RL-ARM User's Guide

MIB Entry

The MIB_ENTRY structure describes the MIB variable. SNMP Agent uses this description to process local MIB variables. This structure is defined in Net_Config.h as follows:

typedef struct mib_entry {        /* << SNMP-MIB Entry Info >>          */
  U8   Type;                      /* Object Type                        */
  U8   OidLen;                    /* Object ID length                   */
  U8   Oid[MIB_OIDSZ];            /* Object ID value                    */
  U8   ValSz;                     /* Size of a Variable                 */
  void *Val;                      /* Pointer to a variable              */
  void (*cb_func)(int mode);      /* Write/Read event callback function */
} MIB_ENTRY;

The components of MIB_ENTRY structure are:

• the Type defines the MIB variable type:

• MIB Type	Description	Size
  MIB_INTEGER	Signed Integer	1, 2 or 4 bytes
  MIB_OCTET_STR	Octet String entry	max. 110 characters
  MIB_OBJECT_ID	Object Identifier entry	max. 17 bytes
  MIB_IP_ADDR	IP Address entry	4 bytes
  MIB_COUNTER	Counter entry	1, 2 or 4 bytes
  MIB_GAUGE	Gauge entry	1, 2 or 4 bytes
  MIB_TIME_TICKS	Time Ticks entry	4 bytes

  The Type component may be or-ed with the MIB_ATR_RO read-only attribute. A read-only variable can not be changed by the SNMP Manager.
• the OID specifies the Object Identification Name of the variable. It is length encoded.
  - OidLen specifies the length of the Oid[] array.
  - Oid[MIB_OIDSZ] array specifies the OID name - a length encoded binary array.
• the Val specifies the Pointer to the variable and it's Size.
  - ValSz specifies the size of Val variable.
  - *Val is a pointer to the actual variable.
• the cb_func specifies a Callback function which is called, when the variable is accessed by SNMP Manager. The callback function is not registered, when the value of cb_func is NULL.

  Parameter mode of the callback function specifies the access mode of SNMP Manager:

  Mode	Type of Access
  MIB_READ	Reads a MIB variable.
  MIB_WRITE	Writes to a MIB variable.