SNMP_SESS_API(3) Net-SNMP SNMP_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 ver-sions versions
sions 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 char-acteristics. characteristics.
acteristics. snmp_sess_session() takes the opaque session handle and returns a pointer to its asso-ciated associated
ciated 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() provide 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 vari-able, variable,
able, 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 values:
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 useable.
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 ALSO
select(2), snmp_api(3), snmp_api.h
4.2 Berkeley Distribution 07 Mar 2002 SNMP_SESS_API(3)
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