filter-rewriter: rewrite tcp packet to keep secondary connection

We will rewrite tcp packet secondary received and sent.
When colo guest is a tcp server.

Firstly, client start a tcp handshake. the packet's seq=client_seq,
ack=0,flag=SYN. COLO primary guest get this pkt and mirror(filter-mirror)
to secondary guest, secondary get it use filter-redirector.
Then,primary guest response pkt
(seq=primary_seq,ack=client_seq+1,flag=ACK|SYN).
secondary guest response pkt
(seq=secondary_seq,ack=client_seq+1,flag=ACK|SYN).
In here,we use filter-rewriter save the secondary_seq to it's tcp connection.
Finally handshake,client send pkt
(seq=client_seq+1,ack=primary_seq+1,flag=ACK).
Here,filter-rewriter can get primary_seq, and rewrite ack from primary_seq+1
to secondary_seq+1, recalculate checksum. So the secondary tcp connection
kept good.

When we send/recv packet.
client send pkt(seq=client_seq+1+data_len,ack=primary_seq+1,flag=ACK|PSH).
filter-rewriter rewrite ack and send to secondary guest.

primary guest response pkt
(seq=primary_seq+1,ack=client_seq+1+data_len,flag=ACK)
secondary guest response pkt
(seq=secondary_seq+1,ack=client_seq+1+data_len,flag=ACK)
we rewrite secondary guest seq from secondary_seq+1 to primary_seq+1.
So tcp connection kept good.

In code We use offset( = secondary_seq - primary_seq )
to rewrite seq or ack.
handle_primary_tcp_pkt: tcp_pkt->th_ack += offset;
handle_secondary_tcp_pkt: tcp_pkt->th_seq -= offset;

Signed-off-by: Zhang Chen <zhangchen.fnst@cn.fujitsu.com>
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/net/colo.h b/net/colo.h
index 6720a3a..7c524f3 100644
--- a/net/colo.h
+++ b/net/colo.h
@@ -62,6 +62,13 @@ typedef struct Connection {
     /* flag to enqueue unprocessed_connections */
     bool processing;
     uint8_t ip_proto;
+    /* offset = secondary_seq - primary_seq */
+    tcp_seq  offset;
+    /*
+     * we use this flag update offset func
+     * run once in independent tcp connection
+     */
+    int syn_flag;
 } Connection;
 
 uint32_t connection_key_hash(const void *opaque);