usrloc: Fix pinging with simple active/backup clusters

In these types of setups, partitioning the pings across the cluster is
incorrect, as the active node must send all pings.

This patch adds the "shared_pinging" module parameter in order to fix
the pinging behavior for these scenarios.

modules/usrloc/dlist.c

@@ -522,7 +522,7 @@ get_domain_cdb_ucontacts(udomain_t *d, void *buf, int *len,
 {
 	static const cdb_key_t aorhash_key = {str_init("aorhash"), 0}; /* TODO */
 	struct list_head *_, *__;
-	int cur_node_idx, nr_nodes, min, max;
+	int cur_node_idx = 0, nr_nodes = 1, min, max;
 	char *cpos;
 	double unit;
 	cdb_filter_t *aorh_filter;
@@ -536,8 +536,9 @@ get_domain_cdb_ucontacts(udomain_t *d, void *buf, int *len,
 	enum cdb_filter_op rhs_op;
 	int shortage;
 
-	cur_node_idx = clusterer_api.get_my_index(
-	         location_cluster, &contact_repl_cap, &nr_nodes);
+	if (shared_pinging)
+		cur_node_idx = clusterer_api.get_my_index(
+		                 location_cluster, &contact_repl_cap, &nr_nodes);
 
 	unit = MAX_DB_AOR_HASH / (double)(part_max * nr_nodes);
 	min = (int)(unit * part_max * cur_node_idx + unit * part_idx);
@@ -646,8 +647,8 @@ get_domain_mem_ucontacts(udomain_t *d,void *buf, int *len, unsigned int flags,
 	if (zero_end)
 		*len -= (int)sizeof(c->c.len);
 
-	if (cluster_mode == CM_FULL_SHARING
-	    || cluster_mode == CM_FULL_SHARING_CACHEDB) {
+	if (shared_pinging && (cluster_mode == CM_FULL_SHARING
+	    || cluster_mode == CM_FULL_SHARING_CACHEDB)) {
 		cur_node_idx = clusterer_api.get_my_index(
 		         location_cluster, &contact_repl_cap, &nr_nodes);
 	}

modules/usrloc/doc/usrloc_admin.xml

@@ -1308,6 +1308,36 @@ modparam("usrloc", "latency_event_min_us_delta", 300000)
 		</example>
 	</section>
 
+	<section id="param_shared_pinging" xreflabel="shared_pinging">
+		<title><varname>shared_pinging</varname> (integer)</title>
+		<para>
+		Only relevant in a "full sharing" or "full sharing cachedb"
+		<xref linkend="param_cluster_mode"/>.  If set to non-zero, the overall
+		pinging workload will be equally spread across cluster nodes with the
+		help of the clustering layer that keeps track of the current number of
+		active nodes.
+		</para>
+		<para>
+		Disabling this parameter may be useful in simple active/backup
+		setups, where only the active node must perform the pinging.
+		</para>
+		<para>
+			<emphasis>
+				Default value is <quote>1 (enabled)</quote>.
+			</emphasis>
+		</para>
+
+		<example>
+		<title>Set <varname>shared_pinging</varname> parameter</title>
+		<programlisting format="linespecific">
+...
+# do not partition the pinging workload across cluster nodes
+modparam("usrloc", "shared_pinging", 0)
+...
+</programlisting>
+		</example>
+	</section>
+
 	</section>
 
 	<section id="exported_functions" xreflabel="exported_functions">

modules/usrloc/ul_mod.c

@@ -146,6 +146,7 @@ char *rr_persist_str;
 /*!< SQL write mode */
 enum ul_sql_write_mode sql_wmode = SQL_NO_WRITE;
 char *sql_wmode_str;
+int shared_pinging;
 
 int use_domain      = 0;   /*!< Whether usrloc should use domain part of aor */
 int desc_time_order = 0;   /*!< By default do not enable timestamp ordering */
@@ -214,6 +215,7 @@ static param_export_t params[] = {
 	{"cluster_mode",       STR_PARAM, &cluster_mode_str  },
 	{"restart_persistency",STR_PARAM, &rr_persist_str    },
 	{"sql_write_mode",     STR_PARAM, &sql_wmode_str     },
+	{"shared_pinging",     INT_PARAM, &shared_pinging    },
 
 	{"use_domain",         INT_PARAM, &use_domain        },
 	{"desc_time_order",    INT_PARAM, &desc_time_order   },

modules/usrloc/ul_mod.h

@@ -120,6 +120,7 @@ extern int cseq_delay;
 extern int ul_hash_size;
 extern int latency_event_min_us_delta;
 extern int latency_event_min_us;
+extern int shared_pinging;
 
 extern db_con_t* ul_dbh;   /* Database connection handle */
 extern db_func_t ul_dbf;