ovsdb: relay: Reflect connection status in _Server database.

It might be important for clients to know that relay lost connection
with the relay remote, so they could re-connect to other relay.

Acked-by: Mark D. Gray <mark.d.gray@redhat.com>
Acked-by: Dumitru Ceara <dceara@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

ovsdb/_server.xml

@@ -71,6 +71,15 @@
       source.
     </column>
 
+    <column name="connected">
+      True if the database is connected to its storage.  A standalone database
+      is always connected.  A clustered database is connected if the server is
+      in contact with a majority of its cluster.  A relay database is connected
+      if the server is in contact with the relay source, i.e. is connected to
+      the server it syncs from.  An unconnected database cannot be modified and
+      its data might be unavailable or stale.
+    </column>
+
     <group title="Clustered Databases">
       <p>
         These columns are most interesting and in some cases only relevant for
@@ -78,14 +87,6 @@
         column is <code>clustered</code>.
       </p>
 
-      <column name="connected">
-        True if the database is connected to its storage.  A standalone or
-        active-backup database is always connected.  A clustered database is
-        connected if the server is in contact with a majority of its cluster.
-        An unconnected database cannot be modified and its data might be
-        unavailable or stale.
-      </column>
-
       <column name="leader">
         True if the database is the leader in its cluster.  For a standalone or
         active-backup database, this is always true.  For a relay database,

ovsdb/ovsdb-server.c

@@ -1194,7 +1194,8 @@ update_database_status(struct ovsdb_row *row, struct db *db)
     ovsdb_util_write_string_column(row, "model",
         db->db->is_relay ? "relay" : ovsdb_storage_get_model(db->db->storage));
     ovsdb_util_write_bool_column(row, "connected",
-                                 ovsdb_storage_is_connected(db->db->storage));
+        db->db->is_relay ? ovsdb_relay_is_connected(db->db)
+                         : ovsdb_storage_is_connected(db->db->storage));
     ovsdb_util_write_bool_column(row, "leader",
         db->db->is_relay ? false : ovsdb_storage_is_leader(db->db->storage));
     ovsdb_util_write_uuid_column(row, "cid",

ovsdb/relay.c

@@ -31,6 +31,7 @@
 #include "ovsdb-error.h"
 #include "row.h"
 #include "table.h"
+#include "timeval.h"
 #include "transaction.h"
 #include "transaction-forward.h"
 #include "util.h"
@@ -47,8 +48,36 @@ struct relay_ctx {
     struct ovsdb_schema *new_schema;
     schema_change_callback schema_change_cb;
     void *schema_change_aux;
+
+    long long int last_connected;
 };
 
+#define RELAY_MAX_RECONNECTION_MS 30000
+
+/* Reports if the database is connected to the relay source and functional,
+ * i.e. it actively monitors the source and is able to forward transactions. */
+bool
+ovsdb_relay_is_connected(struct ovsdb *db)
+{
+    struct relay_ctx *ctx = shash_find_data(&relay_dbs, db->name);
+
+    if (!ctx || !ovsdb_cs_is_alive(ctx->cs)) {
+        return false;
+    }
+
+    if (ovsdb_cs_may_send_transaction(ctx->cs)) {
+        return true;
+    }
+
+    /* Trying to avoid connection state flapping by delaying report for
+     * upper layer and giving ovsdb-cs some time to reconnect. */
+    if (time_msec() - ctx->last_connected < RELAY_MAX_RECONNECTION_MS) {
+        return true;
+    }
+
+    return false;
+}
+
 static struct json *
 ovsdb_relay_compose_monitor_request(const struct json *schema_json, void *ctx_)
 {
@@ -119,6 +148,7 @@ ovsdb_relay_add_db(struct ovsdb *db, const char *remote,
     ctx->schema_change_aux = schema_change_aux;
     ctx->db = db;
     ctx->cs = ovsdb_cs_create(db->name, 3, &relay_cs_ops, ctx);
+    ctx->last_connected = 0;
     shash_add(&relay_dbs, db->name, ctx);
     ovsdb_cs_set_leader_only(ctx->cs, false);
     ovsdb_cs_set_remote(ctx->cs, remote, true);
@@ -306,6 +336,10 @@ ovsdb_relay_run(void)
         ovsdb_txn_forward_run(ctx->db, ctx->cs);
         ovsdb_cs_run(ctx->cs, &events);
 
+        if (ovsdb_cs_may_send_transaction(ctx->cs)) {
+            ctx->last_connected = time_msec();
+        }
+
         struct ovsdb_cs_event *event;
         LIST_FOR_EACH_POP (event, list_node, &events) {
             if (!ctx->db) {

ovsdb/relay.h

@@ -17,6 +17,8 @@
 #ifndef OVSDB_RELAY_H
 #define OVSDB_RELAY_H 1
 
+#include <stdbool.h>
+
 struct json;
 struct ovsdb;
 struct ovsdb_schema;
@@ -31,4 +33,6 @@ void ovsdb_relay_del_db(struct ovsdb *);
 void ovsdb_relay_run(void);
 void ovsdb_relay_wait(void);
 
+bool ovsdb_relay_is_connected(struct ovsdb *);
+
 #endif /* OVSDB_RELAY_H */