Re: [Qemu-devel] [PATCH v2 3/3] filter-rewriter: skip net_checksum_calculate() while offset = 0

[Zhang Chen]

On 02/22/2017 11:46 AM, zhanghailiang wrote:

While the offset of packets's sequence for primary side and
secondary side is zero, it is unnecessary to call net_checksum_calculate()
to recalculate the checksume value of packets.

Signed-off-by: zhanghailiang <zhang.zhanghaili...@huawei.com>
---
  net/filter-rewriter.c | 18 +++++++++++-------
  1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/net/filter-rewriter.c b/net/filter-rewriter.c
index 7e7ec35..c9a6d43 100644
--- a/net/filter-rewriter.c
+++ b/net/filter-rewriter.c
@@ -93,10 +93,12 @@ static int handle_primary_tcp_pkt(RewriterState *rf,
              conn->offset -= (ntohl(tcp_pkt->th_ack) - 1);
              conn->syn_flag = 0;
          }
-        /* handle packets to the secondary from the primary */
-        tcp_pkt->th_ack = htonl(ntohl(tcp_pkt->th_ack) + conn->offset);
+        if (conn->offset) {

This is wrong, conn->offset maybe is a negative value(like -1000),
So you can change here to  "if (conn->offset == 0) {"

+            /* handle packets to the secondary from the primary */
+            tcp_pkt->th_ack = htonl(ntohl(tcp_pkt->th_ack) + conn->offset);

- net_checksum_calculate((uint8_t *)pkt->data, pkt->size);

+            net_checksum_calculate((uint8_t *)pkt->data, pkt->size);
+        }
          /*
           * Case 1:
           * The *server* side of this connect is VM, *client* tries to close
@@ -112,7 +114,6 @@ static int handle_primary_tcp_pkt(RewriterState *rf,
           */
          if ((conn->tcp_state == TCPS_LAST_ACK) &&
              (ntohl(tcp_pkt->th_ack) == (conn->fin_ack_seq + 1))) {
-            fprintf(stderr, "Remove conn "

Here need fix.

              g_hash_table_remove(rf->connection_track_table, key);
          }
      }
@@ -159,10 +160,13 @@ static int handle_secondary_tcp_pkt(RewriterState *rf,
      }

if ((tcp_pkt->th_flags & (TH_ACK | TH_SYN)) == TH_ACK) {

-        /* handle packets to the primary from the secondary*/
-        tcp_pkt->th_seq = htonl(ntohl(tcp_pkt->th_seq) - conn->offset);
+        /* Only need to adjust seq while offset is Non-zero */
+        if (conn->offset) {

Refer to the above comments.

Thanks
Zhang Chen

+            /* handle packets to the primary from the secondary*/
+            tcp_pkt->th_seq = htonl(ntohl(tcp_pkt->th_seq) - conn->offset);

- net_checksum_calculate((uint8_t *)pkt->data, pkt->size);

+            net_checksum_calculate((uint8_t *)pkt->data, pkt->size);
+        }
          /*
           * Case 2:
           * The *server* side of this connect is VM, *server* tries to close

--
Thanks
Zhang Chen