SNMP Subagent Programmer's Guide

Programming Tutorials
SNMP Subagent Programmer’s Guide—119728 2-15
Hello World Program
When the NonStop agent receives requests for a subagent from multiple managers,
it processes them in turn when mgmt_poll() is called, in the order in which they
were received.
If mgmt_poll() returns a value of less than 0, connection with the NonStop agent
was lost. In this case, the while loop terminates; otherwise, trap processing
proceeds.
13. A test is performed to determine whether the value of the MIB object named
helloPrintFreq was changed by the request just processed. If so, a trap is sent before
mgmt_poll() is called again.
This subagent compares two variables (last_freq and helloPrintFreq) to determine
whether the print frequency changed. Alternatively, the value returned by
mgmt_poll() could have been used to detect a change in print frequency. The
mgmt_poll() function returns a 4-bit mask describing the SNMP operation
performed. A value of 1 in the fourth bit indicates a Set request was processed. The
subagent could have examined the value of the mask, then determined whether the
MIB object changed was the print frequency by comparing the values of last_freq
and helloPrintFreq.
14. The mgmt_trap() function generates a trap, in this case the trap described by the
MIB object named helloFreqChange. This function expects two arguments:
•
The pointer returned from the call to mgmt_init_env() (mgmt_env).
•
A pointer to the structure generated by GDMOC when the trap definition was
compiled. To name this structure, GDMOC adds the prefix TRAP_ to the trap
name in the MIB definition. The name of the structure generated in this
example is TRAP_helloFreqChange.
The trap message sent contains the current value of the MIB object named
helloPrintFreq.
15. The current value of the MIB object named helloOutputText is always printed.
16. The value of the MIB object named helloPrintCnt is incremented by 1.
17. Whenever mgmt_poll() fails, this loop, which terminates communication with the
NonStop agent, is executed.
18. The mgmt_del_instance() function de-registers, from the run-time library, MIB
objects made manageable by a previous mgmt_new_instance() call. This function
expects two arguments:
•
The pointer returned from the call to mgmt_init_env() (mgmt_env)
•
The pointer returned from the call to mgmt_new_instance()
(mgmt_hello_handle)
19. The mgmt_term_env() function terminates communication with the NonStop agent.
The only argument this function expects is the pointer identifying the session to
terminate (mgmt_env).