Developing SMUX peers for SNMP agents


The syntax of MIB objects is modeled by the OS (Object Syntax) structure:

              typedef int (*IFP) ();

typedef struct object_syntax { char *os_name; /* syntax name */

int os_type; /* syntax type */ IFP os_decode; IFP os_free; /* free data */

} *OS; #define NULLOS ((OS) 0)

The syntaxes defined by the Internet-standard MIB are already implemented:

Internet-standard MIB defined syntaxes

Syntax Structure type
INTEGER integer
OctetString struct _OctetString
ObjectID struct OIDentifier
NULL char
DisplayString struct _OctetString
IpAddress struct sockaddr_in
NetworkAddress struct sockaddr_in
Counter integer
Gauge integer
TimeTicks integer
ClnpAddress struct _OctetString
where ``syntax'' is the name appearing in a compiled MIB module, and ``structure type'' is the C language data type corresponding to the object's syntax. The structure types are described below.

To take a syntax name and get back the structure, use the routine text2syn().

Here are the structures and routines used to implement some of these low-level MIB abstractions: Integer, OctetString, ObjectID, and IPAddress.

INTEGER, Counter, Gauge, and TimeTicks

integer is used for the INTEGER, Counter, Gauge, and TimeTicks syntaxes. The definition is:

            typedef int integer;

OctetString, DisplayString, and ClnpAddress

struct _OctetString is used for the OctetString, DisplayString, and ClnpAddress syntaxes. The definition is:

               typedef struct _OctetString {
                   unsigned char *octet_ptr;   /* list of octets */
                   long     length;            /* number of elements */


struct OIDentifier is used for the ObjectID syntax. The definition is:

typedef struct OIDentifier { int oid_nelem; /* number of sub-identifiers */

unsigned int *oid_elements; /* the (ordered) list of sub-identifiers */ } OIDentifier, *OID; #define NULLOID ((OID) 0)

IPAddress and NetworkAddress

struct sockaddr_in is used for the IpAddress and NetworkAddress syntaxes. It is assumed that you are familiar with this structure. If not, consult the file /usr/include/sys/netinet/in.h.

Next topic: Objects
Previous topic: Structure and syntax of managed objects

© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003