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;
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)
* 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.
*
* 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 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 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 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 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.
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.