Changed loopback code (less difference between NO_SYS = 0 / 1), added setting LWIP_LOOPBACK_MAX_PBUFS to limit loopback-queued pbufs

src/include/lwip/netif.h

@@ -167,11 +167,15 @@ struct netif {
 #if LWIP_NETIF_HWADDRHINT
   u8_t *addr_hint;
 #endif /* LWIP_NETIF_HWADDRHINT */
-#if ENABLE_LOOPBACK && !LWIP_NETIF_LOOPBACK_MULTITHREADING
+#if ENABLE_LOOPBACK
   /* List of packets to be queued for ourselves. */
   struct pbuf *loop_first;
   struct pbuf *loop_last;
-#endif /* ENABLE_LOOPBACK && !LWIP_NETIF_LOOPBACK_MULTITHREADING */
+#if LWIP_LOOPBACK_MAX_PBUFS
+  u16_t loop_cnt_max;
+  u16_t loop_cnt_current;
+#endif /* LWIP_LOOPBACK_MAX_PBUFS */
+#endif /* ENABLE_LOOPBACK */
 };
 
 #if LWIP_SNMP
@@ -251,9 +255,9 @@ void netif_set_link_callback(struct netif *netif, void (* link_callback)(struct
 
 #if ENABLE_LOOPBACK
 err_t netif_loop_output(struct netif *netif, struct pbuf *p, struct ip_addr *dest_ip);
+void netif_poll(struct netif *netif);
 #if !LWIP_NETIF_LOOPBACK_MULTITHREADING
 void netif_poll_all(void);
-void netif_poll(struct netif *netif);
 #endif /* !LWIP_NETIF_LOOPBACK_MULTITHREADING */
 #endif /* ENABLE_LOOPBACK */
 

src/include/lwip/opt.h

@@ -840,6 +840,14 @@
 #define LWIP_NETIF_LOOPBACK             0
 #endif
 
+/**
+ * LWIP_LOOPBACK_MAX_PBUFS: Maximum number of pbufs on queue for loopback
+ * sending for each netif (0 = disabled)
+ */
+#ifndef LWIP_LOOPBACK_MAX_PBUFS
+#define LWIP_LOOPBACK_MAX_PBUFS         0
+#endif
+
 /**
  * LWIP_NETIF_LOOPBACK_MULTITHREADING: Indicates whether threading is enabled in
  * the system, as netifs must change how they behave depending on this setting