1 files changed, 25 insertions, 1 deletions

diff --git a/ot_socket.c b/ot_socket.c
index 576087f..158459f 100644
--- a/ot_socket.c
+++ b/ot_socket.c
@@ -75,13 +75,37 @@ static int socket_v6(int type) {
   return s;
 }
 
+/* SO_REUSEPORT means three different things. Linux spreads datagrams over
+   the group. FreeBSD permits the bind and spreads nothing, which is what
+   SO_REUSEPORT_LB was added for. Darwin hands every datagram to whichever
+   socket bound last, so a group there starves all but one reader. */
+#if defined(SO_REUSEPORT_LB)
+#define OT_BALANCE_OPTION SO_REUSEPORT_LB
+#elif defined(SO_REUSEPORT) && !defined(__APPLE__)
+#define OT_BALANCE_OPTION SO_REUSEPORT
+#endif
+
+int socket_can_balance(void) {
+#ifdef OT_BALANCE_OPTION
+  return 1;
+#else
+  return 0;
+#endif
+}
+
 /* The only place in the tree that needs to know what a kernel calls this */
 static void socket_set_sharing(int s, socket_sharing sharing) {
   int one = 1;
 
   setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
+#ifdef OT_BALANCE_OPTION
+  if (sharing == SOCKET_BALANCED) {
+    setsockopt(s, SOL_SOCKET, OT_BALANCE_OPTION, &one, sizeof(one));
+    return;
+  }
+#endif
 #ifdef SO_REUSEPORT
-  if (sharing == SOCKET_SHARED)
+  if (sharing != SOCKET_EXCLUSIVE)
     setsockopt(s, SOL_SOCKET, SO_REUSEPORT, &one, sizeof(one));
 #endif
 }