Registering a Sub-Tree with the Agent

After we have set up a connection to the agent and after we have identified ourselves, we must register one or more MIB sub-trees for which we want to be responsible to handle all SNMP requests.

To do so, the subagent must create a DPI-REGISTER packet and send it to the agent. The agent will then send a response to indicate success or failure of the register request.

To create a DPI-REGISTER packet, the subagent uses a call to the mkDPIregister() function, which expects these parameters:

• A timeout value in seconds for this sub-tree. If you specify zero, your overall timeout value that was specified in DPI-OPEN is used. You can specify a different value if you expect longer processing time for a specific sub-tree.

• A requested priority. Multiple subagents may register the same sub-tree at different priorities. For example, 0 is better than 1 and so on. The agent considers the subagent with the best priority to be the active subagent for the sub-tree. If you specify -1, you are asking for the best priority available. If you specify 0, you are asking for a better priority than any existing subagent may already have.

• The MIB sub-tree which you want to control. You must specify this parameter with a trailing dot.

• Your choice of GETBULK processing. You can ask the agent to map a GETBULK into multiple GETNEXT packets or to pass the GETBULK to you.

The function returns a pointer to a static buffer holding the DPI packet if successful. If it fails, it returns a NULL pointer.

Now we must send this DPI-REGISTER packet to the agent with the DPIsend_packet_to_agent() function. This is similar to sending the DPI_OPEN packet. We then wait for a response from the agent. Again, we use the DPIawait_packet_from_agent() function in the same way as we awaited a response on the DPI-OPEN request. Once we have received the response, we must check the return code to ensure that registration was successful.

The following code example demonstrates how to register one MIB sub-tree with the agent.

#include <snmp_dpi.h>             /* DPI 2.0 API definitions */static int handle;                /* handle has global scope */

static void do_register(void)
{
   unsigned char *packet_p;
   int            rc;
   unsigned long  length;
   snmp_dpi_hdr  *hdr_p;

   packet_p = mkDPIregister(          /* Make DPI register    */
                3,                    /* timeout in seconds   */
                0,                    /* requested priority   */
                DPI_SIMPLE_MIB,       /* ptr to the sub-tree  */
                DPI_BULK_NO);         /* GetBulk into GetNext */

   if (!packet_p) exit(1);            /* If it failed, exit   */

   rc  = DPIsend_packet_to_agent(     /* send REGISTER packet */
            handle,                   /* on this connection   */
            packet_p,                 /* this is the packet   */
            DPI_PACKET_LEN(packet_p));/* this is its length   */

   if (rc != DPI_RC_OK) exit(1);      /* If it failed, exit   */

   rc  = DPIawait_packet_from_agent(  /* wait for response    */
            handle,                   /* on this connection   */
            3,                        /* timeout in seconds   */
            &packet_p,                /* gets ptr to packet   */
            &length);                 /* gets packet length   */

   if (rc != DPI_RC_OK) exit(1);      /* If it failed, exit   */

   hdr_p = pDPIpacket(packet_p);      /* parse DPI packet     */
   if (hdr_p == snmp_dpi_hdr_NULL_p)  /* Failed to parse it   */
      exit(1);                        /* so exit              */

   if (hdr_p->packet_type != SNMP_DPI_RESPONSE) exit(1);

   rc = hdr_p->data_u.resp_p->error_code;
   if (rc != SNMP_ERROR_DPI_noError) exit(1);
} /* end of do_register() */