agentx: add AgentX support to Quagga.

--enable-snmp will enable AgentX support in Quagga. SMUX is still here
and can be enabled with --enable-snmp=smux. AgentX support can be
enabled with "agentx" in configuration file. As for SMUX, this command
is not understood by vtysh. It can be disabled with "no agentx",
though there is no real use of this since this command cannot be used
with vtysh.

If "agentx" and "no agentx" command were added to vtysh, it would not
be possible to disable agentx support after enabling it because
NetSNMP does not expose the appropriate methods for this.

The internals of AgentX are hidden by NetSNMP. Therefore, we don't
have a file descriptor to add to the threading system. We do not have
the timers to set either. Therefore, the event loop is modified to
make use of snmp_select_info() from NetSNMP.

Traps are not supported yet.

1 files changed, 49 insertions, 0 deletions

diff --git a/lib/thread.c b/lib/thread.c
index 86d0ff8c..6341dfd7 100644
--- a/lib/thread.c
+++ b/lib/thread.c
@@ -29,6 +29,16 @@
 #include "hash.h"
 #include "command.h"
 #include "sigevent.h"
+
+#if defined HAVE_SNMP && defined SNMP_AGENTX
+#include <net-snmp/net-snmp-config.h>
+#include <net-snmp/net-snmp-includes.h>
+#include <net-snmp/agent/net-snmp-agent-includes.h>
+#include <net-snmp/agent/snmp_vars.h>
+
+extern int agentx_enabled;
+#endif
+
 
 /* Recent absolute time of day */
 struct timeval recent_time;
@@ -1030,6 +1040,11 @@ thread_fetch (struct thread_master *m, struct thread *fetch)
   while (1)
     {
       int num = 0;
+#if defined HAVE_SNMP && defined SNMP_AGENTX
+      struct timeval snmp_timer_wait;
+      int snmpblock = 0;
+      int fdsetsize;
+#endif
       
       /* Signals pre-empt everything */
       quagga_sigevent_process ();
@@ -1065,6 +1080,26 @@ thread_fetch (struct thread_master *m, struct thread *fetch)
             timer_wait = timer_wait_bg;
         }
       
+#if defined HAVE_SNMP && defined SNMP_AGENTX
+      /* When SNMP is enabled, we may have to select() on additional
+	 FD. snmp_select_info() will add them to `readfd'. The trick
+	 with this function is its last argument. We need to set it to
+	 0 if timer_wait is not NULL and we need to use the provided
+	 new timer only if it is still set to 0. */
+      if (agentx_enabled)
+        {
+          fdsetsize = FD_SETSIZE;
+          snmpblock = 1;
+          if (timer_wait)
+            {
+              snmpblock = 0;
+              memcpy(&snmp_timer_wait, timer_wait, sizeof(struct timeval));
+            }
+          snmp_select_info(&fdsetsize, &readfd, &snmp_timer_wait, &snmpblock);
+          if (snmpblock == 0)
+            timer_wait = &snmp_timer_wait;
+        }
+#endif
       num = select (FD_SETSIZE, &readfd, &writefd, &exceptfd, timer_wait);
       
       /* Signals should get quick treatment */
@@ -1076,6 +1111,20 @@ thread_fetch (struct thread_master *m, struct thread *fetch)
             return NULL;
         }
 
+#if defined HAVE_SNMP && defined SNMP_AGENTX
+      if (agentx_enabled)
+        {
+          if (num > 0)
+            snmp_read(&readfd);
+          else if (num == 0)
+            {
+              snmp_timeout();
+              run_alarms();
+            }
+          netsnmp_check_outstanding_agent_requests();
+        }
+#endif
+
       /* Check foreground timers.  Historically, they have had higher
          priority than I/O threads, so let's push them onto the ready
 	 list in front of the I/O threads. */