NETSNMP_SESSION_API(3) Net-SNMP NETSNMP_SESSION_API(3)NAME
snmp_sess_init, snmp_open, snmp_send, snmp_async_send,
snmp_select_info, snmp_read, snmp_timeout, snmp_synch_response,
snmp_close, snmp_perror, snmp_sess_perror, snmp_error,
snmp_api_errstring - netsnmp_session_api functions
SYNOPSIS
#include <net-snmp/session_api.h>
void snmp_sess_init ( netsnmp_session*sess);
netsnmp_session* snmp_open ( netsnmp_session *sess);
/* Input parameter not used in active sessions */
int snmp_send ( netsnmp_session *session,
netsnmp_pdu *pdu);
int snmp_async_send ( netsnmp_session *session,
netsnmp_pdu *pdu,
snmp_callback callback,
void *callbackData);
int snmp_select_info ( int * numfds,fd_set *fdset,
struct timeval *timeout,int *block);
void snmp_read ( fd_set *fdset);
void snmp_timeout ( void );
int snmp_synch_response ( netsnmp_session *session,
netsnmp_pdu *pdu,
netsnmp_pdu **response);
int snmp_close ( netsnmp_session *session);
int snmp_close_sessions ( void );
Error Reporting
(Move to output_api(3))
void snmp_error ( netsnmp_session *session,
int *pcliberr,int *psnmperr,char **pperrstring);
char *snmp_api_errstring ( intsnmperr);
void snmp_perror ( char *msg);
/* for parsing errors only */
void snmp_sess_perror (char *msg,netsnmp_session *sess);
/* all other SNMP library errors */
DESCRIPTION
Snmp_sess_init prepares a netsnmp_session that sources transport char‐
acteristics and common information that will be used for a set of SNMP
transactions. After this structure is passed to snmp_open to create an
SNMP session, the structure is not used.
Snmp_open returns a pointer to a newly-formed netsnmp_session object,
which the application must use to reference the active SNMP session.
snmp_send and snmp_async_send() each take as input a pointer to a net‐
snmp_pdu object. This structure contains information that describes a
transaction that will be performed over an open session.
Consult snmp_api.h for the definitions of these structures.
With the snmp_async_send() call, snmp_read will invoke the specified
callback when the response is received.
Snmp_read, snmp_select_info, and snmp_timeout provide an interface for
the use of the select(2) system call so that SNMP transactions can
occur asynchronously.
Snmp_select_info is given the information that would have been passed
to select in the absence of SNMP. For example, this might include win‐
dow update information. This information is modified so that SNMP will
get the service it requires from the call to select. In this case,
numfds, fdset, and timeout correspond to the nfds, readfds, and timeout
arguments to select, respectively. The only exception is that timeout
must always point to an allocated (but perhaps uninitialized) struct
timeval. If timeout would have been passed as NULL, block is set to
true, and timeout is treated as undefined. This same rule applies upon
return from snmp_select_info.
After calling snmp_select_info, select is called with the returned
data. When select returns, snmp_read should be called with the fd_set
returned from select to read each SNMP socket that has input. If
select times out, snmp_timeout should be called to see if the timeout
was intended for SNMP.
snmp_synch_response is a convenience routine that will send the
request, wait for the response and process it before returning. See
the descriptions of snmp_send , snmp_read etc for details.
DIAGNOSTICS
Previous versions of the library used snmp_get_errno to read the global
variable snmp_errno which may have held the error status within the
SNMP library. The existing method snmp_perror should be used to log
ASN.1 coding errors only.
The new method snmp_sess_perror is provided to capture errors that
occur during the processing of a particular SNMP session.
Snmp_sess_perror calls snmp_error function to obtain the "C" library
error errno , the SNMP library error snmperr , and the SNMP library
detailed error message that is associated with an error that occurred
during a given session.
Note that in all cases except one, snmp_sess_perror should be handed
the netsnmp_session * pointer returned from snmp_open. If snmp_open
returns a null pointer, pass the INPUT netsnmp_session * pointer used
to call snmp_open.
Error return status from snmp_close and snmp_send is indicated by
return of 0. A successful status will return a 1 for snmp_close and
the request id of the packet for snmp_send. Upon successful return
from snmp_send the pdu will be freed by the library.
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_PARSE
SNMPERR_BAD_VERSION
SNMPERR_NOAUTH_DESPRIV
SNMPERR_ABORT
SNMPERR_UNKNOWN_PDU
SNMPERR_TIMEOUT
A string representation of the error code can be obtained with
snmp_api_errstring, and a standard error message may be printed using
snmp_perror that functions like the perror standard routine.
SEE ALSOselect(2), snmp_api.h
V5.7.2 19 May 2011 NETSNMP_SESSION_API(3)
