index = NewIndex = index()
Key = key()
Deletes a complete index structure (i.e. the ets table holding the index). The
index can no longer be referenced after this call. See the warning note
above.
delete(Index, Key) -> NewIndex
Types:
Index = NewIndex = index()
Key = key()
Deletes a key and its value from the index structure. Returns a new
structure.
get(Index, KeyOid) -> {ok, {KeyOid, Value}} | undefined
Types:
Index = index()
KeyOid = oid()
Value = term()
Gets the item with key KeyOid. Could be used from within an SNMP
instrumentation function.
get_last(Index) -> {ok, {KeyOid, Value}} | undefined
Types:
Index = index()
KeyOid = oid()
Value = term()
Gets the last item in the index structure.
get_next(Index, KeyOid) -> {ok, {NextKeyOid, Value}} | undefined
Types:
Index = index()
KeyOid = NextKeyOid = oid()
Value = term()
Gets the next item in the SNMP lexicographic ordering, after KeyOid in
the index structure. KeyOid does not have to refer to an existing item
in the index.
insert(Index, Key, Value) -> NewIndex
Types:
Index = NewIndex = index()
Key = key()
Value = term()
Inserts a new key value tuple into the index structure. If an item with the same
key already exists, the new Value overwrites the old value.
key_to_oid(Index, Key) -> KeyOid
Types:
Index = index()
Key = key()
KeyOid = NextKeyOid = oid()
Converts Key to an OBJECT IDENTIFIER.
new(KeyTypes) -> Index
Types:
KeyTypes = key_types()
Index = index()
Creates a new snmp index structure. The key_types() type is described
above.
snmp 5.2.4 | Ericsson AB |