Improvements in Netlink connections allocation.

net/netlink/Kconfig

@@ -22,11 +22,46 @@ config NET_NETLINK
 
 if NET_NETLINK
 
-config NETLINK_CONNS
+config NETLINK_PREALLOC_CONNS
-	int "Number of Netlink connections"
+	int "Preallocated Netlink connections"
 	default 4
 	---help---
-		Maximum number of Netlink connections (all tasks).
+		Number of Netlink connections (all tasks).
+		
+		This number of connections will be pre-allocated during system boot.
+		If dynamic connections allocation is enabled, more connections may
+		be allocated at a later time, as the system needs them. Else this
+		will be the maximum number of connections available to the system
+		at all times.
+
+		Set to 0 to disable (and rely only on dynamic allocations).
+
+config NETLINK_ALLOC_CONNS
+	int "Dynamic Netlink connections allocation"
+	default 0
+	---help---
+		Dynamic memory allocations for Netlink.
+
+		When set to 0 all dynamic allocations are disabled.
+
+		When set to 1 a new connection will be allocated every time,
+		and it will be free'd when no longer needed.
+
+		Setting this to 2 or more will allocate the connections in
+		batches (with batch size equal to this config). When a
+		connection is no longer needed, it will be returned to the
+		free connections pool, and it will never be deallocated!
+
+config NETLINK_MAX_CONNS
+	int "Maximum number of Netlink connections"
+	default 0
+	depends on NETLINK_ALLOC_CONNS > 0
+	---help---
+		If dynamic connections allocation is selected (NETLINK_ALLOC_CONNS > 0)
+		this will limit the number of connections that can be allocated.
+		
+		This is useful in case the system is under very heavy load (or
+		under attack), ensuring that the heap will not be exhausted.
 
 menu "Netlink Protocols"
 

net/netlink/netlink_conn.c

@@ -51,8 +51,9 @@
 
 /* The array containing all NetLink connections. */
 
-#ifndef CONFIG_NET_ALLOC_CONNS
+#if CONFIG_NETLINK_PREALLOC_CONNS > 0
-static struct netlink_conn_s g_netlink_connections[CONFIG_NETLINK_CONNS];
+static struct netlink_conn_s
+       g_netlink_connections[CONFIG_NETLINK_PREALLOC_CONNS];
 #endif
 
 /* A list of all free NetLink connections */
@@ -106,10 +107,10 @@ static void netlink_response_available(FAR void *arg)
 
 void netlink_initialize(void)
 {
-#ifndef CONFIG_NET_ALLOC_CONNS
+#if CONFIG_NETLINK_PREALLOC_CONNS > 0
   int i;
 
-  for (i = 0; i < CONFIG_NETLINK_CONNS; i++)
+  for (i = 0; i < CONFIG_NETLINK_PREALLOC_CONNS; i++)
     {
       /* Mark the connection closed and move it to the free list */
 
@@ -131,20 +132,29 @@ void netlink_initialize(void)
 FAR struct netlink_conn_s *netlink_alloc(void)
 {
   FAR struct netlink_conn_s *conn;
-#ifdef CONFIG_NET_ALLOC_CONNS
+#if CONFIG_NETLINK_ALLOC_CONNS > 0
   int i;
 #endif
 
   /* The free list is protected by a mutex. */
 
   nxmutex_lock(&g_free_lock);
-#ifdef CONFIG_NET_ALLOC_CONNS
+#if CONFIG_NETLINK_ALLOC_CONNS > 0
   if (dq_peek(&g_free_netlink_connections) == NULL)
     {
-      conn = kmm_zalloc(sizeof(*conn) * CONFIG_NETLINK_CONNS);
+#if CONFIG_NETLINK_MAX_CONNS > 0
+      if (dq_count(&g_active_netlink_connections) +
+          CONFIG_NETLINK_ALLOC_CONNS >= CONFIG_NETLINK_MAX_CONNS)
+        {
+          nxmutex_unlock(&g_free_lock);
+          return NULL;
+        }
+#endif
+
+      conn = kmm_zalloc(sizeof(*conn) * CONFIG_NETLINK_ALLOC_CONNS);
       if (conn != NULL)
         {
-          for (i = 0; i < CONFIG_NETLINK_CONNS; i++)
+          for (i = 0; i < CONFIG_NETLINK_ALLOC_CONNS; i++)
             {
               dq_addlast(&conn[i].sconn.node, &g_free_netlink_connections);
             }
@@ -199,9 +209,22 @@ void netlink_free(FAR struct netlink_conn_s *conn)
 
   memset(conn, 0, sizeof(*conn));
 
-  /* Free the connection */
+  /* If this is a preallocated or a batch allocated connection store it in
+   * the free connections list. Else free it.
+   */
+
+#if CONFIG_NETLINK_ALLOC_CONNS == 1
+  if (conn < g_netlink_connections || conn >= (g_netlink_connections +
+      CONFIG_NETLINK_PREALLOC_CONNS))
+    {
+      kmm_free(conn);
+    }
+  else
+#endif
+    {
+      dq_addlast(&conn->sconn.node, &g_free_netlink_connections);
+    }
 
-  dq_addlast(&conn->sconn.node, &g_free_netlink_connections);
   nxmutex_unlock(&g_free_lock);
 }