NETSNMP_SESS_API(3) Net-SNMP NETSNMP_SESS_API(3)NAME
snmp_sess_init, snmp_sess_open, snmp_sess_session, snmp_sess_send,
snmp_sess_async_send, snmp_sess_select_info, snmp_sess_read,
snmp_sess_timeout, snmp_sess_close, snmp_sess_error - session functions
SYNOPSIS
#include <net-snmp/session_api.h>
void snmp_sess_init(struct snmp_session *session);
void *snmp_sess_open(struct snmp_session *session);
struct snmp_session *snmp_sess_session(void *handle);
int snmp_sess_send(void *handle, struct snmp_pdu *pdu);
int snmp_sess_async_send(void *handle,
struct snmp_pdu *pdu,
snmp_callback callback,
void *callbackData);
int snmp_sess_select_info(void *handle,
int *numfds, fd_set *fdset,
struct timeval *timeout,
int *block);
int snmp_sess_read(void *handle, fd_set *fdset);
void snmp_sess_timeout(void *handle);
int snmp_sess_close(void *handle);
void snmp_sess_error(void *handle, int *pcliberr,
int *psnmperr, char **pperrstring);
DESCRIPTION
These functions define a subset of the API that can be used to manage
single SNMP sessions in a multi-threaded application. Except for
snmp_sess_session(), these functions are single session versions of the
traditional SNMP library API.
Note that these functions use an opaque pointer (handle in the above
prototypes) to identify a single session in lieu of a session pointer
(as in the traditional API).
snmp_sess_init() prepares a struct snmp_session that sources transport
characteristics and common information that will be used for a set of
SNMP transactions. After this structure is passed to snmp_sess_open()
to create an SNMP session, the structure is no longer used. Instead
the opaque pointer returned by snmp_sess_open() is used to refer to
that session henceforth.
SNMP sessions that are created with snmp_sess_open() are not affected
by, and SHOULD NOT BE USED WITH, snmp_select_info(), snmp_read(),
snmp_timeout() nor snmp_close(). Rather the equivalent single session
functions described here should be used.
snmp_sess_init() and snmp_sess_open() each take as input a pointer to a
struct snmp_session object. This structure contains information for a
set of transactions that will share similar transport characteristics.
snmp_sess_session() takes the opaque session handle and returns a
pointer to its associated struct snmp_session.
snmp_sess_send() and snmp_sess_async_send() each take a pdu parameter,
which points to a struct snmp_pdu object containing information that
describes a transaction that will be performed over an open session.
Consult snmp_api.h for the definitions of these structures.
snmp_sess_select_info(), snmp_sess_read() and snmp_sess_timeout() pro‐
vide an interface for the use of the select(2) system call so that SNMP
transactions for a single session can occur asynchronously.
snmp_sess_select_info() is passed the information that would have been
passed to select(2) in the absence of SNMP. For example, this might
include file descriptors associated with the main loop of a graphical
application. This information is modified so that SNMP will get the
service it requires from the call to select(2). In this case, numfds,
fdset and timeout correspond to the nfds, readfds and timeout arguments
to select(2) respectively. The only exception is that timeout must
ALWAYS point to an allocated (but perhaps uninitialized) struct timeval
(it cannot be NULL as for select(2)). If timeout would have been
passed as NULL, block is instead set to true, and timeout is treated as
undefined. This same rule applies upon return from snmp_select_info().
After calling snmp_sess_select_info() , select(2) should be called with
the returned data. When it returns, snmp_sess_read() should then be
called with the fd_set returned from select(2). This will read any
input from this session's SNMP socket. If select(2) times out (that
is, it returns zero), snmp_sess_timeout() should be called to see if a
timeout has occurred on the SNMP session.
DIAGNOSTICS
Error return status from snmp_sess_open() is indicated by return of a
NULL pointer. Error return status from snmp_sess_close() and
snmp_sess_send() is indicated by a return value of 0. A successful
status will return 1.
Further information can be obtained by using snmp_sess_error() to see
what type of error has occurred. This function returns the SNMP
snmp_errno variable, the value of the system errno variable, and a
string interpretation of both variables. The string must be freed
after use by the caller.
For errors returned by snmp_sess_open(), use the corresponding function
snmp_error() instead of snmp_sess_error().
Consult snmp_api.h for the complete set of SNMP library error values.
The SNMP library error value snmperr can be one of the following val‐
ues:
SNMPERR_GENERR A generic error occurred.
SNMPERR_BAD_LOCPORT The local port was bad because it had
already been allocated or permission was
denied.
SNMPERR_BAD_ADDRESS The host name or address given was not use‐
able.
SNMPERR_BAD_SESSION The specified session was not open.
SNMPERR_TOO_LONG
SNMPERR_NO_SOCKET
SNMPERR_V2_IN_V1
SNMPERR_V1_IN_V2
SNMPERR_BAD_REPEATERS
SNMPERR_BAD_REPETITIONS
SNMPERR_BAD_ASN1_BUILD
SNMPERR_BAD_SENDTO
SNMPERR_BAD_RCVFROM
SNMPERR_BAD_PARSE
SNMPERR_BAD_VERSION
SNMPERR_BAD_COMMUNITY
SNMPERR_NOAUTH_DESPRIV
SNMPERR_ABORT
SNMPERR_UNKNOWN_PDU
SNMPERR_TIMEOUT
SEE ALSOselect(2), snmp_api(3), snmp_api.h
V5.6 13 Aug 2010 NETSNMP_SESS_API(3)
