Fixed bug #31535: TCP_SND_QUEUELEN must be at least 2 or else no-copy TCP writes will never succeed.

CHANGELOG

@@ -229,10 +229,14 @@ HISTORY
 
   ++ Bugfixes:
 
+  2010-11-20: Simon Goldschmidt
+  * dns.c: Fixed bug #31535: TCP_SND_QUEUELEN must be at least 2 or else
+    no-copy TCP writes will never succeed.
+
   2010-11-20: Simon Goldschmidt
   * dns.c: Fixed bug #31701: Error return value from dns_gethostbyname() does
     not match documentation: return ERR_ARG instead of ERR_VAL if not
-	initialized or wrong argument.
+    initialized or wrong argument.
 
   2010-10-20: Simon Goldschmidt
   * sockets.h: Fixed bug #31385: sizeof(struct sockaddr) is 30 but should be 16

src/core/init.c

@@ -105,6 +105,9 @@
 #if (LWIP_TCP && (TCP_SND_QUEUELEN > 0xffff))
   #error "If you want to use TCP, TCP_SND_QUEUELEN must fit in an u16_t, so, you have to reduce it in your lwipopts.h"
 #endif
+#if (LWIP_TCP && (TCP_SND_QUEUELEN < 2))
+  #error "TCP_SND_QUEUELEN must be at least 2 for no-copy TCP writes to work"
+#endif
 #if (LWIP_TCP && ((TCP_MAXRTX > 12) || (TCP_SYNMAXRTX > 12)))
   #error "If you want to use TCP, TCP_MAXRTX and TCP_SYNMAXRTX must less or equal to 12 (due to tcp_backoff table), so, you have to reduce them in your lwipopts.h"
 #endif

src/include/lwip/opt.h

@@ -954,7 +954,7 @@
  * as much as (2 * TCP_SND_BUF/TCP_MSS) for things to work.
  */
 #ifndef TCP_SND_QUEUELEN
-#define TCP_SND_QUEUELEN                (4 * (TCP_SND_BUF)/(TCP_MSS))
+#define TCP_SND_QUEUELEN                ((4 * (TCP_SND_BUF) + (TCP_MSS - 1))/(TCP_MSS))
 #endif
 
 /**