[collectd] [PATCH] ping: add MaxMissed option

[Stefan Völkel]

Any host not replying to consecutive MaxMissed PING packets will get
it's name re-resolved via DNS.

This enables the use of dynamic DNS services (like dyndns.org) with the
ping plugin. Prior to this patch, hostnames were resolved once on daemon
start.

The default is -1 (disabled).
---
 src/collectd.conf.pod |    7 +++++++
 src/ping.c            |   44 ++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/src/collectd.conf.pod b/src/collectd.conf.pod
index 43a322b..ab004f6 100644
--- a/src/collectd.conf.pod
+++ b/src/collectd.conf.pod
@@ -2274,6 +2274,13 @@ Default: B<0.9>
 
 Sets the Time-To-Live of generated ICMP packets.
 
+=item B<MaxMissed> I<Packets>
+
+Trigger a DNS resolv after the host has not replied to I<Packets> packets. This
+enables the use of dynamic DNS services (like dyndns.org) with the ping plugin.
+
+Default: B<-1> (disabled)
+
 =back
 
 =head2 Plugin C<postgresql>
diff --git a/src/ping.c b/src/ping.c
index de9c45b..dabba38 100644
--- a/src/ping.c
+++ b/src/ping.c
@@ -45,6 +45,7 @@ struct hostlist_s
 
   uint32_t pkg_sent;
   uint32_t pkg_recv;
+  uint32_t pkg_missed;
 
   double latency_total;
   double latency_squared;
@@ -61,6 +62,7 @@ static hostlist_t *hostlist_head = NULL;
 static int    ping_ttl = PING_DEF_TTL;
 static double ping_interval = 1.0;
 static double ping_timeout = 0.9;
+static int    ping_max_missed = -1;
 
 static int             ping_thread_loop = 0;
 static int             ping_thread_error = 0;
@@ -73,7 +75,8 @@ static const char *config_keys[] =
   "Host",
   "TTL",
   "Interval",
-  "Timeout"
+  "Timeout",
+  "MaxMissed"
 };
 static int config_keys_num = STATIC_ARRAY_SIZE (config_keys);
 
@@ -260,7 +263,37 @@ static void *ping_thread (void *arg) /* {{{ */
         hl->pkg_recv++;
         hl->latency_total += latency;
         hl->latency_squared += (latency * latency);
-      }
+
+        /* reset missed packages counter */
+        hl->pkg_missed = 0;
+      } else
+        hl->pkg_missed++;
+
+      /* if the host did not answer our last N packages, trigger a resolv. */
+      if (ping_max_missed >= 0 && hl->pkg_missed >= ping_max_missed)
+      { /* {{{ */
+        /* we reset the missed package counter here, since we only want to
+         * trigger a resolv every N packages and not every package _AFTER_ N
+         * missed packages */
+        hl->pkg_missed = 0;
+
+        WARNING ("ping plugin: host %s has not answered %d PING requests,"
+          " triggering resolve", hl->host, ping_max_missed);
+
+        /* we trigger the resolv simply be removeing and adding the host to our
+         * ping object */
+        status = ping_host_remove (pingobj, hl->host);
+        if (status != 0)
+        {
+          WARNING ("ping plugin: ping_host_remove (%s) failed.", hl->host);
+        }
+        else
+        {
+          status = ping_host_add (pingobj, hl->host);
+          if (status != 0)
+            WARNING ("ping plugin: ping_host_add (%s) failed.", hl->host);
+        }
+      } /* }}} ping_max_missed */
     } /* }}} for (iter) */
 
     if (gettimeofday (&tv_end, NULL) < 0)
@@ -392,6 +425,7 @@ static int ping_config (const char *key, const char *value) /* {{{ */
     hl->host = host;
     hl->pkg_sent = 0;
     hl->pkg_recv = 0;
+    hl->pkg_missed = 0;
     hl->latency_total = 0.0;
     hl->latency_squared = 0.0;
     hl->next = hostlist_head;
@@ -427,6 +461,12 @@ static int ping_config (const char *key, const char *value) /* {{{ */
       WARNING ("ping plugin: Ignoring invalid timeout %g (%s)",
           tmp, value);
   }
+  else if (strcasecmp (key, "MaxMissed") == 0)
+  {
+    ping_max_missed = atoi (value);
+    if (ping_max_missed < 0)
+      INFO ("ping plugin: MaxMissed < 0, disabled re-resolving of hosts");
+  }
   else
   {
     return (-1);
-- 
1.6.3.3