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Linux 2.6 - man page for snmp_index (linux section 3erl)

snmp_index(3erl)		     Erlang Module Definition			 snmp_index(3erl)

       snmp_index - Abstract Data Type for SNMP Indexing

       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 IDENTI-

       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:


       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),

       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()

       The index() type denotes an snmp index structure.

       The oid() type is used to represent an ASN.1 OBJECT IDENTIFIER.

       The key_types() type is used when creating the index structure, and the key() type is used
       when inserting and deleting items from the structure.

       The key_types() type defines the types of the SNMP INDEX columns for the table. If the ta-
       ble  has  one single INDEX column, this type should be a single atom, but if the table has
       multiple INDEX columns, it should be a tuple with atoms.

       If the INDEX column is of type INTEGER, or derived from INTEGER,  the  corresponding  type
       should  be  integer  .  If  it  is  a  variable length type (e.g. OBJECT IDENTIFIER, OCTET
       STRING), the corresponding type should be string . Finally, if the  type  is  of  variable
       length,	but with a fixed size restriction (e.g. IpAddress), the corresponding type should
       be fix_string .

       For example, if the SNMP table has two INDEX columns, the first one an OCTET  STRING  with
       size  2,  and  the  second  one an OBJECT IDENTIFER, the corresponding key_types parameter
       would be {fix_string, string} .

       The key() type correlates to the key_types() type. If the key_types() is  a  single  atom,
       the  corresponding  key() is a single type as well, but if the key_types() is a tuple, key
       must be a tuple of the same size.

       In the example above, valid keys could be {"hi", "mom"} and  {"no",  "thanks"}  ,  whereas
       "hi" , {"hi", 42} and {"hello", "there"} would be invalid.

       All  API functions that update the index return a NewIndex term. This is for backward com-
       patibility 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  dis-
       carded. 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.

       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

       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.

Ericsson AB				    snmp 4.19				 snmp_index(3erl)

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