SNMP_API(3)
NAME
snmp_open, snmp_close, snmp_send, snmp_read,
snmp_free_pdu, snmp_select_info, snmp_timeout - send and
receive SNMP messages
SYNOPSIS
#include <<sys/types>>
#include <<netinet/in.h>>
#include <<sys/time.h>>
#include <<snmp/snmp.h>>
#include <<snmp/snmp_impl.h>>
#include <<snmp/asn1.h>>
#include <<snmp/snmp_api.h>>
extern int snmp_errno;
extern int snmp_dump_packet;
struct snmp_session *snmp_open(session)
struct snmp_session *session;
int snmp_close(session)
struct snmp_session *session;
int snmp_send(session, pdu)
struct snmp_session *session;
struct snmp_pdu *pdu;
void snmp_read(fdset)
fd_set *fdset;
int snmp_select_info(numfds, fdset, timeout, block)
int *numfds;
fd_set *fdset;
struct timeval *timeout;
int *block;
void snmp_timeout()
void snmp_pdu_create(tag)
int tag;
void snmp_free_pdu(pdu)
struct snmp_pdu *pdu;
DESCRIPTION
Snmp_open, snmp_close, and snmp_send each take as input a
pointer to an object with the following structure. In
addition, snmp_open also returns a pointer to an object
with this structure. This structure contains information
for a set of transactions that will share similar trans-
port characteristics.
typedef struct sockaddr_in ipaddr;
struct snmp_session {
u_char *community; /* community for outgoing requests. */
int community_len; /* Length of community name. */
int retries; /* Number of retries before timeout. */
long timeout; /* Number of uS until first timeout,
then exponential backoff */
char *peername; /* Domain name or dotted IP address
of default peer */
u_short remote_port; /* UDP port number of peer. */
u_short local_port; /* My UDP port number, 0 for default,
picked randomly */
/* Authentication function or NULL if null authentication is used */
u_char *(*authenticator)();
int (*callback)(); /* Function to interpret incoming data */
/* Pointer to data that the callback function may consider
important */
void *callback_magic;
int version; /* SNMP version number */
/* fields to support SNMPv1 community model */
int community_len;
u_char *community;
/* the private keys to use for user-based security */
u_char authKey[16];
u_char privKey[16];
/* fields to support user-based security model in SNMPv2 */
Parameters params;
u_char qoS;
u_char agentID[16];
u_long agentBoots;
int agentTime; /* the agentTime value */
int agentClock; /* the running agentClock */
int userLen;
u_char userName[32];
int MMS;
int contextLen;
u_char contextSelector[64];
/* misc stuff */
int readView;
int writeView;
};
/*
* Set fields in session and pdu to the following to get a default
* or unconfigured value.
*/
#define SNMP_DEFAULT_COMMUNITY_LEN 0 /* for default community name */
#define SNMP_DEFAULT_RETRIES -1
#define SNMP_DEFAULT_TIMEOUT -1
#define SNMP_DEFAULT_REMPORT 0
#define SNMP_DEFAULT_REQID 0
#define SNMP_DEFAULT_ERRSTAT -1
#define SNMP_DEFAULT_ERRINDEX -1
#define SNMP_DEFAULT_ADDRESS 0
#define SNMP_DEFAULT_PEERNAME NULL
#define SNMP_DEFAULT_ENTERPRISE_LENGTH 0
#define SNMP_DEFAULT_TIME 0
/*
* This routine must be supplied by the application:
*
* u_char *authenticator(pdu, length, community, community_len)
* u_char *pdu; The rest of the PDU to be authenticated
* int *length; The length of the PDU (updated by the
* authenticator)
* u_char *community; The community name to authenticate under.
* int community_len The length of the community name.
*
* Returns the authenticated pdu, or NULL if authentication failed.
* If null authentication is used, the authenticator in snmp_session
* can be set to NULL(0).
*/
/*
* This routine must be supplied by the application:
*
* int callback(operation, session, reqid, pdu, magic /* , ... request */ )
* int operation;
* struct snmp_session *session; The session authenticated under.
* int reqid; The request id of this pdu
* (0 for TRAP)
* struct snmp_pdu *pdu; The pdu information.
* void *magic; A link to the data for this routine.
*
* struct request_list *request; The original request -- Note: this
* parameter was added to cmu-snmp-linux-3.5
* and is only avail starting with this
* release; if the request is not known a
* NULL pointer is passed.
*
* Returns 1 if request was successful, 0 if it should be kept pending.
* Any data in the pdu must be copied because it will be freed
* elsewhere.
* Operations are defined below:
*/
#define RECEIVED_MESSAGE 1
#define TIMED_OUT 2
Snmp_send and snmp_free_pdu each take as input a pointer to an
object with the following structure. This structure contains
information that describes a transaction that will be performed
over an open session.
struct snmp_pdu {
ipaddr address; /* Address of peer */
int command; /* Type of this PDU */
u_long reqid; /* Request id */
u_long errstat; /* Error status */
u_long errindex; /* Error index */
/* Trap information */
oid *enterprise; /* System OID */
int enterprise_length;
ipaddr agent_addr; /* address of object generating trap */
int trap_type; /* trap type */
int specific_type; /* specific type */
u_long time; /* Uptime */
struct variable_list *variables;
};
struct variable_list {
struct variable_list *next_variable; /* NULL for last variable */
oid *name; /* Object identifier of variable */
int name_length; /* number of subid's in name */
u_char type; /* ASN type of variable */
union { /* value of variable */
long *integer;
u_char *string;
oid *objid;
} val;
int val_len;
};
Snmp_read, snmp_select_info, and snmp_timeout provide an inter-
face for the use of the select(2) system call so that SNMP trans-
actions 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 window 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 allo-
cated (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 is called with the
fd_set returned from select. This will read all SNMP sockets
with input. If select times out, snmp_timeout should be called
to see if the timeout was intended for SNMP.
DIAGNOSTICS
Error return status from snmp_open is indicated by return
of a null pointer. Error return status from snmp_close
and snmp_send is indicated by return of 0. A successful
status will return a 1. The external integer snmp_errno
may then be checked to see what type of error has occurred
snmp_errno can have 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.
The variable snmp_dump_packet can be set to a value != 0
to force hex dumps of packets sent/read.
Please Note: In the linux port this variable is part of
the library and should not be declared by the application.
SEE ALSO
select(2) snmp_api.h