tcp: retransmit and multi-buffer segment fixes and improvements

- set session state as closed on session manager delete
- enable retransmit as opposed to persist timer after persist timer completes
- properly discard buffer chain bytes when new data overlaps ooo
  segments
- don't use rxt bytes in snd space estimate used on tx path

Change-Id: Id9cab686e532e5fe70c775d5440260e8eb890a9f
Signed-off-by: Florin Coras <fcoras@cisco.com>

1 files changed, 86 insertions, 19 deletions

diff --git a/src/vnet/session/session.c b/src/vnet/session/session.c
index 70a5cd83749..6fe990476e7 100644
--- a/src/vnet/session/session.c
+++ b/src/vnet/session/session.c
@@ -92,38 +92,104 @@ stream_session_create_i (segment_manager_t * sm, transport_connection_t * tc,
   return 0;
 }
 
-/** Enqueue buffer chain tail */
+/**
+ * Discards bytes from buffer chain
+ *
+ * It discards n_bytes_to_drop starting at first buffer after chain_b
+ */
+always_inline void
+session_enqueue_discard_chain_bytes (vlib_main_t * vm, vlib_buffer_t * b,
+				     vlib_buffer_t ** chain_b,
+				     u32 n_bytes_to_drop)
+{
+  vlib_buffer_t *next = *chain_b;
+  u32 to_drop = n_bytes_to_drop;
+  ASSERT (b->flags & VLIB_BUFFER_NEXT_PRESENT);
+  while (to_drop && (next->flags & VLIB_BUFFER_NEXT_PRESENT))
+    {
+      next = vlib_get_buffer (vm, next->next_buffer);
+      if (next->current_length > to_drop)
+	{
+	  vlib_buffer_advance (next, to_drop);
+	  to_drop = 0;
+	}
+      else
+	{
+	  to_drop -= next->current_length;
+	  next->current_length = 0;
+	}
+    }
+  *chain_b = next;
+
+  if (to_drop == 0)
+    b->total_length_not_including_first_buffer -= n_bytes_to_drop;
+}
+
+/**
+ * Enqueue buffer chain tail
+ */
 always_inline int
 session_enqueue_chain_tail (stream_session_t * s, vlib_buffer_t * b,
 			    u32 offset, u8 is_in_order)
 {
   vlib_buffer_t *chain_b;
-  u32 chain_bi = b->next_buffer, len;
+  u32 chain_bi, len, diff;
   vlib_main_t *vm = vlib_get_main ();
   u8 *data;
-  u16 written = 0;
+  u32 written = 0;
   int rv = 0;
 
+  if (is_in_order && offset)
+    {
+      diff = offset - b->current_length;
+      if (diff > b->total_length_not_including_first_buffer)
+	return 0;
+      chain_b = b;
+      session_enqueue_discard_chain_bytes (vm, b, &chain_b, diff);
+      chain_bi = vlib_get_buffer_index (vm, chain_b);
+    }
+  else
+    chain_bi = b->next_buffer;
+
   do
     {
       chain_b = vlib_get_buffer (vm, chain_bi);
       data = vlib_buffer_get_current (chain_b);
       len = chain_b->current_length;
+      if (!len)
+	continue;
       if (is_in_order)
 	{
 	  rv = svm_fifo_enqueue_nowait (s->server_rx_fifo, len, data);
-	  if (rv < len)
+	  if (rv == len)
+	    {
+	      written += rv;
+	    }
+	  else if (rv < len)
 	    {
 	      return (rv > 0) ? (written + rv) : written;
 	    }
-	  written += rv;
+	  else if (rv > len)
+	    {
+	      written += rv;
+
+	      /* written more than what was left in chain */
+	      if (written > b->total_length_not_including_first_buffer)
+		return written;
+
+	      /* drop the bytes that have already been delivered */
+	      session_enqueue_discard_chain_bytes (vm, b, &chain_b, rv - len);
+	    }
 	}
       else
 	{
 	  rv = svm_fifo_enqueue_with_offset (s->server_rx_fifo, offset, len,
 					     data);
 	  if (rv)
-	    return -1;
+	    {
+	      clib_warning ("failed to enqueue multi-buffer seg");
+	      return -1;
+	    }
 	  offset += len;
 	}
     }
@@ -155,22 +221,22 @@ stream_session_enqueue_data (transport_connection_t * tc, vlib_buffer_t * b,
 			     u32 offset, u8 queue_event, u8 is_in_order)
 {
   stream_session_t *s;
-  int enqueued = 0, rv;
+  int enqueued = 0, rv, in_order_off;
 
   s = stream_session_get (tc->s_index, tc->thread_index);
 
   if (is_in_order)
     {
-      enqueued =
-	svm_fifo_enqueue_nowait (s->server_rx_fifo, b->current_length,
-				 vlib_buffer_get_current (b));
-      if (PREDICT_FALSE
-	  ((b->flags & VLIB_BUFFER_NEXT_PRESENT) && enqueued > 0))
+      enqueued = svm_fifo_enqueue_nowait (s->server_rx_fifo,
+					  b->current_length,
+					  vlib_buffer_get_current (b));
+      if (PREDICT_FALSE ((b->flags & VLIB_BUFFER_NEXT_PRESENT)
+			 && enqueued >= 0))
 	{
-	  rv = session_enqueue_chain_tail (s, b, 0, 1);
-	  if (rv <= 0)
-	    return enqueued;
-	  enqueued += rv;
+	  in_order_off = enqueued > b->current_length ? enqueued : 0;
+	  rv = session_enqueue_chain_tail (s, b, in_order_off, 1);
+	  if (rv > 0)
+	    enqueued += rv;
 	}
     }
   else
@@ -179,9 +245,10 @@ stream_session_enqueue_data (transport_connection_t * tc, vlib_buffer_t * b,
 					 b->current_length,
 					 vlib_buffer_get_current (b));
       if (PREDICT_FALSE ((b->flags & VLIB_BUFFER_NEXT_PRESENT) && !rv))
-	rv = session_enqueue_chain_tail (s, b, offset + b->current_length, 0);
-      if (rv)
-	return -1;
+	session_enqueue_chain_tail (s, b, offset + b->current_length, 0);
+      /* if something was enqueued, report even this as success for ooo
+       * segment handling */
+      return rv;
     }
 
   if (queue_event)