opt.h, ip_frag.c, ip_frag.h, ip.c: Added option IP_FRAG_USES_STATIC_BUF (defaulting to off for now) that can be set to 0 to send fragmented packets by passing PBUF_REFs down the stack.

src/include/ipv4/lwip/ip_frag.h

@@ -39,24 +39,25 @@
 #include "lwip/netif.h"
 #include "lwip/ip_addr.h"
 
-#if (IP_FRAG || IP_REASSEMBLY)
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-/* The IP timer interval in milliseconds. */
+#if IP_REASSEMBLY
+/* The IP reassembly timer interval in milliseconds. */
 #define IP_TMR_INTERVAL 1000
 
-void ip_frag_init(void);
+void ip_reass_init(void);
 void ip_reass_tmr(void);
 struct pbuf * ip_reass(struct pbuf *p);
+#endif /* IP_REASSEMBLY */
+
+#if IP_FRAG
 err_t ip_frag(struct pbuf *p, struct netif *netif, struct ip_addr *dest);
+#endif /* IP_FRAG */
 
 #ifdef __cplusplus
 }
 #endif
 
-#endif /* IP_FRAG || IP_REASSEMBLY */
-
 #endif /* __LWIP_IP_FRAG_H__ */

src/include/lwip/opt.h

@@ -264,8 +264,18 @@ a lot of data that needs to be copied, this should be set high. */
 #define IP_REASS_BUFSIZE                5760
 #endif
 
+/* Use a static MTU-sized buffer for IP fragmentation.
+
+    * Otherwise pbufs are allocated and reference the original
+    * packet data to be fragmented.
+
+*/
+#ifndef IP_FRAG_USES_STATIC_BUF
+#define IP_FRAG_USES_STATIC_BUF         1
+#endif
+
 /* Assumed max MTU on any interface for IP frag buffer */
-#ifndef IP_FRAG_MAX_MTU
+#if IP_FRAG_USES_STATIC_BUF && !defined(IP_FRAG_MAX_MTU)
 #define IP_FRAG_MAX_MTU                 1500
 #endif