Author: jhb
Date: Thu Sep 10 21:41:11 2015
New Revision: 287631
URL: https://svnweb.freebsd.org/changeset/base/287631

Log:
  Add a comment that to clarify how to determine the amount of received DDP
  data.
  
  Reviewed by:  np
  Differential Revision:        https://reviews.freebsd.org/D3619

Modified:
  head/sys/dev/cxgbe/tom/t4_ddp.c

Modified: head/sys/dev/cxgbe/tom/t4_ddp.c
==============================================================================
--- head/sys/dev/cxgbe/tom/t4_ddp.c     Thu Sep 10 21:08:54 2015        
(r287630)
+++ head/sys/dev/cxgbe/tom/t4_ddp.c     Thu Sep 10 21:41:11 2015        
(r287631)
@@ -405,6 +405,19 @@ handle_ddp_data(struct toepcb *toep, __b
        }
 
        tp = intotcpcb(inp);
+
+       /*
+        * For RX_DDP_COMPLETE, len will be zero and rcv_nxt is the
+        * sequence number of the next byte to receive.  The length of
+        * the data received for this message must be computed by
+        * comparing the new and old values of rcv_nxt.
+        * 
+        * For RX_DATA_DDP, len might be non-zero, but it is only the
+        * length of the most recent DMA.  It does not include the
+        * total length of the data received since the previous update
+        * for this DDP buffer.  rcv_nxt is the sequence number of the
+        * first received byte from the most recent DMA.
+        */
        len += be32toh(rcv_nxt) - tp->rcv_nxt;
        tp->rcv_nxt += len;
        tp->t_rcvtime = ticks;
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