net/tcp/tcp_backlog.c: Add SOMAXCONN definition and implementaton per OpenGroup.org.

include/sys/socket.h

@@ -220,6 +220,14 @@
                            * operations
                            */
 
+/* The maximum backlog queue length */
+
+#ifdef CONFIG_NET_TCPBACKLOG_CONNS
+#  define SOMAXCONN CONFIG_NET_TCPBACKLOG_CONNS
+#else
+#  define SOMAXCONN 0
+#endif
+
 /****************************************************************************
  * Type Definitions
  ****************************************************************************/

net/tcp/Kconfig

@@ -147,6 +147,16 @@ config NET_TCPBACKLOG
 		Incoming connections pend in a backlog until accept() is called.
 		The size of the backlog is selected when listen() is called.
 
+if NET_TCPBACKLOG
+
+config NET_TCPBACKLOG_CONNS
+	int "TCP backlog conns threshold"
+	default 8
+	---help---
+		Maximum number of TCP backlog connections (all tasks).
+
+endif # NET_TCPBACKLOG
+
 config NET_TCP_SPLIT
 	bool "Enable packet splitting"
 	default n

net/tcp/tcp_backlog.c

@@ -89,6 +89,13 @@ int tcp_backlogcreate(FAR struct tcp_conn_s *conn, int nblg)
 
   if (nblg > 0)
     {
+      /* nblog value must less than SOMAXCONN */
+
+      if (nblg > SOMAXCONN)
+        {
+          nblg = SOMAXCONN;
+        }
+
       /* Align the list of backlog structures to 32-bit boundaries.  This
        * may be excessive on 24-16-bit address machines; and insufficient
        * on 64-bit address machines -- REVISIT