bridge: Allow manual notifications about interfaces' updates.

Sometimes interface updates could happen in a way ifnotifier is not
able to catch.  For example some heavy operations (device reset) in
netdev-dpdk could require re-applying of the bridge configuration.

For this purpose new manual notifier introduced. Its function
'if_notifier_manual_report()' could be called directly by the code
that aware about changes.  This new notifier is thread-safe.

Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Acked-by: Eelco Chaudron <echaudro@redhat.com>

lib/if-notifier-manual.c

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2019 Ilya Maximets <i.maximets@ovn.org>.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <config.h>
+#include "openvswitch/compiler.h"
+#include "openvswitch/thread.h"
+#include "openvswitch/util.h"
+#include "if-notifier.h"
+
+/* Implementation of a manual interface notifier.
+ *
+ * Intended for catching interface events that could not be tracked by
+ * OS specific interface notifiers, e.g. iface updates in netdev-dpdk.
+ * For that purpose 'if_notifier_manual_report()' should be called directly
+ * by the code that aware of interface changes.
+ *
+ * Thread-safety
+ * =============
+ * This notifier is thread-safe in terms of calling its functions from
+ * different thread contexts,  however if the callback passed to
+ * 'if_notifier_manual_set_cb' is used by some other code (i.e. by OS
+ * specific notifiers) it must be thread-safe itself.
+ */
+
+static struct ovs_mutex manual_notifier_mutex = OVS_MUTEX_INITIALIZER;
+static if_notify_func *notify OVS_GUARDED_BY(manual_notifier_mutex) = NULL;
+
+void
+if_notifier_manual_set_cb(if_notify_func *cb)
+{
+    ovs_mutex_lock(&manual_notifier_mutex);
+    notify = cb;
+    ovs_mutex_unlock(&manual_notifier_mutex);
+}
+
+void
+if_notifier_manual_report(void)
+{
+    ovs_mutex_lock(&manual_notifier_mutex);
+    if (notify) {
+        notify(NULL);
+    }
+    ovs_mutex_unlock(&manual_notifier_mutex);
+}