* backend/mcast : add 'ping' option

configs/conf-available/10-backend-mcast.conf

@@ -1,4 +1,5 @@
 [backend:mcast]
 load = libf2b_backend_mcast.so
+; ping = 5
 ; group = 239.255.186.1
 ; port = 3370

src/backends/mcast.c

@@ -28,11 +28,14 @@
 
 #define DEFAULT_MCAST_ADDR "239.255.186.1"
 #define DEFAULT_MCAST_PORT "3370"
+#define DEFAULT_PING_NUM 5
 
 struct _config {
   char name[ID_MAX + 1];
   char error[256];
   bool shared;
+  uint8_t ping_num; /*< current number of ping() call */
+  uint8_t ping_max; /*< max ping() calls before actually send CMD_PING packet */
   char maddr[INET_ADDRSTRLEN];  /**< multicast address */
   char mport[6];                /**< multicast port */
   char iface[IF_NAMESIZE];      /**< bind interface */
@@ -47,6 +50,7 @@ create(const char *id) {
 
   if ((cfg = calloc(1, sizeof(cfg_t))) == NULL)
     return NULL;
+  cfg->ping_max = DEFAULT_PING_NUM;
   strlcpy(cfg->name, id, sizeof(cfg->name));
   strlcpy(cfg->maddr, DEFAULT_MCAST_ADDR, sizeof(cfg->maddr));
   strlcpy(cfg->mport, DEFAULT_MCAST_PORT, sizeof(cfg->mport));
@@ -76,6 +80,10 @@ config(cfg_t *cfg, const char *key, const char *value) {
     strlcpy(cfg->iface, value, sizeof(cfg->iface));
     return true;
   }
+  if (strcmp(key, "ping") == 0) {
+    cfg->ping_max = atoi(value);
+    return true;
+  }
 
   return false;
 }
@@ -151,6 +159,12 @@ bool
 ping(cfg_t *cfg) {
   assert(cfg != NULL);
 
+  cfg->ping_num++;
+  if (cfg->ping_num < cfg->ping_max)
+    return true; /* skip this try */
+
+  /* max empty calls reached, make real ping */
+  cfg->ping_num = 0;
   /* TODO */
 
   return false;