# define IPC_ADDVAL 0
#endif
-#define WRITE_BUFFER_SIZE 4096
+/* The WRITE_BUFFER_SIZE value needs to be chosen such that if we set
+ the socket send buffer size to '1', a write of this size on that
+ socket will block.
+
+ The Linux kernel imposes a minimum send socket buffer size which
+ has changed over the years. As of Linux 3.10 the value is:
+
+ 2 * (2048 + SKB_DATA_ALIGN(sizeof(struct sk_buff)))
+
+ which is attempting to make sure that with standard MTUs,
+ TCP can always queue up at least 2 full sized packets.
+
+ Furthermore, there is logic in the socket send paths that
+ will allow one more packet (of any size) to be queued up as
+ long as some socket buffer space remains. Blocking only
+ occurs when we try to queue up a new packet and the send
+ buffer space has already been fully consumed.
+
+ Therefore we must set this value to the largest possible value of
+ the formula above (and since it depends upon the size of "struct
+ sk_buff", it is dependent upon machine word size etc.) plus some
+ slack space. */
+
+#define WRITE_BUFFER_SIZE 16384
/* Cleanup handling test. */
static int cl_called;
pthread_cleanup_push (cl, NULL);
- /* Just for fun block the cancellation signal. */
sigpause (SIGCANCEL);
pthread_cleanup_pop (0);